Download 2.01 structure of cells.

1.0 MICROSCOPY
Microscopy is the science of study of microscopes. Microscopy is important in study
of micro organisms. The microscope is the basic research tool of the biologist for
studying very small objects. A microscope can be simple or compound.
1.01 SIMPLE MICROSCOPE: A simple microscope is a microscope
that uses only one lens for magnification, and is the original light microscope.It includes
a magnifying glass which is limited to a magnifying power of about ten times. Extremely
small things thus can not be observed with a magnifying glass.
1.02 COMPOUND MICROSCOPE
It is the one that consists of atleast two lenses or two sets of lenses. One lens magnifies
the object being viewed. The other lens magnifies the image produced by the first lens.
The total magnification of the compound microscope is calculated by multiplying the
magnification power of the two lenses.
1.03 STRUCTURE OF COMPOUND MICROSCOPE
The compound microscope has two systems of lenses for greater magnification, 1) the
ocular or eyepiece lens that one looks into and 2) the objective lens, or the lens closest to
the object.
Fig 1: The diagram above is of the structure of a compound microscope.
1.04 FUNCTIONS OF DIFFERENT PARTS OF A COMPOUND MICROSCOPE
Eyepiece Lens: the lens at the top that you look through. It contains a set of lenses that
help to magnify the material being examined. They are usually X10 or X15 power.
Tube: Connects the eyepiece to the objective lenses. It is a long, hollow, up right
cylinder that forms the body of the microscope.
Arm: Supports the tube and connects it to the base. On the arm are located the two
knobs that are used to focus the microscope. The coarse adjustment knob usually the
larger is located near the top of the arm. The fine adjustment knob is usually located at
the bottom of the arm, near the base of the microscope. When the adjustment knobs are
turned, the tube is raised or lowered. In some models, the stage is raised or lowered. This
movement of the tube or stage focuses (sharpens) the image of the specimen being
viewed through a microscope.
Base: The bottom of the microscope, used for support
Illuminator: A steady light source (110 volts) used in place of a mirror. If your
microscope has a mirror, it is used to reflect light from an external light source up
through the bottom of the stage.
Stage: The flat platform where you place your slides. Stage clips hold the slides in
place. If your microscope has a mechanical stage, you will be able to move the slide
around by turning two knobs. One moves it left and right, the other moves it up and
down.
Revolving Nosepiece or Turret: This is the part that holds two or more objective lenses
and can be rotated to easily change power.
Objective Lenses: Usually you will find 3 or 4 objective lenses on a microscope. They
almost always consist of X4, X10, X40 and X100 powers. When coupled with a X10
(most common) eyepiece lens, we get total magnifications of X40 (X4 times X10), X100
, X400 and X1000.
Rack Stop: This is an adjustment that determines how close the objective lens can get to
the slide. It is set at the factory and keeps students from cranking the high power
objective lens down into the slide and breaking things.
Condenser Lens: The purpose of the condenser lens is to focus the light onto the
specimen. Condenser lenses are most useful at the highest powers (400X and above).
Microscopes with in stage condenser lenses render a sharper image than those with no
lens (at 400X
Diaphragm or Iris: Many microscopes have a rotating disk under the stage. This
diaphragm has different sized holes and is used to vary the intensity and size of the cone
of light that is projected upward into the slide
1.05 HOW TO FOCUS A MICROSCOPE:
The proper way to focus a microscope is to start with the lowest power objective lens first
and while looking from the side, crank the lens down as close to the specimen as possible
without touching it. Now, look through the eyepiece lens and focus upward only until
the image is sharp. If you can't get it in focus, repeat the process again. Once the image
is sharp with the low power lens, you should be able to simply click in the next power
lens and do minor adjustments with the focus knob. If your microscope has a fine focus
adjustment, turning it a bit should be all that's necessary. Continue with subsequent
objective lenses and fine focus each time.
MAGNIFYING OBJECTS/ FOCUSING IMAGE USING A MICROSCOPE:
1. When viewing a slide through the microscope make sure that the stage is all the
way down and the 4X scanning objective is locked into place.
2. Place the slide that you want to view over the aperture and gently move the stage
clips over top of the slide to hold it into place.
3. Beginning with the 4X objective, looking through the eyepiece making sure to
keep both eyes open (if you have trouble cover one eye with your hand) slowly
move the stage upward using the coarse adjustment knob until the image becomes
clear. This is the only time in the process that you will need to use the coarse
adjustment knob. The microscopes that you will be using are par focal, meaning
that the image does not need to be radically focused when changing the To
magnify the image to the next level rotate the nosepiece to the 10X objective.
While looking through the eyepiece focus the image into view using only the fine
adjustment knob, this should only take a slight turn of the fine adjustment knob to
complete this task.
4. To magnify the image to the next level rotate the nosepiece to the 40X objective.
While looking through the eyepiece focus the image into view using only the fine
adjustment knob, this should only take a slight turn of the fine adjustment knob to
complete this task. magnification.
Magnification is how much bigger a sample appears to be under the microscope than it
is in real life.
Overall magnification = Objective lens x Eyepiece
lens
Resolution is the ability to distinguish between two points on an image i.e. the amount of
detail. The resolution of an image is limited by the wavelength of radiation used to view
the sample.
1.3 OTHER TYPES OF MICROSCOPES:
Light Microscope: This is the oldest, simplest and most widely-used form of
microscopy. Specimens are illuminated with light, which is focussed using glass lenses
and viewed using the eye or photographic film. Light microscopy has a resolution of
about 200 nm, which is good enough to see cells, but not the details of cell organelles.
1.4 STEPS TAKEN TO PREPARE SLIDE SAMPLES
1. Fixation: Chemicals preserve material in a life like condition. Does not distort the
specimen.
2. Dehydration: Water removed from the specimen using ethanol. Particularly
important for electron microscopy because water molecules deflect the electron
beam which blurs the image.
3. Embedding: Supports the tissue in wax or resin so that it can be cut into thin
sections. Sectioning Produces very thin slices for mounting. Sections are cut with
a microtome or an ulramicrotome to make them either a few micrometres (light
microscopy) or nanometers (electron microscopy) thick.
4. Staining: Most biological material is transparent and needs staining to increase
the contrast between different structures. Different stains are used for different
types of tissues. Methylene blue is often used for animal cells, while iodine in KI
solution is used for plant tissues.
5. Mounting: Mounting on a slide protects the material so that it is suitable for
viewing over a long period.
1.5 ELECTRONIC MICROSCOPE
This uses a beam of electrons, rather than electromagnetic radiation, to "illuminate" the
specimen. This may seem strange, but electrons behave like waves and can easily be
produced (using a hot wire), focused (using electromagnets) and detected (using a
phosphor screen or photographic film). The main problem with the electron microscope
is that specimens must be fixed in plastic and viewed in a vacuum, and must therefore be
dead. Other problems are that the specimens can be damaged by the electron beam and
they must be stained with an electron-dense chemical (usually heavy metals like osmium,
lead or gold). There are two kinds of electron microscope. The transmission electron
microscope (TEM) works much like a light microscope, transmitting a beam of electrons
through a thin specimen and then focusing the electrons to form an image on a screen or
on film. This is the most common form of electron microscope and has the best
resolution. The scanning electron microscope (SEM) scans a fine beam of electron onto
a specimen and collects the electrons scattered by the surface. This has poorer resolution,
but gives excellent 3-dimentional images of surfaces.
1.6 DIFFERENCES BETWEEN TRANSMISSION ELECTRONIC MICROSCOPE
AND SCANNING ELECTRONIC MICROSCOPE.
1.6.1 TRANSMISSION ELECTRON MICROSCOPE (TEM)

Pass a beam of electrons through the specimen. The electrons that pass through
the specimen are detected on a fluorescent screen on which the image is
displayed.

Thin sections of specimen are needed for transmission electron microscopy as the
electrons have to pass through the specimen for the image to be produced.

This is the most common form of electron microscope and has the best
resolution
1.6.2 SCANNING ELECTRON MICROSCOPE (SEM)

Pass a beam of electrons over the surface of the specimen in the form of a
‘scanning’ beam. Electrons are reflected off the surface of the specimen as it has
been previously coated in heavy metals. It is these reflected electron beams that
are focused of the fluorescent screen in order to make up the image.

Larger, thicker structures can thus be seen under the SEM as the electrons do not
have to pass through the sample in order to form the image. This gives excellent
3-dimensional images of surfaces

1.7
However the resolution of the SEM is lower than that of the TEM.
COMPARISON OF THE LIGHT AND ELECTRON MICROSCOPE
Light Microscope
Electron Microscope
Cheap to purchase
Expensive to buy
Cheap to operate.
Expensive to produce electron beam.
Small and portable.
Large and requires special rooms.
Simple and easy sample preparation.
Lengthy and complex sample prep.
Material rarely distorted by preparation.
Preparation distorts material.
Vacuum is not required.
Vacuum is required.
Natural colour of sample maintained.
All images in black and white.
Magnifies objects only up to 2000 times
Magnifies over 500 000 times.
Specimens can be living or dead
Specimens are dead, as they must be
fixed in plastic and viewed in a vacuum
The electron beam can damage
Stains are often needed to make the cells specimens and they must be stained with
visible
an electron-dense chemical (usually
heavy metals like osmium, lead or gold).
1.8
REVISION QUESTIONS
1. What do you mean when you say that an object is in focus ? What does X50
mean on an objective lens? What parts of a microscope must be used to get the
object in focus?
2. Give the function of the following parts of a microscope: Arm , Mirror , Stage
clip , Coarse adjustment.
3. Describe the preparation of wet mount slide. How would the image of letter “ b”
be changed when viewed through the microscope? How does the brightness of an
image change when the magnification is moved from low to high power ?
4. If a microscope slide on slide on stage is moved to the right, in which direction
does the image move?
5. What is the difference between a simple and a compound microscope? How does
the field of view change when you move from low to higher magnification? Draw
a well labeled compound microscope and describe the function of each part.
6. If the eye piece is X10, what power must the objective lens be given to give a
total magnification of X250? Why is water added in making a wet mount slide?
Why should air bubbles be removed from wet mount slides? Why is it difficult to
find an object on the slide when you try to locate it under higher magnification?
2.0
CYTOLOGY
Cytology is the study of cells, and cytologists are scientists that study cells. Cytologists
have discovered that all cells are similar. Cells are all composed chiefly of molecules
containing carbon, hydrogen, oxygen, nitrogen, phosphorus, and sulfur.
2.01 STRUCTURE OF CELLS.
In 1655, the English scientist Robert Hooke made an observation that would change
basic biological theory and research forever. While examining a dried section of cork tree
with a crude light microscope, he observed small chambers and named them cells. Within
a decade, researchers had determined that cells were not empty but instead were filled
with a watery substance called cytoplasm.
All cells contain three basic features:
1. A plasma membrane consisting of a phospholipid bilayer, which is a fatty
membrane that houses the cell.
2. A cytoplasm containing cytosol and organelles. Cytosol is a fluid consisting
mostly of water and dissolved nutrients, wastes, ions, proteins, and other
molecules.
1. Genetic material (DNA and RNA), which carries the instructions for the
production of proteins.
3. Apart from these three similarities, cell structure and form are very diverse and
are therefore difficult to generalize.
2.01
THE CELL THEORY
In its modern form, this theorem has four basic parts:
1. The cell is the basic structural and functional unit of life; all organisms are
composed of cells.
2. All cells are produced by the division of preexisting cells (in other words,
through reproduction). Each cell contains genetic material that is passed down
during this process.
3. All basic chemical and physiological functions - for example, repair, growth,
movement, immunity, communication, and digestion - are carried out inside of
cells.
4. The activities of cells depends on the activities of sub cellular structures within
the cell (these sub cellular structures include organelles, the plasma membrane,
and, if present, the nucleus).
2.02
CELL ORGANELLES
Organelles are microscopic structures found in cells; these organelles carry out specific
functions. There are two classes of organelles.
a. Those that contain their own DNA and genes. Mitochondria and plastids are
organelles that reproduce by dividing like independent cells.
b. Those that do not contain their own DNA; For example, endoplasmic reticulum,
ribosomes, golgi bodies, undulipodia.

Cytoplasm (or Cytosol). This is the solution within the cell membrane. It
contains enzymes for metabolic reactions together with sugars, salts, amino acids,
nucleotides and everything else needed for the cell to function.

Nucleus. This is the largest organelle. Surrounded by a nuclear envelope, which is
a double membrane with nuclear pores - large holes containing proteins that
control the exit of substances such as RNA from the nucleus. The interior is called
the nucleoplasm, which is full of chromatin- a DNA/protein complex containing
the genes. During cell division the chromatin becomes condensed into discrete
observable chromosomes. The nucleolus is a dark region of chromatin, involved
in making ribosomes.

Mitochondrion (pl. Mitochondria). This is a sausage-shaped organelle (8µm
long), and is where aerobic respiration takes place in all eukaryotic cells.
Mitochondria are surrounded by a double membrane: the outer membrane is
simple, while the inner membrane is highly folded into cristae, which give it a
large surface area. The space enclosed by the inner membrane is called the matrix,
and contains small circular strands of DNA. The inner membrane is studded with
stalked particles, which are the site of ATP synthesis.

Chloroplast. Bigger and fatter than mitochondria, chloroplasts are where
photosynthesis takes place, so are only found in photosynthetic organisms (plants
and algae). Like mitochondria they are enclosed by a double membrane, but
chloroplasts also have a third membrane called the thylakoid membrane. The
thylakoid membrane is folded into thylakoid disks, which are then stacked into
piles called grana. The space between the inner membrane and the thylakoid is
called the stroma. The thylakoid membrane contains chlorophyll and stalked
particles, and is the site of photosynthesis and ATP synthesis. Chloroplasts also
contain starch grains, ribosomes and circular DNA.

Ribosomes. These are the smallest and most numerous of the cell organelles, and
are the sites of protein synthesis. They are composed of protein and RNA, and are
manufactured in the nucleolus of the nucleus. Ribosomes are either found free in
the cytoplasm, where they make proteins for the cell's own use, or they are found
attached to the rough endoplasmic reticulum, where they make proteins for export
from the cell. They are often found in groups called polysomes. All eukaryotic
ribosomes are of the larger, "80S", type.

Smooth Endoplasmic Reticulum (SER). Series of membrane channels involved
in synthesising and transporting materials, mainly lipids, needed by the cell.

Rough Endoplasmic Reticulum (RER). Similar to the SER, but studded with
numerous ribosomes, which give it its rough appearance. The ribosomes
synthesise proteins, which are processed in the RER (e.g. by enzymatically
modifying the polypeptide chain, or adding carbohydrates), before being exported
from the cell via the Golgi Body.

Golgi Body (or Golgi Apparatus). Another series of flattened membrane
vesicles, formed from the endoplasmic reticulum. Its job is to transport proteins
from the RER to the cell membrane for export. Parts of the RER containing
proteins fuse with one side of the Golgi body membranes, while at the other side
small vesicles bud off and move towards the cell membrane, where they fuse,
releasing their contents by exocytosis.

Vacuoles. These are membrane-bound sacs containing water or dilute solutions of
salts and other solutes. Most cells can have small vacuoles that are formed as
required, but plant cells usually have one very large permanent vacuole that fills
most of the cell, so that the cytoplasm (and everything else) forms a thin layer
round the outside. Plant cell vacuoles are filled with cell sap, and are very
important in keeping the cell rigid, or turgid. Some unicellular protoctists have
feeding vacuoles for digesting food, or contractile vacuoles for expelling water.

Lysosomes. These are small membrane-bound vesicles formed from the RER
containing a cocktail of digestive enzymes. They are used to break down
unwanted chemicals, toxins, organelles or even whole cells, so that the materials
may be recycled. They can also fuse with a feeding vacuole to digest its contents.

Cytoskeleton. This is a network of protein fibres extending throughout all
eukaryotic cells, used for support, transport and motility. The cytoskeleton is
attached to the cell membrane and gives the cell its shape, as well as holding all
the organelles in position. There are three types of protein fibres (microfilaments,
intermediate filaments and microtubules), and each has a corresponding motor
protein that can move along the fibre carrying a cargo such as organelles,
chromosomes or other cytoskeleton fibres. These motor proteins are responsible
for such actions as: chromosome movement in mitosis, cytoplasm cleavage in cell
division, cytoplasmic streaming in plant cells, cilia and flagella movements, cell
crawling and even muscle contraction in animals.
Functions and Characteristics of the Cytoskeleton
a. They are involved with the transport of organelles and cytoplasmic
streaming.
b. The organelles transport soluble products.
c. They are altered when the cell comes into contact with a substrate; this
may allow for cell to cell communication.
d. These organelles are not dependent on the nucleus for assembly.
e. The organelles for the cytoskeleton are inherited maternally.
Three Organelles that make up the Cytoskeleton
a. Microtubules
b. Actin fibrils
c. Intermediate fibrils

Centriole. This is a pair of short microtubules involved in cell division.

Cilium and Flagellum. These are flexible tails present in some cells and used for
motility. They are an extension of the cytoplasm, surrounded by the cell
membrane, and are full of microtubules and motor proteins so are capable of
complex swimming movements. There are two kinds: flagella (pl.) (no relation of
the bacterial flagellum) are longer than the cell, and there are usually only one or
two of them, while cilia (pl.) are identical in structure, but are much smaller and
there are usually very many of them.

Microvilli. These are small finger-like extensions of the cell membrane found in
certain cells such as in the epithelial cells of the intestine and kidney, where they
increase the surface area for absorption of materials. They are just visible under
the light microscope as a brush border.
 Cell Membrane (or Plasma Membrane). This is a thin, flexible layer round the
outside of all cells made of phospholipids and proteins. It controls how substances
can move in and out of the cell and is responsible for many other properties of the
cell as well. The membranes that surround the nucleus and other organelles are
almost identical to the cell membrane. Membranes are composed of
phospholipids, proteins and carbohydrates arranged in a fluid mosaic structure, as
shown in this diagram.
Figure 12: Structure of cell membrane
The phospholipids form a thin, flexible sheet, while the proteins "float" in the the cell
from the outside environment, and controls the entry and exit of materials. The
phospholipids are arranged in a bilayer, with their polar, hydrophilic phosphate
heads facing outwards, and their non-polar, hydrophobic fatty acid tails facing each
other in the middle of the bilayer.
The proteins usually span from one side of the phospholipid bilayer to the other
(intrinsic proteins), but can also sit on one of the surfaces (extrinsic proteins). They
can slide around the membrane very quickly and collide with each other, but can
never flip from one side to the other.
Proteins comprise about 50% of the mass of membranes, and are responsible for most of
the membrane's properties.

Proteins that span the membrane are usually involved in transporting substances
across the membrane (more details below).

Proteins on the inside surface of cell membranes are often attached to the
cytoskeleton and are involved in maintaining the cell's shape, or in cell motility.
They may also be enzymes, catalysing reactions in the cytoplasm.

Proteins on the outside surface of cell membranes can act as receptors by having a
specific binding site where hormones or other chemicals can bind. This binding
then triggers other events in the cell. They may also be involved in cell signalling
and cell recognition, or they may be enzymes, such as maltase in the small
intestine (more in digestion).
The carbohydrates are found on the outer surface of all eukaryotic cell membranes,
and are usually attached to the membrane proteins. Proteins with carbohydrates
attached are called glycoproteins. The carbohydrates are short polysaccharides
composed of a variety of different monosaccharides, and form a cell coat or
glycocalyx outside the cell membrane.
MEMBRANE MODELS
 To account for permeability of membrane to non-lipid substances, Danielli and
Davson proposed sandwich model (later proved wrong) with phospholipid bilayer
between layers of protein
 In 1972, Singer and Nicolson introduced the currently accepted fluid-mosaic
model of membrane structure.
1. Plasma membrane is phospholipid bilayer in which protein molecules are partially
or wholly embedded.
2. Embedded proteins are scattered throughout membrane in irregular pattern; varies
among membranes.
3. Electron micrographs of freeze-fractured membrane supports fluid-mosaic model.
A. FLUID-MOSAIC MODEL
1. Membrane structure has two components, lipids and proteins.
2. Lipids are arranged into a bilayer
a. Most plasma membrane lipids are phospholipids, which spontaneously arrange
themselves into a bilayer.
b. Nonpolar tails are hydrophobic and directed inward; polar heads are
hydrophilic and are directed outward to face extracellular and intracellular fluids.
c. Glycolipids have a structure similar to phospholipids except the hydrophilic
head is a variety of sugar; they are protective and assist in various functions.
d. Cholesterol is a lipid found in animal plasma membranes; reduces the
permeability of membrane.
e. Glycoproteins have an attached carbohydrate chain of sugar that projects
externally.
f. The plasma membrane is asymmetrical; glycolipids and proteins occur only on
outside and cytoskeletal filaments attach to proteins only on the inside surface.
B. FLUIDITY OF THE PLASMA MEMBRANE
1. At body temperature, the phospholipid bilayer has consistency of olive oil.
2. The greater the concentration of unsaturated fatty acid residues, the more fluid the
bilayer.
3. In each monolayer, the hydrocarbon tails wiggle, and entire phospholipid
molecules can move sideways at a rate of about 2 µm—the length of a prokaryotic cell—
per second.
4. Phospholipids molecules rarely flip-flop from one layer to the other.
5. Fluidity of the phospholipids bilayer allows cells to be pliable.
6. Some proteins are held in place by cytoskeletal filaments; most drift in fluid
bilayer.
C. THE MEMBRANE IS A MOSAIC
1. Plasma membrane and organelle membranes have unique proteins; RBC plasma
membrane contains 50+ types of proteins.
2. Membrane proteins determine most of the membrane’s functions.
3. Channel proteins allow a particular molecule to cross membrane freely (e.g., Clchannels).
4. Carrier proteins selectively interact with a specific molecule so it can cross the
plasma membrane (e.g., Na+ - K+ pump, sodium potassium pump).
5. Receptor proteins are shaped so a specific molecule (e.g., hormone or other
molecule) can bind to it.
6. Enzymatic proteins catalyze specific metabolic reactions.

Cell Wall. This is a thick layer outside the cell membrane used to give a cell
strength and rigidity. Cell walls consist of a network of fibres, which give strength
but are freely permeable to solutes (unlike membranes). Plant cell walls are made
mainly of cellulose, but can also contain hemicellulose, pectin, lignin and other
polysaccharides. There are often channels through plant cell walls called
plasmodesmata, which link the cytoplasms of adjacent cells. Fungal cell walls are
made of chitin. Animal cells do not have a cell wall.
2.1
ARCHITECTURAL PLANS OF CELLS
Cells have evolved two basic architectural plans;
1. Cells without a nucleus = Prokaryotes (can also be spelled prokaryotes)
o
includes the Bacteria and Archaea
o
generally very small, unicellular
2. Cells with a nucleus = Eukaryotes (eukaryotes)
o
include the Animals, Plants, Fungi, and Protests
o
some unicellular, some multicellular forms
2.1.1 Cells are joined by a variety of intracellular junctions

In multicellular organisms, adjacent cells are held together by several types of
specialized junctions.
1. Tight junctions (found in animals): specialized "belts" that bind two cells
tightly to each other, prevent fluid from leaking into intracellular space.
2. Desmosomes (found in animals): intercellular "rivets" that create tight
bonds between cells, but allow fluids to pass through intracellular spaces.
3. Gap junctions (found in animals): formed by two connecting protein
rings embedded in cell membrane of adjacent cells. Allows passage of
water, small solutes, but not macromolecules (proteins, nucleic acids).
4.
Plasmodesmata (found in plants): channels connecting cells; allow free
passage of water and small solutes, but not macromolecules (proteins,
nucleic acids).
2.1.1 EUKARYOTIC CELLS
Eukaryotes are generally more advanced than prokaryotes. There are many unicellular
organisms which are eukaryotic, but all cells in multicellular organisms are eukaryotic.
Characteristics:

Nuclear membrane surrounding genetic material

Numerous membrane-bound organelles

Complex internal structure

Appeared approximately one billion years ago
Examples:

Paramecium

Dinoflagellates

sapiens
Figure 10: Structure of Eukaryotic cell
2.2
PROKARYOTIC CELLS
Prokaryotes are unicellular organisms, found in all environments. Prokaryotes are the
largest group of organisms, mostly due to the vast array of bacteria which comprise the
bulk of the prokaryote classification.
Characteristics:

No nuclear membrane (genetic material dispersed throughout cytoplasm)

No membrane-bound organelles

Simple internal structure

Most primitive type of cell (appeared about four billion years ago)
Examples:

Staphylococcus

Escherichia coli (E. coli)

Streptococcus
2.2.1 METABOLIC DIVERSITY IN PROKARYOTES
1. Heterotroph
Organism that is dependant upon outside sources of organic molecules
(a ) Photoheterotrophes
Organisms that can use light to produce ATP but they msut obtain carbon from another
source. This type of metabolism is only found in prokaryotes
( b ) Chemoheterotrophs
The majority of bacteria are chemoheterotrophs. There are three different types.
1) Saprobes: decomposers that absorb nutrients from dead organic material.
2) Parasites: absorb nutrients from the body fluids of living hosts
3) Phagotrophs: ingest food ad digest it enzymatically within cells or
multicellular bodies
2. Autotroph
Organism that is able to synthesize organic molecules from inorganic substances
a. Photosynthetic Autotrophes (Phototrophs)
Organisms that harness light energy to drive the synthesis of organic compounds from
CO2. These organisms use and inernal membrane system with light harnessing
pigments, (e.g. cyanobacteria, algae, and plants).
b. Chemosynthetic Autotrophs (Chemotrophs)
Organisms that use energy from specific inorganic substances to produce organic
molecules from carbon dioxide and provide life processes
c. Chemoautotrophs
Organisms that need only carbon dioxide as their carbon source. They obtain energy by
oxidizing inorganic substances like hydrogen sulfide, ammonia, ferrous or other ions.
3. Oxygen requirements
Oxygen requirements can also be used in classifying prokaryotes.
a. Obligate aerobes: use oxygen for cellular respiration and
cannot survive without it.
b. Facultative anaerobes: will use oxygen if present, but can
grow by fermentation in an environment without oxygen.
c. Obligate anaerobes: cannot use oxygen and are killed by it.
4. Nitrogen metabolism
Nitrogen is essential in the synthesis of proteins and nucleic acids. Prokaryotes can
metabolize most nitrogenous compounds. Some bacteria can convert ammonia into
nitrates. Other bacteria can convert atmospheric nitrogen to ammonia: this process is
called nitrogen fixation. Cyanobacteria can fix nitrogen. In fact, cyanobacteria only
require light carbon dioxide, atmospheric nitrogen, water and some minerals in order to
survive. They are among the most self-sufficient of all organisms.
Figure 11: Structure of prokaryotic cell.
2.2.2 MOVEMENT OF PROKARYOTES
Prokaryotes move by way of chemotaxis. Chemotaxis is the movement of an organism
towards or away from a chemical. Chemicals that cause the organism to move toward
them (positive chemotaxis) are called attractants. Chemicals that induce the organism to
move away (negative chemotaxis) are called repellents. This response has been studied
extensively. Cheotaxis suggests some type of sensing and response. Bacterial behavior
can be described as a combination of runs and twiddles (tumbles). Run is a steady swim.
Twiddle occurs when an organism stops and jiggles in place. This causes a change in
direction. As bacteria experience higher concentrations of the attractant, the twiddling
movement becomes less frequent and they run for longer periods of time. Temporal
sensing can explain the above phenomenon. Bacteria sense the environment. There are
receptors on the cell which can transfer molecules into the cell. The bacteria swims
towards a higher concentration of the attractant.
2.3 Summary of the Differences Between Prokaryotic and Eukaryotic Cells
PROKARYOTIC CELLS
EUKARYOTIC CELLS
small cells (< 5 µm)
larger cells (> 10 µm)
always unicellular
often multicellular
no nucleus or any membrane-bound
always have nucleus and other membrane-
organelles
bound organelles
DNA is circular, without proteins
DNA is linear and associated with proteins to
form chromatin
ribosomes are small (70S)
ribosomes are large (80S)
no cytoskeleton
always has a cytoskeleton
cell division is by binary fission
cell division is by mitosis or meiosis
reproduction is always asexual
reproduction is asexual or sexual
2.3.1 ENDOSYMBIONT THEORY:
All organelles seem to share many properties with bacteria: contain 70S ribosomes
(whereas rest of eukaryote cells contain 80S ribosomes), divide by binary fission, contain
circular DNA without nucleus, etc. Lynn Margulis proposed endosymbiont hypothesis:
that organelles derived from ancient colonization of large bacteria (became the eukaryotic
cell) by smaller bacteria (became the mitochondria, chloroplast, etc.) .This idea is called
endosymbiosis, and is supported by these observations:

Organelles contain circular DNA, like bacteria cells.

Organelles contain 70S ribosomes, like bacteria cells.

Organelles have double membranes, as though a single-membrane cell had been
engulfed and surrounded by a larger cell.
DIFFUSION AND THE PROBLEM OF SIZE
All organisms need to exchange substances such as food, waste, gases and heat with their
surroundings. These substances must diffuse between the organism and the surroundings.
The rate at which a substance can diffuse is given by Fick's law:
Rate of Diffusion

surface area x concentration
difference
distance
The rate of exchange of substances therefore depends on the organism's surface area that
is in contact with the surroundings. The requirements for materials depend on the volume
of the organism, so the ability to meet the requirements depends on the surface area:
volume ratio. As organisms get bigger their volume and surface area both get bigger, but
volume increases much more than surface area.. This can be seen with some simple
calculations for different-sized organisms. In these calculations each organism is assumed
to be cube-shaped to make the calculations easier. The surface area of a cube with length
of side L is LxL X6 (6L²), while the volume is L³.
Organism
bacterium
amoeba
fly
dog
whale
Length
1 mm
SA (m²)
(10-6
6 x 10-12
m)
100 mm
(10-4
m)
10 mm
(10-2
m)
(100
1m
m)
100 m
m)
(102
6 x 10-8
vol (m³)
SA/vol (m-1)
10-18
6,000,000
10-12
60,000
6 x 10-4
10-6
600
6 x 100
100
6
6 x 104
106
0.06
So as organisms get bigger their surface area/volume ratio gets smaller. A bacterium is
all surface with not much inside, while a whale is all insides with not much surface. This
means that as organisms become bigger it becomes more difficult for them to exchange
materials with their surroundings. In fact this problem sets a limit on the maximum size
for a single cell of about 100 mm. In anything larger than this materials simply cannot
diffuse fast enough to support the reactions needed for life. Very large cells like birds'
eggs are mostly inert food storage with a thin layer of living cytoplasm round the outside.
Organisms also need to exchange heat with their surroundings, and here large animals
have an advantage in having a small surface area/volume ratio: they lose less heat than
small animals. Large mammals keep warm quite easily and don't need much insulation or
heat generation. Small mammals and birds lose their heat very readily, so need a high
metabolic rate in order to keep generating heat, as well as thick insulation. So large
mammals can feed once every few days while small mammals must feed continuously.
2.6 CELL DIFFERENTIATION
Cell differentiation leads to higher levels of organisation:

A tissue is a group of similar cells performing a particular
function. Simple tissues are composed of one type of cell,
while compound tissues are composed of more than one type
of cell. Some examples of animal tissues are: epithelium
(lining tissue), connective, skeletal, nerve, muscle, blood,
glandular. Some examples of plant tissues are: epithelium,
meristem,
epidermis,
vascular,
leaf,
chollenchyma,
sclerenchyma, parenchyma.

An organ is a group of physically-linked different tissues
working together as a functional unit. For example the
stomach is an organ composed of epithelium, muscular,
glandular and blood tissues.

A system is a group of organs working together to carry out
a specific complex function. Humans have seven main
systems: the circulatory, digestive, nervous, respiratory,
reproductive, urinary and muscular-skeletal systems.
2.7 MOVEMENT ACROSS CELL MEMBRANES
Cell membranes are a barrier to most substances, and this property allows materials to be
concentrated inside cells, excluded from cells, or simply separated from the outside
environment. This is compartmentalisation is essential for life, as it enables reactions to
take place that would otherwise be impossible. Eukaryotic cells can also
compartmentalize materials inside organelles. Obviously materials need to be able to
enter and leave cells, and there are five main methods by which substances can move
across a cell membrane:
1.
Lipid Diffusion (or Simple Diffusion)
Figure 13: The diagram above showing the process of simple diffusion across cell
membranes.
A few substances can diffuse directly through the lipid bilayer part of the membrane. The
only substances that can do this are lipid-soluble molecules such as steroids, or very
small molecules, such as H2O, O2 and CO2. For these molecules the membrane is no
barrier at all. Since lipid diffusion is (obviously) a passive diffusion process, no energy is
involved and substances can only move down their concentration gradient. Lipid
diffusion cannot be controlled by the cell, in the sense of being switched on or off.
2.
Osmosis
Osmosis is the diffusion of water across a membrane. It is in fact just normal lipid
diffusion, but since water is so important and so abundant in cells (its concentration is
about 50 M), the diffusion of water has its own name - osmosis. The contents of cells are
essentially solutions of numerous different solutes, and the more concentrated the
solution, the more solute molecules there are in a given volume, so the fewer water
molecules there are. Water molecules can diffuse freely across a membrane, but always
down their concentration gradient, so water therefore diffuses from a dilute to a
concentrated solution.
Figure 14: The diagram above showing the process of osmosis across cell
membranes.
Water Potential. Osmosis can be quantified using water potential, so we can calculate
which way water will move, and how fast. Water potential (ψ, the Greek letter psi,
pronounced "sy") is simply the effective concentration of water. It is measured in units of
pressure (Pa, or usually kPa), and the rule is that water always "falls" from a high to a
low water potential (in other words it's a bit like gravity potential or electrical potential).
100% pure water has Y = 0, which is the highest possible water potential, so all solutions
have ψ < 0, and you cannot get ψ > 0.
Figure 15: The diagram above showing the process of simple diffusion across cell
membranes.
Osmotic Pressure (OP). This is an older term used to describe osmosis. The more
concentrated a solution, the higher the osmotic pressure. It therefore means the opposite
to water potential,
OP.
Cells and Osmosis. The concentration (or OP) of the solution that surrounds a cell will
affect the state of the cell, due to osmosis. There are three possible concentrations of
solution to consider:

Isotonic solution
a solution of equal OP (or concentration) to a cell

Hypertonic solution
a solution of higher OP (or concentration) than a cell

Hypotonic solution
a solution of lower OP (or concentration) than a cell
The effects of these solutions on cells are shown in this diagram:
Figure 16: The diagram above showing the effect of placing animal and plant cells in
hypotonic, isotonic and hypertonic solutions.
These are problems that living cells face all the time. For example:

Simple animal cells (protozoans) in fresh water habitats are surrounded by a
hypotonic solution and constantly need to expel water using contractile vacuoles
to prevent swelling and lysis.

Cells in marine environments are surrounded by a hypertonic solution, and must
actively pump ions into their cells to reduce their water potential and so reduce
water loss by osmosis.

Young non-woody plants rely on cell turgor for their support, and without enough
water they wilt. Plants take up water through their root hair cells by osmosis, and
must actively pump ions into their cells to keep them hypertonic compared to the
soil. This is particularly difficult for plants rooted in salt water.
3.
Passive Transport (or Facilitated Diffusion).
Figure 17: The diagram above showing the process of passive diffusion across cell
membranes.
Passive transport is the transport of substances across a membrane by a trans-membrane
protein molecule. The transport proteins tend to be specific for one molecule (a bit like
enzymes), so substances can only cross a membrane if it contains the appropriate protein.
As the name suggests, this is a passive diffusion process, so no energy is involved and
substances can only move down their concentration gradient. There are two kinds of
transport protein:

Channel Proteins form a water-filled pore or channel in the membrane. This
allows charged substances (usually ions) to diffuse across membranes. Most
channels can be gated (opened or closed), allowing the cell to control the entry
and exit of ions.

Carrier Proteins have a binding site for a specific solute and constantly flip
between two states so that the site is alternately open to opposite sides of the
membrane. The substance will bind on the side where it at a high concentration
and be released where it is at a low concentration.
4.
Active Transport (or Pumping).
Figure 18: The diagram above showing the process of active transport across cell
membranes.
Active transport is the pumping of substances across a membrane by a trans-membrane
protein pump molecule. The protein binds a molecule of the substance to be transported
on one side of the membrane, changes shape, and releases it on the other side. The
proteins are highly specific, so there is a different protein pump for each molecule to be
transported. The protein pumps are also ATPase enzymes, since they catalyse the
splitting of ATP g ADP + phosphate (Pi), and use the energy released to change shape
and pump the molecule. Pumping is therefore an active process, and is the only transport
mechanism that can transport substances up their concentration gradient.
The Na+K+ Pump. This transport protein is present in the cell membranes of all animal
cells and is the most abundant and important of all membrane pumps.
Figure 19: The diagram above showing the function of Na-k pump across cell
membranes.
The Na+K+ pump is a complex pump, simultaneously pumping three sodium ions out of
the cell and two potassium ions into the cell for each molecule of ATP split. This means
that, apart from moving ions around, it also generates a potential difference across the
cell membrane. This is called the membrane potential, and all animal cells have it. It
varies from 20 to 200 mV, but and is always negative inside the cell. In most cells the
Na+K+ pump runs continuously and uses 30% of all the cell's energy (70% in nerve cells).
The rate of diffusion of a substance across a membrane increases as its concentration
gradient increases, but whereas lipid diffusion shows a linear relationship, facilitated
diffusion has a curved relationship with a maximum rate. This is due to the rate being
limited by the number of transport proteins. The rate of active transport also increases
with concentration gradient, but most importantly it has a high rate even when there is no
concentration difference across the membrane. Active transport stops if cellular
respiration stops, since there is no energy.
Figure 20: A graph of rate of transport against concentration difference for
different cell transport mechanisms.
5.
Vesicles
The processes described so far only apply to small molecules. Large molecules (such as
proteins, polysaccharides and nucleotides) and even whole cells are moved in and out of
cells by using membrane vesicles.

Endocytosis is the transport of materials into a cell. Materials are enclosed by a
fold of the cell membrane, which then pinches shut to form a closed vesicle.
Strictly speaking the material has not yet crossed the membrane, so it is usually
digested and the small product molecules are absorbed by the methods above.
When the materials and the vesicles are small (such as a protein molecule) the
process is known as pinocytosis (cell drinking), and if the materials are large
(such as a white blood cell ingesting a bacterial cell) the process is known as
phagocytosis (cell eating).
Figure 21: The diagram above showing the process of Endocytosis across cell
membranes.

Exocytosis is the transport of materials out of a cell. It is the exact reverse of
endocytosis. Materials to be exported must first be enclosed in a membrane
vesicle, usually from the RER and Golgi Body. Hormones and digestive enzymes
are secreted by exocytosis from the secretory cells of the intestine and endocrine
glands.
Sometimes materials can pass straight through cells without ever making contact with
the cytoplasm by being taken in by endocytosis at one end of a cell and passing out by
exocytosis at the other end.
2.10 REVISION QUESTIONS
Identify the letter of the choice that best completes the statement or answers the question.
1. Inside the nuclear envelope the DNA in the form of fine strands is called
a. chromosomes
b. nuclear matrix
c. chromatin
d. nucleolus
2. Not all substances can cross the plasma membrane, for this reason, the cell membrane
is said to be
a. a barrier
wall
b. selectively permeable
c. membrane bound
d. a cell
3. Provides structure and support in plant cells:
a. a nuclear envelope
b. a cell membrane
c. cell wall
d. cytoskeleton
4. Microfilaments and microtubules
a. contain digestive enzymes
c. are sites of protein synthesis
b. function in cell structure and movement
d. are sites of photosynthesis
5. The cell organelle that processes and packages substances produced by the cell is
a. mitochondria
b. ribosomes
c. Golgi apparatus
d. ER
6. The cell organelle that digests molecules, old organelles, and foreign substances is
a. mitochondria
b. ER
c. Golgi apparatus
d. lysosomes
7. What are flagella?
a. long, whip-like projections
c. bundles of chloroplasts
b. short, hair-like projections
d. central vacuoles
8. A prokaryote has
a. a nucleus
b. a cell membrane
c. membrane bound organelles
d. All of the
above
9. The first person to observe and describe microscopic organisms and living cells was
a. Robert Hooke
b. Rudolf Virchow
c. Anton Leeuenhoek
d. Theodor Schwann
10. Are short hair-like projections found on cells, often numerous:
a. flagella
b. ribosomes
c. cilia
d. cytoskeleton
11. Organelle involved in the synthesis of steroids in glands and the breakdown of toxic
waste:
a. soft ER
b. smooth ER
c. rough ER
d. mitochondria
2.11
REVISION QUESTIONS 2
Identify the letter of the choice that best completes the statement or answers the
question.
1. Net movement of water across a cell membrane occurs
a. from a hypotonic solution to a hypertonic solution
c. from a hypertonic
solution to a hypotonic solution
b. from an isotonic solution to another isotonic solution
d. through gated water
channels
2. All forms of passive transport depend on
a. energy from the cell in the form of ATP
c. carrier proteins
b. the kinetic energy of molecules
d. ion channels
3. Sodium-potassium pumps
a. move Na+ ions and K+ ions into cells
c. move Na+ ions and K+ ions
out of cells
b. move Na+ ions out of cells and K+ ions into cells
d. move Na+ ions into cells
and K+ ions out of cells
4. A structure that can move excess water out of unicellular organisms is a
a. carrier protein
b. contractile vacuole
c. ion channel
d. cell membrane
pump
5. Plasmolysis of a human red blood cell would occur if the cell were
a. in an isotonic solution
c. in a hypertonic solution
b. in a hypotonic solution
d. None of the above
6. A cell must expend energy to transport substances using
a. cell membrane pumps
osmosis
b. facilitated diffusion
c. ion channels
d.
3.0CELL CYCLE, DIVISION & CHROMOSOMES
3.2 INTRODUCTION
A typical eukaryotic cell contains DNA that forms a number of distinct chromosomes.
Human somatic (body) cells have 46 chromosomes. When human cells divide, a copy of
each of the 6 chromosomes is inherited by each cell. The organelles must also be
apportioned in the appropriate numbers. This process occurs in the cell cycle.
Traditionally, the cell cycle has been divided into stages: G1 phase, S phase, G2 Phase,
and M Phase. M = Mitosis, S = Synthesis of DNA and histones, G1 and G2 = gap 1 and
gap 2
3.3 TERMS USED:
Let’s review the following terms: chromosome, chromatid, and centromere
(kinetochore).
1. Chromosome
A gene is made up of DNA which codes for one or more polypeptides. A
chromosome is made up of many genes. The DNA in the chromosome is wrapped
around histone and non-histone proteins. Before DNA synthesis, there is only one
double stranded helix of DNA in each chromosome.
2. Chromatid
After DNA synthesis , there are two identical DNA helices connected by a structure
called the centromere. Each DNA helix is called a chromatid.
3. Centromere (Kinetochore)
After DNA synthesis, the chromosome is made up of two identical chromatids
connected by a centromere (Kinetochore). These chromatids are called sister
chromatids.
The Cell cycle is an endless is an repetition of mitosis, cytokinesis, growth, and
chromosomal replication. Some cells, such as fingernail cells, break out of the cycle and
die, thus performing their function. Cells are not static structures, but are created and die.
The life of a cell is called the cell cycle and has four phases:
Figure 22: The structure of the cell cycle.
3.4 IMPORTANCE OF CELL DIVISION

The ability of organisms to reproduce their kind is the one characteristic that best
distinguishes living things from nonliving matter.

The continuity of life is based on the reproduction of cells, or cell division.
Cell division functions in reproduction, growth, and repair.

The division of a unicellular organism reproduces an entire organism, increasing the
population.

Cell division on a larger scale can produce progeny for some multicellular organisms.


This includes organisms that can grow by cuttings.
Cell division enables a multicellular organism to develop from a single fertilized egg
or zygote.

In a multicellular organism, cell division functions to repair and renew cells that die
from normal wear and tear or accidents.

Cell division is part of the cell cycle, the life of a cell from its origin in the division of
a parent cell until its own division into two.
CELL DIVISION BY MITOSIS
Mitosis is a type of cell division that produces genetically identical cells. During mitosis
DNA replicates in the parent cell, which divides into two new cells, each containing an
exact copy of the DNA in the parent cell. The only source of genetic variation in the
cells is via mutations.
Duplication and division of the nucleus and the chromosomes contain therein. The Gap
1, synthesis, and Gap 2 stages have been described as Interphase. The M stage ( Mitosis)
has five phases; Prophase, Prometaphase, Metaphase, Anaphase, and telophase. The
letters IPPMAT describe the cell cycle. Gap 1, synthesis and Gap 2 Phases are all parts
of Interphase.
Interphase occurs first and prepares the cell for mitosis. During interphase, the cells
grows, replicates the DNA and chromosomal proteins, and grows.
INTERPHASE
1. G1 Phase or the Gap 1 Phase
The chromosomes decondense as they enter the G1 Phase; this is a physiologically active
for the cell. The cell synthesizes the necessary enzymes and proteins needed for cell
growth. DNA consists of a single unreplicated helix (with histone and non-histone
proteins. In the G1, the cell may be growing, active, and performing many intense
biochemical activities.
2. S Phase or he Synthesis Phase
DNA and chromosomal proteins are replicated. This phase lasts a few hours.
3. G2 phase of the Gap2 Phase
Between synthesis and mitosis. The mitotic spindle proteins are synthesized. The
mitotic spindle is structure that is involved with the movement of chromosomes during
mitosis.

This is when the cell is not dividing, but is
carrying out its normal cellular functions.
Interphase

chromatin not visible

DNA, histones and centrioles all replicated

Replication of cell organelles e.g. mitochondria,
occurs in the cytoplasm.

chromosomes condense and become visible –
this prevents tangling with other chromosomes.

Due to DNA replication during interphase, each
chromosome consists of two identical sister
Prophase
chromatids connected at the centromere

centrioles move to opposite poles of cell

nucleolus disappears

phase ends with the breakdown of the nuclear
membrane

spindle fibres (microtubules) connect centrioles
to chromosomes
Metaphase

chromosomes align along equator of cell and
attaches to a spindle fibre by its centromere.

centromeres split, allowing chromatids to
separate

chromatids move towards poles, centromeres
first, pulled by kinesin (motor) proteins walking
Anaphase
along microtubules (the track)

Numerous mitochondria around the spindle
provide energy for movement

spindle fibres disperse

nuclear membranes from around each set of
Telophase
chromatids

nucleoli form

In animal cells a ring of actin filaments forms
round the equator of the cell, and then tightens
to form a cleavage furrow, which splits the cell
Cytokinesis
in two.

