Download Cell Structure and Diversity

Cell Structure and Cell Diversity
The Light microscope
Eyepiece This lens magnifies (enlarges) the image e.g. x10
Nosepiece Revolves to allow an objective lens to be used
Objective lenses Magnify the image. Low power (x4), medium power (x10), high power (x40).
Total magnification = Eyepiece (x10) x
objective lens (x40) = 10 x 40 = 400.
Body tube/barrel Holds the eyepiece at one
end and the revolving nosepiece (objective
lenses) at the other end.
Revolving nosepiece Holds and positions the
objective lenses.
Coarse focus wheel Used for initial focussing
with low and medium power.
Fine focus wheel Sharpens the focus after
coarse adjustment. Focus the high-power
objective with this wheel only.
Stage Platform on which slide is placed. Slide is
kept in place by clips. Keep dry.
Condenser Focuses light onto slide.
Diaphragm Controls and adjusts the amount of
light passing to the slide.
Light source Electric bulb or reflecting mirror.
Arm Joins the body tube to the base of the
microscope
A simple microscope uses one lens to magnify
an object e.g. a magnifying glass.
A compound microscope uses two or more lenses to magnify an object (multiply the eyepiece and
objective lens for total magnification)
Electron microscope electrons focussed using magnets onto specimen. As electrons are invisible,
image is shown on TV screen, or micrograph.
Resolution light waves cannot pass through a space that is smaller than 200nm. Electron
microscope can distinguish parts that are only 1nm apart because electrons have a smaller
wavelength.
It is not possible to observe living material with an electron microscope because the beam of
electrons directed onto the specimen consists of minute negatively charged particles which are
readily scattered by atmospheric atoms and molecules.
It is therefore necessary to place the specimen in a vacuum in which living cells immediately die.
Sections of cells and tissues must be extremely thin otherwise electrons will not pass through them
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Light Microscope
Uses light rays & focuses them with x 2
convex lenses to illuminate an object.
Magnifies up to 1400X
Low resolution (up to 200 nm)
It reveals nucleus, cell organelles, cell
walls, vacuoles and chromatin
Portable & relatively inexpensive
Can examine living tissue (thin)
Electron Microscope
Uses a beam of electrons & focuses them with
electromagnets to illuminate an object.
Magnifies up to 500,000 X
High resolution (up to 1 nm) – ‘cos beam of electrons has
a much smaller wavelength than light.
Reveals details of cell organelles & cell structure such as
cilia, flagella & membranes
Not portable & very expensive
Objects dead (in a vacuum)
Image = photomicrograph – a grainy black & white picture
Transmitting Electron Microscope (TEM) - Sends electrons through objects and reveals the most
detail. The TEM uses electromagnets as lenses to focus and magnify the image by bending the
paths of the electrons.
Scanning Electron Microscope (SEM) – Photographs reflected electrons from surfaces and reveals
3D structures. The surface is usually coated with a thin film of gold.
Animal Cell Structure Using a Light Microscope
 All the living matter of a cell is called
protoplasm.
 The cell is surrounded by an outer cell or
plasma membrane.
 The nucleus is the control center of the cell.
 The cytoplasm surrounds the nucleus.
 The cytoplasm is everything within the cell
except for the nucleus.
 There are many small organelles within the
cytoplasm. This is where most of the cell’s
activities take place.
 The cytoplasm is composed of 90% water.
 They cannot be seen using a light microscope.
Plant Cell Structure Using a Light Microscope
 All the living matter of a plant cell is also called protoplasm.
 The cell is surrounded by a cell or plasma
membrane. Unlike the animal cell the plant cell
also has a rigid cell wall surrounding it.
 This is made of cellulose and is very rigid. It
supports the plant cell.
 The nucleus is the control center of the cell.
 The cytoplasm surrounds the nucleus.
 The vacuole is a storage area for the plant cell.
 The vacuole contains cell sap. This is made of
sugars, salts, and pigments.
 The chloroplasts contain chlorophyll. This is
where photosynthesis occurs within the cell.
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Basic cell structure is revealed by the light microscope (1000x) e.g. nucleus, cell membrane,
cytoplasm, cell wall, chloroplast, vacuole.
The electron microscope is used to show the ultrastructure of cells. If gives a high level of
magnification (500,000x) making the detailed structure of organelles visible.
Cell organelles are generally colourless and must be stained to see them
 Iodine for plant cells
 Methylene blue for animal cells
The Cell
 All organisms (living things) are made up of tiny
units called cells.
 The cell is the smallest unit of living mater that
exhibits the characteristics of life.
 Cells are three-dimensional structures
 They are measured in units called micrometres
Plant cells
Have cell walls.
Have chloroplasts
Have chlorophyll.
Large and more
permanent vacuoles.
Store carbohydrates
as starch.
Animal cells
No walls.
