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Cell Structure and Function
All living things are made of ________. Some, like us, contain many millions of
cells. Such organisms are referred to as being _________________. Other
organisms are composed of only one cell and are said to be
________________. Diagrams of some common unicellular organisms are
drawn below.
Most cells are so small that they can only be seen using a microscope. All cells
contain _______________ surrounded by a flexible membrane called the
_________ membrane. Using a very powerful electron microscope, it is
possible to see many of the structures inside a cell. These structures are called
cell ______________ and they are responsible for carrying out the chemical
processes which maintains the cell. These chemical processes contribute to the
cell’s metabolism. Many metabolic reactions are catalysed by ____________.
A series of such reactions is called a _____________ pathway.
The diagrams on handouts 1 and 2 show the organelles that are present in a
typical plant and animal cell, and the table on page 2 summarises the functions
of the various organelles within these cells.
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ORGANELLE
NUCLEUS
MITOCHONDRION
ENDOPLASMIC
RETICULUM
(rough or smooth)
RIBOSOMES
*
FUNCTION
contains chromosomes (DNA) which provide the
recipe for making cell _____________.
site of aerobic ______________ (which in
turn produces ATP).
involved in the ____________ of proteins for
export from the cell.
site of ____________ synthesis – found on
the surface of RER or free in the cytoplasm.
GOLGI APPARATUS involved in the packaging and processing of
(or golgi body)
____________ ready for secretion from the
cell.
SECRETORY
a sac derived from the ________
(GOLGI) VESICLE
__________ containing the finished
___________ which it then secretes from cell
by fusing with the cell ____________.
LYSOSOMES
a sac which contains powerful digestive
___________ which are used to destroy
bacteria.
PLASMA CELL
controls what enters or leaves a cell.
MEMBRANE
CHLOROPLAST
only found in _________ cells; contain
_____________ used to trap light energy
needed for _________________.
VACUOLE
found in many plant cells; contains water with
salts and sugars. Contributes to cell turgor.
CELL WALL
only found in ___________ cells. Made of
cellulose it gives cells strength and rigidity. It
is freely (or totally) permeable.
*
=
only found in animal cells
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Organelles Working Together
The organelles inside a cell do not work in isolation. Instead they work together
in order to synthesise, transport, package and eventually secrete
____________ from the cell. Handout 3 gives some examples of such
proteins.
The nucleus contains the _____________ information (or recipe) needed to
make ______________. Proteins are then synthesised in the
_____________. They are then _______________ by either the rough or
smooth _________________ ________________. Then, they are packaged
and processed ready for secretion in the ________ _____________. Parts
of the golgi apparatus nip off to form secretory _____________ which
contain the finished _____________ (e.g. an ___________ like amylase or a
_____________ like ADH). The secretory vesicle fuses with the cell
_____________ and the ____________ is secreted from the cell.
The diagram below shows how all of these organelles work together. Note how
sacs which detach from the ER join up to form the _________
____________.
Processing and Secretion of a Protein.
The sequence in which these organelles become involved in the production of a
protein for secretion is:
nucleus → ____________ →
→ _________ _____________
______________
→ vesicles
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_______________
What can organelles tell us?
We can work out what the function of a cell is by simply looking at the
organelles (and the number of them) in a cell. For example:
1.
__________ cells and sperm cells contain many _______________
compared to other cells e.g. skin. This is because both of these types of
cells require a lot of energy.
2.
Palisade mesophyll cells in the leaves of plants contain many, many
______________. This is because this is the part of the leaf where
most __________________ occurs.
3.
Cells is our salivary glands, pancreas, liver and pituitary gland, are
abundant in ________ ______________. This is because all of these
types of cells are involved in secreting proteins.
4.
White blood cells contain a lot of _____________. The powerful
digestive enzymes in these organelles help these cells to destroy
bacteria or other foreign bodies (e.g. viruses).
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Cell Structure Related to Function
It is important in Biology to remember that the structure (i.e. how a cell is
built) of a cell is closely related to it’s function. Here are some examples.
CELL TYPE
FUNCTION
HOW STRUCTURE IS
RELATED TO
FUNCTION
To surround and then
destroy bacteria and other
foreign bodies (e.g. viruses).
Able to change their
_________ which then allows
them to surround bacteria.
Contain many
_____________ which then
destroy bacteria.
Present a __________
_____________ _______ in
contact with the soil and so
increases the amount of water
it is able to absorb.
WHITE BLOOD CELL
To absorbs __________
and minerals from the soil.
ROOT HAIR CELL
To fertilise an egg cell.
Has a ________ that it uses
to swim towards the egg. It’s
tail is packed full of
_______________ which
supply it with loads of energy
needed for it’s journey.
These cells (found in our
windpipe) are used to sweep
mucus away from the lungs
and into the nose or mouth.
Covered in tiny hairs called
________. The cilia beat
upwards, wafting the mucus
towards the mouth or nose and
away from the lungs.
To transport oxygen around
the body.
These cells are bi-concave
(like a refresher). This gives
them a large ____________
_______. They also contain
_______________ which
has an affinity (loves) oxygen.
SPERM CELL
EPITHELIAL CELL
RED BLOOD CELL
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ABSORPTION AND SECRETION
There are three main ways in which substances can be absorbed into or
secreted from a cell. These are:
1.
______________
2.
______________
3.
___________ _______________
DIFFUSION
Diffusion is the _________________ of molecules from a region of
_______ concentration to a region of _____ concentration. The difference
that exists between the two regions is called the concentration
_______________.
Diffusion is important to cells because it is the process by which molecules
either ________ or _______ a cell. Substances which enter a cell by
diffusion include __________ and dissolved food like ___________.
Substances that leave a cell by diffusion include ____________
______________. Water can either enter or leave a
cell.
OXYGEN
CARBON DIOXIDE
DISSOLVED FOOD
(e.g. glucose)
OSMOSIS
Osmosis is described as a “special case of diffusion”. Osmosis is defined as:
It is the plasma cell membrane of a cell that acts as a ______________
permeable membrane.
THE MOVEMENT OF WATER MOLECULES FROM A REGION OF HIGH
CONCETRATION TO A REGION OF LOW CONCENTRATION THROUGH A
SELECTIVELY PERMEABLE MEMBRANE.
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THE EFFECT OF OSMOSIS ON CELLS
In order to understand how osmosis affects plant or animal cells, we must be
familiar with the following terms which describe the concentration of water
molecules in a solution surrounding cells compared to the concentration of
water molecules inside the cells.
TYPE OF SOLUTION
So:



CONCENTRATION OF WATER
MOLECULES
has a higher concentration of water
molecules than the cells
has the same concentration of
water molecules than the cells
has a lower concentration of water
molecules than the cells
if cells are placed in a hypotonic solution, water will _________ them
by __________ , and the cells will therefore _______ weight.
if cells are placed in a hypertonic solution, water will _________ them
by __________ , and the cells will therefore _______ weight.
if cells are placed in an isotonic solution, the same number of water
molecules will enter as leave the cells, therefore their weight will stay
the same i.e. they will neither _______ nor ________ weight.
In the experiment drawn below, the bag would ______ weight as water would
________ the bag by __________.
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THE EFFECT OF OSMOSIS ON ANIMAL CELLS
The diagram below shows the effect of osmosis on an animal cell when it is
placed in a hypotonic, isotonic or hypertonic solution.
THE EFFECT OF OSMOSIS ON PLANT CELLS
The diagram below shows the effect of osmosis on a plant cell when it is placed
in a hypotonic, isotonic or hypertonic solution.
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Animal cells will _________ when they are placed in a hypotonic solution, but
plant cells will not. This is because plant cells have a ______ _______ which
prevents this from happening.
Summary
Effect of solution on cells
CELL TYPE
HYPOTONIC
ISOTONIC
HYPERTONIC
ANIMAL
burst
no change
shrink
PLANT
become
TURGID
no change
become
PLASMOLYSED
(or FLACCID)
N.B. Neither diffusion or osmosis require ___________ (ATP) therefore
they are not dependent on the process of ____________
_________________. In other words they are not active but
____________ processes.
ACTIVE TRANSPORT
Apart from diffusion and osmosis, another way in which molecules can
enter or leave a cell is by __________ transport.
During active transport, molecules move from a region of ______
concentration to a region of _______ concentration. Molecules
therefore move against a __________________ ________________.
Since molecules are moving against a concentration gradient, active
transport requires ____________ (ATP).
Since active transport requires energy (ATP), this means that it is
dependent on the process of __________ _______________ which of
course produces energy (ATP).
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Active transport differs from diffusion in two ways:
1.
During diffusion, molecules move from a high concentration to a low
concentration; during active transport, it is the opposite (low to high).
2.
Diffusion is not an energy-requiring process; active transport is in other
words, diffusion is a _____________ process, active transport is an
__________ process.
The diagram below shows how substances can either be actively transported
into or out of a cell across the plasma cell membrane. Note that it is a
_____________ molecule present in the membrane structure that is
responsible for actively transporting molecules into or out of a cell.
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Selective uptake of ions by active transport
The table below shows that an aquatic plant is able to select and accumulate
certain ions via active transport. The data confirms that:

the ions are being absorbed by active transport because there is a
__________ concentration of potassium (K) outside than inside

it is selective because more ______________ than ______________
ions are being absorbed.
Conditions required for active transport
Since active transport requires ______________ (supplied by ATP), this
means that it is dependent on the process of aerobic respiration (which of
course produces ATP). If respiration ceases, so will active transport. Factors
that affect aerobic respiration, will therefore affect respiration. Such factors
include:
 temperature (affects the ____________ that control respiration)

_____________ concentration (as the O2 concentration decreases, so
will the rate of respiration – less ATP = less active transport)