In plant cells vesicles move to the equator, line
up and fuse to form two membranes called the
cell plate. A new cell wall is laid down between
the membranes, which fuses with the existing
cell wall.
3.8.1 Mitosis and Asexual Reproduction
Asexual reproduction is the production of offspring from a single parent using mitosis.
The offspring are therefore genetically identical to each other and to their “parent”- in
other words they are clones. Asexual reproduction is very common in nature, and in
addition we humans have developed some new, artificial methods. The Latin terms in
vivo (“in life”, i.e. in a living organism) and in vitro (“in glass”, i.e. in a test tube) are
often used to describe natural and artificial techniques.
3.8.2 FUNCTION OF MITOSIS
Cell division consists of mitosis (nuclear and chromosomal events) and cytokinesis (cell
membrane and cytoplasm events). Mitotic cell division serves organisms in 2 ways.
1. Single cell organisms
Mitosis allow for and increase in the population. This is a form of asexual
reproduction. There is no exchange of genes between individuals. The colony will
be made up of individuals with genes what are identical to the founder, called clones.
2. Multicellular Organisms
a. Mitosis and cytokinesis allow for an organism to grow in size while
maintaining the surface area volume ratio of its cells.
b. Mitosis and cytokinesis allow for specialization of cell types hrough cell
differentiation.
c. Mitosis and cytokinesis that are dead or damages allow cells to be
replaced.
3.
Abnormal Cell Division
a. Cancer cells
Cancer cells do not respond to normal cell division controls. They divide
excessively and ignore density-dependent inhibition.
b. Metastasis
If cancer cells enter the circulatory system (blood and lymph), then the cancer
can spread to all parts of the body. This spread is called metastasis.
3.9 CYTOKINESIS; DIVISION OF THE CYTOPLASM
1. Animal cells
Cytokinesis usually begins with an cleavage furrow at the metaphase plate by an
indentation in the surface of the cell. It looks as though the cell membrane were
being pulled toward the middle, as if a thread were being wrapped around the cell and
being tightened. On the cytoplasmic side of the furrow is a contractile ring of actin
microfilaments. As the dividing cell’s ring of microfilaments contracts the diameter
of the cell diminished. The furrow is created by actin microfibrills that are found in
the cytoplasm just beneath the cell membrane. The furrow deepens until the cell is
pinched in two.
2. Plant cells
At the time of telophase, small membraneous vesicles filled with polysaccharides,
formed in the golgi complex, form on the metaphaste plate. The vesicles continue to
form to form until they are more or less continuous and forms a double membrane,
which is called the cell plate. The cell plate becomes impregnated with pectin and
forms a cell wall. The cell plate forms across the midline of the plant cell where the
old metaphase plate was located.
1.
Mitosis vs. Meiosis
a. Mitosis
Occurs in haploid, diploid, and popyploid cells.
b. Meiosis
Occurs only in diploid cells and popyploid cells. The nucleus divides twice producing
four nuclei. The chromosomes replicate only once, so each nucleus contains half of the
number of chromosomes
c. Haploid Chromosome
Each haploid chromosome is a new combination of old chromosomes because of crossing
over.
MEIOSIS I
There are two stages of Meiosis: Meiosis I and Meiosis II. Meiosis I is the replication of
chromosomes, crossing over of the chromosomes, and reduction in the chromosome
number from diploid to haploid. Meiosis I is often called the reduction division.
Premeiotic Interphase
G1,S (replication of the chromosomes), and G2.
Meiotic Prophase I: The first stage.
This is long and complex compared with mitotic prophase.
 Nuclear membrane disappears.
 Spindle fibers form.
 The chromosomes condense.
 The homologous chromosomes pair p by touching each other in the appropriate
places. First there is a lot of random movement of chromosomes until the
homologous chromosomes find each other. It is important, for example, that
chromosome #13 find homologous chromosome #13. When the two homologous
touch each other in the same place, a specialized structure called the
synaptonemal complex holds the homologues together.
 The meiotic cell of a human now has 23 genetic entities called tetrads, each
packet containing four chromatids and two centromeres. This is the point when
crossing over occurs. A special enzyme causes the chromatids to unwind,
revealing the strands of DNA. A complex series of events happen and the genetic
material is exchanged between homologues
 Crossing over may occur at the introns.
 Several Thousand base pairs of one strand pairs with the chromatid on another
homologues. These are breakages and the chomatids untangle themselves.
Meanwhile other enzymes are repairing the breaks in the DNA. This process
makes new chromatids and is a source of genetic variation within a population.
 After crossing over, the homologues begin to pull away from each other, except at
the crossing over points called the ciasmata (chiasma – singular)
Metaphase I
In the first metaphase, the tetrads are brought to the metaphase plate. The synaptonemal
complex is lined up on the metaphase plate.
Anaphase I
There is no separation of the centromeres, but the synaptonemal complex separates. This
means that the homologues separate and move to opposite poles. The first meiotic
division reduces the chromosome number by half.
Telophase I
In this phase, the nucleus reorganizes and the nuclear membrane reforms. The
chromosomes decondense.
Cytokinesis I
In this phase, the cytoplasmic division occurs.
MEIOSIS II
Division of the chromosomes, analogous to mitosis
Meiotic Interphase
This involves G1 and G2 phases only. There is no S phase in this Interphase. This phase
may be brief or last a long time.
Prophase II
As in mitotic prophase, there are two sister chromatids attached to a centromeres. The
chromosomes condense, the nucleus disappears, ad the spindle apparatus forms.
Metaphase II
Centromeres move to the metaphase plate during metaphase II.
Anaphase II
During anaphase II, centromeres divide, and sister chromatids separate and move to the
opposite poles.
Telophase II
During Telophase II, the nuclear membrane reforms and chromosomes decondense.
Cytokinesis II
The cytoplasm divides.
Importance of Meiosis
a. Sexual reproduction is reshuffling of the genes of all the successful individuals of the
population. There are virtually infinite possibility combinations of genes.
b. The reduction and division of the chromosomes in the egg and sperm makes
fertilization possible and enables the maintenance of a constant chromosome number
within a species.
3.16 HOMOLOGOUS CHROMOSOMES
Chromosomes
In humans there are 46 chromosomes. Each chromosome consists of a double helix
molecule of DNA. The DNA is folded with proteins to make up a chromosome. One
chromosome represented hundreds of thousands of genes, and each gene is a specific
region of the DNA molecule. A gene’s specific location on the chromosome is called the
its locus. The 46 chromosomes are actually 23 pair of chromosomes. The members of
each pair are called homologous chromosomes (homologues). The two homologues are
functionally equivalent and contain the same kinds of genes arranged in the same order.
Autosomes
one set of chromosomes that does not occur as homologues occurs in males. The X
chromosome and the Y chromosome are not homologues, but pair up in meiosis. In
females, then are two X chromosomes that are homologues. These chromosomes are the
sex chromosomes and the other 22 pairs of chromosomes are called autosomes.
Homologues
During meiosis, three things happen to the homologues .The homologues pair up.
The homologues exchange genetic information. This is called crossing over
The newly scrambled chromosomes separate and go into different daughter cells in such
a way that each daughter cell contains only one of each pair of homologues. These cells
are called gametes or sex cells.
3.18 REVISION QUESTIONS 1
1. What is meant by the concept that cells go through a cell cycle?
2. What are the key roles of cell division?
3. What is the significance of chromosome replication?
4. Sketch and label replicated chromosomes.
5. List the phases of the cell cycle with a brief description of what occurs in each phase.
6. Label the stages and key features of each stage.
7. How does the spindle apparatus distribute chromosomes to the daughter cells?
8. What is the role of the kinetochores and the microtubules?
1.0
HISTOLOGY
Introduction
Every organism, whether it’s body is unicellular or multicellular, is capable of
performing all vital functions such as respiration, ingestion, excretion and reproduction.
A group of cells of the same type or of a mixed type having a common origin and
performing similar functions are called tissues.
1.1
ANIMAL HISTOLOGY
4.1.1 Introduction
The tissues in the body of animals are classified into four basic types, based on their
functional specialization.
1. Epithelial tissue which is meant mainly for protection and absorption.
2. Muscular tissue which is responsible for movement.
3. Connective tissue which connects and binds other tissues.
4. Nervous tissue which is capable of controlling and coordinating various functions.
4.1.2 EPITHELIAL TISSUE
Based on the arrangement of cells, epithelium can be distinguished into three types:
 Simple or unilaminar epithelium, where the cells are arranged in a single layer on
a basement membrane.
 Stratified or multilaminar epithelium, where the cells are arranged in more than
one layer on a basement membrane.
 Pseudo-stratified epithelium, where the cells are arranged in a single layer on a
basement membrane. However, there is a false appearance of more than one layer
due to a difference in the height of the cells and the position of their nuclei.
4.1.3 CHARACTERISTIC FEATURES OF EPITHELIAL CELLS
 The cells always have a definite shape. They are either polygonal or cuboidal
(isodiametric) or rectangular. Very rarely are the cells irregular.
 The cells are compactly arranged on a thin, structure less basement membrane
which is secreted by the cells themselves.
 Due to the compact arrangement, intercellular spaces are usually absent.
However, sometimes small intercellular spaces may be present filled with a
cementing substance.
 The cells are characterised by the presence of a large amount of cytoplasm. It may
be clear and transparent or granular.
 The cells are always uninucleate. The nucleus is large and prominent.
 The cells are capable of undergoing simple mitotic divisions.
4.1.5 FUNCTIONS OF EPITHELIAL CELLS INCLUDE:

movement materials in, out, or around the body.

protection of the internal environment against the external environment.

Secretion of a product.
Glands can be single epithelial cells, such as the goblet cells that line the intestine.
Multicellular glands include the endocrine glands. Many animals have their skin
composed of epithelium. Vertebrates have keratin in their skin cells to reduce water loss.
Many other animals secrete mucus or other materials from their skin, such as earthworms
do. The multicellular glands can be classified into two types:
a) Exocrine glands in which a duct is present for transporting the secretions. e.g.
Liver, sweat gland.
b) Endocrine glands or ductless glands in which a duct is absent. Hence, the
secretions are transported by blood. e.g. Pituitary gland, thyroid gland.
4.1.8 Stratified Epithelium (Multilaminar Epithelium)
Here, the cells are arranged in more than one layer. Stratified epithelium is classified into
the following types based on the shape of the constituent cells.
Stratified squamous epithelium in which, more than one layer of flat, polygonal cells are
found arranged on a basement membrane. It is a characteristic feature of the skin. It also
occurs in the lining of the tongue and the oesophagus.
4.13 MUSCULAR TISSUE
The muscular tissue is a tissue that is capable of bringing about different types of
movements in the body. It is one of the highly specialized animal tissues. It is a derivative
of mesoderm. The muscular tissue exhibits a unique property called contractibility. It is
the capacity of the cells to exhibit regular contractions and relaxations. Hence, it is also
known as contractile tissue. Muscular tissue exhibits the following characteristic features.
 The cells are always elongated and are therefore described as muscle fibres.
 Each muscle fibre usually has a limiting membrane called sarcolemma, in
addition to the cell membrane.
 The cytoplasm in the muscle fibres is specialised for contraction and is known as
sarcoplasm.
 The sarcoplasm always encloses minute, microscopic contractile units called
myofibrils.
 The myofibrils are in turn composed of ultra microscopic units called
myofilaments. The myofilaments are of two types.
a. Thin filaments, which are about 50 A0 in diameter and are composed of a
simple protein, called actin.
b. Thick filaments, which are about 100 A0 in diameter and are composed of
a simple protein called myosin.
 The muscular tissue has a direct blood supply (vascular)
 The muscle fibres have very limited capacity to undergo cell division.
4.14 TYPES OF MUSCULAR TISSUE
The muscular tissue is classified into the following three types
1. Smooth muscle
It is also called unstriped or nonstriated or involuntary or visceral muscle. The smooth
muscle always occurs in the form of thin sheets. Each sheet has a large number of
muscle fibres that are held together by a transparent connective tissue covering.
2. Striated muscle
It is also known as striped or voluntary or skeletal muscle. The striated muscle
occurs in bundles called fascicles. Each fascicle has a large number of muscle fibres
that are held together by connective tissue.
3. Cardiac muscle.
It is also known as heart muscle. The cardiac muscle fibres do not form fasciles. They are
arranged in the form of a network. The muscle fibres are elongated, cylindrical and
branched.
4.18 CONNECTIVE TISSUE
It is another highly specialized animal tissue. It is a derivative of mesoderm. The
specialization in connective tissue is for various specific functions. Following are some
of the functions of connective tissue:
 It connects and binds various other tissues and organs.
 It forms a protective covering around almost all-visceral organs.
 It forms a packing tissue, filling the unused spaces in the body.
 It forms a bedding substance inside various organs, in which the functional units
are enclosed.
 It plays an important role in the transport mechanism in the body.
 Some connective tissue cells produce a substance called heparin, which prevents
clotting of blood inside the body.
 Some connective tissue cells are capable of ingesting disease producing germs by
phagocytosis.
 Some connective tissue cells play an important role in thermoregulation.
4.19 CONNECTIVE TISSUE IS CHARACTERIZED BY THE FOLLOWING
FEATURES
 Presence of very few cells, which are loosely, arranged with prominent
intercellular spaces.
 Presence of a ground substance called matrix secreted by the cells.
 Presence of supporting structures in the matrix called fibres. Usually the fibres are
of two types white fibres made up of a protein called collagen and yellow fibres
made up of a protein called elastin.
4.20 TYPES OF CONNECTIVE TISSUE
Connective tissue is classified into the following major types based on the nature of
matrix.
 Connective tissue proper where, matrix is soft and homogeneous. Fibres are
present.
Types of connective tissue proper (based on the components of matrix)
Areolar tissue
Areolar tissue is the most common and the most widely distributed type of connective
tissue. It has a soft, homogeneous matrix in which both fibres and cells are embedded.
The fibres in the matrix are of two types-white and yellow fibres.
The cells present in the matrix are of four types:
1. Fibrocytes are stellate or star shaped cells, which produce the matrix and white
and yellow fibres.
 Macrophages are irregular, amoeboid cells which can ingest bacteria and other
disease producing germs by phagocytosis.
 Mast cells are spherical or oval cells, which produce the anticoagulant heparin.
 Fat cells are spherical or oval vacuolated cells, which occur in groups. These cells
also called adipocytes, are mainly meant for storage of reserve food (fat) and
thermoregulation.
FIBROUS TISSUE is a modification of the areolar tissue in which the matrix
predominantly contains white fibres. Yellow fibres are reduced
ELASTIC TISSUE is also a modification of the areolar tissue in which the matrix
predominantly contains yellow fibres. Hence, the tissue attains more of flexibility.
 Supporting tissue where, matrix is hard and rigid. Fibres may be present or absent.
 Fluid connective tissue where, matrix is in the liquid form. Fibres are absent
Figure 40: Yellow Elastic Tissue
1.2
PLANT HISTOLOGY
2.1 Introduction
A tissue is an aggregation of cells that have a common origin and structure, and perform
similar functions. Tissues are meant for meeting the physical and physiological needs of
the plant body. An angiosperm plant body shows two major types of tissues namely,
 Meristematic tissue and
 Permanent tissues
Figure 43: The view of the structure of the root and root meristem.
Plant cell types rise by mitosis from a meristem. A meristem may be defined as a region
of localized mitosis. Meristems may be at the tip of the shoot or root (a type known as the
apical meristem) or lateral, occurring in cylinders extending nearly the length of the
plant. A cambium is a lateral meristem that produces (usually) secondary growth.
Secondary growth produces both wood and cork (although from separate secondary
meristems).
4.2.3 Parenchyma
It is the main tissue in the plant body, occurring in almost all regions. It is particularly
abundant in the root and stem. It is the least specialised among the permanent tissues. The
cells of the tissues are called parenchyma cells. These cells are usually spherical or oval
in shape. Parenchyma cells also occur within the xylem and phloem of vascular bundles.
The largest parenchyma cells occur in the pith region, often, as in corn (Zea ) stems,
being larger than the vascular bundles. In many prepared slides they stain green.
TYPES OF PARENCHYMA
In the different regions of the plant body parenchyma cells are involved in different
functions. On this basis, following types of parenchyma can be recognized.
 Chlorenchyma is the parenchyma in which the cells contain large number of
chloroplasts. Chlorenchyma takes part in photosynthesis. It occurs in the leaves
and other green parts of the plant body.
 Prosenchyma is a type of parenchyma where cells are elongated with tapering
ends.
 Arenchyma is the parenchyma in which the cells enclose large intercellular spaces
that are filled with air. Aerenchyma helps in buoyancy and respiration. It is
characteristically found in aquatic floating plants.
 Vascular parenchyma is the parenchyma, which is found associated with the
vascular tissues xylem and phloem. Accordingly, it is distinguished into xylem
parenchyma and phloem parenchyma.
 Medullary parenchyma is the parenchyma, which is found radially arranged in
between the vascular bundles in the stem. It is meant for storage of reserve food.
 Conjunctive parenchyma is the parenchyma, which occurs in the root system. It is
specially meant for storage of water.
 Armed parenchyma is the parenchyma, which is found in the epidermis of leaves
in some gymnosperms. The cells have many spiny projections. It is defensive in
function.
FUNCTIONS OF PARENCHYMA
 Parenchyma is mainly involved in functions like storage and respiration. It
also takes part in other functions like photosynthesis, absorption, secretion and
protection.
4.2.4 COLLENCHYMA
It is a type of simple permanent tissue, which is mainly meant for providing
mechanical support to the shoot system of a plant. Collenchyma is completely absent in
the root. Collenchyma cells support the plant. These cells are charcterized by thickenings
of the wall, the are alive at maturity.
Based on the nature of secondary thickenings in the cell wall, collenchyma can be
distinguished into three types.
 Angular Collenchyma
In this type the deposition of hemi cellulose and pectin occurs only in the angles between
the cells. The cells are compactly arranged and intercellular spaces are absent.
 Lamellar Collenchyma
In this type, the deposition of hemi cellulose and pectin occurs only at the crosswalls
separating the adjacent cells. The cells are compactly arranged without any intercellular
spaces. This type is found usually in the petiole of leaves.
 Lacunar Collenchyma
In which the cells are either spherical or oval in shape and enclose small intercellular
spaces. The deposition of hemi cellulose and pectin occurs only along the border of
intercellular spaces. This type of collenchyma is usually found in the fruit wall.
FUNCTIONS OF COLLENCHYMA
Collenchyma is involved in the following functions in the plant body.

Providing mechanical support

Exchange of respiratory gases

Photosynthesis

Storage of secretory products
4.2.5 SCLERENCHYMA
It is a type of simple permanent tissue mainly meant for providing mechanical support
and protection to different parts of the plant body. Hence, sclerenchyma occurs in all the
parts of the plant body, including the fruit and seed. Sclerenchyma cells support the plant.
Compared to the fibres, the sclereides are much harder since they have a higher amount
of lignin. Sclereids occur in various shapes. Accordingly, they can be distinguished into
1. Brachy sclereids which are oval in shape
2. Microsclereids which are small and needle-like
3. Osteosclereids which are bone shaped and
4. Asterosclereids which are roughly star shaped
4.2.6 XYLEM
Xylem is a term applied to woody (lignin-impregnated) walls of certain cells of plants.
Xylem cells tend to conduct water and minerals from roots to leaves. Xylem is a
heterogeneous tissue made up of four different types of cellular elements. They are:

Xylem tracheids

Xylem tracheae

Xylem fibers and

Xylem parenchyma
On this basis, xylem vessels can be distinguished into five types.

Annular vessels in which the secondary thickening is in the form of rings placed
more or less at equal distance from each other.

Spiral vessels in which the secondary thickenings are present in the form of a
helix or coil.

Scalariform vessels in which the secondary thickenings appear in the form of
cross bands resembling the steps of a ladder.

Reticulate vessels in which the secondary thickenings are irregular and appear in
the form of a network.

Pitted vessels in which the secondary thickenings result in the formation of
depressions on the primary wall called pits.
Types of Xylem
Xylem can be distinguished into two types namely
 Primary xylem and
 Secondary xylem
Primary xylem is the xylem that is formed during normal growth. It is a derivative of
primary meristem. It occurs in both monocots and dicots. In the primary xylem, two types
of xylem vessels can be distinguished, namely protoxylem and metaxylem.
Secondary xylem is the xylem that is formed during secondary growth. It is derivative
of secondary meristem. It is a characteristic feature of only dicots. Secondary xylem is
commonly known as wood. It is of commercial importance since it is extensively used in
the manufacturing of doors, windows and furniture.
4.2.7
PHLOEM CELLS
Phloem is a complex permanent tissue, which is specialized for the conduction of
food and other organic substances. Phloem is also a heterogenous tissue, made up of
four different types of cellular elements, namely,
 Sieve tubes
 Companion cells
 Phloem parenchyma and
 Phloem fibres
TYPES OF PHLOEM
Primary Phloem
Primary phloem is the phloem that is formed during normal growth in the plant body. It is
a derivative of primary meristem. It is found in both monocots and dicots. The primary
phloem is further composed of protophloem and metaphloem.
Secondary Phloem
Secondary phloem is the phloem that is formed during secondary growth. It is a
derivative of secondary meristem. Secondary phloem is characteristic feature of only
dicots. It is also known as bast. It is also of commercial importance since it yields bast
fibers.
4.2.8 EPIDERMAL CELLS
Epidermis
The epidermal tissue functions in prevention of water loss and acts as a barrier to fungi
and other invaders. Thus, epidermal cells are closely packed, with little intercellular
space.
4.2.9 GUARD CELLS
To facilitate gas exchange between the inner parts of leaves, stems, and fruits, plants have
a series of openings known as stomata (singular stoma). Obviously these openings would
allow gas exchange, but at a cost of water loss. Guard cells are bean-shaped cells
covering the stomata opening. They regulate exchange of water vapor, oxygen and
carbon dioxide through the stoma.
4.2.11 SECONDARY GROWTH
Secondary growth is produced by a cambium. It occurs in rows or ranks of cork,
secondary xylem or secondary phloem cells. Cork cells (produced by a cork cambium)
are technically part of the epidermis, and contribute to the bark of woody stems. The
normal process of growth that occurs in every plant body is known as primary growth. It
is the result of the activity of primary meristem. The process of primary growth results in
the formation of primary permanent tissues such as primary xylem, primary phloem and
primary cortex. However in the dicot plants, there is a process of growth that begins after
a known period of primary growth. Such a growth is known as secondary growth. It is the
result of the activity of secondary meristem. It results in the formation of secondary
permanent tissues such as secondary xylem, secondary phloem and secondary cortex. As
a result, secondary growth brings about an increase in the girth of the plant body.
Dicot secondary growth occurs by growth of vascular cambium, to complete a full
vascular cylinder around the plant. Secondary xylem is produced to the inside of the
vascular cambium, secondary phloem to the outside. The living parts of the woody plant
are next to the vascular cambium.
Monocots usually don't have secondary growth. Some, such as bamboo and palm trees,
have secondary growth. Monocot secondary growth differs from dicot secondary growth
in that new bundles are formed at the edge of the stem. These new bundles are close
together, providing support for the stem.
SECONDARY GROWTH IN A DICOT STEM
In a dicot stem, secondary growth occurs both in the stele and cortex. The process occurs
simultaneously but is caused by separate strips of secondary meristem. In the stele,
secondary growth is initiated by vascular cambium, while in the cortex, it is initiated by
cork cambium.
SECONDARY GROWTH IN THE STELE
It is the result of the activity of the vascular cambium, which occurs in between xylem,
and phloem of each vascular bundle. Hence, it is also known as intra-fascicular cambium.
In addition, towards the beginning of secondary growth there is a process of
dedifferentiation in some of the parenchyma cells of the medullary rays, adjoining the
vascular cambium. As a result, these cells now become meristematic and represent the
inter-fascicular cambium. The meristematic cells in the intra-fascicular cambium and
inter-fascicular cambium fuse and result in the formation of a continuous strip of
meristem called cambial ring. The cambial ring at this stage has primary xylem on its
inner surface and primary phloem on its outer surface.
The cambial ring exhibits mitotic activity on both the sides. The mitotic activity on the
inner surface results in the formation of cells, which differentiate into a set of xylem. It
represents the secondary xylem. Similarly, the mitotic activity on the outer surface result
in the formation of cells, which differentiate into a set of phloem. It represents the
secondary phloem. Due to the formation of secondary xylem, the primary xylem becomes
pushed more towards the pith and the pith gets slightly reduced. However, the secondary
phloem grows and completely masks the primary phloem. Hence, it is not visible.
The mitotic activity of the cambial ring is purely seasonal. It occurs only twice during
every year, once in the spring and once in the autumn. Thus, every year two sets of
secondary xylem and two sets of secondary phloem are formed. Each year, the mitotic
division of the cambial ring usually begins in the spring season. The secondary xylem
that is formed in the spring season is therefore known as springwood or early wood,
while the secondary xylem formed in the autumn is known as autumn wood or late wood.
The springwood is generally characterized by the presence of xylem vessels having wider
lumen. This is because, spring is the ideal season for growth and the water requirement of
the plant is more in the spring. The two distinct layers of secondary xylem, the inner
springwood and the outer autumn wood together represent the (or annual ring). One such
annual ring is added every year due to secondary growth. Thus, it is possible to ascertain
the age of a dicot tree by counting the number of annual rings. While every year two sets
of secondary xylem and two sets of secondary phloem are formed, only one set is visible
because the secondary phloem formed later (in the autumn) grows over and masks the
secondary phloem formed earlier (in the spring).
SECONDARY GROWTH IN THE CORTEX
It is the result of the activity of a secondary meristem called cork cambium, which
appears between hypodermis and primary cortex. Some of the parenchyma cells in the
peripheral layers of cortex undergo dedifferentiation and become meristematic. These
cells now represent the cork cambium or phellogen. The cork cambium starts exhibiting
mitotic activity on both the sides, just as the cambial ring in the stele. The mitotic activity
on the inner surface of the cork cambium results in the formation of cells, which undergo
differentiation into a living tissue, called secondary cortex or phelloderm, just above the
primary cortex. The mitotic activity on the outer surface results in the formation of cells,
which undergo differentiation into a dead tissue, called cork or phellem, just below the
epidermis. The cork covers and masks the hypodermis. The tissue resulting from
secondary growth in the cortex the cork, the cork cambium and the secondary cortextogether represent a region called periderm. The periderm along with the primary cortex
represents the bark. In several dicot plants, the bark peels off regularly. Due to the
formation of periderm, the epidermis is subjected to pressure and as a result it breaks at
several places to form openings called lenticels. The lenticels, also known as aerating
pores, enclose a group of living cells called complementary cells. Through these cells
exchange of respiratory gases and to some extent transpiration take place. Thus,
secondary growth in the cortex results in the formation of periderm. Due to the addition
of this region there is an increase in the girth of the cortex.
PLANT ANATOMY - ANATOMY OF A TYPICAL YOUNG DICOT STEM
A transverse section taken through the young stem of Sun-flower reveals the following
details.
Epidermis
Epidermis is the outermost covering of the stem. It is represented by a single layer of
compactly arranged, barrel-shaped parenchyma cells. Intercellular spaces are absent. The
cells are slightly thick walled. Epidermis shows the presence of numerous multicellular
projections called trichomes.
Hypodermis
Hypodermis is a region lying immediately below the epidermis. It is represented by a few
layers of collenchyma cells with angular thickenings.
Cortex
Cortex is the major part of the stem represented by several layers of loosely arranged
parenchyma cells. Intercellular spaces are prominent. Cortex is the major storage organ in
the stem.
Endodermis
Endodermis is the innermost layer of cortex represented by compactly arranged barrel
shaped cells, without any intercellular spaces.
Stele
Stele is the central cylinder of the stem, consisting of pericycle, medullary rays, pith and
vascular bundles
Medullary Rays
Found in between the vascular bundles. They are meant for the storage of food.
Pith
Pith is the innermost part of the stem formed by a group of loosely arranged parenchyma
cells. Intercellular spaces are prominent. The pith is also meant for storage of food.
Vascular bundles
They are eight in number, arranged in form of a broken ring. The vascular bundles are
conjoint, collateral and open. Xylem is on the inner surface and phloem on the outer
surface. Xylem is described as endarch.
DIAGNOSTIC FEATURES OF A YOUNG DICOT STEM
Figure59: Internal structure of a stem
ANATOMY OF A TYPICAL MONOCOT STEM
DIAGNOSTIC FEATURES OF A MONOCOT STEM
ANATOMY OF A TYPICAL DICOT ROOT
DIAGNOSTIC FEATURES OF A DICOT ROOT
ANATOMY OF A TYPICAL MONOCOT ROOT
DIAGNOSTIC FEATURES OF A MONOCOT ROOT
Figure 62: Internal structure of Root
4.2.13
REVISION QUESTIONS 1
1) Cells that support the non-growing parts of plants are called
a) collenchyma
b) parenchyma
c) sclerenchyma
d) meristematic
2) Sugars are transported in vascular plants through which of these structures?
a) phloem
b) tracheids
c) epidermis
d) sclereids
3) Xylem is the tissue in a vascular plant that is used to transport
a) fats
b) sugars
c) water and minerals
d)
cellulose
4) Which plant cells are the most abundant and least structurally specialized?
a) parenchyma
b) collenchyma
c) sclerenchyma
d) phloem
5) Short, wide cells of xylem with no end walls function in water transport when
a) the cells are dead
b) an end wall forms
c) the cells are alive
d) water is
scarce
6) Long, narrow cells of xylem with thin separations between them are known as
a) ground tissue
b) tracheids
c) meristems
d) vessel
elements
7) One example of a plant with a fibrous root system is a
a) carrot
b) cottonwood
c) radish
d) grass
8) Which of the following is found in both roots and stems?
a) buds
b) vascular tissues
c) nodes
d) internodes
9) The driving force for transpiration is provided by
a) water pressure in the roots
c) the evaporation of water from the leaves
b) water tension in the stems
d) the hydrolysis of ATP
10) Which of the following plant cells is dead at maturity?
a) epidermal cell
b) companion cell
c) vessel element
d)
collenchyma cell
11) Primary growth refers to
a) the germination of a seedling
c) an increase in the diameter of a
stem
b) an increase in the length of a plant
d) growth produced by lateral
meristems
12) Intercalary meristems are found in some
a) conifers
b) gymnosperms
c) dicots
d) monocots
13) Most photosynthesis occurs in a portion of the leaf called the
a) vascular bundle
b) spongy mesophyll
c) palisade mesophyll
d) upper
epidermis
14) Which type of plant cell functions in metabolic activities such as photosynthesis,
storage, and healing?
REVISION QUESTIONS 2
1. Which gives the correct sequence of increasing organizational complexity?
a) organ, tissue, cell, organ system, organism
b) cell, organ, organ system, tissue, organism
c) cell, tissue, organ, organ system, organism
d) organism, tissue, cell, organ
system, organ
e) tissue, cell, organ system, organism, organ
2. Which type of tissue lines body cavities and covers body surfaces?
a) muscle tissue b) nervous tissue c) epithelial tissue
d) connective tissue
3. Which type of tissue is responsible for contractions that allow movement of organs or
the entire body?
a) muscle tissue b) nervous tissue
c) epithelial tissue d) connective tissue
4. Which type of tissue is responsible for receiving, interpreting, and producing a
response to stimuli?
a) muscle tissue b) nervous tissue
c) epithelial tissue
d) connective tissue
5. Which tissue includes bone and cartilage?
a) muscle tissue b) nervous tissue c) epithelial tissue d) connective tissue
6. Which tissue includes the epidermis?
a) muscle tissue
b) nervous tissue
c) epithelial tissue
d) connective tissue
7. Digestive juices cannot leak between the epithelial cells lining the lumen because of
a) muscle tissue b) nervous tissue
c) epithelial tissue d) connective tissue
8. Which tissue includes blood and adipose tissue?
a) muscle tissue b) nervous tissue
c) epithelial tissue
d) connective tissue
9. Which of the following statements is Not true about epithelial tissue?
a) Flattened cells are found in squamous epithelium.
b) Columnar epithelium is cubed-shaped with the nucleus near the upper surface of the
cells.
c) Simple epithelium has a single layer of cells in the tissue.
d) Pseudostratified epithelium looks like it has multiple layers, but all the cells are
attached to the same base.
e) Epithelium lining the respiratory tract contains cilia that move particles along its
surface.
10. Which statement about epithelial tissue is Not true ?
a) Stratified epithelium has numerous layers of cells.
b) Epithelial tissue has one free surface and one surface attached to a basement
membrane.
c) Connections between epithelial cells include gap junctions, tight junctions, and spot
desmosomes (adhesion junctions).
d) Cells of the human epithelium contain a waterproof protein called keratin.
e) Glandular epithelium that secretes its product into a duct forms the endocrine glands.
11. Which is Not a function of connective tissue?
a) line body surfaces and cavities
b) bind and support body parts
c) store energy in fat
d) fill spaces
e) produce blood cells
12. Which statement about connective tissue is Not true?
a) Connective tissue contains cells capable of differentiating into muscle and bone in
animals.
b) Loose connective tissue contains fibroblasts, different kinds of fibers, and a nonliving
matrix.
c) Fibrous connective tissue includes bone and cartilage.
d) Blood is a connective tissue that contains a fluid matrix.
e) Adipose tissue provides insulation and padding, as in skin.
ESSAY QUESTIONS
1. What are the TWO different types of vascular tissue in plants? Briefly describe each
kind.
2. How are carbohydrates transported throughout a plant? (Explain the pressure-flow
hypothesis).
3. Describe tracheids and explain their function.
4. What are the lateral meristems of plants, and what is their function?
5.0 CLASSIFICATION OF ORGANISMS
5.1 INTRODUCTION
There are some 10 million species of living organisms (mostly insects), and many
more extinct ones, so they need to be classified in a systematic way. In 1753 the Swede
Carolus Linnaeus introduced the binomial nomenclature for naming organisms. This
consists of two parts: a generic name (with a capital letter) and a specific name (with a
small letter), e.g. Panthera leo (lion) and Panthera tigris (tiger). This system replaced nonstandard common names, and is still in use today. A group of similar organisms is called
a taxon, and the science of classification is called taxonomy.
5.2 IMPORTANCE OF CLASSIFICATION

It makes the study of such a wide variety of organisms easy.

It projects before us a good picture of all life forms at a glance.

It helps us understand the interrelationship among different groups of organisms.

It serves as a base for the development of other biological sciences such as
biogeography etc.

Various fields of applied biology such as agriculture, public health and
environmental biology depend on classification of pests, disease vectors,
pathogens and components of an ecosystem.
5.3 NOMENCLATURE
Carl Linnaeus, father of modern botany, was a Swedish naturalist who laid the foundation
of modern classification and nomenclature in 1758. He devised a binomial system of
nomenclature (naming system) in which an organism is given two names:

A generic name (name of genus) which it shares with other closely related
organisms which has features similar enough to place them in the same group.

A specific name ( name of species) which distinguishes the organism from all
other species. No other organism can have the same combination of genus and
species.
The scientific name derived by using the system of nomenclature is followed all over
the world as they are guided by a set of rules stated in the International Code of
Nomenclature.
5.5 PLANT KINGDOM
CHARACTERISTICS OF PLANTS (KINGDOM PLANTAE)
1. Plants are multicellular eukaryotes with well-developed tissues.
2. Plants live in a wide variety of terrestrial environments.
a. Land existence is an advantage to photosynthesis; water filters much light.
b. Carbon dioxide and oxygen are in higher concentrations and diffuse more
rapidly in air.
3. Land plants must have adaptations to reduce the loss of water.
a. Leaves and stems are covered by a waxy cuticle that holds in water.
b. The leaves have openings (stomates) that open and close to regulate gas and
water exchange.
4. All plants protect the embryo from desiccation and some protect their entire
gametophyte generations.
5. In some plants, pollen grains are transported by wind or animals to the egg, and
the embryo.
5.8.2 THE VIRUSES
A. Viruses are nonliving with varied appearance.
1. All viruses are infectious.
2. In 1884, Pasteur suspected something smaller than bacteria caused rabies; he
chose Latin term for "poison."
3. In 1892, Russian biologist Dimitri Ivanowsky, working with tobacco mosaic
virus, confirmed Pasteur's hypothesis that an infectious agent smaller than a bacterium
existed.
4. With the invention of the electron microscope, these infectious agents smaller
than bacteria could be seen.
B. VIRAL STRUCTURE
1. Virus is similar in size to a large protein, generally smaller than 200 nm in diameter.
2. Many viruses can be purified and crystallized, and the crystals stored for long periods
of time.
3. Viral crystals become infectious when the viral particles they contain invade host
cells.
4. All viruses have at least two parts:
a. An outer capsid is composed of protein subunits.
b. An inner core contains either DNA (deoxyribonucleic acid) or RNA (ribonucleic
acid), but not both.
1) The viral genome at most has several hundred genes; a human cell contains
thousands of genes.
2) The viral envelope is partly host plasma membrane with viral glycoprotein spikes.
3) Viral particles have proteins, especially enzymes (e.g., polymerases), to produce
viral DNA or RNA.
4. Classification of viruses is based on
a. their type of nucleic acid, including whether it is single-stranded or doublestranded;
b. their size and shape; and
c. presence or absence of an outer envelope.
VIRAL REPLICATION
1. Viruses gain entry into and are specific to a particular host cell because portions
of the capsid (or spikes of the envelope) adhere to specific receptor sites on host cell
surface.
2. Viral nucleic acid then enters a cell, where viral genome codes for production of
protein units in the capsid.
3. Virus may have genes for a few special enzymes needed for the virus to reproduce
and exit from a host cell.
4. Virus relies on host enzymes, ribosomes, transfer RNA (tRNA), and ATP for its
own replication.
5. A virus takes over the metabolic machinery of the host cell when it reproduces.
E. REPLICATION OF BACTERIOPHAGES
1. Bacteriophages (phages) are viruses that parasitize a bacterial cell.
2. Lytic cycle is a bacteriophage "life" cycle of five stages where a virus takes over
operation of the bacterium immediately upon entering it and then destroys the bacterium.
a. During attachment, portions of the capsid bind with receptors on the bacterial cell
wall.
b. During penetration, a viral enzyme digests part of cell wall; viral DNA is injected
into a bacterial cell.
c. Biosynthesis involves synthesis of viral components; begins after virus brings about
inactivation of host genes not necessary to viral replication.
d. During maturation, viral DNA and capsids are assembled to produce several
hundred viral particles and lysozyme is produced.
e. When lysozyme disrupts the cell wall, release of the viral particles occurs and the
bacterial cell dies.
3. Lysogenic cycle is a cycle where virus incorporates its DNA into the bacterium but
only later does it produce phage.
a. Following attachment and penetration, viral DNA becomes integrated into
bacterial DNA with no destruction of host DNA; at this point the phage is latent and the
viral DNA is called a prophage.
b. Prophage is replicated along with host DNA; all subsequent cells (lysogenic
cells) carry a copy.
c. Certain environmental factors (e.g., ultraviolet radiation) induce prophage to
enter the biosynthesis stage of the lytic cycle, followed by maturation and release.
5.8.4 THE BACTERIA
A. Gram Stain and Shape
1. The Gram stain procedure (developed by Hans Christian Gram) differentiates
bacteria.
a. Gram-positive bacteria stain purple, whereas Gram-negative bacteria stain pink.
b. This difference is dependent on the thick or thin (respectively) peptidoglycan
cell wall.
2. Bacteria and archaea have three basic shapes.
a. A spirillum is spiral-shaped.
b. A bacillus is an elongated or rod-shaped bacteria
c. Coccus bacteria are spherical.
d. Cocci and bacilli tend to form clusters and chains of a length typical of the
particular species.
B. Types of Bacteria
1. Earlier classification of bacteria was based on metabolism, nutrition, etc.
2. Work by Carl Woese since 1980 has revised bacterial taxonomy based on
similarity of RNA.
3. Twelve groups are now recognized based on bacterial 16S ribosomal RNA
sequences.
C. Cyanobacteria
1. Cyanobacteria are Gram-negative bacteria with a number of unusual traits.
2. They photosynthesize in same manner as plants; are responsible for introducing
O2 into the primitive atmosphere.
3. They were formerly mistaken for eukaryotes and classified with algae.
4. They have pigments that mask chlorophyll; they are not only blue-green but also
red, yellow, brown, or black.
5. They are relatively large (1-50 µm in width).
6. They can be unicellular, colonial, or filamentous.
7. Some move by gliding or oscillating.
8. Some possess heterocysts, thick-walled cells without a nucleoid, where nitrogen
fixation occurs.
9. Cyanobacteria are common in fresh water, soil, on moist surfaces, and in harsh
habitats (e.g., hot springs).
10.Some species are symbiotic with other organisms (e.g., liverworts, ferns, and
corals).
11. Lichens are a symbiotic relationship where the cyanobacteria provide organic
nutrients to the fungus and
the fungus protects and supplies inorganic nutrients.
12. Cyanobacteria were probably the first colonizers of land during evolution.
13. Cyanobacteria "bloom" when nitrates and phosphates are released as wastes;
when they die off, decomposing bacteria use up the oxygen and cause fish kills.
5.8.5 THE ARCHAEA
A. Archaea are Prokaryotes
1. Archaea are prokaryotes with molecular characteristics that distinguish them from
bacteria and eukaryotes.
2. Because archaea and some bacteria are both found in extreme environments (hot
springs, thermal vents, salt basins), they may have diverged from a common ancestor.
3. Later, the eukaryote split from the archaea; archaea and eukaryotes share some
ribosomal proteins not found in bacteria.
B. STRUCTURE AND FUNCTION
1. Archaea has unusual lipids in their plasma membranes that allow them to
function at high temperatures: glycerol linked to hydrocarbons rather than fatty acids.
2. Cell walls of archaea do not contain peptidoglycan found in bacterial cell walls.
3. Only some methanogens have the ability to form methane.
4. Most are chemoautotrophs; none are photosynthetic; this suggests
chemoautotrophy evolved first.
5. Some are mutualistic or commensalistic but none are parasitic-none are known to
cause disease.
TYPES OF ARCHAEA
1. Methanogens live under anaerobic environments (e.g., marshes) where they
produce methane.
a. Methane is produced from hydrogen gas and carbon dioxide and is coupled to
formation of ATP.
EUGLENOIDS
1. Phylum Euglenophyta includes the euglenoids.
2. Euglenoids are small (10-500 µm) freshwater unicellular organisms.
3. One-third of all genera have chloroplasts; those that lack chloroplasts ingest or
absorb their food.
4. Their chloroplasts are surrounded by three rather than two membranes.
a. Their chloroplasts resemble those of green algae.
b. They are probably derived from a green algae through endosymbiosis.
THE GREEN ALGAE
1. Phylum Chlorophyta (green algae) contains about 7,000 species.
2. Most live in the ocean but are more likely found in fresh water; they can even be
found on moist land.
3. Green algae are believed to be closely related to the first plants because both of
these groups
a. have a cell wall that contains cellulose,
b. possess chlorophylls a and b, and
c. store reserve food as starch inside of the chloroplast.
THE DIATOMS
1. Phylum Chrysophyta contains both diatoms and golden brown alga.
2. Some authorities place the diatoms in their own phylum, the Bacillariophyta.
3. Diatoms are the most numerous unicellular algae in the oceans.
THE ZOOFLAGELLATES
1. Phylum Zoomastigophora includes the zooflagellates.
2. They possess from one to thousands of flagella.
3. These protozoa are covered by a pellicle that is often reinforced by underlying
microtubules.
THE CILIATES
1. Phylum Ciliophora contains the ciliates.
2. Ciliates move by coordinated strokes of hundreds of cilia projecting through holes
in a semirigid pellicle.
3. They discharge long, barbed trichocysts for defense and for capturing prey;
toxicysts release a poison.
THE SPOROZOANS
1. Phylum Apicomplexa contains the nonmotile parasitic sporozoans.
2. Phylum name notes the apical complex of organelles that help their invasion of
host cells.
3. Their common name recognizes that they form spores at some point in their life
cycle.
WATER MOLDS
1. Phylum Oomycota includes the water molds.
2. Aquatic water molds parasitize fishes, forming furry growths on their gills, and
decompose remains.
3. Terrestrial water molds parasitize insects and plants; a water mold caused the
1840s Irish potato famine.
THE FUNGI
CHARACTERISTICS OF FUNGI
A. FUNGI ARE MULTICELLULAR EUKARYOTES
1. Fungi are mostly multicellular eukaryotes that share a common mode of nutrition.
2. Similar to animals, they are heterotrophic and consume preformed organic matter.
3. However, animals are heterotrophic by ingestion while fungi are heterotrophic by
absorption.
4. Fungal cells secrete digestive enzymes; following breakdown of molecules, the
nutrients are absorbed.
5. Most fungi are saprotrophic decomposers, breaking down wastes or remains of
plants and animals.
6. Some are parasitic, living off tissues of living plants and animals.
a. Fungi enter leaves through stomates; plants are especially subject to fungal
diseases.
b. Fungal diseases account for millions of dollars in crop losses each year.
c. Fungi also cause human diseases including ringworm, athlete's foot, and yeast
infections.
7. Several types of fungi are adapted to mutualistic relationships with other
organisms.
a. As symbionts of roots, they acquire inorganic nutrients for plants and receive
organic nutrients.
b. Others form an association with a green alga or cyanobacterium to form a
lichen.
B. STRUCTURE OF FUNGI
1. Fungi can be unicellular (e.g., yeasts).
2. Most fungi are multicellular in structure.
a. The thallus (body) of most fungi is a mycelium.
b. A mycelium is a network of hyphae comprising the vegetative body of a
fungus.
c. Hyphae are filaments that provide a large surface area and aid absorption of
nutrients.
d. When a fungus reproduces, a portion of the mycelium becomes reproductive
structures.
3. Fungal cells lack chloroplasts and have a cell wall made of chitin, not cellulose.
a. Chitin, like cellulose, is a polymer of glucose molecules organized into
microfibrils.
b. In chitin, unlike cellulose, each glucose has an attached nitrogen containing
amino group.
4. The energy reserve is glycogen, not starch.
5. Fungi are nonmotile; their cells lack basal bodies and do not have flagella at any
stage in their life.
6. Fungi move to a food source by growing toward it; hyphae can grow up to a
kilometer a day!
7. Nonseptate hyphae lack septa or cross walls; hyphae are multi-nucleated.
8. Septate fungi have cross walls in their hyphae; pores allow cytoplasm and
organelles to pass freely.
9. The septa that separate reproductive cells, however, are complete in all fungal
groups.
C. REPRODUCTION OF FUNGI
1. In general, fungal sexual reproduction involves the following:
haploid hyphae
dikaryotic stage
diploid zygote
I--------------- meiosis------------------I
2. During sexual reproduction, haploid hyphae from two different mating types fuse.
3. If nuclei do not fuse immediately, resulting hypha is dikaryotic (contains paired
haploid nuclei, n + n.)
a. In some species, nuclei pair but do not fuse for days, months or years.
b. The nuclei continue to divide in such a way that every cell has at least one of
each type.
4. When the nuclei fuse, the resulting zygote undergoes meiotic cell division leading
to spore formation.
5. Fungal spores germinate directly into haploid hyphae without embryological
development.
6. Fungal Spore Formation
a. Spores are an adaptation to life on land and ensure that the species will be
dispersed to new locations.
b. A spore is a reproductive cell that can grow directly into a new organism.
c. Fungi produce spores both during sexual and asexual reproduction.
d. Although nonmotile, the spores are readily dispersed by wind.
7. Asexual reproduction can occur by three mechanisms:
a. Production of spores by a single mycelium is the most common mechanism.
b. Fragmentation is when a portion of a mycelium becomes separated and begins
a life of its own.
c. Budding is typical of yeasts; a small cell forms and gets pinched off as it grows
to full size.
5.8.12 NONVASCULAR PLANTS
1. Plants are divided into two main groups: nonvascular and vascular plants.
2. Nonvascular plants include:
a. hornworts (division Anthocerotophyta)
b. liverworts (division Hepatophyta)
c. mosses (division Bryophyta)
3. Nonvascular plants lack specialized tissues for transporting water, minerals, and
organic nutrients.
4. They lack true roots, stems, and leaves, although they have root-like, stem-like, or
leaf-like structures.
5. The gametophyte is the dominant (most conspicuous) generation.
a. Flagellated sperm swim to the vicinity of the egg in a continuous film of water.
b. The saprophyte is attached to and derives nourishment from the photosynthetic
gametophyte.
6. Nonvascular plants are quite small; the largest being is no more than 20 cm tall.
a. Because sexual reproduction involves flagellated sperm, they are usually found
in moist habitats.
b. Mosses compete well in harsh environments because the gametophyte can
reproduce asexually.
7. Mosses can dry up; later, when water is available, they photosynthesize again.
8. The three divisions are individual lines of descent; mosses are more closely
related to vascular plants.
C. LIVERWORTS
1. Division Hepatophyta contains 10,000 species of liverworts.
2. This name arose in ninth century when it was seen as similar to lobes of the liver.
3. Marchantia is a example of this group.
a. It has a flat, lobed thallus about a centimeter in length.
b. The upper surface of thallus is smooth; lower surface bears numerous rhizoids
projecting into soil.
c. It reproduces asexually and sexually.
4. Rhizoids are the root-like hair that anchors a bryophyte and absorbs water and
minerals from the soil.
5. Asexual reproduction involves gemmae in gemmae cups on upper surface of the
thallus.
6. Sexual reproduction depends on antheridia and archegonia.
a. Antheridia are on disk-headed stalks and produce flagellated sperm.
b. Archegonia are on umbrella-headed stalks and produce eggs.
c. Zygote develops into a tiny sporophyte composed of foot, short stalk, and
capsule.
d. Spores produced within the capsule of the gametophyte are disseminated by
wind.
D. MOSSES
1. About 12,000 species of mosses are in the division Bryophyta.
2. Mosses are found in the Arctic through the tropics to parts of the Antarctic.
3. Moss prefers damp, shaded localities; some survive in deserts, others in bogs and
streams.
4. Mosses store much water; when they dry out, they become dormant; when it
rains, become green.
5. Copper mosses live only in the vicinity of copper and serve as an indicator of ore
deposits.
6. Luminous moss lives in caves; cells shaped like lenses focus light on chloroplast
grana.
7. Some "mosses" are not true mosses:
a. Irish moss is an edible alga.
b. Reindeer moss is a lichen.
c. Club mosses are vascular plants.
d. Spanish moss, which hangs from trees in the southern U.S., is a flowering
plant.
8. Most mosses can reproduce asexually by fragmentation.
9. Life cycle begins with alga-like protonema developing from germination of a
haploid spore.
a. Three days of favorable growing conditions produce upright shoots covered
with leafy structures.
1) Rhizoids anchor the protonema, to which the shoots are attached.
2) The shoots bear antheridia and archegonia at their tips.
3) Antheridia produce flagellated sperm which need external water to reach
eggs in archegonia.
4) Fertilization results in a diploid zygote that undergoes mitotic division to
develop a sporophyte.
b. The sporophyte consists of a foot (which grows down into the gametophyte
tissue starting at the
former archegonium), a stalk, and an upper capsule (sporangium) where spores
are produced.
1) At first the sporophyte is green and photosynthetic.
2) At maturity it is brown and nonphotosynthetic.
E. USES OF NONVASCULAR PLANTS
1. Sphagnum (bog or peat moss) has tremendous ability to absorb water and is
important in gardening.
2. Sphagnum does not decay in some acidic bogs; the dried peat can be used as fuel.
F. ADAPTATION OF NONVASCULAR PLANTS
1. Nonvascular plants are limited by lack of structural vascular tissue and need for
water for sperm.
2. They have advantages living on stone walls, etc. and contribute to soil formation.
5.8.13 SEEDLESS VASCULAR PLANTS
A. SEEDLESS VASCULAR PLANTS
1. The seedless vascular plants include:
a. whisk ferns (division Psilotophyta),
b. club mosses (division Lycopodopyta),
c. horsetails, (division Equisetophyta)
d. and ferns (division Pteridophyta).
2. These divisions are not closely related.
5.9 SEED PLANTS AND GYMNOSPERMS
A. THE LIFE CYCLE OF SEED PLANTS
1. Gymnosperms include the:
a. conifers (division Pinophyta)
b. cycads (division Cycadophyta)
c. ginkgo (division Ginkgophyta)
d. gnetophytes (division Gnetophyta)
2. There are separate microgametophytes (male) and megagametophytes (female).
3. Microspores develop immature micro gametophytes, pollen grains, still retained
in a microsporangium.
4. After they are released, pollen grains develop into mature, sperm-bearing
microgametophytes.
5. Pollination is the transfer of pollen to the vicinity of the mega gametophyte.
6. Sperm is delivered to an egg through a pollen tube; no external water is required
for fertilization.
7. The megaspore develops into an egg-bearing mega gametophyte while still
retained within an ovule.
8. An ovule is the sporophyte structure that holds the mega sporangium and then the
mega gametophyte.
9. After fertilization, the ovule becomes an embryonic plant enclosed within the
ovule, which becomes the seed.
10. Both the mega gametophytes and micro gametophytes are dependent upon the
diploid sporophyte.
11. The sporophyte can evolve into diverse forms without any corresponding
changes in the gametophyte.
12. Among seed plants, seeds disperse the sporophytes.
a. Seeds are mature ovules containing embryonic sporophyte and stored food
enclosed in protective seed coat.
b. Seeds are resistant to adverse conditions: dryness and temperature extremes.
c. A food reserve supports the emerging seedling until it can exist on its own.
d. Survival value of seeds contributes greatly to success of seed plants, and their
present dominance.
B. GYMNOSPERM DIVERSITY
1. Gymnosperms produce naked seeds not enclosed in a fruit but exposed on the
surface of sporophylls.
2. Sporophylls are leaves that bear sporangia and are arranged on a cone.
3. Gymnosperms did not begin to flourish until the Mesozoic era.
a. Pangaea had formed and mountain ranges arose producing deserts on the
leeward side.
b. Swamps became much drier and a mass extinction occurred; seedless vascular
plants nearly vanished.
c. This provided an opportunity for first seed plants (including gymnosperms) to
become dominant.
C. CONIFERS
1. About 550 species of conifers are in division Pinophyta.
2. Conifers are cone-bearing trees and shrubs such as pines, hemlocks, and spruces.
3. Conifers usually have evergreen needle-like leaves well adapted to withstand
extremes in climate.
4. Needles have thick cuticle, sunken stomates, and reduced surface area.
5. Conifers are found in nearly all habitats, from equator to subpolar regions, and
comprise the taiga.
6. The oldest and largest trees in existence are conifers:
a. General Sherman tree in California's Sequoia National Park is 84 meters tall, 10
meters in diameter,
and weighs 1,385 tons.
b. Redwoods grow over 90 meters high and exceed 2,000 years old.
c. Bristlecone pines in the Nevada mountains are over 4,500 years old.
7. The life cycle of pines is typical of conifers.
a. Sporophyte is dominant and its sporangia are borne in cones.
b. Two types of cones are pollen cones (small and near the tips of lower branches)
and seed cones.
c. Each scale of a pollen cone has two or more micro sporangia on underside.
d. Within the sporangia, each microsporocyte undergoes meiosis and produces
four microspores.
e. Each microspore develops into a micro gametophyte which is the pollen grain.
f. Each scale of a seed cone has two ovules surrounded by an integument and with
an opening at one end.
g. A mega sporangium is within an ovule; a megasporocyte undergoes meiosis
producing four megaspores.
h. One spore develops into a megagametophyte with 2-6 archegonia, each
containing a single large egg.
i. Once a pollen grain is enclosed within the seed cone, it develops a pollen tube
that digests its way toward a megagametophyte and discharges two non-flagellated
sperm.
j. Fertilization takes place one year after pollination.
k. The ovule matures and becomes the seed, composed of embryo, reserve food
and seed coat.
l. The woody seed cone, opens to release winged seeds in the fall of the second
season.
5.9.1 USES OF GYMNOSPERMS
1. Gymnosperms supply wood used for building construction and paper production.
2. They produce many valuable chemicals extracted from resin.
5.9.2 ADAPTATION OF GYMNOSPERMS
1. Gymnosperms withstand heat, dryness, and cold, as a result of having welldeveloped roots and stems tough, small needles with a thick cuticle.
2. Pollen production has eliminated reliance on external water.
3. Enclosure of the dependent mega gametophyte in an ovule protects it during its
development.
4. Embryo is protected within seed and is provided nutrients that support growth
following germination.
5.10 ANGIOSPERMS
A. ANGIOSPERMS ARE FLOWERING PLANTS
1. Over 235,000 species of angiosperms (flowering plants) belong to division
Magnoliophyta.
2. Angiosperms produce seeds enclosed in fruit.
3. This group contains six times the number of species of all other plants combined.
4. Angiosperms live in all habitats from freshwater to desert and from tropics to
subpolar regions.
5. Flowering plant size ranges from microscopic duckweed to Eucalyptus exceeding
100 m tall.
6. They are important in everyday human life: clothing, food, medicine, and
commercial products.
B. ORIGIN AND EVOLUTION OF ANGIOSPERMS
1. Angiosperms evolved from ancient gymnosperms.
2. By the Jurassic period in middle of the Mesozoic era, many gymnosperms had
features similar to angiosperms.
a. Some had vascular tissue resembling that of angiosperms.
b. Some had sporophylls that resemble early flower parts and were visited by
beetles, early insects.
c. Transitional gymnosperms became extinct; the gnetophyte Ephedra is
considered closest relative.
3. Earliest angiosperms arose in Cretaceous; in Cenozoic, angiosperms diversified as
climate grew cold.
4. Rather than being tall trees, the first angiosperms may have been fast-growing
woody shrubs.
5. Today angiosperms are either woody or herbaceous.
6. Angiosperms adapted to a wide range of climatic zones are perennials or annuals.
a. Perennials live two or more growing seasons; they die back seasonally in
herbaceous plants.
b. Annuals are plants that live for only one growing season.
C. CLASSIFICATION OF FLOWERING PLANTS
1. Angiosperms are divided into two groups: dicotyledons and monocotyledons.
2. Dicotyledons are in class Magnoliopsida and have these features:
a. either woody or herbaceous,
b. flower parts usually in fours and fives,
c. leaves usually net-veined,
d. vascular bundles arranged in a circle within the stem, and
e. produce two cotyledons (seed leaves) at germination.
3. Dicots include buttercup, mustard, maple, cactus, pea, and rose families (and
many more).
4. Monocotyledons are in the class Liliopsida and have these features:
a. most are herbaceous,
b. flower parts are in threes,
c. leaves are usually parallel-veined,
d. vascular bundles are scattered within the stem, and
e. produce one cotyledon (seed leaf) at germination.
5. Monocots include lily, palm, orchid, iris, and grass families (grasses include corn,
rice, wheat, etc.).
5.11 KINGDOM: ANIMALIA
ANIMAL CHARACTERISTICS
They are heterotrophic, multicellular, and eukaryotic.
They are organisms that store carbohydrates as glycogen.
They are organisms that lack cell walls. The intracellular junctions (tight junctions,
desmosomes, and gap junctions) are found only in animals.
These organisms have muscle and nervous tissue.
These organisms reproduce sexually. They have a dominant diploid organism that
produces gametes, either a flagellated sperm or a large, nonmotile egg. These
gametes fuse and undergo mitosis to form a hollow ball called a blastula. This
blastula undergoes gastrulation; then the embryonic tissues differentiate.
Organisms whose life cycle may include many larval stages. Larva is a free-living
sexually immature form. The larva is morphologically different from the adult.
The larval form usually eats different foods and may live in different habitats. The
larva will eventually undergo metamorphosis and change into the adult form.
Animals are divided between invertebrates or vertebrates, radial or bilateral
symmetry, and presence or absence of coelom.
SYMMETRY
1. Radial Symmetry
Body parts are arranged around a central axis like spokes around the hub of a wheel.
Such organisms have a top and bottom; but no front, back, left or right.
a. PHYLUM: PORIFERA (SPONGES)
The cells of sponges are not organized into tissues Sponges exhibit primitive radial
symmetry. There are four classes of sponges, based on skeletal structure. The
skeleton is made up of spicules or spongin. There are many incurrent pores
throughout the body and one osculum, the big hole that acts as an excurrent pore. The
collar cells, choanocytes, line the spongeocoel (inner wall of the sponge) and beat the
flagella to cause water movement out of the osculum. Water then filters through the
pores which the sponge filters to obtain food. Amebocytes in the middle layer
distribute the food to the other cells. Sponges reproduce sexually or asexually.
1. Sexual: Any choanocyte may change and function as a sperm, and certain
amebocytes (which also secrete the skeleton) may change and function as an egg.
Fertilization occurs in the middle layer of the sponge to produce a zygote, which
then develops into a hollow larva with flagella. A sponge is a hermaphrodite, a
single organism that produces both eggs and sperm.
2. Asexual: Budding and gemmules. A gemmule is an amoebocyte that is wrapped in a
ball of spicules. Budding occurs when a small piece of the sponge falls off and
grows into new animals.
Sponges are sessile as adults.
B.PHYLUM: CNIDARIA (COELENTERATA)
Hydra, jellyfish, corals, and sea anemones.
Description
The cells of a coelenterate are arranged into two tissue layers: the gastrodermis, which
lines the gastrovascular cavity and arises from the embryonic endoderm, and the
epidermis from the embryonic ectoderm. Coelenterates have a radial symmetry.
C.
TRIPLOBLASTIC ANIMALS
The triploblastic animals can be grouped into three categories. These are determined
by the presence or absence of a body cavity called the coelom.
1) ACOELOMATES
Simplest arrangement. The three germ layers are packed together and there is no body
cavity other than the digestive cavity and there is no body cavity between he gut and
the outer body wall.
2) PSEUDOCOELOMATES
There is an additional cavity between the endoderm and the mesoderm. This is called
a pseudocoelom because of the location of the cavity and the fact that the cavity does
not have an epithelial lining derived from the mesoderm.
3) COELOMATES
These have a true coelom, a fluid filled cavity that develops within the mesoderm.
Within the coelom, the digestive tract and other internal organs are lined with
epithelial tissue. These tissues are known as mesenteries.
D.
PHYLUM PLATYHELMINTHES: FLATWORMS
These animals have bilateral symmetry. There are acoelomate with three tissue layers
which give rise to specialized organs. There are three classes of flatworm.
1. Class turbellaria: Planaria
a Digestive system
They have a mouth, pharynx, and a branched gastrovacular cavity. There is one
opening, but two-way traffic. Planarians are carnivorous. Through muscular
contractions, the planaria sucks in small pieces of meat.
.
2. CLASS CESTODA: Tapeworm
The head (scolex) is equipped with a ring of hooks and suckers for attachment to
intestine. Te body is divided into proglottids that contain ovaries, testes, and
excretory tubules. The ‘ripe’ proglottids (filled with eggs) break off and come out
with the feces. The life cycle begins when the primary host eats the eggs and becomes
infected. The eggs hatch into larvae, which burrow out and travel to muscle tissue and
encyst (bladderworm). The secondary host may become infected by eating infected
meat (muscle) and larvae grow to an adult form in the intestine. Adult tapeworms can
be up to 20 meters in length.
3. CLASS TREMATODA: FLUKES
These are parasitic, but have a digestive system. The mouth is surrounded by a
sucker, which pumps in nutrients from the host’s intestine or liver. Flukes are
hermaphroditic and the fertilized eggs pass out of the host with feces.
E. PHYLUM NEMATODA: ROUNDWORMS
Roundworms have three tissue layers that from a pseudocoelom. This pseudocoelom
functions as a hydroskeleton.
F. COELOMATES
The remaining invertebrate phyla are Coelomates. With a coelom, surrounded by
lubricating coelomic fluid, the organs can bend, twist, fold back on themselves
(increasing the functional surface area), and slide past one another.
G. PHYLUM ANNELIDA: SEGMENTED WORMS
Annelids are bilateral protosomes. These organisms are divided into body segments
called metameres. These are separated by septa on the inside. Annelids have a
segmented coelom, tubular gut, closed circulatory system, paired nephridia for the
excretory system, and a centralized nervous system with specialized sensory cells.
There are three classes of Annelids
1) CLASS OLIGOCHAETA: EARTHWORMS
The earthworm body is compartmentalized into regular segments. Most of the segments
are identical.
2) CLASS POLYCHAETA: MARINE WORMS
Unique features include lateral appendages (parapodia) per segment, separate genders, a
free-swimming larva (trohophore), no clitellum, and a well0developed head with
tentacles and eyes.
3) CLASS HIRUDINEA: LEECHES
These are mostly found in fresh water in tropical regions and are mostly blood suckers.
There is no head, except for a sucker around the mouth and cutting jaws. There are no
setae or parapodia on segments. The leeches secrete hirudin which is an anticoagulant.
H. PHYLUM MOLLUSCA: SOFT-BODIED
These protosomes exhibit a bilateral symmetry, are unsegmented, and have a true
coelom. Some of their unique features include a muscular foot, mantle, radula, and
gills for breathing
5.12 VERTEBRATES
5. CLASS: AMPHIBIA
There are 4,000 species of modern amphibians, represented by three orders:
a. Urodela
Salamanders
b. Anura
Frogs and toads
c. Apodia
Worm-like caecilians
6. CLASS: REPTILIA
There are 7000 species of reptiles which are represented by three important orders.
a. Chelonia
Turtles
b. Crocodilian
Crocodiles, alligators, and relatives
c. Quamata
Lizards and snakes
7. CLASS: AVES (BIRDS)
There are 8,600 species of birds. They have a light skeleton with many hollow bones.
The reptilian teeth have been replaced by a light horny beak, the neck is long and
flexible, the bones of the trunk are fused together, and their breast bone is enlarged which
acts as a large keel for the attachment of flight muscles.
8. CLASS: MAMMALIA (MAMMALS)
Mammals are fury or hairy animals that produce milk. There are three groups of
mammals: montremes( egg laying), marsupials ( pouched animals), and placentals.
Mammals use a muscular diaphragm to move air. They have a four chambered and lungs
fertilization and development is usually internal(except for montremes). Females have
separate urinary and reproductive tracts. Mammals may have specialized teeth. Milk is
modified sweat which provides the young with high protein, high coloric nutrients.
6.0
BIOCHEMISTRY
Biochemistry is the study of biological molecules such as nucleic acids, proteins,
lipids which form the morphological structures represented by cells and cellular
organelles provide machinery for inheritance and expression of genetic information. The
importance of biochemistry lies in the fundamental understanding it gives us of
physiology that is the way in which biological systems work. This in turn finds an
application in fields like Agriculture (development of pesticides, herbicides etc),
medicine, fermentation industry.
 A polymer is a long molecule consisting of many similar or identical building
blocks linked by covalent bonds.
 The repeated units are small molecules called monomers.
 Some of the molecules that serve as monomers have other functions of their own.