No chloroplasts
No chlorophyll
Few, if any, small,
temporary vacuoles.
Store carbohydrate
as glycogen.
.
Cell Structure Using an Electron Microscope
Under an electron microscope the ultrastructure of the cell becomes visible:
 Ribosomes are structures that make protein. They are manufactured in the nucleolus and are
composed mainly of RNA.
 Mitochondria are responsible for cellular respiration.
 Chloroplasts are the site of photosynthesis in green plants. The green pigment is called
chlorophyll and is stored inside the chloroplasts.
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There are two cell types:
Prokaryotic cells
Single celled
Do not have a nucleus or membrane-enclosed
cell organelles
Are usually small
Do not have mitochondria or chloroplast
Are primitive
e.g. bacteria.
Eukaryotic cells
More developed
Have a nucleus and cell organelles, all of which
are enclosed by membranes
Larger than prokaryotic cells
Contain structures like mitochondria or
chloroplast which are enclosed by membranes
More advanced than prokaryotic cells
e.g. plant cell, animal cell, fungi, amoeba.
Cell ultra-structure - Cell organelles
Biological cell (plasma) membrane (7.5 nm thick)
sss
 The cell membrane is composed of various lipids and proteins arranged in a characteristic
pattern.
 The lipids consist of a double later of phospholipids known as the lipid bilayer, they are
embedded in phospholipid bilayer
 The most acceptable model of the cell membrane is the fluid-mosaic model developed by Singer
and Nicolson (1972), which suggests that the lipid bilayer acts as a matrix into which proteins are
embedded or into which they are absorbed.
Structure:
 The cell membrane is a fluid phospholipid bilayer coated and
embedded with protein.
 Protein gives elasticity and lipid allows fat-soluble
molecules to enter.
 There are temporary pores throughout the membrane.
Function:
 Holds and retains cell contents - thus giving shape, support (provided by proteins) and protection.
 Acts as a semi permeable barrier to control entry and exist of molecules ie. can let small
molecules e.g. water (by osmosis), oxygen and carbon dioxide (by diffusion) through but not
large molecules e.g. salt, sugar, protein.
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 Some membrane proteins are involved in the immune system, while others act as carrier proteins
for transporting materials across the cell membrane. Proteins assist in the active transport of
materials across the membrane (energy needed).
 Thus, the cell can control the amount of water and
salt conc. (osmoregulation).
 Phospholipids affect the fluidity and permeability
of membrane.
Cytoplast
 The area of a cell surrounding the nucleus
 Contains many cell organelles
 Cytosol is the liquid part of the cytoplasm
Structure:
 This is a watery jelly in which cell organelles are suspended. (Protoplasm = cytoplasm + nucleus)
Function:
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Site of metabolism e.g. glycolysis, protein synthesis.
Intercellular transport
Storage of water, lipids, amino acids etc.
Support of cell organelles.
Nucleus (5-10nm diam.)
 The nucleus is surrounded by the nuclear membrane, which allows molecules to enter and leave
the nucleus similar to the plasma membrane.
 Nuclear pores are the openings through which materials
enter and leave the nucleus. The nucleus contains DNA
(deoxyribonucleic acid) arranged in groups called
chromosomes.
 The nucleolus is where ribosomes are made from RNA
(ribonucleic acid).
 Genes are located on the chromosomes. These are the
structures that control the production of protein and thus
determine the characteristics of the organism. The contain
a specific number of chromosomes
 The function of DNA is to code for the production of protein in a cell.
Structure:
 Enclosed by a double membrane.
 Contains chromatin (genetic material) - becomes arranged into chromosomes during cell division.
These are made of protein and DNA. Genes are located along the chromosome. Generally
elongated
 Contains one or more nucleoli.
 Nuclear pores allow passage of mRNA, rRNA, nucleotides.
 Nucleoplasm = a liquid in nucleus surrounding nucleolus and chromatin.
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Function:
 Maintains and controls all the activities of the cell. (by making enzymes
 Contains genetic material.
 Involved in cell division.
Nucleolus
 Found in nucleus and makes ribosomal RNA. It passes through the pores and makes ribosomes in
the cytoplasm.
 Red blood corpuscles and phloem sieve tube elements do not have nuclei.
Mitochondrion (5-10m long)
 Supply energy for cell respiration
 Plentiful in active cells e.g. muscle, nerve, liver, brain,
kidney, neck region of male sperm, apical meristems
(shoot/root tips).
 Few in inactive cells e.g. fat, bone, skin, cortex in plants.
 Not found in bacteria.
Structure:
 Surrounded by a double membrane - the inner one is
folded into cristae.
 Lumen is filled with a dense matrix of water, food, enzymes, some ribosomes and small portions
of DNA - self-duplicating organelles.
Function:
 Release energy in aerobic respiration – Kreb’s cycle occurs in lumen and electron transport chain
occurs in cristae.