The chemical mechanisms that cells use to make and break polymers are similar for
all classes of macromolecules.

Monomers are connected by covalent bonds that form through the loss of a water
molecule. This reaction is called a condensation reaction or dehydration reaction.
BIOLOGICAL MOLECULES

Within cells, small organic molecules are joined together to form larger molecules.

These large macromolecules may consist of thousands of covalently bonded atoms
and weigh more than 100,000 daltons.
The four major classes of macromolecules are carbohydrates, lipids, proteins, and nucleic
acids. Life on Earth evolved in the water, and all life still depends on water. At least
80% of the mass of living organisms is water, and almost all the chemical reactions of
life take place in aqueous solution. The other chemicals that make up living things are
mostly organic macromolecules belonging to the four groups proteins, nucleic acids,
carbohydrates or lipids.
6.2 WATER PROPERTIES
The unique structure of water gives water its seven important properties.
1. Water is a Powerful Solvent
Water is able to dissolve anything polar due to polarity. Water separates ionic substances.
Many covalently bonded compounds have polar regions, the covalent compounds
dissolve in water and are called hydrophilic (water loving) compounds. Nonpolar
substances do not dissolve in water and are called hydrophobic (water fearing).
2. Water is Wet
Water adheres to a surface due to two properties.
Adhesion: The attraction between water and other substances.
Cohesion: The attraction of water molecules to other water molecules.
These two properties allow capillary action.
3. Water has High Surface Tension
Water is attracted to itself, and this attraction, due to hydrogen bonds, is stronger than the
attraction to the air above it.
4. Water has a High Specific Heat
It takes a lot of heat to increases the temperature of water and a great deal of heat must be
lost in order to decrease the temperature of the water. Water heats up as the hydrogen
atoms vibrate (molecular kinetic energy- energy of molecular motion).
5. Water has a high boiling point
A great deal of energy must be present in order to break the hydrogen bonds to change
water from a liquid to a gas.
6. Water is a good evaporative coolant
Because it takes a lot of energy to change water from a liquid to a gas, when the vapor
leaves it takes a lot of energy with it. When humans sweat, water absorbs the heat from
the body. When water turns into water vapor, it takes that energy (heat) with it.
7. Water has a high freezing point and lower density as a solid than a liquid.
Water’s maximum density is 4C, while freezing is 0C. This is why ice floats, this fact
also allows for aeration of still ponds in spring and fall and the reason ponds don’t freeze
from the bottom up.
8. Ionisation. When many salts dissolve in water they ionise into discrete positive
and negative ions (e.g. NaCl Na+ + Cl-). Many important biological molecules
are weak acids, which also ionise in solution (e.g. acetic acid acetate- + H+).
9. pH. Water itself is partly charged (H2O
H+ + OH- ), so it is a source of protons
(H+ ions), and indeed many biochemical reactions are sensitive to pH (log[H+]).
6.3 CARBOHYDRATES
Most carbohydrates have the empirical formula C(H2O)n. Carbohydrates are composed of
covalently bonded atoms of carbon, hydrogen, and oxygen.
1. Monosaccharides
The basic unit of a carbohydrate is a monosaccharide or simple sugar.
Monosaccharides can be burned (oxidized) to yield carbon dioxide, water, and
energy. The principle source of energy for organisms is glucose. Structurally a sugar
consists of a carbon backbone of three or more carbon atoms with either an aldehyde
or carbonyl group on one carbon and hydroxyl groups on each of the other carbons.
The most common monosaccharide is glucose, C6H12O6. Glucose is the form of sugar
generally transported in the human body. A disaccharideis formed by joining two
monosaccharides together. The two monosaccharides are linked by a reaction called a
dehydration or condensation reaction.
• A monomer is a relatively simple and small molecule; many of them can be linked
together to form a polymer.
• A polymer is a large molecule composed of many similar or identical molecular
subunits.
• A polysaccharide consists of many monosaccharides joined together by
condensation reactions.
 Condensation reaction: the joining of two smaller organic compounds resulting
in the formation of a larger organic molecule and the release of a water molecule.
The condensation reaction, a synthesis reaction, is important because it is the
reaction that puts together polymers from monomer units. Synthesis reactions
require energy to complete.
C6H12O6 + C6H12O6  C12H22O11 + H2O
glucose + fructose  sucrose + water
 Hydrolytic cleavage (hydrolysis): With the addition of water, the splitting of a
large organic molecule into two smaller organic molecules. Hydrolysis reactions
liberate energy. Hydrolytic cleavage, or hydrolysis, is the opposite of a
dehydration reaction. For example, in the human digestive system, sucrose
(disaccharide) is split into glucose and fructose (two monosaccharides).
or more
simply
-glucose (used to make
starch and glycogen)
-glucose (used to make
cellulose)
Figure 66: The diagrams above are of the structures of -glucose and -glucose
2.
Disaccharides
Two monosaccharides that are joined by a blycosidic linkage, a covalent bond
between two monosaccharides.
glucose + glucose = maltose
glucose + fructose = sucrose
2C6H12O6  C12H22O11 + H2O
Disaccharides are formed when two monosaccharides are joined together by a
glycosidic bond. The reaction involves the formation of a molecule of water (H2O):
Figure 67: The diagram above showing the structure of disaccharides.
There are three common disaccharides:

Maltose (or malt sugar) is glucose 1-4 glucose. It is formed on digestion of starch
by amylase, because this enzyme breaks starch down into two-glucose units.
Brewing beer starts with malt, which is a maltose solution made from germinated
barley. Maltose is the structure shown above.

Sucrose (or cane sugar) is glucose 1-2 fructose. It is common in plants because it
is less reactive than glucose, and it is their main transport sugar. It is the common
table sugar that you put in your tea.
 Lactose (or milk sugar) is galactose 1-4 glucose. It is found only in mammalian
milk, and is the main source of energy for infant mammals.
3.
Polysaccharides
Glycosidic linkages can be oriented in space. Two monomers can be joined either by an
alpha or beta linkage. By a series of dehydration reactions, many monosaccharides can
be put together to form a polysaccharide. Three examples of polysaccharides are starch,
glycogen, and cellulose. In starch and glycogen the monomers are joined by alpha
linkages; in cellulose the glucose monomers are joined by beta linkages.
a. Starch
Starch is the storage plsacchride in plants and is an important reservoir for energy. There
are two common types of starch.
1)
Amylose: the simplest starch. Consisting of unbranched chains of hundreds
of glucose molecules.
2)
Amylopectrin: large molecule consisting of short glucose chains with other
glucose chains branching off the main chain.
Amylose is simply poly-(1-4) glucose, so is a straight
chain. In fact the chain is floppy, and it tends to coil
up into a helix.
Figure 68: Structure of Amylose
Amylopectin is poly(1-4) glucose with about 4% (16) branches. This gives it a more open molecular
structure than Amylose. Because it has more ends, it
can be broken more quickly than Amylose by
amylase enzymes.
Figure 69: Structure of Amylopectin.
b. Glycogen
Glucogen is the storage polysaccharide in animals. Glycogen is composed of branching
glucose chains, with more branches then amylopectrin. It is found in the liver and
muscles and acts as a temporary storage form of glucose. The liver removes the excess
glucose from the bloodstream, converts the glucose monomers to glycogen via
condensation reactions, and stores it as glycogen. When vertebrates need glucose for
energy, glycogen is converted by hydrolytic cleavage back to glucose.
Figure 70: Structure of Glycogen
c. Cellulose
Cellulose is a structural polysaccharide and is the major building material made by plants.
It is the most abundant organic material in earth. Cellulose is made up of long, straight
glucose molecules. Cellulose is called a structural polysaccharide because it gives the
plant cell its shape, is not soluble, and is very strong. Cellulose is flexible when the plant
cell is young. As the cell grows, the cellulose becomes thicker and more rigid.
Cellulose is indigestible to animals because the linkages are 1-4 beta linkages, and our
enzyme can only break down 1-4 alpha linkages because the shapes are different.
Cellulose is the so-called fiber in our diets. Some bacteria, protests, fungi, and lichens
can break down cellulose. For example, bacteria and protests found in the stomachs of
termites and grazing animals break down the cellulose in the grass and wood to provide
the animal with glucose.
Figure 71 : Structure of cellulose
d. Other structural polysaccharides
1)
Pectin and andarrageenan: these are extracted from algae. Pectin and
carrageenan are put into food items such as jellies, jams, yogurt, ice cream,
and milkshakes to give them a jelly-like or creamy consistency.
2)
Chitin: Chitin is principal component of the exoskeletons of insects and
other arthropods, including lobsters. Chitin is very soft but is combined
with CaCO3 (calcium carbonate or limestone) to become hard. Most
animals cannot digest chitin.
6.4 PROTEINS
A. PROTEIN FUNCTIONS
1. Support proteins include keratin, which makes up hair and nails, and collagen
fibers, which support many organs.
2. Enzymes are proteins that act as organic catalysts to speed chemical reactions
within cells.
3. Transport functions include channel and carrier proteins in the plasma membrane
and hemoglobin
that carries oxygen in red blood cells.
4. Defense functions include antibodies that prevent infection.
5. Hormones include insulin that regulates glucose content of blood.
6. Motion is provided by myosin and actin proteins that make up the bulk of muscle.
Proteins are made of amino acids. Amino
acids are made of the five elements C H O
N S. The general structure of an amino
acid molecule is shown on the right.
There is a central carbon atom (called the
“alpha carbon”), with four different
chemical groups attached to it:
Figure 72 : Chemical composition of

a hydrogen atom

a basic amino group

an acidic carboxyl group

a variable “R” group (or side
proteins
chain)
Amino acids are so-called because they have both amino groups and acid groups, which
have opposite charges. At neutral pH (found in most living organisms), the groups are
ionised as shown above, so there is a positive charge at one end of the molecule and a
negative charge at the other end. The overall net charge on the molecule is therefore zero.
A molecule like this, with both positive and negative charges is called a zwitterion. The
charge on the amino acid changes with pH:
a.
low pH (acid)
neutral pH
high pH (alkali)
charge = +1
charge = 0
charge = -1
R GROUPS
The r group of the amino acid determines the physical and chemical properties of the
protein. R groups can be nonpolar, polar, asidic, or basic. They can also be the site of
the addition of prosthetic groups, inorganic groups that are essential for the functioning of
the protein. These prosthetic groups often determine the protein’s function, as in
hemoglobin. Minerals in our diets are often essential parts of prosthetic groups; for
example, iron (Fe2+) in our diet is essential for the synthesis of the heme group the
prosthetic group in hemoglobin. The activities of some proteins are dependent upon coenzymes, which are small organic groups attached to the protein. Many of these coenzymes cannot be made by animals and must be included I our diets in the form of
vitamins.
6.5 POLYPEPTIDES
Amino acids are joined together by peptide bonds. The reaction involves the formation of
a molecule of water in another condensation polymerisation reaction:
Figure 73: Diagram above showing polymerization reaction in proteins.
When two amino acids join together a dipeptide is formed. Three amino acids form a
tripeptide. Many amino acids form a polypeptide.
In a polypeptide there is always one end with a free amino (NH3) group, called the Nterminus, and one end with a free carboxyl (CO2) group, called the C-terminus.
In a protein the polypeptide chain may be hundreds of amino acids long. Amino acid
polymerises to form polypeptides is part of protein synthesis. It takes place in ribosomes,
and is special because it requires an RNA template. The sequence of amino acids in a
polypeptide chain is determined by the sequence of the genetic code in DNA.
Protein Structure
Polypeptides are just a string of amino acids, but they fold up to form the complex and
well-defined three-dimensional structure of working proteins. To help to understand
protein structure, it is broken down into four levels:
1.
Primary Structure
This is just the sequence of amino acids in the polypeptide chain, so is not really a
structure at all. However, the primary structure does determine the rest of the protein
structure. Finding the primary structure of a protein is called protein sequencing, and
the first protein to be sequenced was the protein hormone insulin, by
the Cambridge biochemist Fredrick Sanger, for which work he got the
Nobel prize in 1958.
2. Secondary Structure
This is the most basic level of protein folding, and consists of a few basic motifs that
are found in all proteins. The secondary structure is held together by hydrogen bonds
between the carboxyl groups and the amino groups in the polypeptide backbone. The
two most common secondary structure motifs are the  -helix and the --sheet.
The  -helix. The polypeptide chain is
wound round to form a helix. It is held
together by hydrogen bonds running
parallel with the long helical axis. There
are so many hydrogen bonds that this is a
very stable and strong structure. Do not
confuse the a-helix of proteins with the
famous double helix of DNA. Helices are
common structures throughout biology.
Figure74: The structure of the  -helix.
The-sheet. The polypeptide chain zigzags back and forward forming a sheet of
antiparallel strands. Once again it is held
together by hydrogen bonds.
Figure 75: The structure of the-sheet.
The  -helix and the  -sheet were discovered by Linus Pauling, for which work he
got the Nobel prize in 1954. There are a number of other secondary structure motifs
such as the  -bend, the triple helix (only found in collagen), and the random coil.
1. Tertiary Structure
This is the compact globular structure formed by the folding up of a whole
polypeptide chain. Every protein has a unique tertiary structure, which is responsible
for its properties and function. For example the shape of the active site in an enzyme
is due to its tertiary structure. The tertiary structure is held together by bonds
between the R groups of the amino acids in the protein, and so depends on what the
sequence of amino acids is. There are three kinds of bonds involved:

Hydrogen bonds, which are weak.

Ionic bonds between R-groups with positive or negative charges, which are quite
strong.

Sulphur bridges – covalent S-S bonds between two cysteine amino acids, which
are strong.
So the secondary structure is due to backbone interactions and is thus largely
independent of primary sequence, while tertiary structure is due to side chain
interactions and thus depends on the amino acid sequence.
2. Quaternary Structure
This structure is found in proteins containing more than one polypeptide chain, and
simply means how the different polypeptide chains are arranged together. The
individual polypeptide chains are usually globular, but can arrange themselves into a
variety of quaternary shapes. E.g.:
1. Haemoglobin,
the
oxygen-carrying
protein in red blood cells, consists of
four globular subunits arranged in a
tetrahedral (pyramid) structure. Each
subunit contains one iron atom and
can bind one molecule of oxygen.
Figure 76: Structure of Haemoglobin
2. Immunoglobulins, the proteins that
make
antibodies,
comprise
four
polypeptide chains arranged in a Yshape. The chains are held together by
sulphur bridges. This shape allows
antibodies to link antigens together,
causing
them
to
clump. Figure 77: Structure of Immunoglobulin,
3. Actin, one of the proteins found in
muscles, consists of many globular
subunits arranged in a double helix to
form
long
filaments.
Figure 78: Structure of Actin
4. Tubulin is a globular protein that
polymerises to form hollow tubes
called microtubules. These form part
of the cytoskeleton, and make cilia
and flagella move.
Figure 79: Structure of Tubulin
These four structures are not real stages in the formation of a protein, but are simply a
convenient classification that scientists invented to help them to understand proteins. In
fact proteins fold into all these structures at the same time, as they are synthesized.
The final three-dimensional shape of a protein can be classified as globular or fibrous.
Globular structure
fibrous (or filamentous) structure
Figure 81: Structure of a fibrous structure of a
Figure 80: Structure of
protein.
Globular structure of a protein.
The vast majority of proteins are globular, including enzymes, membrane proteins,
receptors, storage proteins, etc. Fibrous proteins look like ropes and tend to have
structural roles such as collagen (bone), keratin (hair), tubulin (cytoskeleton) and actin
(muscle). They are usually composed of many polypeptide chains. A few proteins have
both structures: the muscle protein myosin has a long fibrous tail and a globular head,
which acts as an enzyme.
6.6 DENATURATION OF PROTEINS
Factors that determine conformation: A polypeptide will spontaneously arrange itself into
a three dimensional structure. However, if the pH, salt concentration, temperature, or
other environmental aspects are altered, the protein may unravel and lose its shape. This
is called denaturation. A protein that denatures is biologically inactive.
Chemicals can disrupt hydrogen bonds, ionic bonds, or disulfide bridges, and change the
structure of proteins. Excessive heat will also cause the protein to denature.
6.7 TYPES OF PROTEINS
a. BINDING PROTEINS
These have the unique ability to take specific shapes which enable to bind to other
substances. For example, Hemoglobin, a globular protein, binds with oxygen.
b. STRUCTURAL PROTEINS
These help with shapes and structures.
1. Collagen: Collagen consists of long fibrous molecules that clump together to make
large fibers; these fibers are the principle component in connective tissues such as
tendons, ligaments, and muscle coverings.
2. Elastin: Elastin has the ability to stretch and gives elasticity to connective tissues such
as skin. Loss of elastic property over time causes bagginess in the face, neck and
skin.
3. Keratin: Keratin is found in hair, nails, outer layer of skin, feathers, claws, horns, and
scales. Cells fill up with keratin, then die and leave the keratin behind.
6.8
LIPIDS
Lipids are a mixed group of hydrophobic compounds composed of the elements carbon,
hydrogen and oxygen.
Triglycerides
Triglycerides are commonly called fats or oils. They are made of glycerol and fatty acids.
Glycerol is a small, 3-carbon
molecule with three alcohol
groups.
Figure 82: Chemical formula of Glycerol
Fatty acids are long molecules with a polar, hydrophilic end and a non-polar,
hydrophobic “tail”. The hydrocarbon chain can be from 14 to 22 CH2 units long, but it is
always an even number because of the way fatty acids are made. The hydrocarbon chain
is sometimes called an R group, so the formula of a fatty acid can be written as R-COO-.

If there are no C=C double bonds in the hydrocarbon chain, then it is a
saturated fatty acid (i.e. saturated with hydrogen). These fatty acids form straight
chains, and have a high melting point.
Figure 83: Structure of saturated fatty acid.

If there are C=C double bonds in the hydrocarbon chain, then it is an
unsaturated fatty acid (i.e. unsaturated with hydrogen). These fatty acids form
bent chains, and have a low melting point. Fatty acids with more than one double
bond are called poly-unsaturated fatty acids (PUFAs).
Figure 84: Structure of un saturated fatty acid.
One molecule of glycerol joins togther with three fatty acid molecules to form a
triglyceride molecule, in another condensation polymerization reaction:
Figure 85: The polymerization reaction in fatty acids.
Triglycerides are insoluble in water. They are used for storage, insulation and protection
in fatty tissue (or adipose tissue) found under the skin (sub-cutaneous) or surrounding
organs. They yield more energy per unit mass than other compounds so are good for
energy storage. Carbohydrates can be mobilised more quickly, and glycogen is stored in
muscles and liver for immediate energy requirements.

Triglycerides containing saturated fatty acids have a high melting point and tend
to be found in warm-blooded animals. At room temperature thay are solids (fats),
e.g. butter, lard.

Triglycerides containing unsaturated fatty acids have a low melting point and tend
to be found in cold-blooded animals and plants. At room temperature they are
liquids (oils), e.g. fish oil, vegetable oils.
6.9 PHOSPHOLIPIDS
Phospholipids have a similar structure to triglycerides, but with a phosphate group in
place of one fatty acid chain. There may also be other groups attached to the phosphate.
Phospholipids have a polar hydrophilic “head” (the negatively-charged phosphate group)
and two non-polar hydrophobic “tails” (the fatty acid chains). This mixture of properties
is fundamental to biology, for phospholipids are the main components of cell membranes.
Figure 86: The structure of Phospho lipids.
When mixed with water, phospholipids form
droplet spheres with the hydrophilic heads
facting the water and the hydrophobic tails
facing eachother. This is called a micelle.
Figure 87: Structure of a micelle
Alternatively, they may form a double-layered
Phospholipid bilayer. This traps a compartment
of water in the middle separated from the
external water by the hydrophobic sphere. This
naturally-occurring structure is called a
liposome, and is similar to a membrane
surrounding a cell.
Figure 88: Structure of a liposome.
WAXES
Waxes are formed from fatty acids and long-chain alcohols. They are commonly found
wherever waterproofing is needed, such as in leaf cuticles, insect exoskeletons, birds’
feathers and mammals’ fur.
STEROIDS
Steroids are small hydrophobic molecules found mainly in animals. They include:

cholesterol, which is found in animals cell membranes to increase stiffness

bile salts, which help to emulsify dietary fats

steroid hormones such as testosterone, oestrogen, progesterone and cortisol

vitamin D, which aids Ca2+ uptake by bones.
TERPENES
Terpenes are small hydrophobic molecules found mainly in plants. They include vitamin
A, carotene and plant oils such as geraniol, camphor and menthol.
6.10 NUCLEIC ACIDS
Nucleic acids are the largest organic molecule made by organisms. There are two
types: DNA (Deoxyribonucleic Acid) and RNA (Ribonucleic Acid). The pentose
sugar in DNA, deoxyribose, has one fewer oxygen atom than ribose, the sugar in
RNA.
DNA contains an organism’s genetic information. Basically, DNA encodes the
instructions for amino acid sequences of proteins. RNA carries the encoded
information to the ribosomes, carries the amino acids to the ribosome, and is a major
constituent of ribosomes.
1. Structure
Nucleotides are the basic units of both DNA and RNA and can exist as free
molecules. A nucleotide is made up of three parts.
a. Pentose sugar: deoxyribose or ribose.
b. Phosphate: in free nucleotides, they occur as a group of phosphates bonded to
a sugar.
c. Nitrogenous base: there are two types of nitrogenous bases. They are called
bases because of the amine groups, which are basic.
1) Pyrimidines: single ring compounds. The two pyrimidines in DNA are
cytosine and thymine. In RNA, thymine is replaced by Uracil.
2) Purines: double ring bases. The two purines are adenine and guanine.
2. Importance of Nucleic Acids
a.
DNA is the hereditary material; RNA enables proteins to e synthesized
from the DNA instructions.
b.
A cell’s energy source for chemical reactions is stored as ATP (adenosine
triphosphate). Between the phosphate groups are bonds, which can be
broken to yield usable energy, 7 kcal/mole. CAMP (cyclic adenosine
monophosphate) is used as a second messenger in many hormonal
reactions
6.12 BIOCHEMICAL TESTS
These five tests identify the main biologically important chemical compounds. For each
test take a small amount of the substance to test, and shake it in water in a test tube. If the
sample is a piece of food, then grind it with some water in a pestle and mortar to break up
the cells and release the cell contents. Many of these compounds are insoluble, but the
tests work just as well on a fine suspension.

Starch (iodine test). To approximately 2 cm³ of test solution add two drops of
iodine/potassium iodide solution. A blue-black colour indicates the presence of starch
as a starch-polyiodide complex is formed. Starch is only slightly soluble in water, but
the test works well in a suspension or as a solid.

Reducing Sugars (Benedict’s test). All monosaccharides and most disaccharides
(except sucrose) will reduce copper (II) sulphate, producing a precipitate of copper (I)
oxide on heating, so they are called reducing sugars. Benedict’s reagent is an aqueous
solution of copper (II) sulphate, sodium carbonate and sodium citrate. To
approximately 2 cm³ of test solution add an equal quantity of Benedict’s reagent.
Shake, and heat for a few minutes at 95°C in a water bath. A precipitate indicates
reducing sugar. The colour and density of the precipitate gives an indication of the
amount of reducing sugar present, so this test is semi-quantitative. The original pale
blue colour means no reducing sugar, a green precipitate means relatively little sugar;
a brown or red precipitate means progressively more sugar is present.

Non-reducing Sugars (Benedict’s test). Sucrose is called a non-reducing sugar
because it does not reduce copper sulphate, so there is no direct test for sucrose.
However, if it is first hydrolysed (broken down) to its constituent monosaccharides
(glucose and fructose), it will then give a positive Benedict’s test. So sucrose is the
only sugar that will give a negative Benedict’s test before hydrolysis and a positive
test afterwards. First test a sample for reducing sugars, to see if there are any present
before hydrolysis. Then, using a separate sample, boil the test solution with dilute
hydrochloric acid for a few minutes to hydrolyse the glycosidic bond. Neutralise the
solution by gently adding small amounts of solid sodium hydrogen carbonate until it
stops fizzing, then test as before for reducing sugars.

Lipids (emulsion test). Lipids do not dissolve in water, but do dissolve in ethanol.
This characteristic is used in the emulsion test. Do not start by dissolving the sample
in water, but instead shake some of the test sample with about 4 cm³ of ethanol.
Decant the liquid into a test tube of water, leaving any undissolved substances behind.
If there are lipids dissolved in the ethanol, they will precipitate in the water, forming a
cloudy white emulsion. The test can be improved by adding the dye Sudan III, which
stains lipids red.

Protein (biuret test). To about 2 cm³ of test solution add an equal volume of biuret
solution, down the side of the test tube. A blue ring forms at the surface of the
solution, which disappears on shaking, and the solution turns lilac-purple, indicating
protein. The colour is due to a complex between nitrogen atoms in the peptide chain
and Cu2+ ions, so this is really a test for peptide bonds.
REVISION QUESTIONS
Identify the letter of the choice that best completes the statement or answers the question.
1. Lipids are good energy-storage molecules because
a. the can absorb a large amount of energy while maintaining a constant temperature
b. they have many carbon-hydrogen bonds
c. they are composed of many simple sugars
d. they cannot be broken down by enzymes
2. A compound found in living things that supplies the energy in one of its chemical
bonds directly to cells is
a. phosphate
b. RNA
c. ATP
d. alcohol
3. Which of the following groups ot terms is associated with carbohrdrates?
a. monosaccharide, glycogen, cellulose
c. monosaccharide, cellulose, lipid
b. disaccharide, polysaccharide, steroid
d.
atalyzing ds , amino acid,
collengen
4. Compounds containing an amino group, a carboxyl group, and a side group are
a. fatty acids
b. amino acids
c. peptide bonds
d. alanines
5. A fatty acid is a compound made of a chain of carbon atoms plus
a. an acid group at one end
c. acid group at both ends
b. an amino group
d. amino group at both ends
6. What is a peptide bond?
a. an amino acid glycerol group
c. a covalent bond between a polymer and
lipid
b. an amino acid hydrogen group
d. a covalent bond between two amino
acids
7. A monomer is a small, building block of a(n)
a. atom
b. molecule
c. nucleus
d. ion
8. Which of the following use polysaccharide for strength and rigidity?
a. humans
b. amebas
c. animals
d. plants
9. Two polysaccharides that store glucose are
a. waxes and starch
c. starch and glycogen
b. sucrose and cellulose
d. cellulose and glycogen
10. A substrate attaches to the _________ of an enzyme.
a. peptide bond
b. R group
c. active site
d. activator
11. The element that readily bonds to itself, forming long chains and rings, is
a. hydrogen
b. nitrogen
c. carbon
d. oxygen
7.0
ENZYMES
The existence of enzymes has been known for well over a century. Some of the
earliest studies were performed in 1835 by the Swedish chemist Jon Jakob Berzelius who
termed their chemical action catalytic. It was not until 1926, however, that the first
enzyme was obtained in pure form, a feat accomplished by James B. Sumner of Cornell
University. Sumner was able to isolate and crystallize the enzyme urease from the jack
bean. His work was to earn him the 1947 Nobel Prize.
Enzymes are:
 -catalysts, (speeds up a reaction and are not used up)
 -proteins
 -most have names that end in –ase.
 -are specific to a substrate. (only fit with that substrate)
a. metabolism – the chemical reactions that take place in the body
b. substrate – the substance that the enzyme reacts with
c. enzyme – a protein molecule that catalyzes a chemical reaction
d. co-enzyme – a non-protein molecule which assists the enzyme catalyzed reaction by
contributing or accepting atoms .
Enzymes are biological catalysts. There are about 40,000 different enzymes in human
cells, each controlling a different chemical reaction. They increase the rate of reactions
by a factor of between 106 to 1012 times, allowing the chemical reactions that make life
possible to take place at normal temperatures. They were discovered in fermenting yeast
in 1900 by Buchner, and the name enzyme means “in yeast”. As well as catalyzing all the
metabolic reactions of cells (such as respiration, photosynthesis and digestion), they also
act as motors, membrane pumps and receptors.
.1 CHEMICAL NATURE OF ENZYMES
All known enzymes are proteins. They are high molecular weight compounds made up
principally of chains of amino acids linked together by peptide bonds. Enzymes can be
denatured and precipitated with salts, solvents and other reagents. They have molecular
weights ranging from 10,000 to 2,000,000.
Figure 93: The relation ship of Holoenzymes, apoenzymes and cofactors
Many enzymes require the presence of other compounds - cofactors - before their
catalytic activity can be exerted. This entire active complex is referred to as the
holoenzyme; i.e., apoenzyme (protein portion) plus the cofactor (coenzyme, prosthetic
group or metal-ion-activator) is called the holoenzyme.
Apoenzyme + Cofactor = Holoenzyme
According to Holum, the cofactor may be:
1. A coenzyme - a non-protein organic substance which is dialyzable, thermostable and
loosely attached to the protein part.
2. A prosthetic group - an organic substance which is dialyzable and thermostable which
is firmly attached to the protein or apoenzyme portion.
3. A metal-ion-activator - these include K+, Fe++, Fe+++, Cu++, Co++, Zn++, Mn++, Mg++,
Ca++, and Mo+++.
7.2 SPECIFICITY OF ENZYMES
One of the properties of enzymes that makes them so important as diagnostic and
research tools is the specificity they exhibit relative to the reactions they catalyze. A few
enzymes exhibit absolute specificity; that is, they will catalyze only one particular
reaction. Other enzymes will be specific for a particular type of chemical bond or
functional group. In general, there are four distinct types of specificity:

Absolute specificity - the enzyme will catalyze only one reaction.

Group specificity - the enzyme will act only on molecules that have specific
functional groups, such as amino, phosphate and methyl groups.

Linkage specificity - the enzyme will act on a particular type of chemical bond
regardless of the rest of the molecular structure.

Stereochemical specificity - the enzyme will act on a particular steric or optical
isomer.
7.3 NAMING AND CLASSIFICATION
Except for some of the originally studied enzymes such as pepsin, rennin, and trypsin,
most enzyme names end in "ase". The International Union of Biochemistry (I.U.B.)
initiated standards of enzyme nomenclature which recommend that enzyme names
indicate both the substrate acted upon and the type of reaction catalyzed. Under this
system, the enzyme uricase is called urate: O2 oxidoreductase, while the enzyme glutamic
oxaloacetic transaminase (GOT) is called L-aspartate: 2-oxoglutarate aminotransferase.
Enzymes can be classified by the kind of chemical reaction catalyzed.
1. Addition or removal of water
1. Hydrolases - these include esterases, carbohydrases, nucleases, deaminases,
amidases, and proteases
2. Hydrases such as fumarase, enolase, aconitase and carbonic anhydrase
2. Transfer of electrons
1. Oxidases
2. Dehydrogenases
3. Transfer of a radical
1. Transglycosidases - of monosaccharides
2. Transphosphorylases and phosphomutases - of a phosphate group
3. Transaminases - of amino group
4. Transmethylases - of a methyl group
5. Transacetylases - of an acetyl group
4. Splitting or forming a C-C bond
1. Desmolases
5. Changing geometry or structure of a molecule
1. Isomerases
6. Joining two molecules through hydrolysis of pyrophosphate bond in ATP or other
tri-phosphate
1. Ligases
ENZYME STRUCTURE
Enzymes are proteins, and their function is determined by their complex structure. The
reaction takes place in a small part of the enzyme called the active site, while the rest of
the protein acts as “scaffolding”. This is shown in this diagram of a molecule of the
enzyme amylase, with a short length of starch being digested in its active site. The amino
acids around the active site attach to the substrate molecule and hold it in position while
the reaction takes place. This makes the enzyme specific for one reaction only, as other
molecules won’t fit into the active site .Many enzymes need cofactors (or coenzymes) to
work properly. These can be metal ions (such as Fe2+, Mg2+, Cu2+) or organic molecules
(such as haem, biotin, FAD, NAD or coenzyme A). Many of these are derived from
dietary vitamins, which is why they are so important. The complete active enzyme with
its cofactor is called a holoenzyme, while just the protein part without its cofactor is
called the apoenzyme.
How do enzymes work?
There are three ways of thinking about enzyme catalysis. They all describe the same
process, though in different ways, and you should know about each of them.
Reaction Mechanism
In any chemical reaction, a substrate (S) is converted into a product (P):
S P
(There may be more than one substrate and more than one product, but that doesn’t
matter here.) In an enzyme-catalysed reaction, the substrate first binds to the active
site of the enzyme to form an enzyme-substrate (ES) complex, then the substrate is
converted into product while attached to the enzyme, and finally the product is
released. This mechanism can be shown as:
Figure 94: The structure of the reaction of an enzyme and a substrate.
The enzyme is then free to start again. The end result is the same (SP), but a
different route is taken, so that the S P reaction as such never takes place. In bypassing this step, the reaction can be made to happen much more quickly.
Molecule Geometry
The substrate molecule fits into the active site of the enzyme molecule like a key
fitting into a lock (in fact it is sometimes called a lock and key mechanism). Once
there, the enzyme changes shape slightly, distorting the molecule in the active site,
and making it more likely to change into the product. For example if a bond in the
substrate is to be broken, that bond might be stretched by the enzyme, making it more
likely to break. Alternatively the enzyme can make the local conditions inside the
active site quite different from those outside (such as pH, water concentration,
charge), so that the reaction is more likely to happen. It’s a bit more complicated than
that though. Although enzymes can change the speed of a chemical reaction, they
cannot change its direction, otherwise they could make “impossible” reactions happen
and break the laws of thermodynamics. So an enzyme can just as easily turn a product
into a substrate as turn a substrate into a product, depending on which way the
reaction would go anyway. In fact the active site doesn’t really fit the substrate (or the
product) at all, but instead fits a sort of half-way house, called the transition state.
When a substrate (or product) molecule binds, the active site changes shape and fits
itself around the molecule, distorting it into forming the transition state, and so
speeding up the reaction. This is sometimes called the induced fit mechanism.
Energy Changes
The way enzymes work can also be shown by considering the energy changes that take
place during a chemical reaction. We shall consider a reaction where the product has a
lower energy than the substrate, so the substrate naturally turns into product (in other
words the equilibrium lies in the direction of the product). Before it can change into
product, the substrate must overcome an "energy barrier" called the activation energy
(EA). The larger the activation energy, the slower the reaction will be because only a few
substrate molecules will by chance have sufficient energy to overcome the activation
energy barrier.
Figure 96: Agraph showing energy changes when an enzyme acts on a substrate.
1.
Temperature
Enzymes have an optimum temperature at which they work fastest. For mammalian
enzymes this is about 40°C, but there are enzymes that work best at very different
temperatures, e.g. enzymes from the arctic snow flea work at -10°C, and enzymes
from thermophilic bacteria work at 90°C.
Up to the optimum temperature the rate increases geometrically with temperature (i.e.
it's a curve, not a straight line). The rate increases because the enzyme and substrate
molecules both have more kinetic energy so collide more often, and also because
more molecules have sufficient energy to overcome the (greatly reduced) activation
energy. The increase in rate with temperature can be quantified as a Q10, which is the
relative increase for a 10°C rise in temperature. Q10 is usually 2-3 for enzymecatalysed reactions (i.e. the rate doubles every 10°C) and usually less than 2 for nonenzyme reactions.
The rate is not zero at 0°C, so enzymes still work in the fridge (and food still goes
off), but they work slowly. Enzymes can even work in ice, though the rate is
extremely slow due to the very slow diffusion of enzyme and substrate molecules
through the ice lattice.
Above the optimum temperature the rate decreases as more and more of the enzyme
molecules denature. The thermal energy breaks the hydrogen bonds holding the
secondary and tertiary structure of the enzyme together, so the enzyme (and
especially the active site) loses its shape to become a random coil. The substrate can
no longer bind, and the reaction is no longer catalyzed. At very high temperatures this
is irreversible. Remember that only the weak hydrogen bonds are broken at these mild
temperatures; to break strong covalent bonds you need to boil in concentrated acid for
many hours
Figure 97: The graph above shows the effect of temperature on the action of
enzymes.
2.
pH
Enzymes have an optimum pH at which they work fastest. For most enzymes this is
about pH 7-8 (physiological pH of most cells), but a few enzymes can work at
extreme pH, such as protease enzymes in animal stomachs, which have an optimum
of pH 1. The pH affects the charge of the amino acids at the active site, so the
properties of the active site change and the substrate can no longer bind. For example
a carboxyl acid R groups will be uncharged a low pH (COOH), but charged at high
pH (COO-).
Figure 98: The graph above shows the effect of PH on the action of enzymes.
Enzyme concentration
As the enzyme concentration increases the rate of the reaction increases linearly, because
there are more enzyme molecules available to catalyse the reaction. At very high enzyme
concentration the substrate concentration may become rate-limiting, so the rate stops
increasing. Normally enzymes are present in cells in rather low concentrations
Figure 99: The graph above shows the effect of enzyme concentration on the rate of
reaction.
4. Substrate concentration
Figure 100: The graph above shows the effect of substrate concentration on the rate
of reaction.
The rate of an enzyme-catalysed reaction shows a curved dependence on substrate
concentration. As the substrate concentration increases, the rate increases because more
substrate molecules can collide with enzyme molecules, so more reactions will take
place. At higher concentrations the enzyme molecules become saturated with substrate,
so there are few free enzyme molecules, so adding more substrate doesn't make much
difference (though it will increase the rate of E-S collisions). The maximum rate at
infinite substrate concentration is called vmax, and the substrate concentration that give a
rate of half vmax is called KM. These quantities are useful for characterising an enzyme. A
good enzyme has a high vmax and a low KM.
5. Covalent modification
The activity of some enzymes is controlled by other enzymes, which modify the protein
chain by cutting it, or adding a phosphate or methyl group. This modification can turn an
inactive enzyme into an active enzyme (or vice versa), and this is used to control many
metabolic enzymes and to switch on enzymes in the gut (see later) e.g. hydrochloric acid
in stomach activates pepsin activates rennin.
6. Inhibitors
Inhibitors inhibit the activity of enzymes, reducing the rate of their reactions. They are
found naturally, but are also used artificially as drugs, pesticides and research tools.
There are two kinds of inhibitors.
Figure 101: The structure of action inhibitors.
(a) A competitive inhibitor molecule has a similar structure to the normal substrate
molecule, and it can fit into the active site of the enzyme. It therefore competes with the
substrate for the active site, so the reaction is slower. Competitive inhibitors increase KM
for the enzyme, but have no effect on vmax, so the rate can approach a normal rate if the
substrate concentration is increased high enough. The sulphonamide anti-bacterial drugs
are competitive inhibitors.
Figure 102: The structure of action inhibitors.
(b) A non-competitive inhibitor molecule is quite different in structure from the substrate
molecule and does not fit into the active site. It binds to another part of the enzyme
molecule, changing the shape of the whole enzyme, including the active site, so that it
can no longer bind substrate molecules. Non-competitive inhibitors therefore simply
reduce the amount of active enzyme (just like decreasing the enzyme concentration), so
they decrease vmax, but have no effect on KM. Inhibitors that bind fairly weakly and can
be washed out are sometimes called reversible inhibitors, while those that bind tightly
and cannot be washed out are called irreversible inhibitors. Poisons like cyanide, heavy
metal ions and some insecticides are all non-competitive inhibitors.
7. Allosteric Effectors
The activity of some enzymes is controlled by certain molecules binding to a specific
regulatory (or allosteric) site on the enzyme, distinct from the active site. Different
molecules can inhibit or activate the enzyme, allowing sophisticated control of the rate.
Only a few enzymes can do this, and they are often at the start of a long biochemical
pathway. They are generally activated by the substrate of the pathway and inhibited by
the product of the pathway, thus only turning the pathway on when it is needed.
7.7 ENZYME QUESTIONS
1. The diagram below shows the rate of an enzyme controlled reaction. The solid line
indicates the normal relationship between rate and substrate concentration and the dotted
line indicates the relationship when a competitive inhibitor is added.
( a ) Explain how a competitive inhibitor acts

It is similar in shape to the substrate

Therefore fits into the active site
 Thus blocking it preventing substrate entering and slowing reaction rate
(any 2)
(b) Explain why in the graph above the inhibitor is a competitive inhibitor?

The graph shows that at high substrate concentration the effect of the
inhibitor is removed
 This is because as soon as an active site becomes free it is filled with another
substrate molecule
2. The graph below shows the relationship between rate of reaction and temperature of
most enzyme reaction.
( a ) Explain why the relationship is that shown on the graph.

Initially as the temperature increases the amount of kinetic energy of the
particles increases

Therefore there are more successful collisions per unit time

This continues until the rate is at its greatest (the optimum temperature)

At temperatures higher than this Hydrogen bonds holding the polypeptide
chains together begin to break

This affects the tertiary structure of the enzyme (denatures it)

This changes the shape of the active site

Substrate can no longer fit, therefore rate decreases

This continues until 100% of the enzyme molecule are denatured and the
rate of reaction falls to zero
ESSAY QUESTIONS
1. Name 3 things that cause an enzyme to be denatured
2. What is the definition of a substrate
3. What is the definition of an enzyme
4. Give 2 characteristics of enzymes
5. How would the addition of an inhibitor affect an enzyme catalyzed reaction
6. How would a change in pH affect an enzyme reaction
7. What is a co-enzyme, give an example
8. Using lock and key theory of enzyme action, describe how it is that enzymes only react
with specific substances
9. Define activation energy
10. Explain why increasing the temperature of an enzyme reaction to 100 C would
completely stop the reaction.
11. What type of molecule is an enzyme
8.0
RESPIRATION
INTRODUCTION
All living creatures need food. The food is consumed so that energy is obtained. The
energy is utilized by the body for various purposes like locomotion, conduction of
impulses, repair of damaged tissues, building of cell materials, etc. The substance that is
used to release energy is called the substrate. The food consumed has various chemical
compounds such as carbohydrates, proteins, fats, etc. Essentially, the body has a
mechanism by which the food can be broken down into simpler molecules and in the
process, release energy. The most common substrate for respiration is glucose.
Respiration can be broadly defined as "the breakdown of organic compounds into
simpler compounds accompanied by the release of energy in the form of ATP".
RESPIRATION AND BREATHING
In most cases, glucose is oxidised in the presence of oxygen to give carbon dioxide.
Thus, for respiration, an organism has to take in oxygen and give out carbon dioxide.
This is called gaseous exchange. The oxygen taken in is used to break down the
respiratory substrate (e.g., glucose) and energy is released along with carbon dioxide.
This whole process is called respiration.
Since most often the substrate is glucose, the general equation for respiration can be
written as follows:
Or
TYPES OF RESPIRATION
1. Aerobic
2. Anaerobic
Most of plants and animal cells respire aerobically, that is, in the presence of oxygen.
However, there are certain microbes that respire in the absence of free oxygen. This
respiration is called anaerobic respiration. It is also called fermentation. Among plants, it
takes place in yeast, bacteria, etc. Among animals, only certain cells are temporarily
anaerobic (when they are short of oxygen) such as the muscle cells. Anaerobic respiration
is of two types:
1. Alcoholic fermentation
It occurs in plants like the yeast (a fungus). It can be represented as follows:
This process also takes place in higher plants for a very short while and only when free
oxygen is not available. For example, germinating seeds respire anaerobically.
2. Lactic Acid Fermentation
It can be represented as follows:
During this process, no carbon dioxide is released. It is because of the accumulation of
lactic acid that there is fatigue and cramps in the muscles after prolonged exercises. This
process takes place when the small store of ATP in the muscles is used up and energy is
required immediately. It must be noted that the first step of respiration - glycolysis is
common to both aerobic and anaerobic respiration. Thus, in anaerobic respiration also
pyruvic acid is formed. The pyruvic acid is then fermented to ethanol or lactic acid
IMPORTANCE OF ANAEROBIC RESPIRATION
Anaerobic respiration releases less energy, it meets the requirements of the microbes
growing in anaerobic conditions. Fermentation is a commercially important process. It is
used in the following processes:
 Manufacture of alcohol
 Curing of tea leaves, tobacco, etc.
 Formation of curd from milk
 Manufacture of vinegar, an industrially important compound.
STAGES OF RESPIRATION
Respiration takes place in the following two stages:
 External respiration
 Internal respiration
EXTERNAL RESPIRATION
The exchange of gases between the environment and the body is called external
respiration or gaseous exchange. This includes the entry of oxygen and the exit of
carbon dioxide from the cells.
INTERNAL RESPIRATION
Internal respiration is also called tissue respiration or cellular respiration. The biochemical processes involved in respiration which break down the substrate to release
energy take place in the tissues within the cells of an organism. Thus, this is called
cellular respiration.
EXTERNAL RESPIRATION
External respiration may involve organs or structures with specialized surfaces for the
efficient exchange of gases over with air or water pumped by various respiratory
movements. All forms of respiration require some form of gaseous exchange. In aerobic
respiration, Oxygen must enter our blood and Carbon Dioxide must leave the blood
through our lungs. Gaseous exchange is the exchange of Oxygen and Carbon Dioxide
across a respiratory surface. Many animals which live in water or very wet places use
gills for gaseous exchange. Animals which live on dry land use lungs. Our lungs have an
enormous surface area so that Oxygen can get into the blood quickly enough and
Carbon Dioxide can get out of our blood quickly enough. Our lungs contain billions of
very tiny sacs called alveoli. Each alveolus is microscopic; but if we took all the alveoli
in someone's lungs and laid them flat side by side we would end up with a sheet the size
of a tennis court. As well as having a very, very, very large surface area, the walls of out
alveoli are incredibly thin, so the distance between the air in our lungs and the blood in
our capillaries is very, very, very small.
DIFFUSION AND THE PROBLEM OF SIZE
All organisms need to exchange substances such as food, waste, gases and heat with their
surroundings. These substances must diffuse between the organism and the surroundings.
The rate at which a substance can diffuse is given by Fick's law:
So rate of exchange of substances depends on the organism's surface area that's in contact
with the surroundings. Requirements for materials depends on the volume of the
organism, So the ability to meet the requirements depends on the surface area : volume
ratio. As organisms get bigger their volume and surface area both get bigger, but volume
increases much more than surface area. This can be seen with some simple calculations
for different-sized organisms. Although it's inaccurate lets assume the organisms are cube
shaped to simplify the maths - the overall picture is still the same. The surface area of a
cube with length of side L is LxLx6, while the volume is LxLxL.
ORGANISM
SA (M²) VOL. (M³)
S/A:VOL
1 mm
6 x 10-12
10-18
6,000,000:1
amoeba
100 mm
6 x 10-8
10-12
60,000:1
fly
10 mm
6 x 10-4
10-6
600:1
dog
1m
6 x 100
100
6:1
100 m
6 x 104
106
0.06:1
bacterium
whale
LENGTH
So as organisms get bigger their surface area/volume ratio gets smaller. Bacteria are all
surface with not much inside, while whales are all insides without much surface. So as
organisms become bigger it is more difficult for them to exchange materials with their
surroundings.
Organisms also need to exchange heat with their surroundings, and here large animals
have an advantage in having a small surface area/volume ratio: they lose less heat than
small animals. Large mammals keep warm quite easily and don't need much insulation or
heat generation. Small mammals and birds lose their heat very readily, so need a high
metabolic rate in order to keep generating heat, as well as thick insulation. So large
mammals can feed once every few days while small mammals must feed continuously.
Human babies also loose heat more quickly than adults, which is why they need woolly
hats.
SYSTEMS THAT INCREASE THE RATE OF EXCHANGE
Fick's law shows that for a fast rate of diffusion you must have a large surface area, a
small distance between the source and the destination, and maintain a high concentration
gradient. All large organisms have developed systems that are well-adapted to achieving
these goals, as this table shows. For comparison, a tennis court has an area of about
260 m² and a football pitch has an area of about 5000 m².
System
human
circulatory
system
human lungs
Fish gills
High concentration
Large surface area
Small distance
100m of capillaries with a
capillary walls are only
constant blood flow
surface area of 6000m²
one cell thick
replenishes the blood
600 million alveoli with a total
each alveolus is only
constant ventilation
area of 100m²
one cell thick
replaces the air
feathery filaments with
lamellae are two cells
lamellae
thick
gradient
water pumped over
gills in countercurrent
to blood
human small
intestine
7m long, folds, villi and
microvilli give surface area of
2000m²
blood capillaries close
stirred by peristalsis
to surface of villus
and by microvilli
surface area of leaves of 1 tree
Leaves
wind replaces air
is 200m², surface area of
gases diffuse straight
round leaves, and
spongy cells inside leaves of 1
into leaf cells
photosynthesis
tree is 6000m².
1m² area of lawn grass has
root hairs
350m² of root surface area due
to root hairs
counteracts respiration
fairly short route
through root to xylem
transpiration draws
water and solutes away
from roots.
Gas exchange takes place at a respiratory surface - a boundary between the external
environment and the interior of the body. For unicellular organisms the respiratory
surface is simply the cell membrane, but for large multicellular organisms it is part of
specialised organs like lungs, gills or leaves.
Gases cross the respiratory surface by diffusion, so from Fick's law we can predict that
respiratory surfaces must have:

a large surface area

a thin permeable surface

a moist exchange surface
GAS EXCHANGE IN PLANTS
All plant cells respire all the time, and when illuminated plant cells containing
chloroplasts also photosynthesise, so plants also need to exchange gases. The main gas
exchange surfaces in plants are the spongy mesophyll cells in the leaves. Leaves of
course have a huge surface area, and the irregular-shaped, loosely-packed spongy cells
increase the area for gas exchange still further. You are expected to know leaf structure in
the detail shown in the diagram
Figure 107: The structure of a green plant leaf.
Gases enter the leaf through stomata -usually in the lower surface of the leaf. Stomata are
enclosed by guard cells that can swell up and close the stomata to reduce water loss. The
gases then diffuse through the air spaces inside the leaf, which are in direct contact with
the spongy and palisade mesophyll cells. Plants do not need a ventilation mechanism
because their leaves are exposed, so the air surrounding them is constantly being replaced
in all but the stillest days. In addition, during the hours of daylight photosynthesis
increases the oxygen concentration in the sub-stomatal air space, and decreases the
carbon dioxide concentration. This increases the concentration gradients for these gases,
increasing diffusion rate.
The palisade mesophyll cells are adapted for photosynthesis. They have a thin cytoplasm
densely packed with chloroplasts, which can move around the cell on the cytoskeleton to
regions of greatest light intensity. The palisade cells are closely packed together in rows
to maximise light collection, and in plants adapted to low light intensity there may be two
rows of palisade cells.
The spongy mesophyll cells are adapted for gas exchange. They are loosely-packed with
unusually large intercellular air spaces where gases can collect and mix. They have fewer
chloroplasts than palisade cells, so do less photosynthesis.
LENTICELS
In woody stems, the entire surface is covered by bark which is impervious to gases or
water. However, there are certain openings or pores in the layer of bark. These are called
the lenticels. They are visible slightly more raised than the general surface of the stem. At
the base of the lenticels are loosely arranged cells which allow the diffused gases to pass
through them.
GENERAL SURFACE OF THE ROOTS
Gases diffuse in and out of the general surface of the roots. The gases are found in the
soil surrounding the roots. Plants which grow in salty water show specialized roots called
the pneumatophores. These are roots growing out of the surface of water with numerous
pores on their surface.
GASEOUS EXCHANGE IN EARTHWORM
Earthworm has a segmented cylindrical body covered by a thin cuticle below which is
the epidermis. This skin is always kept very moist by the secretion of mucus from the
epidermis and body fluids from the excretory pores. It always lives in moist soil
especially during the day. This prevents their skin from drying or desiccation.
The epidermal layer has blood capillaries, which have looped out from the vascular
system circulating the blood. These blood capillaries are so close to the skin that the
gases can diffuse from the surroundings into and out of the blood through the skin and the
capillary walls. The blood contains haemoglobin in solution which circulates the gases
through the body.
GASEOUS EXCHANGE IN FISH
Gaseous exchange is more difficult for fish than for mammals because the
concentration of dissolved oxygen in water is less than 1%, compared to 20% in air. (By
the way, all animals need molecular oxygen for respiration and cannot break down water
molecules to obtain oxygen.) Fish have developed specialised gas-exchange organs called
gills, which are composed of thousands of filaments. The filaments in turn are covered in
feathery lamellae which are only a few cells thick and contain blood capillaries. This
structure gives a large surface area and a short distance for gas exchange. Water flows
over the filaments and lamellae, and oxygen can diffuse down its concentration gradient
the short distance between water and blood. Carbon dioxide diffuses the opposite way
down its concentration gradient. The gills are covered by muscular flaps called opercula
on the side of a fish's head. The gills are so thin that they cannot support themselves
without water, so if a fish is taken out of water after a while the gills will collapse and the
fish suffocates.
Fish ventilate their gills to maintain the gas concentration gradient. They continuously
pump their jaws and opercula to draw water in through the mouth and then force it over
the gills and out through the opercular valve behind the gills. This one-way ventilation is
necessary because water is denser and more viscous than air, so it cannot be contained in
delicate sac-like lungs found in air-breathing animals. In the gill lamellae the blood flows
towards the front of the fish while the water flows towards the back. This countercurrent
system increases the concentration gradient and increases the efficiency of gas exchange.
About 80% of the dissolved oxygen is extracted from the water.
Figure 108: The inspiration and expiration processes in fish.
Figure 110 : Location of fish gills
The region between the buccal cavity (mouth) and the oesophagus is called the pharynx.
In the pharyngeal region, the wall on either side shows slits which open to the exterior.
These slits are called the gill slits. The gill slits are separated by a tissue called the gill
arch or the branchial arch. There are four pairs of gill arches separating five pairs of gill
slits.
GASEOUS EXCHANGE IN INSECTS
The respiratory system in insects is called the tracheal system. It involves the diffusion of
oxygen directly from the atmosphere into the air-filled tubes. Thus, the diffusion is
through air and hence, is more efficient than the diffusion through water (300,000 times
more) or tissues (1,000,000 times more).
Figure 113 : Grasshopper - Respiratory System
In grasshopper, the tracheal system consists of 10 pairs of spiracles, located laterally on
the body surface. Of these, 2 pairs are thoracic and 8 pairs are abdominal. The spiracles
are guarded by fine hairs to keep the foreign particles out and by valves that function to
open or close the spiracles as required. The spiracles open into small spaces called the
atria that continue as air tubes called the tracheae. The tracheae are fine tubes that have a
wall of single layered epithelial cells. The cells secrete spiral cuticular thickenings around
the tube that gives support to the tubes. The tracheal tubes branch further into finer
tracheoles that enter all the tissues and sometimes, even the cells of the insect. The ends
of the tracheoles that are in the tissue are filled with fluid and lack the cuticular
thickenings. The main tracheal tubes join together to form three main tracheal trunksdorsal, ventral and lateral. At some places, the trachea enlarge to form air sacs which are
devoid of cuticle and serve to store air.
Figure 114 : Tracheal System of Insects
MECHANISM
The first four pairs of spiracles are involved in inspiration or drawing in of air that is
oxygen-rich. This air passes through the trachea and the air sacs to reach the tracheoles.
The ends of the tracheoles are filled with fluid. This end enters into the tissue. The ends
of the tracheoles are also devoid of cuticle and therefore the respiratory surface is very
thin making the diffusion of oxygen into the cells easy. As respiration occurs in the cell,
the products of respiration accumulate in the cell and this forces the fluid in the
tracheoles to enter the tissue. The exit of fluid creates low pressure in the tubes and draws
in more oxygen to the tissues where it is needed. The carbon dioxide produced is detected
by the chemoreceptors which make the muscles near the spiracles contract. This pushes
the air out. The last six pairs of spiracles are involved in expiration of air. Thus, in
grasshopper there is ventilation or circulation of air as the oxygen-rich air is inhaled
through the first four spiracles and the carbon dioxide-rich air is exhaled through the
remaining six pairs of spiracles. In insects, therefore, the respiratory system is
independent of the circulatory system.
Figure 115 : The Functioning of Tracheoles
GASEOUS EXCHANGE IN HUMANS
In humans the gas exchange organ system is the respiratory or breathing system. The
main features are shown in this diagram below. The actual respiratory surface is on the
alveoli inside the lungs. An average adult has about 600 million alveoli, giving a total
surface area of about 100m², so the area is huge. The walls of the alveoli are composed of
a single layer of flattened epithelial cells, as are the walls of the capillaries, so gases need
to diffuse through just two thin cells. Water diffuses from the alveoli cells into the alveoli
so that they are constantly moist. Oxygen dissolves in this water before diffusing through
the cells into the blood, where it is taken up by haemoglobin in the red blood cells. The
water also contains a soapy surfactant which reduces its surface tension and stops the
alveoli collapsing. The alveoli also contain phagocyte cells to kill any bacteria that have
not been trapped by the mucus.
Figure 116: The human gaseous exchange system.
Figure 117 : The structure of the alveoli.
The steep concentration gradient across the respiratory surface is maintained in two ways:
by blood flow on one side and by air flow on the other side. This means oxygen can
always diffuse down its concentration gradient from the air to the blood, while at the
same time carbon dioxide can diffuse down its concentration gradient from the blood to
the air. The flow of air in and out of the alveoli is called ventilation and has two stages:
inspiration (or inhalation) and expiration (or exhalation). Lungs are not muscular and
cannot ventilate themselves, but instead the whole thorax moves and changes size, due to
the action of two sets of muscles: the intercostal muscles and the diaphragm.
Inspiration

The diaphragm contracts and flattens downwards

The external intercostal muscles contract, pulling the ribs up and out

this increases the volume of the thorax

this increases the lung and alveoli volume

this decreases the pressure of air in the alveoli below atmospheric (Boyle's
law)

air flows in to equalise the pressure
Normal

The diaphragm relaxes and curves upwards
expiration

The external intercostal muscles relax, allowing the ribs to fall

this decreases the volume of the thorax

this decreases the lung and alveoli volume

this increases the pressure of air in the alveoli above atmospheric (Boyle's
law)

air flows out to equalise the pressure
Forced

The abdominal muscles contract, pushing the diaphragm upwards
expiration

The internal intercostal muscles contract, pulling the ribs downward

This gives a larger and faster expiration, used in exercise
These movements are transmitted to the lungs via the pleural sac surrounding each lung.
The outer membrane is attached to the thorax and the inner membrane is attached to the
lungs. Between the membranes is the pleural fluid, which is incompressible, so if the
thorax moves, the lungs move too. The alveoli are elastic and collapse if not held
stretched by the thorax (as happens in stab wounds or deliberately to rest a lung).
Figure 118: The processes of inspiration and expiration in gaseous exchange system
of human being.
CONTROLLING BREATHING RATE
But what controls the breathing rate? It is clearly an involuntary process (you don’t have
to think about it), and like many involuntary processes (such as heart rate, coughing and
sneezing) it is controlled by a region of the brain called the medulla. The medulla and its
nerves are part of the autonomic nervous system (i.e. involuntary). The region of the
medulla that controls breathing is called the respiratory centre. It receives inputs from
various receptors around the body and sends output through two nerves to the muscles
around the lungs.
Figure 119: The diagram above showing the control of breathing in human beings.
The respiratory centre depends on information relayed via chemoreceptors that pick up
changes in:

carbon dioxide concentration – levels in the blood go up when the rate of
respiration increases and more carbon dioxide is produced as a waste product.

Oxygen concentration – levels in the blood go down as it is used in respiration to
produce extra ATP as an energy source for exercise.
The chemoreceptors are stimulated by a rise in carbon dioxide levels and a fall in pH and
oxygen in the blood. The respiratory centre received the information as a nerve impulse
from the chemoreceptors and uses this to regulate breathing.
HOW DOES THE RESPIRATORY CENTRE CONTROL
VENTILATION?
Unlike the heart, the muscles that cause breathing cannot contract on their own, but need
nerve impulses from the brain for each breath. The respiratory centre transmits regular
nerve impulses to the diaphragm and intercostal muscles to cause inhalation. Stretch
receptors in the alveoli and bronchioles detect inhalation and send inhibitory signals to
the respiratory centre to cause exhalation. This negative feedback system in continuous
and prevents damage to the lungs.
One difference between ventilation and heartbeat is that ventilation is also under
voluntary control from the cortex, the voluntary part of the brain. This allows you to hold
your breath or blow out candles, but it can be overruled by the autonomic system in the
event of danger. For example if you hold your breath for a long time, the carbon dioxide
concentration in the blood increases so much that the respiratory centre forces you to
gasp and take a breath. Pearl divers hyperventilate before diving to lower the carbon
dioxide concentration in their blood, so that it takes longer to build up.
During sleep there is so little cellular respiration taking place that it is possible to stop
breathing for a while, but the respiratory centre starts it up again as the carbon dioxide
concentration increases. It is possible that one cause of cot deaths may be an
underdeveloped respiratory centre in young babies, which allows breathing to slow down
or stop for too long.
RESPIRATORY VOLUMES
There are totally about 700 million alveoli in the two lungs of an adult human being. This
increases the surface area enormously. The total surface area of the lungs is 70 square
metres which is almost the size of the tennis court. It is nearly 100 times the surface of
the human body (skin).
Thus, the lungs can hold a lot of air, about 6000 ml. This lung capacity is defined as the
maximum air which can be held in the two lungs at any given time. However, during one
breath in and out, the volume of gas exchanged is called the tidal volume. It is about 450
mL during quiet breathing. The volume of air that can be drawn in after normal
inspiration is about 1500 mL and is called the inspiratory reserve volume
(complemental air). The volume of air that can be expelled out after a normal expiration
is about 1500mL and is called the expiratory reserve volume (supplemental air).
Even after forced expiration, some amount of air remains in the lungs. This is called
residual air which is about 1500ml. Some amount of air remains in the various parts of
the respiratory tract also. The air in the trachea and bronchi (where no diffusion occurs) is
called dead space air (350ml). The air remaining in the alveoli or air sacs is alveolar air
(150mL).
The maximum volume of air that can be exchanged in one breath in and out is called the
vital capacity. It is about 5000mL.
The above information is represented in the given graph below:
Figure 120: Lung Volumes and Lungs Capacities
The instrument that is used to measure the lung volume is called spirometer.
GASEOUS EXCHANGE IN AMPHIBIANS
Frogs respire through skin as well as the lungs. The oxygen rich air enters the skin or
lungs. From here the blood picks up the oxygen and transports it to the tissues of various
organs. From the tissues the blood picks up carbon dioxide and transports it back to the
skin or the lungs from where it is expired into the outer atmosphere.
GASEOUS EXCHANGE QUESTIONS
1. The amoeba which is a single celled organism does not have a specialised system for
gaseous exchange. Explain why this organism has no need of such a system and why
humans need a complex system involving specialised surfaces and mechanisms of
ventilation
Single celled organisms

have a large S/A to volume ratio which increases rate of diffusion and they
have short diffusion distances to all parts of the organism
Mammals

have a small S/A to volume ratio

have long diffusion pathways

they have a waterproof/gastight skin

therefore they need a moist internal gas exchange surface with a large S/A
2. How does a molecule of oxygen reach and then enter ther cells of the spongy
mesophyll in a dicotoledonous leaf

oxygen diffuses onto the leaf down a diffusion gradient

through the stoma

into the air spaces in the leaf

along a diffusion gradient

it then dissolves in the moisture layer on cell walls
oxygen now in solution enters the cells by simple diffusion over the cell
3. Explain how oxygen from atmospheric air reaches the capilaries surrounding the
alveoli in the lungs of a mammal

Muscular contraction forces diaphragm down;

intercostal muscles contract moving ribs up and out;

increases thorax volume

pressure in thorax falls below atmospheric

air flows in through trachea and bronchi

oxygen diffuses into alveoli (they are too delicate for mass flow)

oxygen dissolves into moisture film on alveoli wall
oxygen diffuses (the short distance) into the capillary
CELLULAR RESPIRATION
Glucose is a carbohydrate - a compound of carbon and hydrogen. The bonds between
the carbon and the hydrogen atoms are very strong. In the cells, the substrate, often
glucose, is broken down into carbon dioxide and water in the presence of oxygen. This
process breaks the bonds between carbon and hydrogen and thus releases energy. This is
called respiration.
The equation for cellular respiration is usually simplified to:
glucose + oxygen  carbon dioxide + water (+ energy) carbon dioxide + water
(+ energy)
But in fact respiration is a complex metabolic pathway, comprising at least 30 separate
steps. To understand respiration in detail we can break it up into 3 stages:
Figure 123: The cellural respiration.
Before we look at these stages in detail, there are a few points from this summary.

The different stages of respiration take place in different parts of the cell. This
allows the cell to keep the various metabolites separate, and to control the stages
more easily.

The energy released by respiration is in the form of ATP.

Since this summarises so many separate steps (often involving H+ and OH- ions
from the solvent water), it is meaningless to try to balance the summary equation.

The release of carbon dioxide takes place before oxygen is involved. It is
therefore not true to say that respiration turns oxygen into carbon dioxide; it is
more correct to say that respiration turns glucose into carbon dioxide, and oxygen
into water.

Stage 1 (glycolysis) is anaerobic respiration, while stages 2 and 3 are the aerobic
stages.
MITOCHONDRIA
Much of respiration takes place in the mitochondria. Mitochondria have a double
membrane: the outer membrane contains many protein channels called porins, which let
almost any small molecule through; while the inner membrane is more normal and is
impermeable to most materials. The inner membrane is highly folded into folds called
christae, giving a larger surface area. The electron microscope reveals blobs on the inner
membrane, which were originally called stalked particles. These have now been
identified as the enzyme complex that synthesises ATP, are is more correctly called ATP
synthase (more later). The space inside the inner membrane is called the matrix, and is
where the Krebs cycle takes place. The matrix also contains DNA, tRNA and ribosomes,
and some genes are replicated and expressed here.
Figure 124: The structure of a mitochondria.
13.8 Aerobic and Anaerobic Respiration
Respiration is not a single reaction, but consists of about 30 individual reaction steps. For
now we can usefully break respiration into just two parts: anaerobic and aerobic.
The first part of respiration is simply the
The second part of respiration is the complete
breakdown of glucose to a compound called
oxidation of pyruvate to carbon dioxide and
pyruvate. This doesn’t require oxygen, so is
water. Oxygen is needed for this, so it is
described as anaerobic respiration (without
described as aerobic respiration (with air). It
air). It is also called glycolysis and it takes
takes place in the mitochondria of cells and
place in the cytoplasm of cells. It only
produces far more ATP: 34 molecules of ATP
produces 2 molecules of ATP per molecule
per molecule of glucose.
of glucose.
Normally pyruvate goes straight on to the
aerobic part, but if there is no oxygen it is
converted to lactate (or lactic acid) instead.
Lactate stores a lot of energy, but it isn’t
wasted: when oxygen is available it is
converted back to pyruvate, which is then
used in the aerobic part of respiration.
Details of Respiration
Fats (mainly triglycerides) can also be used in
aerobic respiration (but not anaerobic) to
produce ATP.
Figure 125: The details of respiration.
1. Glucose enters cells from the tissue fluid by passive transport using a specific glucose
carrier. This carrier can be controlled (gated) by hormones such as insulin, so that
uptake of glucose can be regulated.
2. The first step is the phosphorylation of glucose to form glucose phosphate, using
phosphate from ATP. Glucose phosphate no longer fits the membrane carrier, so it
can’t leave the cell. This ensures that pure glucose is kept at a very low concentration
inside the cell, so it will always diffuse down its concentration gradient from the
tissue fluid into the cell. Glucose phosphate is also the starting material for the
synthesis of pentose sugars (and therefore nucleotides) and for glycogen.
3. Glucose is phosphorylated again (using another ATP) and split into two triose
phosphate (3 carbon) sugars. From now on everything happens twice per original
glucose molecule.
4. The triose sugar is changed over several steps to form pyruvate, a 3-carbon
compound. In these steps some energy is released to form ATP (the only ATP formed
in glycolysis), and a hydrogen atom is also released. This hydrogen atom is very
important as it stores energy, which is later used by the respiratory chain to make
more ATP. The hydrogen atom is taken up and carried to the respiratory chain by the
coenzyme NAD, which becomes reduced in the process.
NAD+ + 2H  NADH + H+
(oxidised form )
(reduced form)
NB Rather then write NADH, examiners often simple refer to it as reduced NAD or
reduced coenzyme
Pyruvate marks the end of glycolysis, the first stage of respiration. In the presence of
oxygen pyruvate enters the mitochondrial matrix to proceed with aerobic respiration,
but in the absence of oxygen it is converted into lactate (in animals and bacteria) or
ethanol (in plants and fungi). These are both examples of anaerobic respiration.
Pyruvate can also be turned back into glucose by reversing glycolysis, and this is
called gluconeogenesis.
5. Once pyruvate has entered the inside of the mitochondria (the matrix), it is converted
to a compound called acetyl coA. Since this step is between glycolysis and the Krebs
Cycle, it is referred to as the link reaction. In this reaction pyruvate loses a CO2 and a
hydrogen to form a 2-carbon acetyl compound, which is temporarily attached to
another coenzyme called coenzyme A (or just coA), so the product is called acetyl
coA. The CO2 diffuses through the mitochondrial and cell membranes by lipid
diffusion, out into the tissue fluid and into the blood, where it is carried to the lungs
for removal. The hydrogen is taken up by NAD again.
6. The acetyl CoA then enters the Krebs Cycle, named after Sir Hans Krebs, who
discovered it in the 1940s at Leeds University. It is one of several cyclic metabolic
pathways, and is also known as the citric acid cycle or the tricarboxylic acid cycle.
The 2-carbon acetyl is transferred from acetyl coA to the 4-carbon oxaloacetate to
form the 6-carbon citrate. Citrate is then gradually broken down in several steps to reform oxaloacetate, producing carbon dioxide and hydrogen in the process. As before,
the CO2 diffuses out the cell and the hydrogen is taken up by NAD, or by an
alternative hydrogen carrier called FAD. These hydrogens are carried to the inner
mitochondrial membrane for the final part of respiration.
GLYCOLYSIS
Most foods contain usable energy; stored in complex organic compounds such as
proteins, carbohydrates, and fats. All cells break down complex organic compounds into
simpler molecules. Cells use some of the energy that is released in this process to make
ATP.
OBJECTIVES:
1. Identify the two major steps of cellular respiration.
2. Describe the major events in Glycolysis.
3. Compare lactic acid fermentation with alcoholic fermentation.
4. Calculate the efficiency of glycolysis.
HARVESTING CHEMICAL ENERGY
1. Autotrophs, such as plants, use photosynthesis to convert light energy from the Sun
into Chemical energy, which is stored in Carbohydrates and other Organic Compounds.
2. Both Autotrophs and Heterotrophs depend on these Organic Compounds for the energy
to Power Cellular Activities.
3. By Breaking Down Organic Molecules into simpler molecules, CELLS RELEASE
ENERGY.
4. Some of the energy is used to make ATP from ADP and Phosphate. ATP is the Main
Energy Currency of Cells.
5. The Complex Process in which Cells Make ATP by Breaking Down Organic
Molecules is known as cellular respiration. or the process by which food molecules are
broken down to release energy for work is called cellular respiration.
6. Cellular Respiration takes place in two stages.
STAGE 1 - Cellular Respiration begins with a Biochemical Pathway called
GLYCOLYSIS, that takes place in the Cells Cytosol, yields a relatively Small amount
of ATP and does not require oxygen.
STAGE 2 - The Second Stage of Cellular Respiration is called aerobic respiration or
oxidative respiration, and follows Glycolysis. Oxidative Respiration takes place within
the Mitochondria. This is far more effective than Glycolysis at recovering energy from
food molecules. aerobic respiration is the method by which plant and animal cells get the
majority of their energy.
7. There are two types of cellular respiration: aerobic (presence of oxygen) and
anaerobic (absence of oxygen) respiration or fermentation.
8. Because they operated in the Absence of Oxygen, the fermentation pathways are said
to be anaerobic pathways.
9. If oxygen is present, the products of glycolysis enter the pathways of aerobic
respiration.
10. Aerobic respiration produces a much larger amount of atp, up to 20 times more atp
produced.
GLYCOLYSIS
1. Both types of pathways begin with Glycolysis.
2. Glycolysis is a pathway in which one six-carbon molecule of glucose is oxidized to
produce two three-carbon molecules of pyruvic acid or pyruvate.
3. The word "glycolysis" means "the splitting of glucose". in a series of ten reactions, a
molecule of glucose is split into two identical smaller molecules, each called pyruvic acid
or pyruvate.
4. GLYCOLYSIS is the process by which glucose is converted to pyruvic acid, and some
of its energy is released.
5. Glycolysis occurs in the cytosol of the cell.
6. Whether or not Oxygen is present, Glycolysis splits (by oxidation) glucose into threecarbon molecules of pgal. pgal is then converted to three-carbon pyruvic acid.
7. Glucose is a Stable molecule that DOES NOT Break down Easily.
8. For a Molecule of Glucose to undergo Glycolysis, a Cell must First "SPEND" ATP to
energize the Glucose Molecule. The ATP provides the Activation Energy needed to
begin Glycolysis.
9. Although atp (energy) is used to begin glycolysis, the reactions that make up the
process eventually produce a net gain of two atp molecules.
10. Glycolysis is followed by the break down of pyruvic acid.
11. Like other Biochemical Pathways, Glycolysis consists of a series of Chemical
Reactions. These reactions can be condensed into four main steps:
STEP 1 - Two phosphates are attached to glucose, forming a new six-carbon
compound. the phosphate groups come from two atp, which are converted to ADP.
STEP 2 - The Six-Carbon Compound formed in Step 1 is split into two Three-Carbon
Molecules of G3P.
STEP 3 - The two g3p molecules are oxidized, and each receives a phosphate group
forming two new three-carbon compounds. the phosphate groups are provided by two
molecules of NAD+ (nicotinamide adenine dinucleotide) forming NADH.
STEP 4 - The Phosphate Groups added in Step 1 and Step 3 are Removed from the
Three-Carbon Compounds. This reaction produces Two molecules of Pyruvic Acid.
Each Phosphate Group is combines with a molecule of ADP to make a molecule of ATP.
Because a total of Four Phosphate Groups were Added, four molecules of atp are
produced.
Two ATP molecules were used in step 1, but four are produced in step 4. therefore,
glycolysis has a net yield of two atp molecules for every molecule of glucose that is
converted into pyruvic acid. what happens to the pyruvic acid depends on the type of cell
and on whether oxygen is present.
Figure 126 : An Outline of Glycolysis
KREBS CYCLE
As the Krebs cycle dismantles pyruvate, CO2 is produced. The carbon and oxygen come
from the pyruvate, which is being torn apart. The electrons are what’s important. The
Krebs Cycle only gives us two molecules of ATP. Added withe the two molecules of
ATP made in Glycolysis, the total is now a meager four molecules of ATP. The
remainder of the ATPs come from the Electron Transport System, which takes the
electrons produced in the Krebs Cycle and makes ATP. It takes place in the
mitochondria. The pyruvic acid formed during glycolysis is oxidised and forms carbon
dioxide and water. This reaction also releases molecules called the coenzymes: NADH2
and FADH2. The hydrogen atoms associated with these are the hydrogen atoms released
during the oxidation of pyruvic acid.
The Krebs cycle has FIVE Main Steps :
ALL Five Steps occur in the Mitochondrial Matrix.
STEP 1 - A two-carbon molecule of acetyl COA combines with a four-carbon
compound, oxaloacetic acid , to produce a six-carbon compound citric acid.
STEP 2 - citric acid releases a co2 molecule and a hydrogen atom to form a fivecarbon compound. by losing a hydrogen atom with its electron, citric acid is oxidized.
the hydrogen atom is transferred to NAD+, reducing it to NADH.
STEP 3 - The Five-Carbon Compound Releases a CO2 Molecule and a Hydrogen
Atom, forming a Four-Carbon Compound. NAD+ is reduced to NADH. A Molecule of
ATP is also Synthesized from ADP.
STEP 4 - The Four-Carbon Compound Releases a Hydrogen Atom to form another
Four-Carbon Compound. The Hydrogen is used to Reduce FAD (Flavin Adenine
Dinucleotide) to FADH2, a Molecule similar to NAD+ that Accepts Electron during
Redox Reactions.
STEP 5 - The Four-Carbon Compound Releases a Hydrogen Atom to regenerate
oxaloacetic acid, which keeps the Krebs cycle operating. the hydrogen atom reduces
NAD+ TO NADH.
THE RESPIRATORY CHAIN
The respiratory chain (or electron transport chain) is an unusual metabolic pathway in
that it takes place within the inner mitochondrial membrane, using integral membrane
proteins. These proteins form four huge trans-membrane complexes called complexes I,
II, II and IV. The complexes each contain up to 40 individual polypeptide chains, which
perform many different functions including enzymes and trans-membrane pumps. In the
respiratory chain the hydrogen atoms from NADH gradually release all their energy to
form ATP, and are finally combined with oxygen to form water.
Figure 127: The respiratory chain.
1. NADH molecules bind to Complex I and release their hydrogen atoms as protons
(H+) and electrons (e-). The NAD molecules then returns to the Krebs Cycle to collect
more hydrogen. FADH binds to complex II rather than complex I to release its
hydrogen.
2. The electrons are passed down the chain of proteins complexes from I to IV, each
complex binding electrons more tightly than the previous one. In complexes I, II and
IV the electrons give up some of their energy, which is then used to pump protons
across the inner mitochondrial membrane by active transport through the complexes.
Altogether 10 protons are pumped across the membrane for every hydrogen from
NADH (or 6 protons for FADH).
3. In complex IV the electrons are combined with protons and molecular oxygen to form
water, the final end-product of respiration. The oxygen diffused in from the tissue
fluid, crossing the cell and mitochondrial membranes by lipid diffusion. Oxygen is
only involved at the very last stage of respiration as the final electron acceptor, but
without the whole respiratory chain stops.
4. The energy of the electrons is now stored in the form of a proton gradient across the
inner mitochondrial membrane. It’s a bit like using energy to pump water uphill into a
high reservoir, where it is stored as potential energy. And just as the potential energy
in the water can be used to generate electricity in a hydroelectric power station, so the
energy in the proton gradient can be used to generate ATP in the ATP synthase
enzyme. The ATP synthase enzyme has a proton channel through it, and as the
protons “fall down” this channel their energy is used to make ATP, spinning the
globular head as they go. It takes 4 protons to synthesise 1 ATP molecule.
This method of storing energy by creating a protons gradient across a membrane is called
chemiosmosis. Some poisons act by making proton channels in mitochondrial
membranes, so giving an alternative route for protons and stopping the synthesis of ATP.
This also happens naturally in the brown fat tissue of new-born babies and hibernating
mammals: respiration takes place, but no ATP is made, with the energy being turned into
heat instead.
HOW MUCH ATP IS MADE IN RESPIRATION?
We can now summarise respiration and see how much ATP is made from each
glucose molecule. ATP is made in two different ways: Some ATP molecules are made
directly by the enzymes in glycolysis or the Krebs cycle. This is called substrate level
phosphorylation (since ADP is being phosphorylated to form ATP).
·
Most of the ATP molecules are made by the ATP synthase enzyme in the respiratory
chain. Since this requires oxygen it is called oxidative phosphorylation. Scientists
don’t yet know exactly how many protons are pumped in the respiratory chain, but
the current estimates are: 10 protons are pumped by NADH; 6 by FADH; and 4
protons are needed by ATP synthase to make one ATP molecule. This means that
each NADH can make 2.5 ATPs (10/4) and each FADH can make 1.5 ATPs (6/4).
Previous estimates were 3 ATPs for NADH and 2 ATPs for FADH, and these
numbers still appear in most textbooks, although they are now know to be wrong.
(You don’t need to know these numbers, so don’t worry). Two ATP molecules are
used at the start of glycolysis to phosphorylate the glucose, and these must be
subtracted from the total.
The table below is an “ATP account” for aerobic respiration, and shows that 32
molecules of ATP are made for each molecule of glucose used in aerobic respiration.
This is the maximum possible yield; often less ATP is made, depending on the
circumstances. Note that anaerobic respiration (glycolysis) only produces 2 molecules of
ATP.
Stage
Glycolysis
Link
Reaction
Krebs Cycle
molecules produced per glucose
2 ATP used
4 ATP produced (2 per triose phosphate)
2 NADH produced (1 per triose
2phosphate)
NADH produced (1 per pyruvate)
2 ATP produced (1 per acetyl coA)
6 NADH produced (3 per acetyl coA)
2 FADH produced (1 per acetyl coA)
Total
Final ATP
Final ATP
yield
yield
(old method)
(new method)
-2
4
6
6
2
18
4
38
-2
4
5
5
2
15
3
32
Other substances can also be used to make ATP. Triglycerides are broken down to fatty
acids and glycerol, both of which enter the Krebs Cycle. A typical triglyceride might
make 50 acetyl CoA molecules, yielding 500 ATP molecules. Fats are a very good
energy store, yielding 2.5 times as much ATP per g dry mass as carbohydrates. Proteins
are not normally used to make ATP, but in times of starvation they can be broken down
and used in respiration. They are first broken down to amino acids, which are converted
into pyruvate and Krebs cycle metabolites and then used to make ATP.
Respiratory Substrates and Respiratory Quotient (RQ)
It is sometimes useful to deduce which substrate is being used in a person’s metabolism
at a specific time. This can be done is the volume of oxygen taken in, and the volume of
carbon dioxide given out are measured. From this data the respiratory quotient (RQ) can
be calculated:
RESPIRATORY QUOTIENT
If one observes the equation of respiration, the number of moles of oxygen needed is
equal to the number of moles of carbon dioxide produced. This CO2:O2 ratio is called the
"respiratory quotient". For carbohydrates it is 1 as can be seen below:
Different substrates give different RQ values. The more the value of RQ more is the
efficiency. Some of the substrates and their RQs are given below
: Respiration Quotients of a Variety of Substrates
The values of RQ to be expected vary depending of which substances are broken down
by respiration.