Ribosomes (14-18nm)
 Found in large numbers in the liver
 Make proteins
Structure:
 Small granular structures made of two sub-units.
 Made of RNA (ribonucleic acid) and protein.
 Found free in cytoplasm or attached to folded membranes
Function:
 Protein synthesis
 Free ribosomes make protein used by cell and those on tubes make proteins for export.
Cell wall (0.5-1nm thick)
 Plants only
 Secreted by cell membrane.
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Structure:
 Made of cellulose.
 Adjacent cells are stuck together by calcium pectate the middle lamella of pectin
Function:
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Gives strength, support and protection to the cell.
Controls cell growth and shape.
Prevents osmotic bursting of cell membrane.
Fully permeable to allow the free movement of molecules through it
Vacuoles
 Usually one in plants - very large & permanent.
 Small, temporary and more in animals because they excrete their waste (often called vesicles).
Structure:
 Fluid-filled spaces surrounded by a membrane
Function:
 Temporary storage of food (sugars, amino acids, fats), water, salts (help in osmoregulation),
pigments, tannins, gases (O2 & CO2), wastage and excretory products.
 The cell sap makes the cells turgid.
 To give shape and structure to the cell.
 For expansion during cell growth.
Chloroplasts (2-5nm) (plant cells only)
 Both mitochondria and chloroplasts have a double membrane and DNA.
 Having DNA supports the theory that chloroplasts and mitochondria were once independent
prokaryotic organisms that lived symbiotically inside large eukaryotic cells.
Structure
 Double membrane
 Contain chlorophyll and DNA - self-duplicating.
Function
 Used to make food (carbohydrate) by photosynthesis – light phase in grana and dark phase in
stroma.
Lysosomes
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Suicide sacs
Found in animal cells
Contain acid and enzymes to digest faulty cell parts
Destroys faulty cell parts by autolysis
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Cell Diversity
Cells are not identical – they diversify their structure to suit their function
A tissue is a group of similar cells that are adapted to carry out the same function
Plant tissues
Dermal tissue
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Surrounds and encloses plants
Protection and prevents water loss
Found in stem, leaf and roots
Contain rectangular cells, with thick, strong walls
Has a waterproof layer (the cuticle)
Eg. epidermis
Ground tissue
storage (starch, sugar and salts)
Meristematic tissue
cell division mitosis (growth)
Vascular tissue
transports materials around the plant, found in all parts of plant,
arranged in vascular bundles
water and minerals around the plant
food from the leaves to the other parts of the plant
Xylem transports
Phloem transports
Animal Tissues
Connective tissue
 Joins and supports certain parts of the body
 Consists of cells contained in the matrix (a surrounding substance) (eg. plasma for blood)
 Eg. cartilage, tendons, ligaments, bones, blood. and adipose tissue
Muscle Tissue
can contract and relax (movement)
Nervous Tissue
composed of nerve cells called neurons carry electrical impulses to and
from brain
Tissue Culture
Tissue culture is the growth of cells or tissues, in or on an artificial medium outside an organism
The tissue sample is removed from a plant or animal and grown in glassware (in vitro) or in a
bioreactor under carefully controlled conditions
In vitro – growing inside body
Growth is by mitosis (replication) and produces a cluster of identical offspring - a clone
Eg. organ transplant
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Conditions necessary for Tissue growth
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Oxygen (for respiration)
Nutrients (food for growth)
Growth factors and hormones
Correct pH
Optimum temperature
Sterile conditions (in sterile conditions bacteria will multiply at 1 billion / 10 hrs)
Freedom from competition
Stages in Tissue Culture
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Skin cells obtained
Enzymes added
Individual Cells isolated
Controlled culture medium
Sheets of cells grown
Applications of tissue cultures
Virus reproduction
 Hela cells used to grow and investigate viruses
Micro propagation of plants
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Produces exact copies
Quickly produces mature plants
Doesn’t need pollinators or seeds
Producing plants that are disease resistant and virus free
Growing human tissue for organ transplants
 Skin grafts
 Liver cells
 Pancreas cells
Producing biotechnology products
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Insulin
Interferon
Pregnancy testing kits
Drug testing kits
Cancer testing kits
Micropropagation – growth of large numbers of identical plants from pieces of an original plant. A
suitable plant is selected, cut into minute pieces (cell size) and grown artificially, then transplanted
into soil and grown as normal
Advantages – large numbers, quick, genetically identical, cheap
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Organs
An organ is a structure composed of a number of tissues that work together to carry out one or
more functions
Plant organs
Root
Stem
Leaf
Flower
Seeds
Fruit
Animal organs
Heart
Stomach
Intestine
Liver
Lungs
Skin
Organ systems
A system consists of a number of organs working together to carry out one or more functions
Animal systems
Digestive system
Endocrine system
Nervous system
Skeletal system
Circulatory system
Reproductive system
Urinary system
Muscular system
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