Carbohydrates (glucose) 1.0

protein 0.9

fat (lipids) 0.7
It is interesting to know which substrate is being metabolised. Under normal conditions
the human RQ is in the range of 0.8-0.9, indicating that some fats and proteins, as well as
carbohydrates, are used for respiration. Values greater than 1.0 are obtained when
anaerobic respiration is in progress.
Measuring respiratory rate can be done by using a respirometer.
Figure 128: A respirometer.
The potassium hydroxide solution acts to remove carbon dioxide from the surrounding
air.
This means that any carbon dioxide, which is produced by respiration, is
immediately absorbed so that it does not affect the volume of air remaining. Therefore,
any changes in volume, which do take place, must be due to the uptake of oxygen. A
manmeter and the calibrated scale measure these changes. Tube B acts as a control.
ENERGY AND EXERCISE
More energy is used for muscle contraction in animals than for any other process. The
proteins in muscle use ATP to provide the energy for contraction, but the exact way in
which the ATP is made varies depending on the length of the contraction. There are five
sources of ATP:
1.
ATP stored in muscles
A muscle cell stores only enough ATP for a few seconds of contraction. This ATP was
made by respiration while the muscle was relaxed, and is available for immediate use.
2.
ATP from creatine phosphate
Creatine phosphate is a short-term energy store in muscle cells, and there is about ten
times more creatine phosphate than ATP. It is made from ATP while the muscle is
relaxed and can very quickly be used to make ATP when the muscle is contracting.
This allows about 30 seconds of muscle contraction, enough for short bursts of
intense activity such as a 100 metre sprint.
3.
ATP from anaerobic respiration of glucose
Anaerobic respiration doesn’t provide much ATP (2 ATP molecules for each glucose
molecule), but it is quick, since it doesn’t require oxygen to be provided by the blood. It
is used for muscle activities lasting a few minutes. There is not much glucose as such in
muscle cells, but there is plenty of glycogen, which can be broken down quickly to make
quite large amounts of glucose.
The end product of anaerobic respiration is lactate, which gradually diffuses out of
muscle cells into the blood and is carried to the liver. Here it is converted back to
pyruvate.
Some muscles are specially adapted for anaerobic respiration and can therefore only
sustain short bursts of activity. These are the white (or fast twitch) muscles (such as
birds’ breast muscle and frogs legs) and they are white because they contain few
mitochondria and little myoglobin. Mitochondria are not needed for anaerobic
respiration.
4.
ATP from aerobic respiration of glucose
For longer periods of exercise muscle cells need oxygen supplied by the blood for
aerobic respiration. This provides far more energy (36 molecules of ATP from each
molecule of glucose), but the rate at which it can be produced is limited by how
quickly oxygen can be provided. This is why you can’t run a marathon at the same
speed as a sprint.
Muscles that are specially adapted for aerobic respiration are called red (or slow
twitch) muscles (such as heart, leg and back muscles). They are red because they
contain many mitochondria (which are red) and a lot of the red protein myoglobin,
which is similar to haemoglobin, but is used as an oxygen store in these muscles.
Myoglobin helps to provide the oxygen needed for aerobic respiration.
5.
ATP from aerobic respiration of fats
The biggest energy store in the body is in the form of triglycerides, which store more
energy per gram than glucose or glycogen. They are first broken down to fatty acids
and glycerol, and then fully oxidised to carbon dioxide and water by aerobic
respiration. Since fats are insoluble it takes time to “mobilise” them (i.e. dissolve and
digest them), so fats are mainly used for extended periods of exercise, and for the
countless small contractions that are constantly needed to maintain muscle tone and
body posture.
MUSCLE FATIGUE
Most muscles can’t keep contracting for ever, but need to have a rest. This is called
muscle fatigue. It starts after 30s to 5 mins of continuous contraction (depending on
muscle type) and can be quite painful. It is caused by the build-up of two chemicals
inside muscle cells.

Phosphate from ATP splitting. This tends to drive the muscle ATPase reaction
backwards and so reduces muscle force.
Lactate from anaerobic respiration. This lowers the pH and so slows the enzymes
involved in muscle contraction.
SIGNIFICANCE OF RESPIRATION
 Respiration is an important process in nature. It is a process by which the solar
energy trapped by the plants in the food can be utilized. The organic compounds
are broken down to release energy. This energy is in the form of ATP molecules
and is made available for all the vital activities of the organism. ATP can also be
stored.
 Photosynthesis utilizes carbon dioxide and releases oxygen whereas respiration
makes use of this oxygen and releases carbon dioxide, which is then used by
plants. Respiration and photosynthesis are complementary to each other and
together maintain the delicate oxygen-carbon dioxide balance in nature.
 Some of the energy released by respiration is also in the form of heat. This heat
energy contributes significantly in the warm-blooded animals towards the body.
EXPERIMENTS ON RESPIRATION
1. To Demonstrate that Carbon Dioxide is Released during Respiration
Figure 129 : To Demonstrate Evolution of Carbon Dioxide During Respiration
The experiment is set up as shown. Bottle C is covered with a black cloth to prevent
photosynthesis.
On opening the stop cork near the aspirator, the lime water in D turns milky after
sometime. However, the lime water in B does not turn milky.
Why does the lime water in D turn milky?
The lime water in D turns milky because the air given out from the seeds contains carbon
dioxide.
Why does the lime water in B remain clear?
This is because the soda lime in A absorbs the carbon dioxide and it is this air that is
entering the flask B.
REVISION QUESTIONS
Identify the letter of the choice that best completes the statement or answers the
question.
1. When living cells break down molecules, energy is
a. stored as ADP.
c. released as heat.
b. stored as ATP.
d. Both b and c
2. Which of the following is the best explanation for the presence of both
chloroplasts and mitochondria in plant cells?
a. In the light, plants are photosynthetic autotrophs. In the dark, they are
heterotrophs.
b. If plants cannot produce enough ATP in the process of photosynthesis to meet
their energy needs, they can produce it in aerobic respiration.
c. Sugars are produced in chloroplasts. These sugars can be stored in the plant for
later use, converted to other chemicals, or broken
down in aerobic respiration to yield ATP for the plant to use to meet its
energy needs.
d. The leaves and sometimes the stems of plants contain chloroplasts, which
produce ATP to meet the energy needs of these plant parts.
The roots of plants contain mitochondria, which produce ATP to meet the
energy needs of these plant parts.
3. In cellular respiration, the most energy is transferred during
a. glycolysis.
b. lactic acid fermentation.
c. the Krebs cycle.
d. the electron transport chain
4. Electrons are donated to the electron transport chain by
a. ATP and NADH.
c. ATP and NAD+.
b. FADH2 and NADH.
d. NAD+ and ATP.
5. If the formation of 38 molecules of ATP requires 266 kcal of energy and the
complete oxidation of glucose yields 686 kcal
of energy, how efficient is cellular respiration at extracting energy from glucose?
a. 20%
b. 25%
c. 39%
d. 100%
6. The breakdown of organic compounds to produce ATP is known as
a. cellular respiration
b. alcoholic fermentation
fermentation
d. photosynthesis
c. lactic-acid
7. Glycolysis begins with glucose and produces
a. PGAL
b. lactic acid
c. acetyl CoA
d. pyruvic acid
8. An important molecule generated by both lactic acid fermentation and alcoholic
fermentation is
a. ATP
b. NADH
c. CO2
d. NAD+
9. In the first step of aerobic respiration, pyruvic acid from glycolysis produces
CO2, NADH, H+, and
a. citric acid
b. acetyl CoA
c. oxzloacetic acid
d.
lactic acid
10. The electron transport chain is driven by two products of the Krebs cyclea. oxaloacetic acid and citric acid
b. H2O and CO2
c. NADH and FADH2
d. acetyl CoA and ATP
9.0
NUTRITION
INTRODUCTION
Nutrition can be defined as the process by which an organism obtains food which is used
to provide energy and materials for its life sustaining activities. Thus the term nutrition
includes the means by which an organism obtains its food and also the processes by
which the nutrients in the food are broken down to simpler molecules for utilization by
the body.
NUTRIENTS
Food contains various organic and inorganic substances. Those which are required by the
organisms to carry out life functions are called nutrients. Nutrients are of various types carbohydrates, fats, proteins, vitamins and minerals.
The various nutrients carry out different functions such as:
 energy production
 synthesis of materials for growth and repair of the tissues
 synthesis of materials necessary for carrying out and maintaining life functions
 synthesis of materials for immune system
Modes of Nutrition
The mechanism by which organisms obtain food are referred to as modes of nutrition.
The organisms either synthesize their own food or obtain food prepared by other
organisms in various ways. There are basically two modes of nutrition - autotrophic and
heterotrophic.
 Autotrophic Nutrition
'Auto' means self and 'trophic' refers to food. So, the organisms which synthesise their
own food are called the autotrophs and the process is called autotrophic nutrition.
Autotrophs include all green plants and some bacteria such as the nitrifying bacteria. The
source of energy for the autotrophs may be either light energy or chemical energy.
Accordingly they are classified as
1. Photoautotrophic
2. Chemoautotrophic
Photoautotrophic
Photoautotrophic organisms synthesize food with the help of light energy of the sun,
carbon dioxide and water. The process of synthesis of food in this method is called
photosynthesis.
For example:
 cyanobacteria (blue-green bacteria, prokaryotes)
 algae and all green plants.
All these use water as the source of hydrogen.
However, there are some other photoautotrophic bacteria, such as the green sulphur
bacteria which derives the hydrogen from hydrogen sulphide as follows:
Chemoautotrophic/Chemotrophic/Chemosynthetic
Chemoautotrophic organisms synthesise food with the help of chemical energy. They do
not require sunlight. Thus they include organisms which are found deep in the soil where
sunlight does not penetrate such as nitrifying bacteria. These organisms use carbon
dioxide and water as sources of carbon and hydrogen but obtain energy from chemical
compounds.
For example:
Compounds such as ammonia and nitrite are oxidized in order to release energy.
Examples of chemosynthetic bacteria are nitrifying bacteria such as Nitrobacter and
Nitrosomonas, hydrogen bacteria and iron bacteria.
 Heterotrophic Nutrition
'Hetero' refers to other or different and 'trophic' refers to food. Thus, those organisms
which obtain their food from other organisms are called heterotrophic and the process of
obtaining the food from other organisms is called heterotrophic nutrition.
Types of Heterotrophic Nutrition
1. Saprophytic
'Sapros' refers to rotten and 'trophic' refers to food. Saprotrophic nutrition is the process
by which the organisms feed on dead and decaying matter. The food is digested outside
the cells or even the body of the organism - extracellular digestion. The organism secretes
digestive juices that contain enzymes directly on to the food. The digestion makes the
food soluble and it is then absorbed by the organism.
Examples of saprophytes:
(plants which have saprotrophic nutrition) are Rhizopus (bread mould), Mucor (pin
mould), Yeast, Agaricus (mushroom), many bacteria etc.
2. Parasitic
Parasitism is defined as an association between individuals of two different species which
is beneficial to one and generally harmful to another. The benefiting partner is called the
parasite and the other partner is called the host. The parasite is dependent on the host for
food or shelter or both. Parasites may be ectoparasites, that which live on the outer
surface of the host (ticks, mites, leeches) or may be endoparasites, that which live inside
the body of the host (tapeworm, liver fluke). Parasites are also classified as obligate or
facultative. Obligate parasites have to live parasitically at all times. Facultative parasites
may feed parasitically or saprophytically. There are certain plants which grow in
nitrogen-deficient conditions and they meet this requirement by feeding on insects. They
are called the insectivorous plants. The above-mentioned types of nutrition divided the
different organisms under three categories. They are:
i.
PRODUCERS
They are the autotrophs. Their activity sustains all the organisms as they alone can trap
the solar energy into food. This in turn is used by the next category.
ii.
CONSUMERS
Those that feed directly on the plants are called herbivores and those that feed on the
latter are called carnivores.
iii.
DECOMPOSERS
They are the saprophytic and saprozoic organisms that decompose the dead plant and
animals before feeding on them.
NUTRITION IN PLANTS
Most plants are autotrophic. They synthesize their own food. The green plants, also called
the producers, trap the solar energy and convert it into chemical energy of the food. The
biochemical reactions in the body which result in the formation of chemical compounds
are collectively called anabolic reactions.
FACTORS THAT INFLUENCE PLANT NUTRITION
A. AVAILABILITY OF NUTRIENTS FOR PLANTS
The availability depends on soil characteristics and symbiotic fungi and bacteria. Mineral
content depends on the parent rock from which the soil was formed. In most soils,
mineral content is also dependent on biological factors.
B. THE ROLE OF SYMBIOSIS
1. Mycorrhizae
Fungi extract nutrients (phosphates and water) from the soil and make them available to
plants. This enables plants to prosper in nutrient poor soil. Some studies suggest that the
fungi also screen out chemicals from toxic soils.
2. Rhizobium and Nitrogen fixing
79% of the earth’s atmosphere is made up of nitrogen, but plants can’t use nitrogen in
this form. The triple covalent bond between the two nitrogens is a very strong bond.
Plants are dependent upon two nitrogen-containing ions: ammonium (NH4+) and nitrate
(NO3-).
PHOTOSYNTHESIS
Photosynthesis can be defined as a process which utilises carbon dioxide and water in the
presence of sunlight and chlorophyll to synthesize carbohydrates like glucose. 'Photo'
refers to light and 'synthesis' means preparation. Thus, photosynthesis is the process by
which the green plants use light energy of the sun to synthesize carbohydrates.
Carbohydrates like the simple sugars (glucose) can be stored as starch. Photosynthesis is
a series of biochemical reactions which can be essentially summarized as follows:
carbon dioxide + water (+ light energy)  glucose + oxygen
PHOTOSYNTHESIS – REACTANTS
 Carbon Dioxide
During photosynthesis, carbon dioxide is converted into carbohydrates and this is called
fixing of carbon dioxide. Many processes like respiration, combustion, volcanic activity,
etc. release carbon dioxide into the atmosphere. This carbon dioxide of the atmosphere is
used by the terrestrial plants while hydrophytes use the carbon dioxide dissolved in the
water.
 Water
During photosynthesis, hydrogen of water is used to fix carbon dioxide and its oxygen is
released. Water is obtained through the root hairs by absorption.
 Chlorophyll
They are pigments capable of absorbing radiant energy of the sun. Pigments are
chemically porphyrin molecules which have a metal ion at the centre. The metal ion in
haemoglobin is iron and in chlorophyll, it is magnesium. There are two types of
photosynthetic pigments - chlorophylls and carotenoids. Chlorophylls are the main
pigments as they are involved in the conversion of light energy into chemical energy. The
carotenoids also absorb light energy but they pass it to the chlorophyll molecules.
Chlorophylls are blue-green (chlorophyll-a) or green (chlorophyll-b) in colour whereas
carotenoids are orange (carotenes) or yellow (xanthophyll).
Figure 131: Photosynthetic pigments
 Radiant Energy
The radiant energy from the sun is the source of both light and heat energy to
photosynthesis. Light energy is harvested by the pigments in order to carry out the
breaking down of water molecule into hydrogen and oxygen. This is an energy-intensive
process. Sunlight can be split into seven different colours which is called the spectrum
.Each colour is associated with different quantity of energy. Different pigments absorb
different colour lights. Chlorophyll pigments absorb red and violet portions of the light
and reflect green portion. Hence, they appear green. Leaves look green because they
absorb most of the violet and red region of the incident light. These pigments cannot
absorb the green region of the spectrum. Therefore they reflect the green light and appear
green in colour. The biochemical reactions which convert carbon dioxide into
carbohydrates are controlled by enzymes. These enzymes require an optimum
temperature to be active. The temperature is maintained by the heat energy of the sun.
 Minerals
Minerals like magnesium are essential as they form the structure of the pigment
molecules. In fact, deficiency of magnesium results in the yellowing of leaves. Minerals
are obtained through water in the form of dissolved salts.
IMPORTANCE OF PHOTOSYNTHESIS
1. It makes both carbon and energy available to living organisms.
2. It produces the oxygen in atmosphere.
3. It provides energy to the depleting reserves of oil and gas.
Leaves and Leaf Structure
Plants are the only photosynthetic organisms to have leaves (and not all plants have
leaves). A leaf may be viewed as a solar collector crammed full of photosynthetic cells.
The raw materials of photosynthesis, water and carbon dioxide, enter the cells of the leaf,
and the products of photosynthesis, sugar and oxygen, leave the leaf.
13.2 Chloroplasts
Photosynthesis takes place entirely within chloroplasts. Like mitochondria, chloroplasts
have a double membrane, but in addition chloroplasts have a third membrane called the
thylakoid membrane. This is folded into thin vesicles (the thylakoids), enclosing small
spaces called the thylakoid lumen. The thylakoid vesicles are often layered in stacks
called grana. The thylakoid membrane contains the same ATP synthase particles found in
mitochondria. Chloroplasts also contain DNA, tRNA and ribososomes, and they often
store
the
products
of
photosynthesis
as
starch
grains
and
lipid
droplets.
Figure 134: The structure of a chroloplast.
STAGES OF PHOTOSYNTHESIS
To understand photosynthesis in detail we can break it up into 2 stages:

The light-dependent reactions use light energy to split water and make some ATP
and energetic hydrogen atoms. This stage takes place within the thylakoid
membranes of chloroplasts, and is very much like the respiratory chain, only in
reverse.

The light-independent reactions don’t need light, but do need the products of the
light-dependent stage (ATP and H), so they stop in the absence of light. This stage
takes place in the stroma of the chloroplasts and involve the fixation of carbon
dioxide and the synthesis of glucose.
THE LIGHT-DEPENDENT REACTIONS
The light-dependent reactions take place on the thylakoid membranes using four
membrane-bound protein complexes called photosystem I (PSI), photosystem II (PSII),
cytochrome complex (C) and ferredoxin complex (FD). In these reactions light energy is
used to split water, oxygen is given off, and ATP and hydrogen are produced.
Figure 136: The light dependent reactions.
1. Chlorophyll molecules in PSII absorb photons of light, exciting chlorophyll electrons
to a higher energy level and causing a charge separation within PSII. This charge
separation drives the splitting (or photolysis) of water molecules to make oxygen (O2),
protons (H+) and electrons (e-):
2H2O
O2 + 4H+ + 4e-
Water is a very stable molecule and it requires the energy from 4 photons of light to
split 1 water molecule. The oxygen produced diffuses out of the chloroplast and
eventually into the air; the protons build up in the thylakoid lumen causing a proton
gradient; and the electrons from water replace the excited electrons that have been
ejected from chlorophyll.
2. The excited, high-energy electrons are passed along a chain of protein complexes in
the membrane, similar to the respiratory chain. They are passed from PSII to C, where
the energy is used to pump 4 protons from stroma to lumen; then to PSI, where more
light energy is absorbed by the chlorophyll molecules and the electrons are given more
energy; and finally to FD.
3. In the ferredoxin complex each electron is recombined with a proton to form a
hydrogen atom, which is taken up by the hydrogen carrier NADP. Note that while
respiration uses NAD to carry hydrogen, photosynthesis always uses its close relative,
NADP.
4. The combination of the water splitting and the proton pumping by the cytochrome
complex cause protons to build up inside the thylakoid lumen. This generates a proton
gradient across the thylakoid membrane. This gradient is used to make ATP using the
ATP synthase enzyme in exactly the same way as respiration. This synthesis of ATP is
called photophosphorylation because it uses light energy to phosphorylate ADP.
13.5 The Light-Independent Reactions
The light-independent, or carbon-fixing reactions, of photosynthesis take place in the
stroma of the chloroplasts and comprise another cyclic pathway, called the Calvin Cycle,
after the American scientist who discovered it.
Figure 137: The light independent reaction.
1. Carbon dioxide binds to the 5-carbon sugar ribulose bisphosphate (RuBP) to form 2
molecules of the 3-carbon compound glycerate phosphate. This carbon-fixing
reaction is catalysed by the enzyme ribulose bisphosphate carboxylase, always known
as rubisco. It is a very slow and inefficient enzyme, so large amounts of it are needed
(recall that increasing enzyme concentration increases reaction rate), and it comprises
about 50% of the mass of chloroplasts, making the most abundant protein in nature.
Rubisco is synthesised in chloroplasts, using chloroplast (not nuclear) DNA.
2. Glycerate phosphate is an acid, not a carbohydrate, so it is reduced and activated to
form triose phosphate, the same 3-carbon sugar as that found in glycolysis. The ATP
and NADPH from the light-dependent reactions provide the energy for this step. The
ADP and NADP return to the thylakoid membrane for recycling.
3. Triose phosphate is a branching point. Most of the triose phosphate continues through
a complex series of reactions to regenerate the RuBP and complete the cycle. 5 triose
phosphate molecules (15 carbons) combine to form 3 RuBP molecules (15 carbons).
4. Every 3 turns of the Calvin Cycle 3 CO2 molecules are fixed to make 1 new triose
phosphate molecule. This leaves the cycle, and two of these triose phosphate
molecules combine to form one glucose molecule using the glycolysis enzymes in
reverse. The glucose can then be used to make other material that the plant needs.
DARK REACTION
Carbon-Fixing Reactions are also known as the Dark Reactions (or Light Independent
Reactions). Carbon dioxide enters single-celled and aquatic autotrophs through no
specialized structures, diffusing into the cells. Land plants must guard against drying out
(desiccation) and so have evolved specialized structures known as stomata to allow gas to
enter and leave the leaf. The Calvin Cycle occurs in the stroma of chloroplasts (where
would it occur in a prokaryote?). Carbon dioxide is captured by the chemical ribulose
biphosphate (RuBP). RuBP is a 5-C chemical. Six molecules of carbon dioxide enter the
Calvin Cycle, eventually producing one molecule of glucose.
The first stable product of the Calvin Cycle is phosphoglycerate (PGA), a 3-C chemical.
The energy from ATP and NADPH energy carriers generated by the photosystems is
used to attach phosphates to (phosphorylate) the PGA. Eventually there are 12 molecules
of glyceraldehyde phosphate (also known as phosphoglyceraldehyde or PGAL, a 3-C),
two of which are removed from the cycle to make a glucose. The remaining PGAL
molecules are converted by ATP energy to reform 6 RuBP molecules, and thus start the
cycle again. Remember the complexity of life, each reaction in this process, as in Kreb's
Cycle, is catalyzed by a different reaction-specific enzyme.
C-4 Pathway
Some plants have developed a preliminary step to the Calvin Cycle (which is also
referred to as a C-3 pathway), this preamble step is known as C-4. While most C-fixation
begins with RuBP, C-4 begins with a new molecule, phosphoenolpyruvate (PEP), a 3-C
chemical that is converted into oxaloacetic acid (OAA, a 4-C chemical) when carbon
dioxide is combined with PEP. The OAA is converted to Malic Acid and then transported
from the mesophyll cell into the bundle-sheath cell, where OAA is broken down into PEP
plus carbon dioxide. The carbon dioxide then enters the Calvin Cycle, with PEP returning
to the mesophyll cell. The resulting sugars are now adjacent to the leaf veins and can
readily be transported throughout the plant. The capture of carbon dioxide by PEP is
mediated by the enzyme PEP carboxylase, which has a stronger affinity for carbon
dioxide than does RuBP carboxylase When carbon dioxide levels decline below the
threshold for RuBP carboxylase, RuBP is catalyzed with oxygen instead of carbon
dioxide. The product of that reaction forms glycolic acid, a chemical that can be broken
down by photorespiration, producing neither NADH nor ATP, in effect dismantling the
Calvin Cycle. C-4 plants, which often grow close together, have had to adjust to
decreased levels of carbon dioxide by artificially raising the carbon dioxide concentration
in certain cells to prevent photorespiration. C-4 plants evolved in the tropics and are
adapted to higher temperatures than are the C-3 plants found at higher latitudes. Common
C-4 plants include crabgrass, corn, and sugar cane. Note that OAA and Malic Acid also
have functions in other processes, thus the chemicals would have been present in all
plants, leading scientists to hypothesize that C-4 mechanisms evolved several times
independently in response to a similar environmental condition, a type of evolution
known as convergent evolution.
PHOTORESPIRATION.
Photorespiration occurs when the CO2 levels inside a leaf become low. This happens on
hot dry days when a plant is forced to close its stomata to prevent excess water loss. If the
plant continues to attempt to fix CO2 when its stomata are closed, the CO2 will get used
up and the O2 ratio in the leaf will increase relative to CO2 concentrations. When the
CO2 levels inside the leaf drop to around 50 ppm, Rubisco starts to combine O2 with
RuBP instead of CO2. The net result of this is that instead of producing 2 3C PGA
molecules, only one molecule of PGA is produced and a toxic 2C molecule called
phosphoglycolateis produced.
C3 PHOTOSYNTHESIS : C3 plants.

Called C3 because the CO2 is first incorporated into a 3-carbon compound.

Stomata are open during the day.

RUBISCO, the enzyme involved in photosynthesis, is also the enzyme involved in the
uptake of CO2.

Photosynthesis takes place throughout the leaf.

Adaptive Value: more efficient than C4 and CAM plants under cool and moist
conditions and under normal light because requires less machinery (fewer enzymes
and no specialized anatomy)..

Most plants are C3.
C4 PHOTOSYNTHESIS : C4 PLANTS.

Called C4 because the CO2 is first incorporated into a 4-carbon compound.

Stomata are open during the day.

Uses PEP Carboxylase for the enzyme involved in the uptake of CO2. This enzyme
allows CO2 to be taken into the plant very quickly, and then it "delivers" the CO2
directly to RUBISCO for photsynthesis.

Photosynthesis takes place in inner cells (requires special anatomy called Kranz
Anatomy)

Adaptive Value:
o
Photosynthesizes faster than C3 plants under high light intensity and high
temperatures because the CO2 is delivered directly to RUBISCO, not allowing it to
grab oxygen and undergo photorespiration.
o
Has better Water Use Efficiency because PEP Carboxylase brings in CO2 faster and
so does not need to keep stomata open as much (less water lost by transpiration) for
the same amount of CO2 gain for photosynthesis.

C4 plants include several thousand species in at least 19 plant families. Example:
fourwing saltbush pictured here, corn, and many of our summer annual plants.
CAM Photosynthesis : CAM plants. CAM stands for Crassulacean Acid Metabolism

Called CAM after the plant family in which it was first found (Crassulaceae) and
because the CO2 is stored in the form of an acid before use in photosynthesis.

Stomata open at night (when evaporation rates are usually lower) and are usually
closed during the day. The CO2 is converted to an acid and stored during the
night. During the day, the acid is broken down and the CO2 is released to
RUBISCO for photosynthesis

o
Adaptive Value:
Better Water Use Efficiency than C3 plants under arid conditions due to opening
stomata at night when transpiration rates are lower (no sunlight, lower temperatures,
lower wind speeds, etc.).
o
May CAM-idle. When conditions are extremely arid, CAM plants can just leave their
stomata closed night and day. Oxygen given off in photosynthesis is used for
respiration and CO2 given off in respiration is used for photosynthesis. This is a little
like a perpetual energy machine, but there are costs associated with running the
machinery for respiration and photosynthesis so the plant cannot CAM-idle forever.
But CAM-idling does allow the plant to survive dry spells, and it allows the plant to
recover very quickly when water is available again (unlike plants that drop their
leaves and twigs and go dormant during dry spells).

CAM plants include many succulents such as cactuses and agaves and also some
orchids and bromeliads
FACTORS AFFECTING PHOTOSYNTHESIS
LIGHT INTENSITY
Low light intensity lowers the rate of photosynthesis. As the intensity is increased the rate
also increases. However, after reaching an intensity of 10,000 lux (lux is the unit for
measuring light intensity) there is no effect on the rate. Very high intensity may, in fact,
slow down the rate as it bleaches the chlorophyll. Normal sunlight (usually with an
intensity of about 100,000 lux) is quite sufficient for a normal rate of photosynthesis.
Figure 145: Open and Closed Stomata
CARBON DIOXIDE CONCENTRATION
In the atmosphere, the concentration of carbon dioxide ranges from .03 to .04 %.
However, it is found that 0.1% of carbon dioxide in the atmosphere increases the rate of
photosynthesis significantly. This is achieved in the greenhouses which are enclosed
chambers where plants are grown under controlled conditions. The concentration is
increased by installing gas burners which liberate carbon dioxide as the gas burns. Crops
like tomatoes, lettuce are successfully grown in the greenhouses. These greenhouse crops
are found to be bigger and better-yielding than their counterparts growing in natural
conditions.
The following graph shows how different concentrations affect the rate of photosynthesis.
Figure 146 : The following graph shows how different concentrations affect the rate
of photosynthesis
TEMPERATURE
An optimum temperature ranging from 25oC to 35oC is required for a good rate. At
temperatures around 0oC the enzymes stop working and at very high temperatures the
enzymes are denatured. Since both the stages of photosynthesis require enzyme activity,
the temperature has an affect on the rate of photosynthesis.
Figure 147: Graph Showing Effect of Temperature on Rate of Photosynthesis
CHLOROPHYLL CONCENTRATION
The concentration of chlorophyll affects the rate of reaction as they absorb the light
energy without which the reactions cannot proceed. Lack of chlorophyll or deficiency of
chlorophyll results in chlorosis or yellowing of leaves. It can occur due to disease,
mineral deficiency or the natural process of aging (senescence). Lack of iron,
magnesium, nitrogen and light affect the formation of chlorophyll and thereby causes
chlorosis.
WATER
Water is an essential factor in photosynthesis. The effect of water can be understood by
studying the yield of crops which is the direct result of photosynthetic activity. It is found
that even slight deficiency of water results in significant reduction in the crop yield. The
lack of water not only limits the amount of water but also the quantity of carbon dioxide.
This is because in response to drying the leaves close their stomata in order to conserve
water being lost as water vapour through them.
POLLUTION
Pollution of the atmosphere with industrial gases has been found to result in as much as
15% loss. Soot can block stomata and reduce the transparency of the leaves. Some of the
other pollutants are ozone and sulphur dioxide. In fact, lichens are very sensitive to
sulphur dioxide in the atmosphere. Pollution of water affects the hydrophytes. The
capacity of water to dissolve gases like carbon dioxide and oxygen is greatly affected.
APPLICATION
Study of photosynthesis and the factors affecting it helps us understand the most
important biochemical life sustaining processes. All plants and animals are dependent on
the sun for energy. This energy is made available to them by the process of
photosynthesis. Man, like other animals, is dependent on the plants for his food.
Scientists are constantly working towards developing new varieties of crops which give
better yield of crops. With the population explosion and resulting pressure on land
resources, the percentage of land available for cultivation is reducing at an alarming rate.
This means that in the restricted space, the crops have to yield more. All this has been
possible so far with the understanding of the photosynthesis. Greenhouse plants and crops
in unfriendly freezing conditions have been possible due to the study of the factors
affecting photosynthesis.
Studies have shown that there are a group of plants called the C4 plants which are more
efficient in harnessing carbon dioxide from the atmosphere. Since the atmospheric level
of the gas is only 0.3 to 0.4% and maximum crop yield is reported at 1% level, these
plants are ideal for cultivation as they can draw maximum carbon dioxide from the
atmosphere, greatly increasing the yield. One of the areas of current focus is the better
understanding of the mechanism of C4 plants.
COMPENSATION POINT
The rate of photosynthesis is not constant throughout the day. It's rate is affected by the
intensity of light. The actual requirement of the light intensity for maximum
photosynthesis in a plant depends on the type of plant and also on its habitat. Generally,
average sunlight intensity is sufficient for photosynthesis except on rainy or cloudy days.
The rate of photosynthesis increases with increasing intensity of light and decreases with
decreasing intensity of light. During early morning or late evenings when the rate of
photosynthesis becomes equal to the rate of respiration, there will not be any net
exchange of gases (CO2 and O2) between the plant and the surrounding environment. The
light intensity, at which the photosynthetic intake of carbon dioxide is equal to the
respiratory output of carbon dioxide is called the compensation point.
EXPERIMENTS RELATED TO PHOTOSYNTHESIS
To test for the presence of starch in leaves
The occurrence of starch in the leaves proves that photosynthesis has taken place. Starch
can be tested with the help of iodine solution. This is done in the following manner:
 The leaf is first decolourised by treating it in 90% ethanol (alcohol) solution. It is
then rinsed in hot water to remove all alcohol and to soften the tissue.
 The leaf is now colourless. Then iodine solution (brown in colour) is poured over
the leaf.
 The leaf turns blue-black indicating that it contains starch.
To prove that light is required for photosynthesis
Take a potted plant and destarch it by keeping it in darkness for 24 hours. To one of
the leaves attach a piece of metal foil or paper on both sides. Leave the plant in
sunlight for 48 hours. Then take the leaf and remove its metal foil. Decolourise the
leaf as in the above experiment and test for starch.
a. Will the entire leaf be blue-black?
No, the portion covered by the strip of metal foil will not be blue-black.
b. Why?
This is because there is no starch in that area. The area was deprived of
light which is needed for photosynthesis. Hence, no photosynthesis took
place in that area.
c. How does the plant get destarched on keeping it in darkness for 24
hours?
The plant cannot carry out photosynthesis in the absence of light and all
the starch present in the leaves is used up. Thus the leaves are destarched
To prove that carbon dioxide is necessary for photosynthesis
Figure 148 : Investigating the Need for Carbon Dioxide in Photosynthesis
Take a potted plant. Destarch it. Insert one of its leaves in a bottle containing potassium
hydroxide (KOH) solution as shown in the figure. KOH absorbs all carbon dioxide in the
bottle. Leave the set up in sunlight for 48 hours. Test the leaf for starch.
a. Which portion of the leaf will test postitive for starch?
The portion of the leaf that was outside the bottle will test positive and
turn blue-black.
b. Why?
The portion inside the bottle does not get carbon dioxide and thus, no photosynthesis
takes place in that region.
To prove that chlorophyll is required for photosynthesis
Take a variegated leaf (a leaf that is variously coloured such as Coleus or Croton).
Decolourise it. Then test it for starch. The leaf will only give blue-black colour in
patches.
Why does the leaf give blue-black colour only in patches?
The variegated leaf contains chlorophyll only in patches and hence the photosynthetic
activity is restricted to those patches. Thus, only those areas give blue-black colour.
To prove that oxygen is evolved during photosynthesis
Figure 149 : Experiment to show release of oxygen during photosynthesis
Take a few healthy twigs of Hydrilla, a water plant. Place it in a funnel and invert the
funnel in a beaker of water. Invert a test-tube over the stem of the funnel. Leave the setup in sunlight. After sometime, bubbles can be seen rising in the test-tube. Remove the
test-tube carefully and insert a glowing splinter deep into it. The splinter burns brightly.
a. Which gas is collected by the downward displacement of water in the
test-tube?
Oxygen. This is because the glowing splinter burns brightly.
b. Why does oxygen evolve?
In sunlight the hydrilla twig carries out photosynthesis. During this process,
carbon dioxide is taken in and oxygen is released. Hence, oxygen is liberated.
ESSAY QUESTIONS
1. Describe the internal structure and external structure of a chloroplast.
2. Does increasing the temperature always increase the rate of photosynthesis? Explain
your answer.
3. Explain the difference between the roles of photosystem I and photosystem II in
photosynthesis?
4. Explain why the leaves of some plants look green during the summer then turn yellow,
orange, red,
or brown during the fall?
5. What plant structures control the passage of water out of a plant and carbon dioxide
into a plant? Explain
how they control the passage of water out of a plant and carbon dioxide into a plant.
6. What happens to the electrons that are lost by photosystem II? What happens to the
electrons
that are lost by photosystem I?
7. Photosynthesis is said to be "Saturated" at a certain level of CO2. Explain what this
means?
8. Where does the energy in the Calvin cycle come from?
9. What is the fate of most of the G3P molecules in the fourth step of the Calvin cycle
and Why is this important?
What happens to the remaining G3P molecules? What organic compound can be made
from G3P?
10. Explain how CAM plants differ from C3 and C4 plants? How does this difference
allow CAM
plants to exist in hot, dry conditions?
11. Define biochemical pathway and explain how the Calvin cycle is an example of a
biochemical pathway.
In what part of the chloroplasts does the Calvin cycle take place?
12. Explain how the function of the chloroplasts is related to its structure.
13. Explain what happens to the components of water molecules that are split during the
light reactions of photosynthesis? (HINT: Name the three products that are produced
when water molecules are split during the light reactions and explain what each product
is used for.)
14. Describe the structure and function of the thylakoids of a chloroplasts.
15. Explain how is ATP synthesized in photosynthesis? What is this process called?
REVISION QUESTIONS 2
Identify the letter of the choice that best completes the statement or answers the
question.
1. What is the term for the ability to perform work?
a. heterotrophy
b. expenditure
c. energy
d. autotrophy
2. Animals that Cannot make their own food are
a. heterotrophs
b. autotrophs
c. photosynthesizers
3. Which are Not autotrophs?
a. animals
b. plants
d. grana
c. algae
d. some prokaryotes
4. During photosynthesis, a reduction reaction
a. adds electrons to a molecule
b. subtracts electrons from a molecule
c. oxidizes a molecule
d. destroys a molecule
5. The protein that adds a phosphate group to ADP is
a.G3P
b. RuBP
c. ATP synthase
d. carotenoids
_6. The components of visible light are called the
a. photosystem
b. biochemical pathway
c. carotenoids
spectrum
7. Chlorophyll a
a. absorbs mostly orange-red and blue-violet light
pigment
b. is responsible for the red color of many autumn leaves
light
d. visible
c. is an accessory
d. absorbs mostly green
8. The energy that is used to establish the proton gradient across the thylakoid membrane
comes from the
a. synthesis of ATP
b. synthesis of NADPH
c. passage of electrons along the electron transport chain in photosystem II
d. splitting of water
9. For every three molecules of CO2 that enters the Calvin cycle, the cycle produces one
molecule of
a. RuBP
b. 3-PGA
c. G3P
d. NADPH
10. As light intensity increases, the rate of photosynthesis
a. continues to decrease
c. initially decreases and then levels off
b. continues to increase
d. initially increases and then levels off
11. The name of the three-carbon molecule in the Calvin Cycle
a. RuBP
b. 3-PGA
c. G3P
d. NADPH
12. Type of pigments that absorb blue and green light are
a. chlorophylls
b. carotenoids
c.G3P
d. visible spectrum
13. What product of the light reactions of photosynthesis is released and does not
participate further in photosynthesis?
a. ATP
b. NADPH
c. H2O, water
d. O2, oxygen
14. Where does the energy for the Calvin cycle originate?
a. ATP and NADPH produced by light reactions
b. O2 produced by the light reactions
c. the sun's heat
d. photons of light
15. The Calvin cycle begins when CO2 combines with a five-carbon carbohydrate called
a. RuBP
b. 3-PGA
c. G3P
d. NADPH
16. Water participates directly in the light reactions of photosynthesis by
a. donating electrons to NADPH
c. donating electrons to
photosystem II
b. accepting electrons from the electron transport chain
d. accepting electrons from
ADP
17. Disk-shaped structures with photosynthetic pigments are known as
a. Krebs cycle
b. thylakoids
c. carbohydrates
d. synthesizers
18. The process by which autotrophs convert sunlight into energy is called
a. photosynthesis
b. oxidation
c. pigmentation
d. photosystemizing
19. A molecule that can absorb certain light wavelengths and reflect others is a
a. photosystem
b. matrix
c. refractory structure
d. pigment
20. What are the most common group of photosysnthetic pigments in plants?
a. chloroplasts
b. stroma
c. chlorophylls
d. thylakoids
NUTRITION IN ANIMALS
All animals are heterotrophic (there are exceptions like Euglena, which has
chlorophyll). The different modes of heterotrophic nutrition have already been dealt
with in the earlier part of the chapter. Of all the methods of heterotrophism, holozoic
is the most commonly found.
Holozoic nutrition involves the following steps:

ingestion- taking large pieces of food into the body

digestion- breaking down the food by mechanical and chemical means

absorption- taking up the soluble digestion products into the body's cells

assimilation- using the absorbed materials

egestion- eliminating the undigested material
(Do not confuse egestion, which is the elimination of material from a body cavity, with
excretion, which is the elimination of waste material produced from within the body's
cells.)
Nutrition in Amoeba
Nutrition in amoeba is holozoic. Thus, solid food particles are ingested which are
then acted upon by enzymes and digested. It is an omnivore, feeding on both plants
and animals. Its diet includes bacteria, microscopic plants like the diatoms, minute
algae, microscopic animals like other protozoa, nematodes and even dead organic
matter.
Since it is a unicellular organism, amoeba does not have any specialised structure or
organ for the process of nutrition. It takes place through the general body surface with
the help of pseudopodia.
Mechanism of Nutrition
Ingestion
The food is ingested at the point where it comes in touch with the cell surface with
the help of pseudopodia. Pseudopodia engulf the food into the cytoplasm. The process
of ingestion takes about two minutes.
Some methods of ingestion reported in amoeba are
Circumvallation - When the prey is active, a food cup is formed with the help of
pseudopodia.
Circumfluence - When the prey is inactive and the amoeba rolls over it.
Import - The food passively sinks into the body on contact.
Invagination - Pseudopodia secretes a sticky and toxic fluid which adheres and kills
the prey. It is then taken in by invagination.
Pinocytosis - Also called cell drinking. There are pinocytosis channels at certain
points through which the cell ingests the food.
Digestion in Amoeba
Digestion in amoeba is intracellular taking place within the cell. The food taken in
remains in a food vacuole or gastric vacuole formed by the cell membrane and small
part of the cytoplasm. The vacuoles are transported deeper into the cells by
cytoplasmic movements. Here they fuse with lysosomes that contain enzymes. Two
enzymes amylase and proteinase have been reported. Thus, amoeba can digest sugars,
cellulose and proteins. Fats, however, remain undigested.
The contents of the vacuole become lighter and the outline of the vacuole becomes
indefinite indicating that the digestion is complete.
Absorption
Since the food on digestion is converted into liquid diffusible form, it is readily
absorbed by the cytoplasm. The vacuole becomes progressively smaller as the food is
absorbed by diffusion.
Assimilation
All the parts of the cell get the nutrients by the cyclic movement of the cytoplasm
called the cyclosis. These nutrients are used to build new protoplasm. In this manner
the food is assimilated.
Egestion
The egestion takes place by exocytosis. There is no particular point from which the
egestion takes place. As the amoeba moves forward, the undigested matter is shifted
to the back and eliminated as food pellets through a temporary opening formed at any
nearest point on the plasmalemma.
Nutrition in Grasshopper
Nutrition in grasshopper (Poecilocerus pictus) is holozoic and as the name indicates is a
herbivore, feeding on different kinds of vegetation like the grasses, germinating grains,
leafy vegetation, etc.
Figure : Grasshopper - External Features
It bites off pieces of vegetation and has to grind it before digesting them. Thus its mouth
parts are modified accordingly for selecting the appropriate food, biting and chewing the
food.
Mouthparts of Grasshopper
The body of the grasshopper is segmented into three portions head, thorax and the
abdomen. The mouth parts are attached to the ventral side (underside) of the head portion
and surrounds the mouth or the oral cavity which faces down.
Figure : Grasshopper – Mouthparts
The different mouthparts are:
Labrum or the upper lip
It is a broad, roughly rectangular shaped structure.
Lingua or the hypopharynx
A membranous tongue-like structure found attached beneath the labrum.
Mandibles
A pair of hard, horny, heavy, large, with jagged inner edges and dark coloured triangular
structures found one on either side. The two mandibles move in horizontal motion and
crush food between them.
Maxillae
A pair of structures lying outside and behind the mandibles. Each of them consist of 5segmented sensory maxillary palp in addition to other parts. The maxillae are used to
manipulate the food before it enters the mouth.
Labium
Forms the broad median lower lip consisting of several parts in addition to a pair of 3segmented labial palps on either side.
The maxillary and labial palps have sense organs which help them to chose a suitable
vegetation.
The mandibles and the maxillae grind the food by moving it laterally.
The labrum and labium help to hold the food between the mandibles and the maxillae.
Digestive System of Grasshopper
Digestion takes place in specialised cavities joined together to form a continuous canal. It
is called the alimentary canal.
Figure : Grasshopper - Digestive System
The alimentary canal is divided into three main portions:
Foregut
It consists of the mouth surrounded by the mouthparts. The mouth cavity is called the
pharynx. It continues as the oesophagus that is short, narrow and thin-walled. The canal
then enlarges into crop which is also thin-walled. The crop opens into short, muscular
organ, the gizzard or the proventriculus. A pair of Salivaryglands lie outside and below
the crop.
Each salivary gland is branched, the secretions of all the branches pouring into a common
duct. The two ducts, one of each side, open into the mouth cavity at the labium. The
entire foregut is lined with chitin. In the gizzard, the chitin (a polysaccharide forming the
major constituent in the exoskeleton of arthropods and in the cell walls of fungi) forms
teeth and plate to facilitate grinding of the food.
Midgut
Midgut consists entirely of stomach or ventriculus. At the junction of the gizzard and
stomach are six pairs of gastric caecae ('gastric' means pertaining to stomach). These are
pouch-like structures arranged in a ring-like manner around the anterior end of the
stomach. The anterior lobe of each pair of the caecae extends over the proventriculus and
the posterior lobe extends over the ventriculus.
The caecae secrete digestive juices and pour them into the stomach. The midgut is not
lined by chitin or cuticle but by a peritrophic membrane. This membrane protects the
stomach wall from abrasions and is fully permeable to enzymes and digested food.
Hindgut
Hindgut is a coiled structure consisting of anterior ileum, middle colon and posterior
rectum. The rectum opens to the exterior through the anus. The hindgut is lined with
cuticle. At the junction of the stomach and ileum are attached numerous long tubules
called the Malpighian tubules.
Mechanism of digestion
Digestion starts at the mouth with the mandibles and the maxillae chewing the food. It is
also acted upon by enzymes of salivary juice, the salivary carbohydrases which partially
digest the food. The food is then swallowed with the help of lubrication provided by the
salivary juice.
The food then enters the oesophagus and then into the crop. Here, the masticated food is
temporarily stored.
The food then passes into the gizzard which acts as the grinding chamber. At the junction
of the gizzard and the stomach is a valve called the pyloric valve. It allows the passage of
only the thoroughly digested food into the stomach and also, prevents the regurgitation of
food from the stomach.
The ground food then enters the stomach. The digestive enzymes secreted by the gastric
caecae act upon the food in the stomach. These enzymes include amylase, maltase,
invertase, tryptase and lipase. The digested food is absorbed through the stomach walls
into the surrounding space which is called the haemocoel. From here, it is transported to
the different body parts.
In the hindgut, absorption of water takes place and the undigested food is formed into
almost dry pellets. These are excreted through the anus as faeces
The human digestive system is well adapted to all of these functions. It comprises a long
tube, the alimentary canal or digestive tract (or simply gut) which extends from the
mouth to the anus, together with a number of associated glands. The digestive systems
made up of different tissues doing different jobs. The lining wall of the alimentary canal
appears different in different parts of the gut, reflecting their different roles, but always
has these four basic layers:
Figure 30:The internal structure of a stomach.

The mucosa, which secretes digestive juices and absorbs digested food. It is often
folded to increase its surface area. On the inside, next to the lumen (the space
inside the gut) is a thin layer of cells called the epithelium. Mucosa cells are
constantly worn away by friction with food moving through the gut, so are
constantly being replaced.

The submucosa, which contains blood vessels, lymph vessels and nerves to
control the muscles. It may also contain secretory glands.

The muscle layer, which is made of smooth muscle, under involuntary control. It
can be subdivided into circular muscle (which squeezes the gut when it contracts)
and longitudinal muscle (which shortens the gut when it contracts). The
combination of these two muscles allows a variety of different movements.

The serosa, which is a tough layer of connective tissue that holds the gut
together, and attaches it to the abdomen.
16.1 Parts of the Alimentary Canal
Figure 201: The structure of alimentary canal.
1.
Mouth (Buccal cavity)
The teeth and tongue physically break up the food into small pieces with a larger
surface area, and form it into a ball or bolus. The salivary glands secrete saliva, which
contains water to dissolve soluble substances, mucus for lubrication, lysozymes to kill
bacteria and amylase to digest starch. The food bolus is swallowed by an involuntary
reflex action through the pharynx (the back of the mouth). During swallowing the
trachea is blocked off by the epiglottis to stop food entering the lungs.
2.
Oesophagus (gullet)
This is a simple tube through the thorax, which connects the mouth to the rest of the
gut. No digestion takes place. There is a thin epithelium, no villi, a few glands
secreting mucus, and a thick muscle layer, which propels the food by peristalsis. This
is a wave of circular muscle contraction, which passes down the oesophagus and is
completely involuntary. The oesophagus is a soft tube that can be closed, unlike the
trachea, which is a hard tube, held open by rings of cartilage.
3. Stomach
This is an expandable bag where the food is stored for up to a few hours. There are
three layers of muscle to churn the food into a liquid called chyme. This is gradually
released in to the small intestine by a sphincter, a region of thick circular muscle that
acts as a valve. The mucosa of the stomach wall has no villi, but numerous gastric pits
(104 cm-2) leading to gastric glands in the mucosa layer. These secrete gastric juice,
which contains: hydrochloric acid (pH 1) to kill bacteria (the acid does not help
digestion, in fact it hinders it by denaturing most enzymes); mucus to lubricate the
food and to line the epithelium to protect it from the acid; and the enzymes pepsin and
rennin to digest proteins.
4. Small Intestine
This is about 6.5 m long, and can be divided into three sections:
(a) The duodenum (30 cm long). Although this is short, almost all the digestion takes
place here, due to two secretions: Pancreatic juice, secreted by the pancreas
through the pancreatic duct. This contains numerous carbohydrase, protease and
lipase enzymes. Bile, secreted by the liver, stored in the gall bladder, and released
through the bile duct into the duodenum. Bile contains bile salts to aid lipid
digestion, and the alkali sodium hydrogen carbonate to neutralise the stomach
acid. Without this, the pancreatic enzymes would not work. The bile duct and the
pancreatic duct join just before they enter the duodenum. The mucosa of the
duodenum has few villi, since there is no absorption, but the submucosa contains
glands secreting mucus and sodium hydrogen carbonate.
(b) The jejunum (2 m long) and
(c) The ileum (4 m long). These two are similar in humans, and are the site of final
digestion and all absorption. There are numerous glands in the mucosa and
submucosa secreting enzymes, mucus and sodium hydrogen carbonate.
The internal surface area is increased enormously by three levels of folding: large
folds of the mucosa, villi, and microvilli. Don't confuse these: villi are large
structures composed of many cells that can clearly be seen with a light
microscope, while microvilli are small sub-cellular structures formed by the
folding of the plasma membrane of individual cells. Microvilli can only be seen
clearly with an electron microscope, and appear as a fuzzy brush border under the
light microscope.
Figure 202: Folds in mucosa, villi, microvilli.
Circular and longitudinal muscles propel the liquid food by peristalsis, and mix
the contents by pendular movements - bi-directional peristalsis. This also
improves absorption.
5.
Large Intestine
This comprises the caecum, appendix, ascending colon, transverse colon, descending
colon and rectum. Food can spend 36 hours in the large intestine, while water is
absorbed to form semi-solid faeces. The mucosa contains villi but no microvilli, and
there are numerous glands secreting mucus. Faeces is made up of plant fibre (cellulose
mainly), cholesterol, bile, mucus, mucosa cells (250g of cells are lost each day),
bacteria and water, and is released by the anal sphincter. This is a rare example of an
involuntary muscle that we can learn to control (during potty training).
16.2 Chemistry of Digestion
1.
Digestion of Carbohydrates
By far the most abundant carbohydrate in the human diet is starch (in bread, potatoes,
cereal, rice, pasta, biscuits, cake, etc), but there may also be a lot of sugar (mainly
sucrose) and some glycogen (in meat).

Salivary amylase starts the digestion of starch. Very little digestion actually takes
place, since amylase is quickly denatured in the stomach, but is does help to clean
the mouth and reduce bacterial infection.

Pancreatic amylase digests all the remaining starch in the duodenum. Amylase
digests starch molecules from the ends of the chains in two-glucose units, forming
the disaccharide maltose. Glycogen is also digested here.

Disaccharidases in the membrane of the ileum epithelial cells complete the
digestion of disaccharides to monosaccharides. This includes maltose from starch
digestion as well as any sucrose and lactose in the diet. There are three important
disaccharidase enzymes:

The monsaccharides (glucose, fructose and galactose) are absorbed by active
transport into the epithelial cells of the ileum, whence they diffuse into the blood
capillaries of the villi. Active transport requires energy in the form of ATP, but it
allows very rapid absorption, even against a concentration gradient. The
membrane-bound disaccharidases and the monosaccharide pumps are often
closely associated:
Figure 203:Absorption of monossacharides into epitherial cells of villi.

The carbohydrates that make up plant fibres (cellulose, hemicellulose, lignin, etc)
cannot be digested, so pass through the digestive system as fibre.
2.
Digestion of Proteins

Rennin (in gastric juice) converts the soluble milk protein caesin into its insoluble
calcium salt. This keeps in the stomach longer so that pepsin can digest it. Rennin
is normally only produced by infant mammals. It is used commercially to make
cheese.

Pepsin (in gastric juice) digests proteins to peptides, 6-12 amino acids long.
Pepsin is an endopeptidase, which means it hydrolyses peptide bonds in the
middle of a polypeptide chain. It is unusual in that it has an optimum pH of about
2 and stops working at neutral pH.

Pancreatic endopeptidases continue to digest proteins and peptides to short
peptides in the duodenum. Different endopeptidase enzymes cut at different
places on a peptide chain because they have different target amino acid
sequences, so this is an efficient way to cut a long chain up into many short
fragments, and it provides many free ends for the next enzymes to work on.

Exopeptidases in the membrane of the ileum epithelial cells complete the
digestion of the short peptides to individual amino acids. Exopeptidases remove
amino acids one by one from the ends of peptide chains. Carboxypeptidases work
from the C-terminal end, aminopeptidases work from the N-terminal end, and
dipeptidases cut dipeptides in half.

The amino acids are absorbed by active transport into the epithelial cells of the
ileum, whence they diffuse into the blood capillaries of the villi. Again, the
membrane-bound peptidases and the amino acid transporters are closely
associated.
Protease enzymes are potentially dangerous because they can break down other
enzymes (including themselves!) and other proteins in cells. To prevent this they are
synthesised in the RER of their secretory cells as inactive forms, called zymogens.
These are quite safe inside cells, and the enzymes are only activated in the lumen of
the intestine when they are required.

Pepsin is synthesised as inactive pepsinogen, and activated by the acid in the
stomach

Rennin is synthesised as inactive prorennin, and activated by pepsin in the
stomach

The pancreatic exopeptidases are activated by specific enzymes in the duodenum

The membrane-bound peptidase enzymes do not have this problem since they are
fixed, so cannot come into contact with cell proteins.
The lining of mucus between the stomach wall and the food also protects the cells
from the protease enzymes once they are activated.
3.
Digestion of Triglycerides

Fats are emulsified by bile salts to form small oil droplets called micelles, which
have a large surface area.

Pancreatic lipase enzymes digest triglycerides to fatty acids and glycerol in the
duodenum.

Fatty acids and glycerol are lipid soluble and diffuse across the membrane (by
lipid diffusion) into the epithelial cells of the villi in the ileum.

In the epithelial cells of the ileum triglycerides are re-synthesised (!) and combine
with proteins to form tiny lipoprotein particles called chylomicrons.

The chylomicrons diffuse into the lacteal - the lymph vessel inside each villus.
The emulsified fatty droplets give lymph its milky colour, hence name lacteal.

The chylomicrons are carried through the lymphatic system to enter the
bloodstream at the vena cava, and are then carried in the blood to all parts of the
body. They are stored as triglycerides in adipose (fat) tissue.

Fats are not properly broken down until they used for respiration in liver or
muscle cells.
4.
Digestion of Nucleic acids

Pancreatic nuclease enzymes digest nucleic acids (DNA and RNA) to nucleotides
in the duodenum.

Membrane-bound nucleotidase enzymes in the epithelial cells of the ileum digest
the nucleotides to sugar, base and phosphate, which are absorbed.
5.
Other substances
Many substances in the diet are composed of small molecules that need little or no
digestion. These include sugars, mineral ions, vitamins and water. These are absorbed
by different transport mechanisms:

Cholesterol and the fat-soluble vitamins (A, D, E, K) are absorbed into the
epithelial cells of the ileum by lipid diffusion

Mineral ions and water-soluble vitamins are absorbed by passive transport in the
ileum

Dietary monosaccharides are absorbed by active transport in the ileum

Water is absorbed by osmosis in the ileum and colon.
16.5
REVISION QUESTIONS
Identify the choice that best completes the statement or answers the question.
1. Nutrients provide the body with the energy and materials it needs for
a. growth.
b. repair.
c. maintenance.
d. All of the above
2. All essential amino acids
a. must be obtained from the foods we eat.
b. are made in our body in sufficient quantities.
c. are found in gelatin.
d. None of the above
Figure 205: Diagram of an organic molecule.
3. Refer to the illustration above. Most of the energy in the molecule shown is stored in
the
a. carbon-oxygen bonds.
b. carbon-hydrogen bonds.
c. oxygen-hydrogen bonds.
d. carbon-oxygen double bond.
4. Refer to the illustration above. The structure shown is most likely a portion of a
a. fat molecule.
c. protein molecule.
b. carbohydrate molecule.
d. amino acid molecule.
5. Vitamin K
a. is soluble in fat.
b. assists with blood clotting.
c. is found in green vegetables.
d. All of the above
6. Vitamins are organic compounds that
a. help activate enzymes during chemical reactions.
b. provide energy for metabolism.
c. help form cell membranes.
d. are not obtained from food.
7. Excessive amounts of vitamins such as vitamins A, D, E, and K
a. lead to excellent health.
b. can be harmful.
c. present no problem since they are not stored in the body.
d. prevent beriberi.
8. Brain cells and red blood cells receive most of their energy directly from
a. proteins.
b. glucose.
c. cellulose.
d. deoxyribose.
9. Most of the body’s energy needs should be supplied by dietary
a. carbohydrates.
b. vitamins.
c. fats.
d. proteins.
10. The first portion of the small intestine is the
a. colon.
b. duodenum.
c. esophagus.
11. The pharynx is
a. located in the colon.
b. located in the back of the throat.
d. rectum.
c. also called the voice box.
d. None of the above
12. Which of the following provides a passage for both food and air?
a. the esophagus
c. the pharynx
b. the trachea
d. the duodenum
13. The function of the digestive system is to
a. chemically break down food.
b. mechanically break apart food.
c. absorb nutrient materials.
d. All of the above
14. small intestine : large intestine ::
a. large intestine : small intestine
b. stomach : large intestine
c. esophagus : stomach
d. small intestine : esophagus
9.0 TRANSPORTATION IN ORGANISMS
9.1 INTRODUCTION
In unicellular organisms a single cell carries out all the life processes as the cell itself
is the organism. In advanced forms like the few-celled algae, protozoa, sponges, etc., the
size of the organism ensures that all the cells are not very far from each other. The uptake
of materials from the environment is through the general body surface and the transport
within the cells is by diffusion and the transport from one part of the body to the other is
by cell to cell movement of substances. However, more advanced multicellular forms
need a transportation mechanism. However, the transport of materials across the plant or
animal body occurs by processes broadly called the mass flow system.
9.2 IMPORTANCE OF STUDYING TRANSPORTATION
 Transportation whether in plants or animals is the key to the efficient assimilation
of the nutrients that the organisms synthesize, get from their environment or
digest.
 The study of transport mechanisms in plants helps us to understand the uptake of
the various types of substances and their passage through the plants. This has
helped a great deal in developing fungicides, pesticides, growth regulators, etc.
and how they should be administered to the plants.
 In animals too the study of transport has helped us in developing new and more
effective drugs.
9.3 TRANSPORT IN PLANTS
The transport in higher plants is with the help of the vascular system. Thus, these plants
are also called the vascular plants. The materials to be transported across the plant body
are water, minerals and food. Apart from these nutrients, substances like the hormones
also have to be transported.
VASCULAR TISSUE
The transport of materials takes place through specialised tissue called the vascular
tissue. The vascular tissue is of two types:

Xylem
It is the vascular tissue that transports water across the plant body. Xylem is made up
of four different types of cells. They are tracheids, vessels, xylem fibres and xylem
parenchyma. Of these only tracheids and vessels are involved in the transport of water
and minerals. Tracheids are elongated dead cells that have sloping end walls. The
cavity is empty as the cells are dead. The walls are thickened with a material called
lignin. The xylem vessels and tracheids together form long tubes that have a narrow
diameter. Thus they function as capillaries (narrow tubes) to transport water.
Figure 179: The structure of xylem

Phloem
It is the vascular tissue that transports organic substances like sucrose across the plant
body. It is made up of four types of cells - sieve tubes, companion cells, phloem
fibres and phloem parenchyma. Except for phloem fibres, all the other three types of
cells are living. Sieve tubes and companion cells are mainly involved in the transport
of the materials.
 Sieve Tubes
They are tubes formed by cells that are joined end to end. The end walls of these cells
have perforations. The mature sieve tube cells are enucleated. The cytoplasm of the
sieve tube cells is continuous through the perforations of the end walls. This helps in
the transport of materials.
 Companion Cells
They are smaller cells associated with the sieve tubes. They have dense cytoplasm
and elongated nucleus. It is in contact with the sieve tube cell through pores in the
wall.
Figure 180: Structure of phloem.
9.5 PROCESSES INVOLVED IN TRANSPORT
There are some physical principles and biological processes that explain the transport
of materials across the plant body. They are as follows:
 Diffusion
It is a physical process that involves the movement of solute particles from the region
of their higher concentration to the region of their lower concentration.
 Osmosis
It is a physical process in which the solvent (water) moves from the region of its
higher concentration to the region of its lower concentration across a semi-permeable
membrane.
 Active Transport
The transport of materials across the cell membranes with the help of energy is called
active transport.
 Osmotic Pressure
The pressure built up inside the cells as a result of the entry of water is called osmotic
pressure. The entry of water into the cells is regulated by the solutes in the cell.
 Turgor Pressure
The positive osmotic pressure developed inside a cell as a result of entry of water is
called turgor pressure. When the cells are full of water, they are called turgid and
when they lose water, they are called flaccid.
 Water Potential
It is the potential energy associated with water. For example, water at a height has
more water potential and will, therefore, flow down. When water is present in a dilute
solution it has higher potential and will therefore move towards the concentrated
solution.
 Potential Gradient
The difference in the potential energy between two regions or across the cell
membrane is called potential gradient.
 Ionic Gradient
The difference in the concentrations of the ions across a membrane is called ionic
gradient. Since these ions are charged chemical molecules, ionic gradient is also
called electrochemical gradient.’
 Adhesion
The attraction between two unlike molecules is called adhesion.
 Cohesion
The attraction between two like molecules is called cohesion.
9.6 WATER TRANSPORT IN PLANTS
Vast amounts of water pass through plants. A large tree can use water at a rate of 1 dm³
min-1. Only 1% of this water is used by the plant cells for photosynthesis and turgor, and
the remaining 99% evaporates from the leaves and is lost to the atmosphere. This
evaporation from leaves is called transpiration.
9.6.1 TRANSPIRATION
Transpiration is the loss of water from the aerial parts of the plant in the form of water
vapour. Transpiration may be of the following types:
 Stomatal : Transpiration taking place through the stomata is called
stomatal transpiration.
 Cuticular : The surface of the plant is covered by a thin layer of cuticle
through which water vapour is lost during transpiration. This is called
cuticular transpiration.
 Lenticular : The process of loss of water vapour through the lenticels is
called lenticular transpiration.
Stomata
Stomata are openings, generally on the under surface of the leaves. These openings are
guarded by bean-shaped cells (dumb-bell shaped in grasses) called the guard cells. The
walls of the guard cells facing the stomata are thickened. Due to an increase in the
concentration of K+ ions inside the guard cells, the water potential reduces. This results in
water entering the guard cells and they become turgid. The outer thin walls bulge which
pulls the thicker inner walls apart, opening the stomata. For closure the reverse occurs loss of K+ ions, increased water potential, exit of water and the cells become flaccid. This
brings the inner walls close together and closes the stomata. Transpiration is maximum
during the day, from morning to midday. This is the time stomata remain open. They
close during the evenings and at night when the transpiration rate is low.
9.6.2 IMPORTANCE OF TRANSPIRATION

Transpiration is responsible for uptake of water from the soil.

It is responsible for movement of water and dissolved minerals from the roots to
different parts of the plant.

It results in cooling of the leaf surfaces, thereby protecting them from excessive
heat.
9.6.3 FACTORS AFFECTING TRANSPIRATION
The potometer can be used to investigate how various environmental factors affect the
rate of transpiration.
 Light. Light stimulates the stomata to open allowing gas exchange for
photosynthesis, and as a side effect this also increases transpiration.
 Temperature. High temperature increases the rate of evaporation of water from
the spongy cells, and reduces air humidity, so transpiration increases.
 Humidity. High humidity means a higher water potential in the air, so a lower
water potential gradient between the leaf and the air, so less evaporation.
 Air movements. Wind blows away saturated air from around stomata, replacing
it with drier air, so increasing the water potential gradient and increasing
transpiration.
The movement of water through a plant can be split into three sections: through the roots,
stem and leaves:
Figure 181: Movementof water through roots.
Water moves through the root by two paths:

The Symplast pathway consist of the living cytoplasms of the cells in the
root (10%). Water is absorbed into the root hair cells by osmosis, since the cells
have a lower water potential that the water in the soil. Water then diffuses from
the epidermis through the root to the xylem down a water potential gradient. The
cytoplasms of all the cells in the root are connected by plasmodesmata through
holes in the cell walls, so there are no further membranes to cross until the water
reaches the xylem, and so no further osmosis.

The Apoplast pathway consists of the cell walls between cells (90%).
The cell walls are quite thick and very open, so water can easily diffuse through
cell walls without having to cross any cell membranes by osmosis. However the
apoplast pathway stops at the endodermis because of the waterproof casparian
strip, which seals the cell walls. At this point water has to cross the cell membrane
by osmosis and enter the symplast. This allows the plant to have some control
over the uptake of water into the xylem.
The uptake of water by osmosis actually produces a force that pushes water up the
xylem. This force is called root pressure, which can be measured by placing a
manometer over a cut stem, and is of the order of 100 kPa (about 1 atmosphere). This
helps to push the water a few centimetres up short and young stems, but is nowhere
near enough pressure to force water up a long stem or a tree. Root pressure is the
cause of guttation, sometimes seen on wet mornings, when drops of water are forced
out of the ends of leaves.
2. Movement through the Stem
The xylem vessels form continuous pipes from the roots to the leaves. Water can
move up through these pipes at a rate of 8m h-1, and can reach a height of over 100m.
Since the xylem vessels are dead, open tubes, no osmosis can occur within them. The
driving force for the movement is transpiration in the leaves. This causes low pressure
in the leaves, so water is sucked up the stem to replace the lost water. The column of
water in the xylem vessels is therefore under tension (a stretching force). Fortunately
water has a high tensile strength due to the tendency of water molecules to stick
together by hydrogen bonding (cohesion), so the water column does not break under
the tension force. This mechanism of pulling water up a stem is sometimes called the
cohesion-tension mechanism.
3.
Movement through the Leaves
The xylem vessels ramify in the leaves to form a branching system of fine vessels
called leaf veins. Water diffuses from the xylem vessels in the veins through the
adjacent cells down its water potential gradient. As in the roots, it uses the symplast
pathway through the living cytoplasm and the apoplast pathway through the nonliving cell walls. Water evaporates from the spongy cells into the sub-stomatal air
space, and diffuses out through the stomata.
Figure 182: Movement of through leaves.
9.6.4 TRANSPIRATION PULL
The cells around the stomata absorb water from the neighbouring cells. Ultimately water
is drawn from the xylem in the leaves. This results in a negative water potential in the
upper portions of the xylem tube. Negative water potential means low pressure. Low
pressure draws the water up from the lower regions - first the stem and then the roots of
the xylem tube that have positive water potential and therefore, high pressure. The water
moves up the plant as a result of the potential gradient. This gradient has developed due
to transpiration. So, the force with which the water is pulled up the xylem is called the
transpiration pull. The transpiration pull results in a continuous stream of water called
the transpiration stream. It is a continuous stream of water extending from the xylem of
the leaves to the xylem of the roots. In fact, transpiration pull can occur only when there
is a continuous column of water. This continuity is maintained by the cohesive and
adhesive properties of water. Adhesion causes the water molecules to adhere to the
xylem walls and because of cohesion, the water molecules remain together and move up
as a stream
9.7 TRANSPORT OF MINERALS
Minerals are absorbed from the soil along with water as they are dissolved in water. They
are taken up in the ionic form. For example, potassium is taken up as K+ ions. They are
transported through the xylem along with the water. Some of the mineral ions like the
nitrates enter into the phloem along with the prepared food and are then transported along
the phloem
9.8 SOLUTE TRANSPORT IN PLANTS
The phloem contains a very concentrated solution of dissolved solutes, mainly sucrose,
but also other sugars, amino acids, and other metabolites. This solution is called the sap,
and the transport of solutes in the phloem is called translocation. The main mechanism is
thought to be the mass flow of fluid up the xylem and down the phloem, carrying
dissolved solutes with it. Plants don’t have hearts, so the mass flow is driven by a
combination of active transport (energy from ATP) and evaporation (energy from the
sun). This is called the mass flow theory, and it works like this:
Figure 184: Solute transport in plants
1.
Sucrose produced by photosynthesis is actively pumped into the phloem
vessels by the companion cells.
2. This decreases the water potential in the leaf phloem, so water diffuses from the
neighbouring xylem vessels by osmosis.
3. This is increases the hydrostatic pressure in the phloem, so water and dissolved
solutes are forced downwards to relieve the pressure. This is mass flow: the
flow of water together with its dissolved solutes due to a force.
4. In the roots the solutes are removed from the phloem by active transport into the
cells of the root.
5. At the same time, ions are being pumped into the xylem from the soil by active
transport, reducing the water potential in the xylem.
6. The xylem now has a lower water potential than the phloem, so water diffuses
by osmosis from the phloem to the xylem.
7. Water and its dissolved ions are pulled up the xylem by tension from the leaves.
This is also mass flow.
9.9 TRANSLOCATION EXPERIMENTS
1.
Puncture Experiments
If the phloem is punctured with a hollow tube then the sap oozes out, showing that
there is high pressure (compression) inside the phloem (this is how maple syrup is
tapped). If the xylem is punctured then air is sucked in, showing that there is low
pressure (tension) inside the xylem. This illustrates the main difference between
transport in xylem and phloem: Water is pulled up in the xylem, sap is pushed down
in the phloem.
2.
Ringing Experiments
Since the phloem vessels are outside the xylem vessels, they can be selectively
removed by cutting a ring in a stem just deep enough to cut the phloem but not the
xylem. After a week there is a swelling above the ring, reduced growth below the ring
and the leaves are unaffected. This was early evidence that sugars were transported
downwards in the phloem.
3.
Radioactive Tracer Experiments
In a typical experiment a plant is grown in the lab and one leaf is exposed for a short time
to carbon dioxide containing the radioactive isotope 14C. This 14CO2 will be taken up by
photosynthesis and the 14C incorporated into glucose and then sucrose. The plant is then
frozen in liquid nitrogen to kill and fix it quickly, and placed onto photographic film in
the dark. The resulting autoradiograph shows the location of compounds containing 14C.
This experiment shows that organic compounds (presumably sugars) are transported
downwards from the leaf to the roots.
4.
Aphid Stylet Experiments
Aphids, such as greenfly, have specialized mouthparts called stylets, which they use
to penetrate phloem tubes and sup of the sugary sap therein. If the aphids are
anaesthetised with carbon dioxide and cut off, the stylet remains in the phloem so
pure phloem sap can be collected through the stylet for analysis.
9.10 TRANSPORTATION IN ANIMALS
9.10.1 CIRCULATORY SYSTEM
The transport system in animals is called the circulatory system. The materials are
transported from one part of the body to another by a mass flow system which is the
circulatory system. Materials to be transported include digested food, respiratory gases,
hormones, excretory products, etc. The digested food includes sugars like glucose, amino
acids, fatty acids and their derivatives.
9.10.3 TYPES OF CIRCULATORY SYSTEMS
There are two types of blood circulatory systems:

Open circulatory system

Closed circulatory system
Open Circulatory System
The blood enters and circulates in the interstitial spaces (space between the
tissues).
Figure : Open Circulatory System
The exchange of materials between the cells and the blood is done directly. There are few
blood vessels but they are not extensive. The blood vessels are open-ended as they open
into the common cavities called the haemocoel. For example: Insects
Closed Circulatory System
The blood always remains inside the blood vessels and never comes in direct contact with
the cells. The materials enter and exit the blood vessels through the walls. The blood
flows in the blood vessels under high pressure such that it reaches all the parts of the
body in good time. The blood vessels are branched into fine capillaries which are actually
involved in the exchange of materials. For example: Mammals (including man)
Figure : Closed Circulatory System
The components of the closed circulatory system in man are:

A fluid that can carry all the materials to be transported (blood)

A pumping organ that can push the fluid through the body - as time taken is
important (heart)

Many tubes through which the fluid can flow through the body (blood vessels)
9.10.5 HUMAN CIRCULATORY SYSTEM
Humans have a double circulatory system with a 4-chambered heart. In humans the right
side of the heart pumps blood to the lungs only and is called the pulmonary circulation,
while the left side of the heart pumps blood to the rest of the body – the systemic
circulation. The circulation of blood round the body was discovered by William Harvey
in 1628.
There are three circulatory pathways operating in man. They are:

Systemic

Hepatic Portal

Pulmonary
Systemic
It is the most widespread circulatory pathway. It accounts for supply of oxygenated blood
to all the parts of the body and collection of deoxygenated blood from the tissues. The
left ventricle of the heart opens into a major artery called the aorta. The aorta branches
just above the heart to form the coronary arteries that supply blood to the heart walls. The
aorta continues and then branches into two main arteries, one artery going up and the
other coming down. The artery going up branches off as subclavian artery to the shoulder
and continues as the carotid artery that supplies to the head and neck region. The
downward branch of the aorta branches off as it proceeds down into hepatic artery to the
liver, mesentric artery to the stomach and intestine, renal artery to the kidneys and iliac
artery to the genitals and legs. The arteries in the organs divide into arterioles and then
into the capillaries. These capillaries join together to form the venules that join together
to form the veins. The iliac vein carries deoxygenated blood from the genitals and legs,
the renal vein from the kidneys and hepatic vein from the liver. All these veins join
together to form the inferior vena cava, one of the two great veins. The jugular vein that
brings deoxygenated blood from the head and neck region and the subclavian vein that
brings from the shoulder region join together to form the superior vena cava, the other
great vein. The vena cavae return the blood to the right auricle of the heart.
As the blood passes through the intestinal walls, it takes in the abosrbed food. When the
blood passes through the kidneys, all the nitrogenous wastes are removed. The absorbed
food and oxygen is distributed in the tissues and wastes and carbon dioxide is picked up.
Hepatic Portal
In the systemic circulation, the organs receive the blood from the vessel coming directly
from the heart. However, a portal circulation connects two organs. A portal vein is that
which connects two organs without the involvement of heart in between. This means that
the portal veins begin and end with capillaries. There are two portal systems in man. One
is between hypothalamus and pituitary gland and the other is between the gut and the
liver. The portal system between the gut (stomach and intestines) and the liver is called
the hepatic portal system. The hepatic portal vein goes from the stomach and the
intestines to the liver. The hepatic vein leaves the liver with the deoxygenated blood.
This means that the stomach and intestines receive blood directly from the heart by way
of mesentric artery. However, there is no mesentric vein that carries deoxygenated blood
to the inferior vena cava like the other lower body organs. The vein from the stomach and
intestine goes to the liver. This is probably to regulate the substances going out of the gut
into the blood. For example, if the blood from the gut contains more glucose, the liver
can convert it to glycogen and store it. The blood leaving the liver will have the correct
level of glucose.
Pulmonary
The circulation of blood between heart and lungs for purification of blood is called
pulmonary circulation. During pulmonary circulation, the right ventricle of the heart
pumps blood into the pulmonary artery. The pulmonary artery takes the deoxygenated
blood to the lungs where it is oxygenated. The oxygenated blood is returned by the
pulmonary vein to the left auricle in the heart. The presence of pulmonary circulation
ensures that all the blood before being pumped once again to the different parts of the
body is oxygenated. This helps the mammals and the birds to maintain high metabolic
rates and makes them more efficient.
BLOOD VESSELS
Blood vessels are classified as organs. Blood circulates in a series of different kinds of
blood vessels as it circulates round the body. Each kind of vessel is adapted to its
function.
Veins and Venules
Figure 71: Structure of veins
Function is to carry blood from
tissues to the heart
Thin walls, mainly collagen, since
blood at low pressure
Capillaries
Arteries and Arterioles
Figure 72: Structure of
Figure 73: structure of
capillaries
arteries.
Function is to allow exchange of
materials between the blood and
the tissues
Very thin, permeable walls, only
one cell thick to allow exchange
of materials
Large lumen to reduce resistance
Very small lumen. Blood cells
to flow.
must distort to pass through.
Many valves to prevent back-flow
No valves
Function is to carry blood
from the heart to the tissues
Thick walls with smooth
elastic layers to resist high
pressure and muscle layer to
aid pumping
Small lumen
No valves (except in heart)
Blood at low pressure
Blood pressure falls in capillaries.
Blood usually deoxygenated
Blood changes from oxygenated
(except in pulmonary vein)
to deoxygenated (except in lungs)
Blood at high pressure
Blood usually oxygenated
(except in pulmonary
artery)
9.12.1 BLOOD
It is a red coloured, viscous, alkaline (pH about 7.4) fluid flowing through the body of
higher animals. The adult human body consists of 5-6 litres of blood. It has two
components:

Fluid plasma

Solid formed elements
The elements include corpuscles and platelets.
9.12.2 FUNCTIONS OF BLOOD

Transport of Nutrients
The food is digested into the simplest of the forms in the digestive system. Blood carries
the digested food or the nutrients absorbed from the intestine to the liver and then to other
parts of the body. The food transported includes glucose, fatty acids, amino acids,
glycerol, etc.

Transport of Respiratory Gases
Oxygen is transported from the lungs to the cells and carbon dioxide is transported from
the cells to the lungs. The transport of these gases is chiefly due to the pigment
haemoglobin.

Transport of Excretory Wastes
The cells are constantly undergoing metabolic reactions that produce numerous wastes.
Some of these wastes are toxic and can be harmful. The wastes have to be constantly
removed to the regions where they are either excreted or rendered harmless. Blood
transports the wastes to liver, kidney, intestines and skin.

Transport of Hormones
The hormones are synthesised far from their site of action. Thus, blood is necessary
for transporting the hormones.

Role in Immune System
The leucocytes are phagocytic and engulf the bacteria and other micro-organisms that
attack the body cells. The lymphocytes secrete antibodies, that are special protein
molecules that act against specific proteins present on the surface of the germs. These
proteins are called the antigens.

Maintenance of pH
The proteins act as buffers in regulating the acid and base concentration in blood.

Maintenance of Water Content
The blood circulates materials between itself, the tissue fluid and the cells. The tissue
fluid should have the correct water content. If the fluid has less water, it will
dehydrate the cells by drawing water out. If the fluid has more water, the cells are
swollen with water as the excess water enters the cell.

Regulation of Blood Pressure
The water level in the blood changes the volume of the blood which affects the blood
pressure.

Role in Temperature Regulation
Heat is distributed evenly throughout the body as the blood circulates. The heat from the
deeper warmer tissues are carried to the surface cooler parts.

Role in Homoeostasis
Homeostasis means maintaining same state. The above aspects pH, ionic concentration,
water, blood pressure, temperature, etc. have to be maintained at optimum levels in order
to maintain homeostasis.

Role in Clotting
The blood contains platelets that secrete substances called the thromboplastin on being
damaged. This substance initiates reactions that result in the formation of blood clots.
The blood clots prevent excessive flow of blood.
The four main components in blood are shown in the diagram below:
Figure 76: The composition of blood.
There are dozens of different substances in blood, all being transported from one part of
the body to another. Some of the main ones are listed in this table:
Substance
Where
Reason
Oxygen
Red blood cells Transported from lungs to all cells for respiration
Carbon dioxide
Plasma
Transported from all cells to lungs for excretion
Nutrients (e.g. glucose,
amino acids, vitamins,
Plasma
lipids, nucleotides)
Waste products (e.g.
urea, lactic acid)
Plasma
Ions (e.g. Na+, K+,
2+
2+
-
Ca , Mg , Cl , HCO3,
Plasma
Transported from small intestine to liver and from liver
to all cells
Transported from cells to liver and from liver to
kidneys for excretion
Transported from small intestine to cells, and help
buffer the blood pH.
HPO2-, SO2-)
Hormones
Plasma
Transported from glands to target organs
Proteins (eg albumins)
Plasma
Amino acid reserve
Blood clotting factors
Plasma
Antigens and antibodies Plasma
Water
Plasma
Bacteria and viruses
plasma
Heat
Plasma
At least 13 different substances (mainly proteins)
required to make blood clot.
Part of immune system
Transported from large intestine and cells to kidneys
for excretion.
Transported from muscles to skin for heat exchange.
9.13 PLASMA
It forms about 55% of the blood (about 3 litres). Its composition is as follows:

Water (92%)

Soluble components
The soluble components are:

Proteins (7%) - includes hormones, enzymes, globulin antibodies, albumin
and fibrinogen. (Blood plasma without fibrinogen and other clotting factors
is called Serum and is a yellow watery fluid).

Nutrients - include glucose, amino acids, fatty acids and glycerol

Metabolic Substances - include vitamins, lactic acid, urea and uric acid
(non-protein nitrogenous substances - NPN)

Inorganic Ions (0.9%) - include sodium, potassium, calcium, magnesium,
chlorine and radicals like sulphate, phosphate, etc.

Pigments - include small amounts of bilirubin, carotenes, etc. that give the
plasma its characteristic yellow colour.
9.14 FUNCTIONS OF PLASMA

Maintains osmotic pressure and viscosity of the blood

Helps in transport of various substances like the hormones, enzymes, etc.

Acts as a protein reservoir

Helps in clotting of blood

Helps in regulating body temperature
9.15 FORMED ELEMENTS
The formed elements are found freely suspended in the liquid plasma.
There are three types of formed elements:

Red blood corpuscles (RBCs)

White blood corpuscles (WBCs)

Platelets
9.16 RED BLOOD CORPUSCLES (RBCS)
They are small biconcave circular cells also called erythrocytes.

They are thicker at the edges than in the centre.

The erythrocytes are flexible so that they can pass through the narrow capillaries
easily.

They number 5 million per cubic mm in adult males and 4.5 million per cubic mm
in adult females. Their number is higher in early infancy. The cells are composed
of a network of fats and proteins between which are enmeshed numerous
pigments called the haemoglobin which give the blood its colour.

Haemoglobin is composed of an iron containing pigment called haeme and a
protein called globin. The haemoglobin pigments combine with oxygen to form
oxyhaemoglobin in the lungs. Around the body cells, the oxyhaemoglobin
dissociates due to low oxygen concentration. Here, some of them combine with
the carbon dioxide.

Haemoglobin has a strong affinity for carbon monoxide (CO) with which it forms
a stable compound. When carbon monoxide is present in the inhaled air the
pigments prefer it to oxygen thereby greatly reducing the oxygen supplied to the
body. This is called carbon monoxide poisoning and can even result in death. This
is one of the reasons why the vehicle exhaust gases that contain carbon monoxide
are harmful.

The red blood cells do not have nucleus, mitochondria or endoplasmic reticulum.
The lack of nucleus creates more space inside the cell for the haemoglobin. Lack
of mitochondria means that all the oxygen carried by the cell is transported and
none of it is used by the cells.

The red blood cells are synthesised in the bone marrows of ribs, sternum and
vertebrae at the rate of 1.2 million cells per second. The life span of the cells is
only about 120 days. They are destroyed in the liver. The iron part is retained and
the pigment is excreted in the bile juice as bilirubin.
9.17 FUNCTIONS OF ERYTHROCYTES

They are carriers of oxygen and carbon dioxide

They maintain the viscosity of blood

They maintain acid-base balance

They maintain ionic balance

The disintegration of haemoglobin leads to formation of many other pigments
like the bilirubin, biliverdin, etc. in the liver
RBC have specific features (listed below) that make it efficient in absorbing and
transporting respiratory gasses:

They have a small size - They are much smaller than most other cells in the body.
This means that all the haemoglobin molecules are close to the surface, allowing
oxygen to be picked up and release rapidly.

Shape - RBC are biconcave shapes discs. It allows the cell to contain a lot of
haemoglobin while still allowing efficient diffusion through the plasma
membrane

Organelles – RBC do not contain either nuclei or mitochondria. This allows
more space inside the cell for haemoglobin.
9.18 WHITE BLOOD CORPUSCLES (WBCS)

They are also called leucocytes. They lack haemoglobin and are therefore
colourless. They are nucleated and amoeboid.

The amoeboid nature of the leucocytes helps them to squeeze through the walls of
the blood vessels in order to engulf bacteria. They do not contain haemoglobin.
They number 6000 to 8000 per cubic mm. The ratio of WBC to RBC is 1:7.
They are of five distinct types whose life span varies from 12 hours to 300 days.
The leucocytes are basically of two types:

Granular leucocytes

Agranular leucocytes
Lymphocytes
They are produced in the lymph system. Their nucleus is large and occupies most of the
cell. The cytoplasm is basophilic. They are more in number in children than in adults.
They have a life span of 100 - 200 days. Their functions are phagocytosis and antibodyproduction.
Monocytes
They are produced in the bone marrow. They have a large kidney-shaped nucleus. The
cytoplasm is more than in lymphocytes. They number 100 to 700 per cubic mm. They
function as tissue macrophages feeding on damaged tissues.
9.20 PLATELETS
They are round biconvex cells that do not have a distinct nucleus. They are also called the
thrombocytes. They number 250,000 to 400,000 per cubic mm of blood. Their life span is
8 to 14 days. They are involved in blood clotting. They are destroyed in the spleen.
9.21 FUNCTIONS OF PLATELETS

Role in Blood Clotting
The damaged platelets release a substance called thromboplastin. This sets in action, a
series of reactions that result in the formation of clots. These clots block the site of the
injury, avoiding excess loss of blood.

Role in Repair of Damaged Endothelium
Endothelium is the inner wall of the blood vessels. The platelets stick to the damaged
portion of the endothelium and prevent loss of blood. The platelets are not allowed to
stick to healthy endothelium by the secretion of a substance called prostacyclin.
Thrombosis is a condition during which a clot is formed in the narrowed portion of the
blood vessels. The narrowing occurs due to the deposition of substances like the
cholesterol. This also prevents secretion of prostacyclin which allows the platelets to
stick to the walls of the vessels. This results in the formation of clots that can cause
blockage of the blood vessels. These blockages in the important vessels can also lead to
death.

Clot Retraction
The clot formed is made denser and smaller by the action of platelets.
9.22 PROCESS OF BLOOD CLOTTING
Excessive loss of blood is prevented from the cut blood vessels by the formation of clots.
This process is also called coagulation. The steps involved in clotting of blood are:

Damaged platelets secrete thromboplastin or thrombokinase.

Thrombokinase is an enzyme that changes prothrombin (present in the blood) to
thrombin in the presence of calcium ions.

Thrombin combines with soluble fibrinogen present in the blood and forms
insoluble fibrin.

Fibrin forms thread-like structures that form a sticky mass. This forms a network
of a sticky substance at the damaged portion of the blood vessel.

This network does not allow the corpuscles to pass through. Only the plasma is
allowed to pass through and this plasma which lacks the fibrinogen is called the
serum.

The mass that is formed at the cut becomes denser and denser and is called the
clot.
9.23 THE LYMPHATIC SYSTEM
The lymphatic system consists of a network of lymph vessels flowing alongside the
veins. The vessels lead towards the heart, where the lymph drains back into the blood
system at the superior vena cava. There is no pump, but there are numerous semilunar valves, and lymph is helped along by contraction of muscles, just as in veins.
Lymph vessels also absorb fats from the small intestine, where they form lacteals
inside each villus. There are networks of lymph vessels at various places in the body
(such as tonsils and armpits) called lymph nodes where white blood cells develop.
These become swollen if more white blood cells are required to fight an infection.
Figure 40: The structure of human lymphatic system.
Remember the difference between these four solutions:
Plasma
The liquid part of blood. It contains dissolved glucose, amino acids, salts
and vitamins; and suspended proteins and fats.
Serum
Purified blood plasma used in hospitals for blood transfusions.
Tissue Fluid The solution surrounding cells. Its composition is similar to plasma, but
without proteins (which stay in the blood capillaries).
Lymph
The solution inside lymph vessels. Its composition is similar to tissue
fluid, but with more fats (from the digestive system).
9.24 TISSUE FLUID
These substances are all exchanged between the blood and the cells in capillary beds.
Substances do not actually move directly between the blood and the cell: they first diffuse
into the tissue fluid that surrounds all cells, and then diffuse from there to the cells.
Figure 79: The diagram showing the formation of Tissue fluid.
1. At the arterial end of the capillary bed the blood is still at high hydrostatic
pressure, so blood plasma is squeezed out through the permeable walls of the
capillary. Cells and proteins are too big to leave the capillary, so they remain in the
blood.
2. This fluid now forms tissue fluid surrounding the cells. Materials are exchanged
between the tissue fluid and the cells by all four methods of transport across a cell
membrane. Gases and lipid-soluble substances (such as steroids) cross by lipid
diffusion; water crosses by osmosis, ions cross by facilitated diffusion; and glucose
and amino acids cross by active transport.
3. At the venous end of the capillary bed the blood is at low pressure, since it has
lost so much plasma. Water returns to the blood by osmosis since the blood has a low
water potential. Solutes (such as carbon dioxide, urea, salts, etc) enter the blood by
diffusion, down their concentration gradients.
4. Not all the plasma that left the blood returns to it, so there is excess tissue fluid.
This excess drains into lymph vessels, which are found in all capillary beds. Lymph
vessels have very thin walls, like capillaries, and tissue fluid can easily diffuse inside,
forming lymph.
9.25 THE HEART
Figure 81: The structure of human heart.
The human heart has four chambers: two thin-walled atria on top, which receive blood,
and two thick-walled ventricles underneath, which pump blood. Veins carry blood into
the atria and arteries carry blood away from the ventricles. Between the atria and the
ventricles are atrioventricular valves, which prevent back-flow of blood from the
ventricles to the atria. The left valve has two flaps and is called the bicuspid (or mitral)
valve, while the right valve has 3 flaps and is called the tricuspid valve. The valves are
held in place by valve tendons (“heart strings”) attached to papillary muscles, which
contract at the same time as the ventricles, holding the vales closed. There are also two
semi-lunar valves in the arteries (the only examples of valves in arteries) called the
pulmonary and aortic valves. The left and right halves of the heart are separated by the
inter-ventricular septum. The walls of the right ventricle are 3 times thinner than on the
left and it produces less force and pressure in the blood. This is partly because the blood
has less far to go (the lungs are right next to the heart), but also because a lower pressure
in the pulmonary circulation means that less fluid passes from the capillaries to the
alveoli. The heart is made of cardiac muscle, composed of cells called myocytes. When
myocytes receive an electrical impulse they contract together, causing a heartbeat. Since
myocytes are constantly active, they have a great requirement for oxygen, so are fed by
numerous capillaries from two coronary arteries. These arise from the aorta as it leaves
the heart. Blood returns via the coronary sinus, which drains directly into the right atrium.
THE CARDIAC CYCLE
When the cardiac muscle contracts the volume in the chamber decrease, so the pressure
in the chamber increases, so the blood is forced out. Cardiac muscle contracts about 75
times per minute, pumping around 75 cm³ of blood from each ventricle each beat (the
stroke volume). It does this continuously for up to 100 years. There is a complicated
sequence of events at each heartbeat called the cardiac cycle.
It consists of three stages:

Auricular Systole or Ventricular Diastole
In the first stage, the auricles or the atria contract with enough pressure to squeeze out all
the blood from their cavities into the corresponding ventricles. During this time, the
openings from the vena cavae in the right auricle and opening of the pulmonary vein in
the left auricles remain closed because of the contraction of the auricles. The semilunar
valves guarding the opening of the arteries (aorta and pulmonary artery) are also closed.
The auriculo ventricular valves remain open letting blood flow under pressure from the
auricles to the ventricles. During this stage, auricles contract and ventricles remain
relaxed. This stage is therefore called auricular systole or ventricular diastole.

Auricular Diastole or Ventricular Systole
In the second stage, the auricles relax (diastole). Just as they relax, the flaps of the
auriculo ventricular valves snap close. This makes the sound heard as the first heart beat.
Once the auriculo ventricular valve is closed, the ventricle contracts (systole). The
semilunar valves open as the blood rushes into the arteries from the ventricles.

Joint Diastole or Auricular and Ventricular Diastole
In the last stage, the ventricles start to relax (diastole). This gradually brings down the
pressure and at the same time the semilunar valves snap shut to prevent backflow of
blood into the heart as the pressure has come down. This produces the second heart beat
sound. With the closure of the semilunar valves the ventricles relax further and the
auriculo ventricular valves open. Thus, at this stage, both auricles and ventricles are in
diastole and hence, the stage is called joint diastole.
The occurrence of the periodic series of events during one heartbeat is called a cardiac
cycle. During one heartbeat, there are two heart sounds - 'lub' and 'dub'. 'lub' is the first
sound and 'dub' is the second sound.
9.27 EXERCISE AND HEART RATE
The rate at which the heart beats and the volume of blood pumped at each beat (the stroke
volume) can both be controlled. The product of these two is called the cardiac output –
the amount of blood flowing in a given time:
heart
rate
(beats/m
in)
stroke
volume
(cm3/ beat)
cardiac
output
(cm3/min)
at rest
75
75
5 600
at
exerci
se
180
120
22 000
As the table shows, the cardiac output can increase dramatically when the body
exercises. There are several benefits from this:

to get oxygen to the muscles faster

to get glucose to the muscles faster

to get carbon dioxide away from the muscles faster

to get lactate away from the muscles faster

to get heat away from the muscles faster
But what makes the heart beat faster? Again, this is an involuntary process and is
controlled a region of the medulla called the cardiovascular centre, which plays a similar
role to the respiratory centre. The cardiovascular centre receives inputs from various
receptors around the body and sends output through two nerves to the sino-atrial node in
the heart.
Figure 84: Effect of exercises on rate of heart beat.
9.28 HOW DOES THE CARDIOVASCULAR CENTRE
CONTROL THE HEART?
The cardiovascular centre can control both the heart rate and the stroke volume. Since the
heart is myogenic, it does not need nerve impulses to initiate each contraction. But the
nerves from the cardiovascular centre can change the heart rate. There are two separate
nerves from the cardiovascular centre to the sino-atrial node: the sympathetic nerve
(accelerator nerve) to speed up the heart rate and the parasympathetic nerve (vagus nerve)
to slow it down.
The cardiovascular centre can also change the stroke volume by controlling blood
pressure. It can increase the stroke volume by sending nerve impulses to the arterioles to
cause vasoconstriction, which increases blood pressure so more blood fills the heart at
diastole. Alternatively it can decrease the stroke volume by causing vasodilation and
reducing the blood pressure.
9.29 HOW DOES THE CARDIOVASCULAR CENTRE
RESPOND TO EXERCISE?
When the muscles are active they respire more quickly and cause several changes to the
blood, such as decreased oxygen concentration, increased carbon dioxide concentration,
decreased pH (since the carbon dioxide dissolves to form carbonic acid) and increased
temperature. All of these changes are detected by various receptor cells around the body,
but the pH changes are the most sensitive and therefore the most important. The main
chemoreceptors (receptor cells that can detect chemical changes) are found in:

The walls of the aorta (the aortic body), monitoring the blood as it leaves the
heart

The walls of the carotid arteries (the carotid bodies), monitoring the blood to
the head and brain

The medulla, monitoring the tissue fluid in the brain
The chemoreceptors send nerve impulses to the cardiovascular centre indicating that
more respiration is taking place, and the cardiovascular centre responds by increasing the
heart rate.
A similar job is performed by temperature receptors and stretch receptors in the muscles,
which also detect increased muscle activity.
Exercise affects the rest of the circulation as well as increasing cardiac output. When
there is an increase in exercise, the muscles respire faster, and therefore need a greater
oxygen supply. This can be achieved by increasing the amount of blood flowing through
the capillaries at the muscles. A large increase in blood flowing to one part of the body
must be met by a reduction in the amount of blood supplying other parts of the body,
such as the digestive system. Some organs need a stable blood supply (to supply enough
oxygen and glucose for respiration), to work efficiently what ever the body is doing. The
three main organs that require a constant blood supply are:

The heart needs a constant blood supply otherwise the heart muscle would starve
of oxygen and glucose, making it unable to pump more blood, and might cause a
heart attack.

The brain needs a constant blood supply otherwise the brain would reduce ability
to react to danger and might result in unconsciousness/death.

The kidneys need a constant blood supply otherwise there would be a build-up of
toxins in the blood.
9.32 REVISION QUESTIONS 1
1. State the main functions of the circulatory system.
2. Name the three major parts of the circulatory sytem.
3. Describe the difference between pulmonary circulation and the systemic ciculation.
4. Describe the main parts of the heart.
5. Describe how the two sides of the heart differ in terms of the kind of blood they
receive and pump, INCLUDE: Where does the blood come from? How does it enter the
heart? How does it exit the heart? Where does it go to?
6. Explain the difference between diastole and systole.
7. How is heart contraction rate controlled?
8. What are the components of Blood, and the function of each component?
9. Compare ateries, veins, and capillaries. In your answer, discuss the types of tissue in
them, function, and type of blood generally carried.
10. Describe the structure, operation, and function of the lymphatic system.
11. What are the Three Functions of Blood?
12. Identify the structure that prevents blood from mixing between the left and right sides
of the heart. Explain what prevents blood from flowing from the ventricles backward
into atria.
13. Identify the structure that controls the heartbeat, and describe the process by which it
regulates the heartbeat.
14. Identify the stages and structures involved in the clotting process.
9.33 REVISION QUESTIONS 2
Identify the choice that best completes the statement or answers the
question.
1. The ventricles are
a. the upper chambers of the heart.
b. the chambers of the heart that pump blood to the lungs and the rest of the body.
c. the chambers of the heart that receive blood from the lungs and the rest of the body.
d. lower chambers of the heart that contract separately.
2. Refer to the illustration above. Structure 4 is the
a. right atrium.
b. left atrium.
c. right ventricle.
d. left ventricle.
3. Refer to the illustration above. The aorta is structure
a. 2.
b. 3.
c. 5.
d. 6.
4. Refer to the illustration above. The vessels labeled “2” carry deoxygenated blood. The
vessels are
a. the pulmonary arteries.
c. parts of the aorta.
b. the pulmonary veins.
d. parts of the atria.
5. Refer to the illustration above. Blood in chamber 1
a. is full of oxygen.
c. has a low concentration of oxygen.
b. is going toward the lungs.
d. has very little plasma.
6. Vessels that carry blood away from the heart are called
a. veins.
b. capillaries.
c. arteries.
d. venules.
7. The heart chamber that receives blood from the venae cavae is the
a. left atrium.
b. right atrium.
c. left ventricle.
d. right ventricle.
8. Blood entering the right atrium
a. is full of oxygen.
b. is returning from the lungs.
c. is deoxygenated.
d. is low in plasma and platelets.
9. Oxygenated blood from the lungs is received by the
a. left ventricle.
b. right atrium.
c. left atrium.
d. right ventricle.
10. Which type of blood vessel is both strong and elastic?
a. capillary
b. artery
c. vein
d. venule
11. An artery has a much thicker muscle layer than
a. a vein.
b. a venule.
c. a capillary.
d. All of the above
12. The smallest and most numerous blood vessels in the body are the
a. venules.
b. veins.
c. arteries.
d. capillaries.
13. An artery
a. usually carries oxygen-rich blood.
b. has thin, slightly elastic walls.
c. has valves that prevent blood from flowing backward.
d. All of the above
14. If a blood vessel has valves, it is probably
a. a vein.
c. a venule.
b. an artery.
d. part of the lymphatic system.
CONTROL AND COORDINATION
Introduction
As the complexity of the individuals, plants or animals increases the different cells and
organs become separated from each other by greater distance. Thus it becomes necessary
to have a system by which the different parts of the organisms can function as a single
unit. This is possible only if the different parts can coordinate with each other and carry
out a particular function. To carry out a simple function such as picking up an object
from the ground there has to be coordination of the eyes, hands, legs and the vertebral
column. The eyes have to focus on the object, the hands have to pick it up and grasp it,
the legs have to bend and so does the back bone (vertebral column). All these actions
have to be coordinated in such a manner that they follow a particular sequence and the
action is completed. A similar mechanism is also needed for internal functions of the
body. At the same time, the internal conditions of the body should be maintained
constant. This is called homeostasis. Homeostasis is derived from 'homeo' meaning same
and 'stasis' meaning standing still. The internal conditions of the body are maintained at a
constant by controlling the physiology of the organism.
COORDINATION IN PLANTS
The higher plants do not show locomotion. However, locomotion is seen in structures
like sperm cells of ferns and mosses that swim towards the egg. The other movements
shown by the plants are associated with the growth of the plants. For example, the shoot
system moves towards sunlight and the root system towards earth. Thus, the plants also
respond to their environment.
The movement of plants in the direction of stimulus is known as 'tropism'. There are
mainly three types of tropism. They are:
Phototropism - Bending towards light
Geotropism - Downward movement in response to gravity
Chemotropism - Movement in response to chemical activity
One plant response to environmental stimulus involves plant parts moving toward or
away from the stimulus, a movement known as a tropism. Nastic movements are plant
movements independent of the direction of the stimulus. Apart from these, nastic
movement may also be observed in some plants. This is the movement of plant parts
caused by an external stimulus but unaffected in direction by it. Example: The leaves of
the 'touch -me - not' plant droop on touching.
GROWTH REGULATORS
The growth of the plants, their development and their responses to the environment are
controlled or coordinated with the help of chemicals. These chemicals are called the
growth regulators as they either promote or inhibit the growth of the plants.
Flowering and seed germination are regulated by the duration of light. This is known as
photoperiodism. Plants respond to photoperiodism by a specialized pigment called
phytochrome present in very small quantity. Growth in plants has three stages - cell
division, cell enlargement and cell differentiation. These stages are controlled by
different growth regulators.
Growth substances are also called the phytohormones. The phytohormones have been
put in five different categories based on their actions.
They are:

Auxins

Gibberellins

Cytokinins

Ethylene

abscissic acid
The regulators associated with cell enlargement and differentiation are: auxins and
gibberellins

The regulators associated with cell division: cytokinins

The regulators associated with ageing: ethylene

The regulators associated with dormancy of buds: abscissic acid
AUXINS
Auxins are phytohormones that are mainly concerned with cell enlargement. They affect
the plasticity of the cell walls and induce them to grow. The name 'auxin' was derived
from the Greek word 'auxein' meaning to increase.
FUNCTIONS

It causes elongation of stem (high concentration) and root (low concentration).

It promotes root initiation in cuttings and callus. (Callus is an undifferentiated
mass of cells from which the entire plant body can be grown by tissue culture
techniques.)

It also promotes root development.

It causes differentiation of xylem cells in calluses.

Apical dominance
All shoot tips end in an apical bud, the division of which results in the growth of the
stem. In the presence of apical buds, the lateral buds (present in the axils of leaves) do
not grow into branches. This is called apical dominance. If the apical bud is removed,
the lateral buds show growth. On application of IAA to the cut ends, the lateral buds
are again inhibited. So, auxins cause apical dominance.

Parthenocarpy
It is the development of fruits without fertilization and formation of seeds or embryo.
Therefore, the fruits are seedless. Auxins help in parthenocarpic development of fruits
like guava, papaya, banana, orange and tomato which are seedless.

Delay in Abscission
If the leaves and fruits stop producing auxin, they fall. Presence of auxins gives
them maximum time for fruits to ripen by maintaining them on the trees.
COMMERCIAL APPLICATIONS OF AUXINS
Many synthetic auxins have been developed because they are found useful in many ways.
These synthetic auxins are cheaper to develop than the natural auxins.
Some of the uses of synthetic auxins are given below:

Fruiting: Naphthalene acetic acid (NAA) and indolebutyric acid (IBA) help in
natural or parthenocarpic fruit setting that increases crop yield in tomato, pepper,
figs, etc.

Rooting: It is an important technique to reproduce genetically similar plants,
especially ornamental plants. The cuttings are dipped in rooting powders containing
NAA or IBA. This promotes root initiation and stimulates their development.

Weeding: 2,4-dichlorophenoxyacetic acid (2,4-D) and 2,3,6-trichlorobenzoic acid
(benzoic acid) are used to kill dicot weeds among the monocot (cereal) crops as the
latter are unaffected.

Storage: 2-methyl-4-chlorophenoxyacetic acid (MCPA) inhibits sprouting of buds
in potatoes and hence is used in their storage.
GIBBERELLINS
Gibberellins are plant hormones that are mainly responsible for cell elongation. They
cause the cells to grow in length. Chemically, they are a class of compounds called the
terpenes (related to lipids) and are weak acids.
FUNCTIONS OF GIBBERELLINS

Gibberellins cause stem elongation by affecting cell elongation. This can result in
stem elongation of dwarf varieties (peas and maize) and rosette plants (cabbage).
In the latter, it is called bolting.

Causes leaf expansion

Promotes fruit growth

Breaks bud dormancy

Breaks seed dormancy

Promotes flowering in long-day plants and inhibits the flowering in short-day
plants. (Long-day plants are those which require sunlight for a longer period
during the day.)
COMMERCIAL APPLICATIONS OF GIBBERELLINS

It is used along with auxins to induce parthenocarpy. For example, it is used to
develop seedless grapes.

It is used to increase fruit size and bunch length in grapes.

GA-3 (gibberellic acid), a gibberellin that has been most studied, is used in the
brewing industry. It causes the barley seeds to produce the starch-digesting
enzymes like maltase, amylase. This process is called the malting.
CYTOKININS
They are phytohormones that induce cell divisions even in mature tissues. They were
named 'cytokinins' as the cell division is also called cytokinesis (Cyto-cell, Kinesisbreaking). They belong to a group of compounds called the kinetins. Chemically, they are
similar to adenine, a nucleotide in DNA and RNA. Cytokinins are synthesized in the
fruits and seeds where rapid cell division takes place.
FUNCTIONS OF CYTOKININS

They promote cell division, in the presence of auxins

They delay the process of ageing (senescence) in leaves

They promote growth of lateral bud

They break bud and seed dormancy
COMMERCIAL APPLICATIONS OF CYTOKININS

They are used in tissue culture to induce cell division in mature tissues.

They also induce development of shoot and roots along with auxin, depending on
the ratio.

They are used to delay senescence in fresh leaf crops like cabbage and lettuce.

They are used to keep flowers fresh.
ETHYLENE
Ethylene is a gaseous growth regulator that speeds up the ripening process. It is a gas
produced by most of the plant organs. Chemically, ethylene (ethene) is an unsaturated
hydrocarbon.
FUNCTIONS OF ETHYLENE

It promotes ripening of fruit.

It sometimes promotes flowering.

It inhibits stem growth.

It promotes abscission of fruits and leaves.
COMMERCIAL APPLICATIONS OF ETHYLENE

It is used to stimulate ripening of fruits. For example, tomatoes and citrus fruits.

It is applied to rubber trees to stimulate flow of latex.
ABSCISSIC ACID (ABA)
It is a growth inhibitor that results in dormancy and abscission. They are all now
commonly called as abscissic acid. It is synthesized in stem, leaves, fruits and seeds.
FUNCTIONS OF ABSCISSIC ACID

It is a growth inhibitor, causing bud and seed dormancy.

It results in abscission of leaves and fruits.

It is produced during stress.
For example: During drought, it causes growth suppression that conserves energy. It also
controls water loss during dry conditions by causing closure of stomata.
COMMERCIAL APPLICATIONS OF ABSCISSIC ACID

It is used as a spray on trees to regulate dropping of fruits.
CONTROL AND COORDINATION IN ANIMALS
Animals are different from plants because of their ability of locomotion. This ability
probably developed as they have to search for food, unlike the plants that are autotrophic.
Since they move from one place to another, the animals have to continuously encounter
changes in their environment. In order to maintain a steady state within the body
(homeostasis), all animals should be able to perceive these changes and adapt to them.
With increasing complexity in their structure, the number and types of cells in the animal
body increased. Thus it became necessary to have some coordinating mechanism. Two
systems have been developed for better control and coordination of the various activities
of the organisms. These systems are the nervous system and the endocrine system.
The nervous system is made up of units called the neurons which relay information by
generating electric potential. The endocrine system, on the other hand, is made up of
glands that secrete chemicals called the hormones. They are secreted into blood that
carries them to the sites of action.
THE HUMAN NERVOUS SYSTEM
The human nervous system controls everything from breathing and producing digestive
enzymes, to memory and intelligence.
The nervous system carries out the following functions:

It perceives the changes around us through our senses.

It controls and coordinates all the activities of the muscles in response to the
changes outside.

It also maintains the internal environment of the body by coordinating the
functions of the various internal organs and the involuntary muscles.

It stores the previous experiences as memory that helps us to think and analyse
our reactions.

It conducts messages between different parts of the body.
UNITS OF NERVOUS SYSTEM
The units of nervous system are specialised cells called the neurons. The general
structure of a neuron is as follows:
Neuron
A neurone has a cell body with extensions leading off it. Numerous dendrons and
dendrites provide a large surface area for connecting with other neurones, and carry
nerve impulses towards the cell body. The messages from the cyton are carried away by
the long axon which ends in many fine branches. The branches end in synaptic knobs.
Within the axon branches are synaptic vesicles that release chemicals like adrenaline and
acetylcholine into the space outside the synaptic knobs.
Types of Neurons
Based on their structure and function, the neurons are classified into three:
Sensory Neurons
The neurons that conduct impulses from the receptors or sense organs to the central
nervous system are called the sensory neurons.
Motor Neurons
The neurons that conduct impulses from the central nervous system to the effectors
(muscles or glands) are called the motor neurons.
Motor Neurons
The neurons that conduct impulses from the central nervous system to the effectors
(muscles or glands) are called the motor neurons.
Nerve Fibres and Nerves
The long axons of neurons along with the associated structures are called the nerve
fibres. The fibres may be enclosed within sheaths called as myelin sheath. However, the
action potential is not generated in the areas where there is a sheath over the fibre. Along
the fibres there are regions where the myelin sheath is absent. These regions are called
the nodes of Ranvier. The action potential jumps from one node to the other.
Many nerve fibres are bunched together to form a nerve. The bundles of fibres are
enclosed within connective tissue called the epineurium.
Transmission of Messages
The messages are transmitted in the form of electrical impulses along the fibres of the
neurons.
Neurotransmitters
 Acetylcholine (Ach)
- released by all motor neurones, activating skeletal muscles
- involved in the parasympathetic nervous system (relaxing responses)
- cholinergic synapses
 Noradrenaline
This is another transmitter substance which may be in some synapses instead of
acetylcholine, e.g. some human brain synapses and sympathetic nervous system
synapses. Synapses result in an appreciable delay, up to one millisecond. Therefore
slows down the transmission in nervous system.
Impulse
The impulse is received by the dendrites and passed through the cell body to the axon. An
impulse is an electrical disturbance.
All along the nerve fibre, the cytoplasm is more electronegative than the outside and is
thus having a potential. This is due to the differential distribution of sodium and
potassium ions across the membrane. This potential is called the resting potential.
When the dendrite receives the neurotransmitters, they change the properties of the cell
membrane which in turn changes the distribution of the ions across the membrane.
This results in a different potential called the action potential. The change in potential is
then transmitted along the neuron to the ends of the axon. Here, the impulse induces the
release of the neurotransmitter. In this manner, the message is transmitted as a wave of
impulse along the lengths of connecting neurons.
Synapse
The junction between the axon and the dendrites of the next neuron is called the synapse.
At the synapse, the axon fibres and dendrites are not in direct contact. The space between
them is called synaptic cleft. Within the axons are synaptic vesicles having chemicals
called nuerotransmitters. The impulses that reach the ends of the axon fibres make the
vesicles release these chemicals into the synaptic cleft. The chemicals reach the dendrites
of the next neuron. This sets up a new impulse which is transmitted to the axon. The
speed of transmission is about 120 m/s.
The synapse consists of:

a presynaptic ending that contains neurotransmitters, mitochondria and other cell
organelles,

a postsynaptic ending that contains receptor sites for neurotransmitters and,

a synaptic cleft or space between the presynaptic and postsynaptic endings. It is
about 20nm wide.
An action potential cannot cross the synaptic cleft between neurones. Instead the nerve
impulse is carried by chemicals called neurotransmitters. These chemicals are made by
the cell that is sending the impulse (the pre-synaptic neurone) and stored in synaptic
vesicles at the end of the axon. The cell that is receiving the nerve impulse (the post-
synaptic neurone) has chemical-gated ion channels in its membrane, called
neuroreceptors. These have specific binding sites for the neurotransmitters.
1. At the end of the pre-synaptic neurone there are voltage-gated calcium channels.
When an action potential reaches the synapse these channels open, causing calcium
ions to flow into the cell.
2. These calcium ions cause the synaptic vesicles to fuse with the cell membrane,
releasing their contents (the neurotransmitter chemicals) by exocytosis.
3. The neurotransmitters diffuse across the synaptic cleft.
4. The neurotransmitter binds to the neuroreceptors in the post-synaptic membrane,
causing the channels to open. In the example shown these are sodium channels, so
sodium ions flow in.
5. This causes a depolarisation of the post-synaptic cell membrane, which may initiate an
action potential, if the threshold is reached.
6. The neurotransmitter is broken down by a specific enzyme in the synaptic cleft; for
example the enzyme acetyl cholinesterase breaks down the neurotransmitter
acetylcholine. The breakdown products are absorbed by the pre-synaptic neurone by
endocytosis and used to re-synthesise more neurotransmitter, using energy from the
mitochondria. This stops the synapse being permanently on.
Different types of synapses
 Excitatory ion channel synapses - neuroreceptors are Na+ channels. When Na+
channels open, local depolarisaition occurs, if threshold is reached then action
potential is initated
 Inhibitory ion channels - neuroreceptors are Cl- channels. When Cl- channels
open, hyperpolarisation occurs, making action potential less likely
 Non channel synapses - neuroreceptors are membrane-bound enzymes. When
activated, they catalyse the 'messenger chemical', which in turn can affect the
sensitivity of the ion channel receptors in the cell.
 Neuromuscular junctions - synapses formed between motor neurones and
muscle cells. Always use the neurotransmitter acetylchline, and are always
excitatory.
 Electrical synapses - the membranes of the two cells actually touch and they
chare proteins. The action potential can pass directly from one membrane to the
next when one postsynaptic neuron is excited/inhibited by more than one
presynaptic neuron. Thus several neurons converge and release their
neurotransmitters towards one neuron.
Receptors
Receptors are structures at the ends of the nerve fibres that collect the information to be
conducted by the nerves. These receptors may be specialised sense organs like the
Meissner's corpuscles of the skin, specialised nerve endings like the Pacinian corpuscles
of skin or the specialised organs, the sense organs.
Effectors
Effectors are muscles or glands which work in response to the stimulus received from the
motor nerves.
Parts of the Nervous System - Central Nervous System
The human nervous system can be divided into three main parts:

Central nervous system

Peripheral nervous system

Autonomic nervous system
Central Nervous System
It is made up of the brain and the spinal cord which is the continuation of the brain. Brain
and spinal cord are surrounded by membranes called the meninges. There are three layers
- outermost dura mater, middle arachnoid and the inner pia mater. The space between the
arachnoid and pia mater is filled with the cerebrospinal fluid (CSF). It acts as a shock
absorber. An infection of the meninges is called meningitis.
BRAIN
It is the part of the central nervous system that is present in the head and protected by the
skull, dorsally and laterally. The box that houses the brain within the skull is called the
cranium. It has three main regions - the fore brain, the mid brain and the hind brain. The
three regions have different parts that have specific functions.
The Human Brain
Fore Brain
It is made up of cerebrum, hypothalamus and thalamus.
Cerebrum
It is the largest part of the brain and is made up of two hemispheres called the cerebral
hemispheres. The two hemispheres are joined together by a thick band of fibres called the
corpus callosum. The cerebrum is made up of four distinct lobes - frontal, parietal,
temporal and occipetal. The outer portion of the cerebrum is called the cortex and the
inner part is called the medulla. The cortex consists of the cells of the neurons and
appears grey in colour. It is also called the grey matter. The medulla consists of the
fibres of the neurons and is white. The cortex is highly convoluted which increase the
surface area. It is believed that higher the number of convolutions, higher is the
intelligence. The cerebrum has sensory areas, association areas and motor areas.
The sensory areas receive the messages, the association areas associate this information
with the previous and other sensory informations and the motor areas are responsible of
the action of the voluntary muscles. Cerebrum is responsible for the intelligence,
thinking, memory, consciousness and will power. There are also other important
functions associated with the cerebrum.
Thalamus
It is an area which coordinates the sensory impulses from the various sense organs - eyes,
ears and skin and then relays it to the cerebrum.
Hypothalamus
Hypothalamus, though a small region situated below the thalamus, is an important region
of the brain. It receives the taste and smell impulses, coordinates messages from the
autonomous nervous system, controls the heart rate, blood pressure, body temperature
and peristalsis. It also forms an axis with the pituitary which is the main link between the
nervous and the endocrine systems. It also has centres that control mood and emotions.
Mid Brain
It is a small portion of the brain that serves as a relay centre for sensory information from
the ears to the cerebrum. It also controls the reflex movements of the head, neck and eye
muscles. It provides a passage for the different neurons going in and coming out of the
cerebrum.
Hind Brain
It consists of cerebellum, pons and medulla oblongata.
Cerebellum
Cerebellum is like cerebrum. It consists of outer grey cortex and inner white medulla. It
is responsible for maintaining the balance while walking, swimming, riding, etc. It is also
responsible for precision and fine control of the voluntary movements. For example, we
can do actions like eating while talking or listening. One has to concentrate for talking
sensibly. However the action of eating, while talking is done automatically. This is
controlled by the cerebellum.
Pons
Pons literally means bridge. It serves as a relay station between the lower cerebellum and
spinal cord and higher parts of the brain like the cerebrum and mid brain.
Medulla Oblongata
It is a small region of the brain. It is hidden as it is well protected because of its
importance. It has the cardiovascular centre and the breathing centre. It also controls
activites such as sneezing, coughing, swallowing, salivation and vomiting.
Spinal Cord
It is a collection of nervous tissue running along the back bone. It is, in fact, protected
by the vertebral column. It is a continuation of the brain. It consists of a central canal that
has cerebrospinal fluid that is continuous with the fluid in the brain. The canal is
surrounded by an H-shaped grey area that is made up of nerve cells, dendrites and
synapses. Outer to this is the white area that is made up of the axons. This arrangement is
reverse of what is seen in the brain - outer grey and inner white portions. The four ends of
the H-shape appear like horns extending into the white matter. The upper (dorsal) horn
contains the sensory or afferent neurons entering the grey matter and the lower (ventral)
horn contains the motor or efferent neurons leaving the grey matter.
The white matter consists of ascending and descending tracts of neurons connecting the
different parts of the body with the brain.
The functions of the spinal cord are:
 Coordinating simple spinal reflexes
 Coordinating autonomic reflexes like the contraction of the bladder
 Conducting messages from muscles and skin to the brain
 Conducting messages from brain to the trunk and limbs
PERIPHERAL NERVOUS SYSTEM
The peripheral nervous system is made up of nerves that connect the different parts of the
body (peripheral tissues) to the central nervous system.
As mentioned earlier, there are three types of nerves based on their composition:
 sensory (afferent)
 motor (efferent)
 mixed
Cranial Nerves
Cranial nerves are those that connect the different parts of the body to the brain. There
are 12 pairs of cranial nerves. Cranial nerves may be sensory, motor or mixed.
For example:
 1st and 2nd pairs of cranial nerves are Olfactory (pertaining to smell) and Optic
(pertaining to sight) respectively. They are both sensory in nature.
 The 4th pair is trochlear nerves that are motor and help in the movement of the
eyeball muscle.
 The 7th pair of nerves is the facial nerves that control the taste buds, salivary
glands, facial and neck muscles. These nerves are mixed nerves.
Spinal Nerves
There are 31 pairs of spinal nerves. The spinal nerves are all mixed having both sensory
and motor fibres. The sensory fibres and motor fibres separate just before entering the
spinal cord into dorsal root and ventral root.
The Dorsal Root
The dorsal root is made up of the following:
Dorsal Root Ganglion
It is a collection of the sensory nerve cell bodies. (Ganglia are centres of collection of
nerve cell bodies).
Sensory or Afferent Nerve Fibres
Sensory or afferent nerve fibres conduct messages from the peripheral tissues to the
spinal cord. They finally join the grey matter of the spinal cord. They produce the
sensation of touch, pain or reflex actions (involuntary movements).
The Ventral Root
The ventral root contains only the motor nerve fibres that conduct messages from the
spinal cord to the peripheral tissues. The nerve cell bodies of the motor nerves are in the
grey matter of the spinal cord.
Autonomic Nervous System
It is also called the visceral nervous system as it controls the functioning of the visceral
(internal) organs.
Autonomic Nervous System
The autonomic nervous system (ANS) consists of two sets of motor neurons and a
collection of ganglia. The two sets of neurons are:
Pre-ganglionic Nerve Fibres
They are neurons that emerge from the CNS and enter the ganglions. Their nerve cells are
in the CNS.
Post-ganglionic Nerve Fibres
They are the neurons that leave the ganglions and reach the smooth muscle/ gland. Their
nerve cells are in the ganglions. The preganglionic nerve synapses with the dendrites of
the post ganglionic nerve in the ganglions.
The ANS consists of two divisions:
 Sympathetic Nervous System
It has the following features:
1. It is entirely made up of spinal nerves of the chest (thoracic) and waist
(lumbar) region.
2. It has ganglia close to the spinal cord.
3. The ganglia are linked to each other.
4. The pre-ganglionic nerve fibre is shorter than the post-ganglionic nerve
fibre.
5. Generally it has an accelerating effect which prepares the body for action
in emergencies
6. Its functions include
-
dilation of pupils
-
increase rate and force of heart beat
-
increase in secretion of sweat
-
decreases urine output
-
releases adrenaline at the effector (gland or muscle)
-
inhibition of peristalsis
-
dilation of blood vessels to brain and skeletal muscle
Parasympathetic Nervous System
It has the following features:
 It is made up of four pairs of cranial nerves and three pairs of sacral nerves.
 The ganglia are far away from the spinal cord and close to the effectors.
 The ganglia are not linked to each other.
 The pre-ganglionic nerve fibre is longer than the post-ganglionic nerve fibre.
 Generally it has a slowing-down effect which balances the effect of the
sympathetic system
 Its functions include
-
constriction of pupils
-
decrease rate and force of heart beat
-
decrease in secretion of sweat
-
increases urine output
-
releases acetylcholine at the effector (gland or muscle)
-
stimulation of peristalsis
-
constriction of blood vessels to brain and skeletal muscle
REFLEX ACTION
When the stimulation of a receptor results in a spontaneous, involuntary reaction, it is
called reflex action or simply reflex.
Reflexes are of two types:
 SIMPLE OR UNCONDITIONED OR NATURAL REFLEX
In this type of reflex, the brain is not involved. The receptor is stimulated which is
conducted to the spinal cord by the effector. The effector neuron from the spinal cord
conducts a response to the muscle or the gland. This causes an immediate reaction. It
does not involve any thinking or reasoning. It is a natural response and will occur even in
new-born babies. For example, blinking of eyes when strong light falls on the eyes.
Types of Simple Reflex
Simple reflex is also of two types. They are as follows:
1. In the first type, only the sensory and motor neurons of the spinal nerves are
involved.
2. The moving away of hand in response to pin-prick or heat is an example of this
type.
Figure : The Pathway for a Reflex Action - the Reflex Arc
In the above diagram, it can be seen that the pathway of conduction is in the form of an
arc. Thus, these pathway is also called the reflex arc
 COMPLEX OR CONDITIONED REFLEX
This type of reflex involves the brain but it is also as fast as the simple reflex.
Salivation on smelling one's favourite food is an example of conditional reflex. The
individual recognises the smell and based on a previous experience, the response
(salivation) occurs. The recognition of the previous experience involves the association
centres of the brain.
A series of experiments were conducted by Ivan Pavlov, a Russian biologist which
demonstrated conditioned reflex. He found that when a bell was rung every time a dog
was given food, the dog showed salivation only at the sound of the bell. The ringing of
the bell is called the conditioned stimulus. The dog had, thus, 'learnt' to associate the
sound of the bell to food and this made it salivate at the sound of the bell.
Figure : A Conditioned Reflex Arc
ENDOCRINE SYSTEM - HORMONAL CONTROL
Glands are of two types:
 Exocrine glands: - are those which pour their secretions into a duct. For example,
sweat glands, tear glands, etc.
 Endocrine glands: - are those which are richly supplied with blood vessels and
pour their secretions directly into the blood vessels. The secretions reach their
target through blood. These glands are called the ductless glands as they do not
have ducts. For example, thyroid, adrenal, etc.
The control and coordination of the different bodily functions is also done with the help
of the endocrine system. This system exerts chemical control over the activities. These
chemicals are secreted from organs called endocrine glands.
The secretions of the endocrine glands are called hormones. Hormones have the
following characteristics:
 They may be proteinaceous or non-proteinaceous (amino acids or steroids).
 They are secreted as per need and not stored, only excreted.
 Their secretion may be regulated by nerves or by feedback effect.
 They are transported by blood.
 They mostly cause long-term effects like growth, change in behaviour, etc.
 They do not catalyse any reactions.
 They function by stimulating or inhibiting the target organs.
Hormones can be defined as secretions that are poured into blood in order to reach a
specifc target organ. The human endocrine system consists of the following glands:
Hypothalamus, Pineal, Thyroid, Parathyroid, Pituitary, Thymus, Adrenal, Pancreas,
Ovary in female, Testes in male.
HOW HORMONES WORK
1. A hormone does not seek out a particular organ; to the contrary, the organ is awaiting
the arrival of the hormone.
2. Cells that can react to a hormone have specific receptor proteins on their plasma
membrane or in their cytoplasm that combine with the hormone in a "lock-and-key"
manner. The specific shape of the hormone must match the specific shape of the receptor
protein.
3. Receptors are proteins that are located both inside the cytoplasm and on the surface of
a target cell.
4. Therefore, certain cells respond to one hormone and not another, depending on their
receptor proteins.
5. Hormones are chemical messengers that influence the metabolism of the recipient cell.
6. Fitting the hormone molecule into the receptor changes the receptor's shape, which
causes the cell's activities to change.
7. The main effect of a hormone on a cell is to change the activity or amounts of enzymes
(speed up chemical reactions) present in that cell.
PITUITARY GLAND
Pituitary gland has the following features:
 It is a pea shaped gland that is located below the hypothalamus in the brain.
 It is under the control of the hypothalamus and in turn controls many functions in
the body.
 It is made up of three lobes - anterior, middle and posterior. They secrete
hormones in response to the secretion of neurohormones by the hypothalamus.
Hormones Produced by Pituitary
Anterior Lobe
Anterior lobe of the pituitary produces six hormones:
1. Thyroid stimulating hormone (TSH) which stimulates thyroid gland to produce
thyroxine.
2. Growth Hormone (GH) stimulates overall growth of the body. Its deficiency
causes dwarfism and over-production causes gigantism.
3. Adrenocorticotrophic hormone (ACTH) stimulates the adrenal cortex to produce
corticosteroids that defend the body.
4. Follicle stimulating hormone (FSH) stimulates testes to produce sperms and ovary
to produce hormone oestrogen and ova (eggs).
5. Luteinizing hormone (LH) stimulates testes to produce male hormone testosterone
and in female, stimulates corpus luteum production which forms progesterone, a
female hormone.
6. Prolactin maintains the pregnancy and stimulates the secretion of milk.
POSTERIOR LOBE
Posterior lobe secretes two hormones:
1. Vasopressin or antidiuretic hormone (ADH) helps in maintaining blood pressure
and preventing the kidneys from excreting very dilute urine. Lack of this hormone
causes diabetes insipidus where glucose in urine does not show because the urine
is very dilute.
2. Oxytocin helps in contraction of uterus during delivery.
PINEAL, THYROID AND PARATHYROID GLANDS
Pineal
 It is a small round gland in the brain.
 It secretes melatonin that regulates the sexual cycle.
THYROID
It is a butterfly-shaped, bilobed gland that is situated at the base of the larynx. The two
lobes are joined by an isthmus. The hormone secreted is thyroxine.
Functions of Thyroxine
 Thermoregulation - it regulates the production of body heat by regulating
respiration
 regulates metabolic rate
 regulates mental and physical development
 helps in absorption of glucose from intestine
Result of Undersecretion of Thyroxine
 Simple goitre in which there is enlargement of thyroid due to lack of iodine
 Cretinism which is dwarfism and mental retardation due to imperfect
development of thyroid
 Myxoedema in which the thyroid does not function properly and the person
becomes sluggish with swollen face and hands
RESULT OF OVERSECRETION OF THYROXINE
Oversecretion results in exophthalmic goitre in which the person shows a marked
increase in metabolic rate, protrusion of eyes, rapid heart rate and shortness of breath.
Parathyroid
They are present as two pairs at the back of the thyroid. They secrete parathormone
which is important in calcium and phosphorus metabolism
 Deficiency of parathormone causes brittle bones.
 Oversecretion of parathormone softens the teeth and bones.
THYMUS AND PANCREAS
Thymus
 It is a gland that is prominent behind the breastbone in children.
 It gradually decreases in size in adults.
 It secretes hormone called thymosin. Thymosin helps in the production of
lymphocytes.
PANCREAS
 It is a narrow gland present at the junction of stomach and duodenum.
 It is both an exocrine and an endocrine gland. The exocrine part secretes digestive
juices which it pours into a duct. The endocrine portion (also called the islets of
Langerhans) has three types of cells:
-
alpha
-
beta
-
delta
-
The alpha cells produce glucagon that increases the conversion of
glycogen into glucose, increasing the level of glucose in blood.
-
The beta cells produce insulin that increase the conversion of glucose into
glycogen, decreasing the level of glucose in blood. Undersecretion of
insulin causes diabetes mellitus, high blood sugar.
-
The delta cells secrete somatostatin that inhibits the secretion of insulin
and glucagons
ADRENAL AND GONADS
Adrenal
The adrenal glands are present on top of the kidneys and appear cap-like on top of each
kidney. Each adrenal gland has two layers - outer cortex and inner medulla.
The adrenal cortex secretes hormones like the glucosteroids, mineralocorticoids and
cortisones. Glucosteroids increase the blood sugar level in times of stress by converting
protein into glucose. Mineralocorticoids control the excretion of sodium and potassium.
Some of the cortical cells also secrete sex hormones that can cause premature sexual
maturity, feminine traits in male and masculine traits in female.
The adrenal medulla secretes two hormones:
 Adrenaline
 Noradrenaline
Of the above adrenaline is an important hormone as it causes 'fight or flight response'.
This means that it prepares the body to react in emergency situations by various means
like selective dilation and constriction of blood vessels, increase in glucose levels (for
more energy), raising blood pressure, etc.
Gonads
Gonads are the reproductive organs. The male gonads are the testes and the female
gonads are the ovaries. Both produce hormones under the influence of hormones of the
pituitary (see under pituitary gland). Testes produce testosterone which produces the
secondary sexual characteristics like moustache and beard. Ovaries along with the eggproduction, secrete oestrogen from the mature follicle that produces the secondary sexual
characteristics like enlargement of breasts. It also prepares for the monthly menstruation.
After ovulation, another hormone, progesterone is produced from corpus luteum that
maintains the pregnancy.
FEEDBACK MECHANISM
It is a method of controlling the hormone production. In some cases the production of
hormones is controlled by the nervous system. In other cases, the hormone itself acts as a
control. For example: Pituitary secretes TSH that stimulates the thyroid to secrete
thyroxine. When the level of thyroxine increases, it makes the pituitary stop the
production of TSH. This in turn stops the production of thyroxine. Thus, its production is
controlled. This is called the feedback mechanism.
NEGATIVE FEEDBACK MECHANISMS -REGULATING HORMONE
RELEASE
1. Because the body produces more than 30 hormones, it must be able to regulate the
release of these hormones.
2. Negative feedback mechanisms in the body involve interactions of the nervous,
endocrine, and circulatory systems.
3. In negative feedback, the final step in a series of events inhibits the initial signal in the
series.
4. The hypothalamus, the anterior pituitary, and the other endocrine controlled by the
anterior pituitary are all involved in a self-regulating negative feedback mechanism.
5. Negative feedback is a process by which a change in an environment causes a
response that returns conditions to their original state. (figure 50-10)
POSITIVE FEEDBACK
Release of an Initial Hormone Stimulates Release or Production of other Hormones or
Substances, which STIMULATES Further Release of the Initial Hormone.
THE EYE
Figure 232: The structure of human eye.
PARTS OF THE EYE:
Is a thin protective covering of epithelial cells. It protects the cornea
Conjunctiva against damage by friction (tears from the tear glands help this process by
lubricating the surface of the conjunctiva)
Cornea
Is the transparent, curved front of the eye which helps to converge the light
rays which enter the eye
Is an opaque, fibrous, protective outer structure. It is soft connective
Sclera
tissue, and the spherical shape of the eye is maintained by the pressure of
the liquid inside. It provides attachment surfaces for eye muscles
Has a network of blood vessels to supply nutrients to the cells and remove
Choroid
waste products. It is pigmented that makes the retina appear black, thus
preventing reflection of light within the eyeball.
Has suspensory ligaments that hold the lens in place. It secretes the
Ciliary
aqueous humour, and contains ciliary muscles that enable the lens to
body
change shape, during accommodation (focusing on near and distant
objects)
Is a pigmented muscular structure consisting of an inner ring of circular
muscle and an outer layer of radial muscle. Its function is to help control
Iris
the amount of light entering the eye so that:
- too much light does not enter the eye which would damage the
retina
- enough light enters to allow a person to see
Pupil
Lens
Is a hole in the middle of the iris where light is allowed to continue its
passage. In bright light it is constricted and in dim light it is dilated
Is a transparent, flexible, curved structure. Its function is to focus
incoming light rays onto the retina using its refractive properties
Is a layer of sensory neurones, the key structures being photoreceptors (rod
Retina
and cone cells) which respond to light. Contains relay neurones and
sensory neurones that pass impulses along the optic nerve to the part of the
brain that controls vision
Fovea
(yellow
spot)
A part of the retina that is directly opposite the pupil and contains only
cone cells. It is responsible for good visual acuity (good resolution)
Blind spot
Vitreous
humour
Aqueous
humour
Is where the bundle of sensory fibres form the optic nerve; it contains no
light-sensitive receptors
Is a transparent, jelly-like mass located behind the lens. It acts as a
‘suspension’ for the lens so that the delicate lens is not damaged. It helps
to maintain the shape of the posterior chamber of the eyeball
Helps to maintain the shape of the anterior chamber of the eyeball
Visual Transduction
Visual transduction is the process by which light initiates a nerve impulse. The structure
of a rod cell is:
Figure 236: The structure of a rod cell.
The detection of light is carried out on the membrane disks in the outer segment. These
disks contain thousands of molecules of rhodopsin, the photoreceptor molecule.
Rhodopsin consists of a membrane-bound protein called opsin and a covalently-bound
prosthetic group called retinal. Retinal is made from vitamin A, and a dietary deficiency
in this vitamin causes night-blindness (poor vision in dim light). Retinal is the lightsensitive part, and it can exists in 2 forms: a cis form and a trans form:
In the dark retinal is in the cis form, but when it absorbs a photon of light it quickly
switches to the trans form. This changes its shape and therefore the shape of the opsin
protein as well. This process is called bleaching. The reverse reaction (trans to cis
retinal) requires an enzyme reaction and is very slow, taking a few minutes. This explains
why you are initially blind when you walk from sunlight to a dark room: in the light
almost all your retinal was in the trans form, and it takes some time to form enough cis
retinal to respond to the light indoors. The final result of the bleaching of the rhodopsin
in a rod cell is a nerve impulse through a sensory neurone in the optic nerve to the brain.
However the details of the process are complicated and unexpected. Rod cell membranes
contain a special sodium channel that is controlled by rhodopsin. Rhodopsin with cis
retinal opens it and rhodopsin with trans retinal closes it. This means in the dark the
channel is open, allowing sodium ions to flow in and causing the rod cell to be
depolarised. This in turn means that rod cells release neurotransmitter in the dark.
However the synapse with the bipolar cell is an inhibitory synapse, so the
neurotransmitter stops the bipolar cell making a nerve impulse. In the light everything is
reversed, and the bipolar cell is depolarised and forms a nerve impulse, which is passed
to the ganglion cell and to the brain
Figure 237: The structure of rod in light and cones in darkness.
17.13
Rods and Cones
Rods
Outer segment is rod shaped
Cones
Outer segment is cone shaped
106 cells per eye, found mainly in the fovea,
109 cells per eye, distributed throughout the
so can only detect images in centre of
retina, so used for peripheral vision.
retina.
Good sensitivity – can detect a single
Poor sensitivity – need bright light, so only
photon of light, so are used for night vision. work in the day.
Only 1 type, so only monochromatic vision.
3 types (red green and blue), so are
responsible for colour vision.
Many rods usually connected to one bipolar Each cone usually connected to one bipolar
cell, so poor acuity (i.e. rods are not good cell, so good acuity (i.e. cones are used for
at resolving fine detail).
resolving fine detail such as reading).
17.14
Accommodation
Accommodation refers to the ability of the eye to alter its focus so that clear images of
both close and distant objects can be formed on the retina. Cameras do this by altering the
distance between the lens and film, but eyes do it by altering the shape and therefore the
focal length of the lens. Remember that most of the focusing is actually done by the
cornea and the job of the lens to mainly to adjust the focus. The shape of the lens is
controlled by the suspensory ligaments and the ciliary muscles.

Light rays from a distant object are almost parallel so do not need much
refraction to focus onto the retina. The lens therefore needs to be thin and “weak”
(i.e. have a long focal length). To do this the ciliary muscles relax, making a
wider ring and allowing the suspensory ligaments (which are under tension from
the pressure of the vitreous humour) to pull the lens out, making it thinner.
Figure 238: Focusing of light rays from distant object by an eye.

Light rays from close objects are likely to be diverging, so need more
refraction to focus them onto the retina. The lens therefore needs to be thick and
“strong” (i.e. have a short focal length). To do this the ciliary muscles contract,
making a smaller ring and taking the tension off the suspensory ligaments, which
allows the lens to revert to its smaller, fatter shape.
Figure 239: Focusing of light rays from near object by an eye
The suspensory ligaments are purely passive, but the ciliary muscles are innervated with
motor neurones from the autonomic nervous system, and accommodation is controlled
automatically by the brain.
THE IRIS
The retina is extremely sensitive to light, and can be damaged by too much light. The iris
constantly regulates the amount of light entering the eye so that there is enough light to
stimulate the cones, but not enough to damage them. The iris is composed of two sets of
muscles: circular and radial, which have opposite effects (i.e. they’re antagonistic). By
contracting and relaxing these muscles the pupil can be constricted and dilated:
Figure 50: The control of light entering the eye by the iris.
The iris is under the control of the autonomic nervous system and is innervated by two
nerves: one from the sympathetic system and one from the parasympathetic system.
Impulses from the sympathetic nerve cause pupil dilation and impulses from the
parasympathetic nerve causes pupil constriction. The drug atropine inhibits the
parasympathetic nerve, causing the pupil to dilate. This is useful in eye operations.
The iris is a good example of a reflex arc.
THE SKIN
Figure 241: The structure of human skin.
Functions of The Skin



Protects against
o
infection
o
'wear and tear' of daily use
o
water loss
o
rain and water in the environment
o
damage from ultraviolet rays
o
heat loss
Regulates Body Temperature by
o
insulation against heat loss
o
cooling when the body is too hot
Senses
o
touch
o
pressure

o
heat
o
cold
o
pain
Excretes
o

small amounts of body waste (urea) in sweat
Produces
o
oils and sebum to condition skin and hair
o
melanin to block harmful UV rays
o
keratin to harden outer layer of skin
o
vitamin D to prevent rickets and strengthen bones
o
hair, fingernails and toenails
Skin Layers

Epidermis ('outer skin') made up of 2 layers:
o
Stratum Corneum

means 'hornlike layer'

made up of tough, dead cells, resembling shingles on a roof

made tough and waterproof by being rich in the protein keratin

constantly flaking off and rubbing away

mainly responsible for waterproofing, protection against
infection, and resistance against wear and tear
o
Stratum Germinativum

produces new skin cells to replace worn away stratum corneum

constantly growing:
1. cells divide into 2 newer cells
2. older cells are pushed upward
3. become filled with keratin
4. flatten out
5. die and become part of the stratum corneum

produces melanin, a brown pigment, which helps block
ultraviolet light from reaching and damaging lower layers of the
skin


produces hairs (from hair follicle) and nails
Dermis
o
contains

hair roots

skin glands

environmental sensors for touch, pressure, heat, cold, pain

blood vessels, especially capillaries

connective tissue to hold it all together

arrector muscles to make hairs stand on end (and cause
goosebumps)
Skin Glands

Sweat Glands (called in advanced textbooks 'eccrine glands')
o
resemble coiled and twisted tubes in the dermis
o
open at pores on the surface of the skin
o
especially common on palms of hands, soles of feet, and on the scalp
o
produce sweat to cool skin by evaporation
o
sweat contains dilute salt water and some dissolved body wastes
o
some specialized sweat glands (called in advanced textbooks 'apocrine
glands') produce secretions with characteristic odours in armpits and
elsewhere

Sebaceous Glands
o
sometimes called oil glands
o
found in the dermis at the bases of hairs
o
release secretions onto the skin between the hair and the hair follicle
o
compact, lumpy in shape
o
produce sebum, a secretion rich in oils
o
the function of sebum is to condition, lubricate, and waterproof the skin
and hair
o
when plugged, they may develop into pimples
Skin Sense Receptors

Touch Receptors found in 2 forms:
o
sensory nerve endings wrapped around the bases of hairs

o
o




very sensitive to extremely light touch
touch sensory corpuscles

shown as containing a zig-zag line, weaving back and forth inside

sensitive to skin contact
triggering of many touch receptors in sequence may cause a 'tickle'
Pressure Receptors
o
shown as having concentric rings like a slice of an onion
o
respond to pressure on skin
o
can tell how tightly an object is being held
Heat Receptors
o
shown as having an irregular or leaf-like shape
o
respond to warmth
Cold Receptors
o
small, simple corpuscles, may have a dot or loose nerve endings inside
o
may occur in clusters, like buds on a branching twig
o
respond to cooling
Pain Receptors
o
simple, branching nerve endings, without corpuscles
o
respond to skin damage by sending pain signals
o
if stimulated by chemicals, may give an itching sensation
Other Structures

Arrector Muscles (called in advanced textbooks 'arrector pili')
o
connect base of hair with bottom of stratum germinativum
o
when they contract,

they make the hair stand erect, thickening the fur of animals, but
just causing a 'prickly' sensation in humans


a 'goosebump' is formed at the base of the hair
Hair Follicle
o
capsule in the skin which surrounds the root and lower shaft of a hair
o
lined with stratum germinativum-type cells which create the hair
The Skin Produces...

Vitamin D
o
required by the body to make strong bones and teeth
o
needed for normal calcium and phosphorus metabolism
o
15 minutes exposure to sunlight, on face, arms, and hands, twice a week
will supply the body's vitamin D needs
o
sunlight acts on cholesterol in the skin, to create a chemical that the liver
turns into vitamin D
o
lack of vitamin D causes rickets in children (soft bones that deform easily)
and brittle, delicate bones in adults
o

milk is a good dietary source of vitamin D in Canada
Melanin
o
brown pigment, found in skin, hair, and the iris of the eye
o
acts as a natural sunblock
o
produced in stratum germinativum
o
exposure to sunlight causes increased production of melanin, resulting in a
suntan
o
various skin tones, freckles, birthmarks, etc. are caused by varying
amounts of melanin

Keratin
o
tough protein, found in large amounts in stratum corneum of skin,
fingernails, toenails, hooves and horns of animals
o
manufactured in stratum germinativum, and concentrates in cells as they
move upward into the stratum corneum
Temperature Regulation

When it is Too Warm
1. capillary sphicters in skin open up to allow more blood to flow through
skin capillaries
2. body heat is radiated away from the skin
3. sweat glands release sweat onto the skin surface
4. sweat takes heat away from the blood in skin capillaries as it evaporates

When it is Too Cold
1. capillary sphincters in skin close to reduce blood flow to the skin, and
keep body heat in the core
2. arrector muscles contract, causing goosebumps (and little effect otherwise)
3. body muscles rapidly contract and release (shivering), to generate heat and
help warm the body

Hypothermia
o
dramatic lowering of core temperature of the body
o
body unable to warm itself
o
symptoms include lack of coordination, slurred speech, drowsiness, while
often feeling warm under cold conditions
o
treatment involves warming the body with hot water bottles, warm drinks,
etc.
THE EAR
The Three Major Sections of the Ear
Figure 242: The major sections of the ear.



Outer Ear
o
Made up of the Pinna, Auditory Canal, and Eardrum
o
Opens to the outside, and air-filled
o
Captures sound waves in the air, and 'funnels' them toward the eardrum
Middle Ear
o
Contains the Ossicles (hammer, anvil, and stirrup)
o
Transmits and amplifies vibrations from the eardrum to the inner ear
o
Air-filled, and connected to the pharynx by the Eustacian Tube
Inner Ear
o
filled with liquid (perilymph and endolymph)
o
includes the Cochlea

o
converts sound vibrations into nerve impulses
includes the Utricle and Saccule, and Semicircular Canals

responsible for static and dynamic balance
PARTS OF THE EAR AND THEIR FUNCTIONS
Figure 243: The structure of the ear.

Pinna (called 'auricle')
o
catches and concentrates sound vibrations from the air
o
reflects sound waves into auditory canal
o
gives some sense of sound direction, by partially blocking sounds from
behind, and strengthening sounds from the front

Auditory Canal (may be called 'ear canal')
o
carries sound waves from the outside to the eardrum
o
filled with air
o
lined with thin skin containing fine hairs and cells which secrete ear wax
o

ear wax is called cerumen

cerumen helps protect the eardrum against drying and against infection
auditory canal slants downwards toward the outside, to help drain fluids,
including cerumen

Ear Drum (medical name is 'Tympanic Membrane')
o
thin membrane, or skin, which completely seals the inner end of the auditory
canal
o
function is to convert sound waves from the air into movement
o
vibrates when sound waves hit it, and causes the bones of the middle ear to
move
o
easily damaged or punctured if objects are poked into the ear, resulting in
deafness

Ossicles
o

three small bones in the middle ear

hammer (malleus)

anvil (incus)

stirrup (stapes)
o
the smallest bones in the human body
o
transmit sound from the eardrum to the inner ear
o
they double the movement of the sound vibrations
Eustachian Tube
o
connects the middle ear with the pharynx
o
makes sure that the pressure on both sides of the eardrum is equal, so that it
can move freely
o
o
if the eustachian tube is blocked,

the pressure cannot be equalized

the eardrum becomes stretched tightly

hearing will become less sensitive, and a ringing may be heard

fluid may collect in the middle ear

an earache may result
young children have a more horizontal eustachian tube, making drainage of
fluids from the middle ear more difficult, and making middle-ear problems
more common
o
children who have very frequent middle-ear problems may require a tiny tube
to be installed temporarily at the bottom of the eardrum, to prevent buildup of
pressure or fluid in the middle ear

Oval Window
o
tiny membrane in the inner ear, through which vibrations from sound waves
enter the cochlea
o
the stirrup of the middle ear rests upon it
o
because it is so small compared to the eardrum, when sound vibrations pass
through it, they are amplified 30 times

Cochlea
o
tube-like structure in the inner ear, which is wound up like a snail shell
o
filled with fluids (endolymph and perilymph)
o
contains the organ of Corti

complex structure running along the middle of the full length of the
cochlea

converts sound vibrations into nerve signals

responds to vibration of the fluid in the inner ear

contains sound receptor cells with tiny hairs which are easily damaged
by loud sounds, such as those from loud music or very noisy machinery,
causing hearing impairment

Round Window
o
another thin membrane between the cochlea and middle ear, round in shape
o
absorbs the sound waves which enter the cochlea through the oval window
o
permits free movement of the fluids in the cochlea, allowing sound waves to
travel easily through it

Acoustic Nerve (may be called 'auditory nerve')
o
transmits nerve signals from the ear to the brain
o
carries sound information from the cochlea , and balance information from the
semicircular canals, utricle, and saccule

Semicircular Canals
o
function to give a sense of angular acceleration, or head turning
o
three fluid-filled canals, all at right angles to each other, correspond to the
three planes of movement
o
as the head moves or rotates, fluid in one or more of the canals 'remains
behind', and pulls on sensory hairs, sending a message to the brain of the head
movement
o
continued spinning gives the liquid in the canals time to 'catch up', but the
liquid keeps moving when the spinning stops, sending a false message to the
brain of spinning in the opposite direction

Utricle
o
fluid-filled sac, under the semicircular canals
o
responsible for detecting linear acceleration (straight-line movement forward
and back or side to side) and static balance, or head position
o
contains a small patch of hair cells attached to grains of calcium carbonate,
called otoliths
o
grains of calcium carbonate are pulled downward by gravity, or tend to remain
behind as the head starts to move sending nerve signals from the hair cells

Saccule
o
fluid-filled sac under the utricle
o
Same function as the utricle (linear acceleration detector and static balance)
but forward and back and up and down.
Overview of Hearing
1. vibrating objects such as vocal cords, loudspeakers, or musical instruments set up
compression waves in the air
2. these compression waves strike the whole surface of the pinna, and are focussed
into the auditory canal, amplifying the strength of the vibrations by 2
3. the eardrum vibrates with the sound waves, causing the hammer (malleus) to
move in the middle ear
4. the hammer causes the anvil (incus) to move, and the incus moves the stirrup
(stapes), again amplifying the strength of the vibrations by 2
5. the vibrations of the stirrup push against the oval window, amplifying the
movement of the eardrum by another 30 times
6. the oval window sends waves through the perilymph of the cochlea, which in turn
vibrate the hair cells of the organ of Corti
o
low notes cause more hairs to vibrate, stimulating sections of the organ of
Corti further in from the oval window
o
higher notes cause fewer hairs to vibrate, stimulating sections of the organ
of Corti closest to the oval window
o
very low notes are recognized and distinguished by the actual rate of the
sound pulses
7. the temporal lobe of the brain (on the sides of the head, above the ears)interprets
and decodes these signals as sounds that we hear
Deafness
There are 2 types of deafness:
1. Conduction Deafness
o
Caused by interference in the transfer of sound from the outside up to the oval
window. may result from

buildup of earwax

scarring or tears in the eardrum due to


'boxing the ears'

nearby explosions

improper use of cotton swabs to clean the ears, etc.
damage to the middle-ear ossicles
2. Nerve Deafness
o
caused by damage to nerve cells or sensory cells
o
may result from damage to

hair cells in the organ of corti due to

very loud machinery, jet engines, etc.

portable music systems with headphones played too loud

very loud music such as rock concerts, or being in the
middle of a symphony orchestra

the acoustic nerve (usually tumor)

the brain (usually physical injury or tumor in the temporal lobe of the
brain)
Damage to the organ of corti by loud music, etc., can be reduced by wearing protective
earplugs or special sound-blocking ear protectors
REVISION QUESTIONS
Identify the choice that best completes the statement or answers the question.
1. The central nervous system consists of
a. the brain and spinal cord.
c. the brain stem and cerebellum.
b. the spinal nerves only.
d. the cerebrum and spinal cord.
2. Gray matter includes
a. cell bodies of neurons.
c. myelin.
b. synapses.
d. nodes.
3. Refer to the illustration above. Structure 2 in the diagram is the
a. reticular formation.
c. cerebellum.
b. brain stem.
d. cerebrum.
4. limbic system : processing information about emotions and memory ::
a. cerebellum : maintaining balance and posture
b. brain stem : providing nerve connections for consciousness
c. hypothalamus : connecting the brain to the spinal cord
d. reticular formation : regulating body temperature and blood pressure
5. Which part of the spinal cord contains dendrites, unmyelinated axons, and the cell
bodies of neurons?
a. gray matter
c. ventral root
b. dorsal root
d. white matter
6. Which part of the spinal cord contains motor neurons?
a. gray matter
c. ventral root
b. dorsal root
d. All of the above
7. Information is carried from the central nervous system to a muscle or gland by
a. sensory neurons.
c. reticular neurons.
b. afferent neurons.
d. motor neurons.
8. Sensory neurons transmit messages
a. from the central nervous system to a muscle or gland.
b. from the brain to the spinal cord.
c. from the environment to the spinal cord or brain.
d. within the brain.
9. Motor neurons transmit messages
a. from the environment to the brain.
b. from the environment to the spinal cord.
c. from the spinal cord to the brain.
d. from the central nervous system to a muscle or gland.
10. The peripheral nervous system
a. is not linked to the central nervous system.
b. provides pathways to and from the central nervous system.
c. consists of the cerebellum and spinal cord.
d. is composed only of motor neurons.
11. The autonomic nervous system controls
a. reflexes.
b. voluntary movement.
c. involuntary functions of the internal organs.
d. locomotion.
12. The body’s response to a physical threat involves activity of the
a. autonomic nervous system.
c. sympathetic nervous system.
b. peripheral nervous system.
d. All of the above
13. A reflex
a. may involve two or three neurons.
b. is not learned.
c. is not under conscious control.
d. All of the above
14. Extensions at one end of a neuron’s body that receive input are called
a. axons.
b. synapses.
c. cell bodies.
d. dendrites.
15. Nodes of Ranvier
a. strengthen axons.
b. slow the nerve impulse.
c. occur in dendrites.
d. are gaps in the myelin sheath.
16. The myelin sheath
a. transmits impulses from one neuron to another.
b. insulates the synapses.
c. nourishes the neurons.
d. insulates the axons.
17. The sodium-potassium pump
a. rebuilds axon fibers.
b. restores resting potential.
c. creates a stimulus.
d. is found only in the peripheral nervous system.
18. Which statement about the resting potential of a neuron is true?
a. There are many times more sodium ions outside the neuron’s membrane than inside.
b. Sodium ions are in balance inside and outside the neuron’s membrane.
c. There are fewer potassium ions inside the neuron’s membrane than outside.
d. Potassium and sodium ions are equal on both sides of the neuron’s membrane.
GROWTH, REGENERATION AND AGEING
GROWTH AT DIFFERENT LEVELS
Definition
Growth is defined as an increase in the size and weight of an organism due to synthesis of
new protoplasm. Growth takes place at 2 different levels in an organism.
STRATEGIES OF GROWTH
 Molecular Levels
Growth at the molecular level involves the synthesis of new molecules.
 Cellular level
Growth at the cellular level involves four stages

Cell expansion: an increase in the size of the cell due to formation of new
protoplasm.

Cell division: the cells increase in number due to mitotic cell division

Cell differentiation: the cells became specialized to per form specific roles in the
organism.

Matrix formation: addition of intercellular materials, termed apoplasmatic
substance, secreted by the cells between them.
MECHANISM OF GROWTH
At the cellular level, growth is the increase in the amount of protoplasm (nuclues +
cytoplasm). During growth, the synthesis of complex molecules like proteins nucleic
acids and carbohydrates is at a higher rate than the rate at which the complex molecules
are broken down.
During growth, the anabolic process dominates the catabolic activity. The materials
formed during anabolism- the proteins, provide the building blocks for the growth of the
organism and the carbohydrates supply the extra energy needed for growth. This is called
positive growth. If the anabolic and catabolic processes are balanced, there is no addition
to the bulk of the body and so no growth takes place. When decomposition exceeds
synthesis, as in fasting, first the internal food reserve in the form of glycogen and fats is
catabolised to run the metabolic depletion of the living matter. This phenomenon is called
degrowth or negative growth.
TYPES OF GROWTH
The growth of multi-cellular organisms is of four kinds with regard to the growth and
multiplication of the body cells.
 Multiplicative Growth or Embryonic Growth
In multi cellular organisms, growth occurs by an increase in the number of cells of the
organism. The increase in the number of cells is due to mitotic cell division. In this type
of growth, the average cell size remains the same, or increases insignificantly.
Example:
Growth of embryos, prenatal growth in mammals
 Auxetic growth
In some organisms like Ascaris, growth occurs as a result of increase in the size of their
cells. The number of cells remains the same. The body grows in size because of the
enlargement of its cells. Auxetic growth is found in nematodes, rotifers and tunicates. In
certain tissues of higher animals like the body muscles, auxetic growth is seen.
 Accretionary growth
During post embryonic growth, and also in the adult, all the body cells are not capable of
undergoing division. This is because they have become differentiated. But at some
locations, undifferentiated cells are present which divide mitotically and replace the worn
out differentiated cells as and when needed. These cells are called reserve cells.
Example:
Bone marrow of vertebrates contains unspecialised cells that continuously produce blood
cells to replace worn out ones.
Cells of Malpighian layer of epidermis of human skin produce new cells which replace
the worn out cells of the outer layers of epidermis.
 Appositional growth
It is the addition of new layers on the previously formed layers. If is the characteristic
type of growth, seen in rigid materials.
Example:
Addition of lamellae in the formation of bone
CELL REPRODUCTION AND CELL GROWTH
At the cellular level, growth of multi cellular organisms is governed by two main
activities

Reproduction of individual cells of body by mitotic cell divisions

Growth of cells by synthesizing new protoplasm.
The interphase stage of the cell cycle is differentiated into G1, S and G2 phases.
During these phases new materials such as nucleic acids and proteins are synthesized and
accumulated in the cells so that cells and their nuclei increases in size. The cells grow up
to a limited extent after which these cells enter cell division.
The growth of the individual cells comprising the body is the most important factor of
growth in all multi cellular animals. After attaining a specific nuclear cytoplasmic ratio,
the cells divide and multiply adding to the size of the organism.
ANIMALS GROWTH CURVE
The growth rate of an individual at different periods of life can be represented in a growth
curve by plotting the weight of individual at different time intervals (in years) on a graph
paper. For example a human baby can be weighted from birth till adult hood when
growth stops. Plot the weight in kilograms against time in months or years. This gives a
growth curve. This is a simple S-shaped sigmoid curve.
The S - Shaped sigmoid curve is characteristic of all higher animals including man. The
difference between the initial and final weight or initial and final size of an individual for
any period of time is the absolute increase.
PHASES OF GROWTH
Growth of an organism can be differentiated into the following periods.

Lag period
It is the first period during growth phase, where the curve rises gradually. The organism
is getting prepared for growth by synthesizing enzymes and accumulating substances to
metabolize protoplasmic components.

Exponential period
During this period growth begins slowly at first and becomes rapid later on. Hence the
curve rises steeply. As a result the organism enlarges doubling and redoubling in size.
This phase is also called as logarithmic phase.

Deaccelerating growth period
The exponential growth does not continue indefinitely. It is followed by a period when
growth proceeds more slowly and finally ceases altogether. The curve therefore rises
slowly and these become horizontal, signifying limit of growth. During this phase, the
rate of acceleration is exactly equal to catabolism.
STAGES OF GROWTH PERIOD IN MAN
Growth period in man may be divided into 5 stages.

Prenatal stage - 9 months of embryonic life

Infantile stage - Birth to 10 months of age

Early childhood - 10 months to 5 years of age

Juvenile stage - 5 years to 14 years or the time of puberty

Adolescent and post adolescent stage - 14 years to 20 - 22 years
PATTERNS OF GROWTH
Two patterns of growth are commonly seen in animals regarding the proportion of the
various body parts.

Isometric growth: In this growth pattern, an organ grows at the same rate as the
rest of the body. As the organism growths, the size remains proportional.
Examples: Fish and Locust

Allometric growth: In this pattern, the organ grows at a different rate from which
the body grows. The external form of the organism changes as the body grows.
Example:
Mammals show differential growth of human body parts.
Different parts of the human body, such as the head, limbs and internal organs do not
grow uniformly or simultaneously. This can be seen by examining photographs form
birth to childhood. The new born baby has an unproportionately large head and
comparatively short legs. Due to slow growth of head and fast growth of limbs during the
post embryonic phase the body shape and proportion between the different parts of the
body changes.
HORMONAL CONTROL OF GROWTH RATE IN MAN
The period extending from birth up to 10 - 13 years is called childhood. During this
period, the growth is very slow. Growth during this period is controlled by the hormone
thymus, secreted by the thymosin gland. During puberty (between 14 - 18 years) there is
enhanced activity of 2 growth hormones - thyroxin and the somatotropic hormone (STH)
secreted by the thyroid gland and anterior pituitary gland respectively. Due to this,
growth is also enhanced during this period. Growth is at its peak during puberty. The
increase in the amount of the sex hormones - testosterone in male and estrogens and
progesterone in females also helps in establishing the secondary sexual characters
At the age of 18 years when puberty comes to an end and a fully grown sexually mature
male and female are formed, the physical growth of the body starts declining and by the
age of 22 - 23 years ceases completely.
REGENERATION
If the tail of a house lizard is cut, the missing part develops again from the remaining part
of the tail. In some cases, regeneration is so advanced that an entire multicellular body is
reconstructed from a small fragment of tissue. Our body spontaneously loses cells from
the surface of the skin and replaced by newly formed cells. This is due to regeneration.
Regeneration can be defined as the natural ability of living organisms to replace worn out
parts, repair or renew damaged or lost parts of the body, or to reconstitute the whole body
from a small fragment during the post embryonic life of an organism. Regeneration is
thus also a developmental process that involves growth, morphogenesis and
differentiation.
Types of Regeneration

Physiological Regeneration
There is a constant loss of many kinds of calls due to wear and tear caused by day-today activities. The replacement of these cells is known as physiological regeneration
Example:

Replacement of R.B.C's
The worn out R.B.C's are deposited in the spleen and new R.B.C's regularly produced
from the bone marrow cells, since the life span of R.B.C's is only 120days.

Replacement of Epidermal Cells of the Skin
The cells from the outer layers of epidermis are regularly peeled off by wear and tear.
These are constantly being replaced by new cells added by the malpighian layer of the
skin.

Reparative Regeneration
This is the replacement of lost parts or repair of damaged body organs. In this type of
regeneration, wound is repaired or closed by the expansion of the adjoining epidermis
over the wound.
Example:

Regeneration of limbs in salamanders

Regeneration of lost tail in lizard

Healing of wound

Replacement of damaged cells.
AGEING
Ageing can be defined as the progressive deterioration in the structure and function of the
cells, tissues, organ and organ systems of the organism with advancing age.
The field of developmental biology that deals with the process of ageing is known as
gerontology
The scientists who study the science of ageing are called gerontologists.
Pace of ageing
The effects of ageing vary widely in different groups. Bacteria, viruses and many
protozoans are free from ageing, but none of multicellular organisms live forever. Even
under the most favourable conditions, some live for only a short period while others live
for decades or even centuries.
Example: Turtles live for about 150 years. Even different types of cells have different
longevity. In general, cells that differentiate and stop dividing are subjected to changes of
ageing than those that are capable of dividing throughout their life.
Maximum life span
Maximum life span is the maximum number of years survived by any member of a
species. Average life span is the average number of years survived by members of a
population.
Life expectancy is the number of years an individual can expect to live. It is based on the
average life spans.
Thus, maximum life span is the characteristic of a species while life expectancy is the
characteristic of population.
Ageing
Ageing is accompanied by impairment of physiological functions. This is termed as
senescence. Senescence results in decreased ability to deal with a variety of stresses and
an increased susceptibility of the body to diseases
Symptoms of ageing at the level of the organism:

Heart - The efficiency of the heart decreases with increasing age. In a 70 year old
man, the heart pumps only 65% blood per minute as compared to a 30 year old
man.

Oxygen uptake by blood - Oxygen uptake is reduced with advance in age.

Decrease of blood volume - The production of RBC from the bone marrow
decreases and so the volume of blood also decreases.

Kidney - Kidneys become less efficient in extracting wastes from the blood.
There is a reduction in the number of kidney tubules, which leads to a decreased
output of urine and difficulty in passing urine. Bladder capacity decrease.

Lungs - The capacity of the lungs for intake of air decreases. So there is a
decreased oxygen supply to the various tissues. This leads to breathlessness and
inflammation of mucous membrane.

Digestive system - The number of taste buds on the tongue is reduced to about
one-third. The secretion of digestive juices also decreases with old age.

Body fat - There is redistribution of fat to deeper parts of the body from the skin.
In women, fat is generally stored in the hips and thighs, while in men it is stored
in the abdominal area.

Retention of water - The capacity of body cells to retain water decreases. This
makes the skin dry and wrinkled.

Nerve impulse - The rate at which the nerve impulse is propogated reduces with
age. Brain also loses some neurons.

Muscles - Muscle mass in the body decreases by about 22% for women and 23%
for men.

Sight - Difficulty in seeing close objects begins by about 40 itself. In later ages,
ability to distinguish finer details declines, they become susceptible to glare and
greater difficulty sets in to see things at low levels of illumination.

Hearing - Sense of hearing reduces with age.
Cellular Changes During Aging
The outward signs of ageing are the result of changes taking place at the cellular and
extracellular levels.

Morphological changes: Accumulation of exhaustion pigments. The exhaustion
pigments lipofusion, yellow pigments and brown deposits which are byproducts
of unsaturated lipid oxidation, accumulate in the cell.

Appearance of lipid vacuoles: Small lipid vacuoles appear in the cytoplasm.

Decline in cell volume: Cells exhibit hypertrophy or a decrease in cell volume.

Nuclear pykinosis: With advancing age, the nucleus shrinks and stains deeply.
Such a nucleus is called pykinotic. This is due to the condensation of the nuclear
material.
Other changes associated with ageing are,

Increase in cholesterol levels

Increase in blood globulin

Decrease in alkaline and acid phosphatases

Decrease in cellular respiration.
Sub Cellular Changes

Plasma membrane: The permeability of the plasma membrane decreases due to
the accumulation of calcium in the membrane.

Endoplasmic reticulum: In the cytoplasm of old cells, granular ER decreases. In
the nerve cells, nissl granules are decreased.

Mitochondria: Mitochondria become degenerated in the cells of old tissues. This
leads to a reduced rate of respiration.

Nucleus: With ageing, there is an accumulation of chromosomal aberration and
gene mutations. This disturbs the normal functioning of the DNA.
Extra Cellular changes
There is an increase in the amount of collagen proteins deposition in the intercellular
spaces. This influences the permeability of cell membranes, affects the speed of diffusion
of substances in and out and significantly influences the process of ageing.
Theories of Ageing
Many theories have been proposed to explain the process of ageing. The important ones
have been listed.
1) Programmed theories
This theory brings in the concept of internal biological clock to explain the process of
ageing from childhood.
This theory has three sub-categories:

Endocrine theory
According to this theory, biological clocks act through hormones, which are the
secretions of the endocrine glands, to control the pace of ageing.
It has been observed that the production of some of the hormones declines with age.
Sex hormones like oestrogen and testosterone levels also fall off.
Human growth hormone (GH) levels decrease with age.

Programmed senescence theory
According to this theory, ageing is the result of the sequential switching on and off of
certain given, with senescence.

Immunological theory
According to this theory, programmed decline in the functioning of the immune
system leads to increased vulnerability to infectious diseases thus causing
ageing and death.
2) Damage or Error theories
This theory blames the external or environmental forces that gradually damages the
internal cells and organs leading to ageing.
Living theory
According to this theory, ageing is the by-product of metabolism. Therefore greater is
the organisms rate of metabolism, shorter is its life span and vice versa.
Wear and tear theory
According to this theory, cells and tissues have vital parts that wear out resulting in
ageing.
Somatic mutation theory
According to this theory genetic mutations occur and accumulate with increasing age,
causing cells to deteriorate and malfunction.
Ageing and death
Biological ageing affects everybody. It is a deleterious process, which affects the
functioning of the cells, tissues, organs and finally the organism itself.
Like ageing, death is also a biological event. It occurs due to breakdown in body
functioning. Causes of death in humans are many. A few of them are:
i)
Tissues of vital organs become weakened due to ageing disrupting various
physiological processes causing death.
ii)
Malfunctioning of the bodys immune system reduces the resistance of the
body to different antigens. As a result the individual is more prone to diseases,
which may ultimately cause his death.
Definitions
 Accretionary growth: Post embryonic growth in some special cells to
reinforce and replace the worn out differentiated cells.
 Ageing: Progressive deterioration in the structures and functions of cells
tissues and organs.
 Aldolase: An enzyme secreted by the liver.
 Autotomy: A spontaneous self mutilation of body where lost parts are
restored by regeneration process.
 Auxetic growth: Volume of the body increases due to growth of body
cells and not by increase in the number of cells.
 Blastema: Cellular aggregation of newly formed cells to heal the injury.
 Degrowth: Catabolism of the body is greater than anabolism and reserve
food is utilized for performing normal metabolism.
 Epimorphosis: Proliferation of new cells from the surface of wound to
reform the severed body parts.
 Gerontology: A branch of Biology dealing with the ageing process.
 Lag Phase: Period of slow growth.
 Morphallaxis: The reconstitution of the whole body even from a small
fragment of body part.
 Regeneration: A replacement, repair or restoration of lost or damaged
body parts.
 Reparative Regeneration: Repairing of some body parts due to
proliferation of localized cells from the edges of wound.
 Restorative Regeneration: Regeneration of severed body parts from left
out fragment of the body.
REPRODUCTION
Introduction
Reproduction is defined as the production of individuals of the same species, that is the
next generation of the species. While it is one of the fundamental characteristics of living
things, it is not an essential life process. An individual can live without reproducing, but,
a species cannot survive without reproduction.
Thus, reproduction ensures that there is competition and only the fittest and the best
survive and reach the reproductive age. This ensures that the advantageous characteristics
are transmitted to the next generation and any aberrations occurring during the
reproductive process are removed during competition.
Methods of Reproduction
 Asexual reproduction involves only one parent and the offspring is genetically
similar to the parent.
 Sexual reproduction involves two parents and the offspring has a fusion of the
characteristics of both the parents.
Types of Asexual Reproduction
 Fission
Fission occurs in lower plants and animals such as the bacteria, blue-green algae and
protozoa. In this process, the cell divides after the genetic material has divided. If the cell
divides into two it is called binary fission.
 Budding
It is seen in certain fungi and multicellular animals. In budding, the parent cell or body
gives out a lateral outgrowth called the bud.
 Spore Formation
It is generally seen in bacteria and most fungi. One of the cells enlarges and forms the
sporangium (literally meaning spore sac). The nucleus divides many times and then the
daughter nuclei are surrounded with protoplasm bits to form daughter cells called spores.
 Fragmentation
It takes place in some lower plants and animals such as some worms. The mature
organism breaks up into two or more pieces or fragments. The fragments then grow into
complete organisms.
For example: Spirogyra, an alga.
 Regeneration
Regeneration of new plants from the vegetative parts of the parent plant is called
vegetative propagation or vegetative reproduction. Vegetative propagation is done with
the help of vegetative parts such as roots, stem or leaves.
 Artificial Vegetative Propagation or Cloning
Vegetative propagation produces the next generation that is genetically identical to the
parent. Such an organism that is genetically identical to the parent is called a clone. In
case of plants with advantageous characteristics, the characteristics can be preserved by
producing clones.
 Cutting
Cutting involves removing a piece of the parent plant - stem, root or leaf, and planting it
in a suitable medium. At first roots are produced and then the shoot with the leaves.
 Layering
Layering is the method of inducing certain branches of the parent plant to produce roots
by bending and pegging them to the ground around the parent plant leaving the tips
exposed. Once the roots develop the branch is then cut off from the parent body.
The branch that produces the roots is called the layer.
 Grafting
It is the transfer of a part of one plant to the stump of another plant. The part taken from a
plant is a portion of the stem with many buds. This portion is called scion and is selected
for the quality of its fruit. The stump to which the scion is attached is called the stock.
 Budding or Bud Grafting
It is a variation of the grafting method explained above. In this method, the scion is a bud
along with some bark. A 'T'-shaped cut is made on the stock into which the scion is
inserted and bound with a tape.
 Parthenogenesis and Tissue Culture
Parthenogenesis is a form of reproduction in which the ovum develops into a new
individual without fertilisation. Natural parthenogenesis has been observed in many
lower animals (it is characteristic of the rotifers), especially insects, e.g., the aphid. In
many social insects, such as the honeybee and the ant, the unfertilized eggs give rise to
the male drones and the fertilized eggs to the female workers and queens.
Tissue culture is based on the concept of cellular totipotency. That is all the
multicellular organisms basically are formed from a single cell (the zygote), by repeated
multiplication and differentiation. Thus a single cell can develop into a whole organism
or in other words, the cell is totipotent. This is because it contains the full set of genetic
information needed to make the organism. This is called cellular totipotency
ADVANTAGES AND DISADVANTAGES OF VEGETATIVE PROPAGATION
Advantages
1. The offsprings are genetically identical and therefore advantageous traits can be
preserved.
2. Only one parent is required which eliminates the need for special mechanisms such
as pollination, etc
3. It is faster. For example, bacteria can multiply every 20 minutes. This helps the
organisms to increase in number at a rapid rate that balances the loss in number due
to various causes.
4. Many plants are able to tide over unfavourable conditions. This is because of the
presence of organs of asexual reproduction like the tubers, corm, bulbs, etc.
5. Vegetative propagation is especially beneficial to the agriculturists and
horticulturists. They can raise crops like bananas, sugarcane, potato, etc that do not
produce viable seeds. The seedless varieties of fruits are also a result of vegetative
propagation.
6. The modern technique of tissue culture can be used to grow virus-free plants.
Disadvantages
1. The plants gradually lose their vigour as there is no genetic variation. They are
more prone to diseases that are specific to the species. This can result in the
destruction of an entire crop.
2. Since many plants are produced, it results in overcrowding and lack of nutrients.
SEXUAL REPRODUCTION
In sexual reproduction new individuals are produced by the fusion of haploid gametes
to form a diploid zygote. Sperm are male gametes, ova (ovum singular) are female
gametes. Meiosis produces cells that are genetically distinct from each other; fertilization
is the fusion of two such distinctive cells that produces a unique new combination of
alleles, thus increasing variation on which natural selection can operate. Sexual
reproduction mostly occurs in higher multicellular plants and animals. However, it is also
seen in lower organisms like the bacteria, Spirogyra (an alga) and Paramoecium (a
protozoan). Bacteria show a primitive type of sexual reproduction called genetic
recombination. In the higher organisms, sexual reproduction involves the production of
sex cells or gametes and their subsequent fusion to produce a new individual.
Sexual Reproduction in Plants
The plants that sexually reproduce have the reproductive structures called the flowers.
The flower is a condensed shoot with the nodes present very close to each other. The
different parts of the plant are attached to the nodes.
Parts of a Flower
 Calyx is the outermost and most often green in colour. The individual units of
calyx are called the sepals. It protects the inner whorls at bud stage.
 Corolla is the next inner whorl and is often coloured brightly. The individual
units of corolla are called petals. They serve to attract bees, birds, etc which are
the agents of pollination.
 Androecium is the male reproductive part of the flower. The individual units of
androecium are called the stamens. Each stamen has a thread-like filament at the
free end of which is attached the four-lobed anther.
 Gynoecium is the female reproductive part of the flower. The individual units are
called the carpels or pistils. A flower may have one to many carpels, either fused
or free. Each carpel is made up of the basal ovary, middle style and the upper
stigma.
Figure 271: The structure of a flower.
POLLINATION
Transfer of pollen grains to the stigma is called pollination. If the pollen grains are
transferred to the stigma of the same flower, the pollination is called self-pollination or
autogamy. If the pollen grains are transferred to the stigma of another flower of the same
species, the pollination is called cross-pollination or allogamy. Cross pollination is
brought about by various agencies like wind, water, bees, birds, bats and other animals
including man. The anthers on maturity burst open with force and this is called
dehiscence. This releases the pollen grains with force which are then carried by wind and
water to other plants.
FERTILISATION
On reaching the stigma, the pollen grains put out a tube. This is called germination of the
pollen grain. The tip of the tube contains the male nuclei. The tube grows and enters the
ovule where it bursts at the tip releasing the male gametes. One of the male gametes fuses
with the egg, the female gamete. The fusion of the male gamete with the female gamete is
called fertilisation. This results in the formation of zygote that is diploid. The zygote
develops into the embryo. The other male gamete fuses with the polar nuclei. This results
in the formation of a triploid nucleus called the endosperm nucleus. Since the process of
fertilisation involves two fusions, it is called double fertilisation. The divisions of the
endosperm nucleus result in the formation of the endosperm that nourishes the growing
embryo. The ovule then becomes the seed and the ovary changes into fruit.
Figure : Fertilisation in a Flowering Plant
SEED GERMINATION
1. Many plants are easily grown from seeds. Although its embryo is alive, a Seed will
Not Germinate, or Sprout, until it is exposed to Certain Environmental Conditions.
2. Delaying of Germination often assures the survival of the plant. If Seeds that mature
in the fall were to sprout immediately, the young plant could be killed by cold weather.
3. If all a plant's seeds were to sprout at once and all of the New Seeds Died before
producing seeds, the species could become Extinct.
4. Many seeds will not germinate even when exposed to conditions ideal for
Germination. Such seeds exhibit dormancy, which is a state of reduced metabolism.
CONDITIONS NEEDED FOR GERMINATION
1. Environmental Factors, such as Water, Oxygen, and Temperature Trigger Seed
Germination.
2. Most Seeds are Very dry and must absorb Water to Germinate.
3. Water Softens the Seed Coat and Activates Enzymes that convert Starch in the
Cotyledons or Endosperm into Simple Sugars, which provided energy for the embryo to
grow.
4. As the embryo begins to grow, the soften seeds coat cracks open, enabling the Oxygen
needed for Cellular Respiration to reach the embryo.
5. Seeds will only Germinate it the Temperature is within a certain Range. Many Seeds
need Light for Germination, this prevents the seeds from sprouting it they are buried to
deeply.
6. Some Seeds Germinate only after being exposed to Extreme Conditions, After
Freezing or passing through a digestive system that breaks down the Seed Coat.
PROCESS OF GERMINATION
1. The first Visible Sign of Seed Germination is the emergence of the radicle (root).
2. Soon after the Radicle Breaks the Seed Coat, the shoot begins to Grow.
3. In some Seeds (Dicot, Bean) the Hypocotyl curves and become hooked-shaped. Once
the hook breaks through the soil, the Hypocotyl Straightens.
4. The Plumule's Embryonic Leaves unfold, synthesize Chlorophyll, and begin
Photosynthesis. After their Stored Nutrients are used up, the shrunken Cotyledons fall
off.
5. In contrast (Monocot, Corn), the Cotyledon of the Corn Seed Remains Underground
and transfers Nutrients from the Endosperm to the growing Embryo.
6. The Corn Hypocotyl Does not Hook or Elongate, and the Cotyledons remains Below
Ground. The Corn Plumule is protected by a Sheath (Coleoptile) as it passes through the
soil.
7. When the Shoot breaks through the soil surface, the Leaves of the Plumule unfold.
SEXUAL REPRODUCTION IN ANIMALS
Sexual reproduction is seen in nearly all animals. In animals reproduction also involves
production of gametes that are haploid cells. In unicellular organisms like the
protozoans, the gamete-producing individuals are called gametocytes. In multicellular
organisms, the gametes are produced by the reproductive organs. The male gametes
called the sperms are produced by the male reproductive part and the female gametes
called the eggs are produced by the female reproductive part. Production of sperms is
called spermatogenesis and production of eggs is called oogenesis.
The male gamete of one individual fertilizes with the female gamete of another
individual to produce the zygote. The fertilisation may be external or internal.
 External fertilization
External fertilisation takes place in animals like the fish and frog where the eggs are
released from the body of the females into the water outside.These eggs are then fertilised
by the sperms produced by the male species. The fishes and frogs are oviparous, that is
they lay eggs.
 Internal Fertilisation
Organisms like birds, insects, reptiles are also oviparous. However, in these organisms
the fertilisation is internal. Internal fertilisation occurs in mammals also. In internal
fertilisation the sperms are released into the body of the females during copulation.
Human Reproductive System
The reproductive system comprises of two different parts:
 Primary reproductive system: - that includes the gamete-producing organs, the
testes and the ovaries.
 Accessory reproductive system : -that includes the glands, passages and other
such associated structures.
Female Reproductive System
The female reproductive system consists of a pair of ovaries, a pair of oviducts, uterus,
vagina and vulva. The main functions of the female reproductive system are to produce
eggs, receive the sperms, provide the site for fertilisation, implantation of the growing
embryo and development of the foetus. It also produces hormones that control the various
stages of ovulation and maintenance of pregnancy.
 Ovaries are a pair of oval structures that are present one on either side. The
ovaries produce eggs, one at a time, every alternate month. The eggs are produced
by the germinal epithelial cells of the ovary.
 Oviducts/Fallopian tubes are a pair of tubes of about 12cm in length. They run
from the ovaries of each side to the uterus. At the ovarian end the tube is funnelshaped with the end of the tube thrown into number of folds. These folds are
ciliated which help to sweep the egg produced by the ovary into the fallopian
tube. The fallopian tubes are the sites for fertilisation of the egg by the sperms.
 Uterus is a pear-shaped structure, broader on the upper end and narrower on the
lower end. The upper end is called the body of the uterus and the lower end is
called the cervix. At the upper end, it receives the oviducts of either side whereas
the lower end the cervix opens into the vaginal canal that opens to the outside.
The uterine wall has three layers. They are the innermost endometrium made up of
several glands and blood vessels, the middle myometrium made of smooth muscles and
the outer perimetrium made of connective tissue. The inner surface of the uterus provides
a site for the implantation of the embryo. The uterine wall plays an important role during
childbirth. Cervix is made of sphincter muscle that controls the opening and closing of
the uterus.
 Vagina is a 9cm long muscular tube that receives the penis during copulation. It
is lined with epithelial cells. The secretions of the vaginal canal are acidic which
is not conducive to the sperms as semen is alkaline. The vaginal opening in young
females is partially covered with a thin mucous membrane called hymen. This is
often broken early in females during play or strenuous work
 Vulva is the external female genitalia. It comprises of the mons veneris, which is
the raised pubis. The vaginal opening has two pair of folds on either side. The
outer fold is thicker with hair, sweat glands and sebaceous glands and is called
labia majora. The inner folds are thinner and devoid of hair. They are called labia
minora. Covered by the upper part of the folds is the female equivalent of the
penis called the clitoris. It is also an erectile and highly sensitive organ.
Figure 303: Oogenesis process.
The ovary contains many follicles composed of a developing egg surrounded by an outer
layer of follicle cells. Each egg begins oogenesis as a primary oocyte. At birth each
female carries a lifetime supply of developing oocytes, each of which is in Prophase I. A
developing egg (secondary oocyte) is released each month from puberty until menopause,
a total of 400-500 eggs.
Male Reproductive System
The male reproductive system comprises of the following:
 Testes
The male reproductive system comprises of a pair of testes that are present in a thinwalled sac called the scrotum. The scrotum is contained within the abdominal cavity in
the embryonic stage. Shortly before birth, they come down and remain outside
throughout life. This is because the testes cannot produce sperms at the body temperature.
A temperature 2-3 degrees lower is ideal for the production of sperms. The scrotal sacs
hang loose when it is hot and when it is cold the skin of the scrotal sacs contracts and this
keeps them in close contact with the body.
 Duct System
From the seminiferous tubules, the sperms are passed into a network of 10-12 ducts
called the efferent ducts or the vasa efferentia. They are then passed into a highly coiled
tubular part called the epididymis. Epididymis is an organ that extends from the top of
the testis along its side to its back. It therefore, has three parts - head (upper), body
(middle) and tail (hind). It temporarily stores the sperms.
 Glands
The various glands associated with the male reproductive system are as follows:
1. Seminal Vesicles
A pair of seminal vesicles are glands that are present behind the urinary bladder. Each
sperm duct has the seminal vesicle of its side secreting a fluid into the common
ejaculatory duct. This fluid along with the sperms is called the semen, a milky fluid.
2. Prostate Gland
It is a bi-lobed gland near the opening of the urethra. The prostate gland also pours its
secretion into the urethra. It is alkaline and mixes with the semen.
3. Cowper's Glands
They are a pair of small ovoid glands that secrete lubricating fluid into the urethra just
before it enters the penis.
The secretions of these glands make the sluggish sperms more active and help in the
passage of sperms through the duct system and then in the ejaculation.
 Penis
Penis is a muscular organ containing erectile tissue. The tissue is richly supplied with
blood vessels. On sexual stimulation the penis is gorged (supplied) excess with blood
which causes it to become erect. During sexual intercourse, the penis is inserted into the
vagina of the females before ejaculation. Ejaculation is the release of sperms by the penis
to the outside.
Menstruation and Menstrual Cycle
Unlike males where sperms can be produced through out the life of man, in females the
reproductive phase only lasts till the age of 45-50years. This phase is characterised by the
presence of menstrual cycle.
Each menstrual cycle typically lasts for 28 days. Thus it occurs every month. Each cycle
has the following phases:

Menstrual Phase
It lasts for the first 3-4 days. During this phase the inner lining of the uterus is shed which
causes the blood vessels to rupture. This causes bleeding and is called menstruation. The
first occurrence of menstruation is termed menarche. It stops by the age of 45-50 years
and is called menopause.
In the ovary, during this phase, the follicles where the eggs are produced are growing.
Follicles are structures formed by the aggregation of the germinal epithelial cells of the
ovary.

Follicular Phase
In this phase, the follicles grow further. The FSH stimulates one of the follicles. The
stimulated follicle grows in size.
T.S. of Ovary of a Mammal
One of the cells of this follicle becomes bigger and separated from the rest by a follicular
cavity. This cell becomes the egg. The outer layer of cells of this follicle is called theca
interna. This layer secretes a hormone called oestrogen. This follicle is called the
Graafian follicle. This phase lasts from the 6th to the 10th day.
In the uterus, this phase sees the inner wall of the uterus being built up again in order to
receive the product of fertilization, if there is one. It is again supplied with blood vessels.

Ovulatory Phase
When the follicle is mature, the pituitary gland secretes another hormone called
luteinizing hormone (LH). LH stimulates the follicle to rupture and release the egg. The
release of egg is called ovulation and occurs between the 10th and the 16th day. The egg
moves along the oviduct during this time and may be fertilized by the sperm. If not, it
starts disintegrating.

Luteal Phase
This phase lasts between the 16th and the 28th day. Once the egg is released, the Graafian
follicle re-aggregates to form corpus luteum. The corpus luteum secretes two pregnancy
hormones - progesterone and relaxin. The degenerating corpus luteum is called corpus
albicans. In the uterus, its lining is thickened further. At the end of 28 days, if fertilisation
has not taken place, the lining is shed along with the egg. This starts a new cycle all over
again.
FERTILISATION
Fertilization can be defined as the fusion of the sperm nucleus with the egg nucleus to
form a diploid cell known as zygote .The fertilization is internal in the human
reproductive system. It is achieved by the insertion of the male organ, penis into the
vagina of the female. The sperms are deposited in the vagina of the females during a
process called as copulation or sexual intercourse.
STRUCTURE OF A SPERM
Each sperm is a small cell of about 50um length and 2.5um diameter.
Structure of a Sperm

It consists of a head, middle piece and the tail regions. The head consists of the
nucleus and a structure called the acrosome at the tip.

The acrosome secretes lytic substances that break down the walls of the egg for
fertilization.

The beating of the tail propels the sperm forward at the rate of 1-4 mm per
minute.
FERTILISATION OF HUMAN EGG
Each egg or ovum is a spherical cell much bigger than the sperm. It mainly consists of a
single nucleus and some reserve food made of lipid droplets.
Fertilisation of Human Egg
In the fallopian tubes, many sperms surround an egg. However, only one enters the egg
leaving behind the tail. The enzymes of the acrosome digest the several layers of tissue to
reach the egg cytoplasm. Once the sperm is inside, the male and female nuclei become
lighter and are called pro-nuclei. The two pro-nuclei fuse forming a zygote.
Once a sperm enters an egg, the thickening of the outer walls of the egg blocks the entry
of other sperms. The foetus remains attached to the mother through an umbilical cord
which is embedded in a tissue called placenta at one end. The placenta in turn is
embedded into the uterine wall and is richly supplied with blood vessels. The nutrients
from the mother's blood pass into the umbilical cord and the waste from the foetus pass
into the mother's blood through the placenta.
Fertilization and Cleavage
Fertilization has three functions:
1. transmission of genes from both parents to offspring
2. restoration of the diploid number of chromosomes reduced during meiosis
3. initiation of development in offspring
Steps in Fertilization




Contact between sperm and egg
Entry of sperm into the egg
Fusion of egg and sperm nuclei
Activation of development
Cleavage
Cleavage is the first step in development of ALL multicelled organisms. Cleavage
converts a single-celled zygote into a multicelled embryo by mitosis. Usually, the zygotic
cytoplasm is divided among the newly formed cells. Frog embryos divide to produce
37,000 cells in a little over 40 hours. The blastula is produced by mitosis of the zygote,
and is a ball of cells surrounding a fluid-filled cavity (the blastocoel). The decreasing size
of cells increases their surface to volume ratio, allowing for more efficient oxygen
exchange between cells and their environment.
Gastrulation
Gastrulation involves a series of cell migrations to positions where they will form the
three primary cell layers.

Ectoderm forms the outer layer.

Endoderm forms the inner layer.

Mesoderm forms the middle layer.
REPRODUCTIVE DISEASES
The diseases/disorders affecting the reproductive system are of many types. Some are due
to malfunctioning gonads, others are due to pathogens.

Infertility in Females
The common causes of infertility among females is the inability to produce ova, mainly
due to hormonal problems, blocked oviducts, damaged uterus and cervix, presence of
anti-sperm antibodies in female reproductive system, etc.

Infertility in Males
Infertility in Males may be due to absence of sperm, low sperm count, abnormal sperms,
autoimmunity (presence of antibodies in the male reproductive system itself), premature
ejaculation and impotence.

Menstrual Disorders
Hormonal imbalances in the body result in menstrual disorders such as painful, irregular
or excessive menstruation.

Sexual Transmitted Diseases
The common diseases are syphilis and gonorrhea. Syphilis is characterized by sores
around the anus, vagina, penis, lips, fingers, nipples, etc. In the later stages it results in
fever and skin rashes. If untreated, it can result in insanity, heart damage or blindness.
AIDS

It is the most serious and challenging health problem confronting the world today.
It is also a sexually transmitted disease. AIDS stands for Acquired Immuno
Deficiency Syndrome. It is caused by human immuno deficiency virus (HIV). It
spreads through transfer of bodily fluids such as blood and semen.
POPULATION CONTROL
Increasing population is a serious issue, particularly in developing countries. It is
necessary for every generation to produce more off springs because many individuals do
not survive to reach the reproductive age due to natural causes. However, man has upset
this equation as he has been successful in bringing down the mortality rate. There has
been a tremendous increase in the population of human beings and also the animals and
plants useful to them. This has created a strain on the natural resources that are shared by
all creatures on earth.
There are various ways in which pregnancy can be planned or prevented. Some of them
are:

Mechanical Methods
In this type of contraception, a physical barrier is placed to prevent the entry of sperms
into the uterus. It includes condoms used by males, intrauterine device (IUD) and
diaphragm cap used by females.

Hormonal Methods
It involves the intake of synthetic hormones by the females to prevent ovulation. These
are called oral contraceptive pills and have to be taken as per doctor's advice.

Natural Methods
Total avoidance of sexual intercourse or abstinence is, of course, the only sure
contraceptive method. However, there is a rhythm method which involves avoiding
intercourse during the time of ovulation that is for about a week. However rhythm
method is not a reliable method.

Sterilisation
Sterilisation is a surgical procedure that involves cutting of the tubes that conduct the
gametes. In males it is called vasectomy in which each vas deferens is cut and the cut
ends are tied back. In females, it is called tubectomy in which the oviducts are cut and the
cut ends are tied back.
REVISION QUESTIONS
Identify the choice that best completes the statement or answers the question.
1. A sperm cell consists of a tail used for locomotion, a midpiece containing
mitochondria, and a head that contains
a. semen.
b. DNA.
c. RNA.
d. mucus.
2. Refer to the illustration above. Sperm are produced in the structure labeled
a. “1.”
b. “5.”
c. “3.”
d. “6.”
3. Refer to the illustration above. The structure that connects the epididymis to the urethra
is labeled
a. “1.”
b. “7.”
c. “6.”
d. “2.”
4. Refer to the illustration above. The tube that carries urine during excretion and semen
during ejaculation is labeled
a. “1.”
b. “2.”
c. “6.”
d. “4.”
5. Which of the following structures of the male reproductive system is located within the
pelvic cavity?
a. testis
b. seminal vesicle
c. epididymis
d. urethra
6. The testes
a. produce sperm.
b. produce male hormones.
c. are suspended in the scrotum.
d. All of the above
7. Production of sperm is regulated by luteinizing hormone (LH) and follicle-stimulating
hormone (FSH), which are produced by
a. the testes.
c. the bulbourethral gland.
b. the hypothalamus.
d. the pituitary gland.
8. ovary : egg production ::
a. seminal vesicle : sperm production
b. female reproductive system : sperm production
c. testes : sperm production
d. ovary : fertilization
9. The process by which sperm leave the male’s body is called
a. secretion.
b. diffusion.
c. ejaculation.
d. locomotion.
10. The muscular structure in which the fetus develops is the
a. vagina.
b. cervix.
c. fallopian tube.
d. uterus.
11. The fallopian tubes
a. secrete estrogen.
b. produce eggs.
c. extend from the ovaries to each side of the uterus.
d. All of the above
12. Refer to the illustration above. The structure labeled “3” is
a. a fallopian tube.
b. the uterus.
c. the urethra.
d. a ureter.
13. Refer to the illustration above. Eggs mature in the structure labeled
a. “1.”
b. “4.”
c. “6.”
d. “5.”
14. Refer to the illustration above. Fertilization usually occurs in the structure labeled
a. “1.”
b. “3.”
c. “6.”
d. “2.”
15. The entrance to the uterus is called the
a. vagina.
b. cervix.
c. vulva.
d. diaphragm.
16. Refer to the illustration above. The structure labeled “2” is
a. a sperm cell.
b. an egg cell.
c. a follicle.
17. Sperm and eggs are both
a. haploid.
b. tetraploid.
c. diploid.
d. the cervix.
d. None of the above
18. In which of the following ways are mature human sperm and eggs similar?
a. They have the same number of chromosomes in their nuclei.
b. They are the same size.
c. They are both equipped with a flagellum to allow movement.
d. They are both produced after ovulation.
19. The gamete produced by the female reproductive system is called a(n)
a. sperm.
b. ovary.
c. ovum.
d. follicle.
20. Eggs are produced in the
a. ovaries.
b. uterus.
c. fallopian tubes.
d. vagina.
21. The ruptured follicle left in the ovary after ovulation develops into a
a. corpus luteum.
b. chorion.
c. zygote.
d. cervix.