_____________ availability (since it is the main respiratory substrate)
All of the above factors indirectly affect active transport because they
directly affect ____________ _______________. The graph at the top of
the next page shows how temperature can affect the rate at which nitrate ions
are active absorbed.
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Remember, temperature affect the ______________ that control aerobic respiration.
Description:
As temperature increases to 30oC, the rate of active
transport _____________. Above 30 oC, the rate of active transport
________________.
Explanation:
As the temperature increases up to 30oC , the enzyme
controlling respiration will be becoming more active. More respiration = more ATP for
active transport. As the temperature goes above 30 oC, the rate of active transport
decreases, because the enzymes are being ________________.
The graph below shows how oxygen concentration can affect the rate at
which nitrate ions are active absorbed.
Remember, oxygen concentration affects rate of aerobic respiration.
Description:
As oxygen concentration increases to 30%, the rate of active
transport _____________. Above 30%, the rate of active transport remains
________________.
Explanation:
More oxygen =
more aerobic respiration
more respiration = more ATP/energy.
active transport requires ATP/energy
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Cell membranes
Cells are enclosed by a membrane called the _________ cell membrane. In
addition, many organelles such as mitochondria, endoplasmic reticulum, golgi
apparatus, chloroplasts and the nucleus itself are bound by one or two plasma
membranes.
The plasma membrane is composed of ___________ and
________________ (fat) molecules. The phospholipids form two layers (called
a bi-layer) which can move – making the membrane ___________ (flexible).
The protein molecules are dispersed throughout the phospholipids forming a
_________ pattern – and they too can move freely within the membrane.
For this reason, the membrane is described as ________ - _________.
Because membranes are composed of ____________ and
__________________, they are easily damaged by _______ temperatures,
acids and by fat solvents such as ___________. This can be demonstrated by
using plant cells which have a coloured sap (e.g. beetroot). When the membrane
of these cells is damaged, the coloured sap leaks out into the surrounding fluid.
The protein molecules in the membrane have many functions. These include:

___________ which speed up many reactions e.g. protein synthesis.

receptor sites for hormones which then influence the activity of the cell.

proteins which actively transport materials across the membrane using ATP
as a source of __________.
proteins which form _______ (or channels) in the membrane through which
molecules can enter or leave the cell by ______________ .

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The membrane is described as being ______________ permeable, because it
will only allow some molecules to pass through and this depends on the
_______ of the molecule.
Experiment to demonstrate the structure of the plasma
membrane.
We can do an experiment to demonstrate the structure of the plasma
membrane. To do this we would use a plant whose cells contain a coloured sap
(in their vacuoles). An example of a plant we could use is _____________,
which has red/purple sap.
If a piece of beetroot “bleeds” this means that the plasma membranes
surrounding the cells themselves and the plasma membranes surrounding their
vacuoles have been damaged. This damage is irreversible.
The investigation as shown below was set up for one hour:
Results
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TEST
TUBE
DOES BLEEDING
OCCUR?
TREATMENT
A
B
C
D
Explanation
A
Bleeding __________ occur because water does not affect the
structure of the plasma membrane.
B
Bleeding __________ occur because the acid denatures the
_____________ molecules in the membrane which causes it to break
down. This then allows the sap to leak out of the cell and the surrounding
liquid turns red.
C
Bleeding __________ occur because the alcohol dissolves the
__________________ molecules in the membrane which causes it to
break down. This then allows the sap to leak out of the cell and the
surrounding liquid turns red.
D
Bleeding __________ occur because the high _________________
denatures the _____________ molecules in the membrane which
causes it to break down. This then allows the sap to leak out of the cell
and the surrounding liquid turns red.
NOTE
Neither water or a salt or sugar solution will damage the
plasma membrane - as long as they are at a ______
temperature.
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The Cell Wall
The cell wall is the non-living outer boundary of _________ cells. It is mainly
composed of a structural carbohydrate called _____________, which is laid
down in ___________ as shown in the diagram below. This is what gives a
plant cell it’s shape and keeps it fairly rigid.
Unlike the membrane, the cell wall is totally (or freely) _____________ - in
other words it does not prevent anything from leaving or entering a cell.
It is the cell wall which prevents a plant cell from bursting when it is placed in a
________________ solution.
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Aerobic Respiration
The whole point of aerobic respiration is to release the ____________
energy in the food we eat. ___________ is needed to release this energy.
The equation below summarises aerobic respiration.
FOOD
+
(e.g. glucose)
OXYGEN
→
___________
____________
+ _____________ + ENERGY
Most of this energy ends up being ___________ in our cells in a compound
called ATP ( ______________ _______________), but some of this energy
ends up being lost as ________.
ATP
ATP is a compound which is made from adenosine and three phosphates (Pi). It
is made by joining a molecule of ADP (adenosine ____________) with a single
phosphate (Pi) molecule. To join these two molecules together requires energy.
This energy comes from our ________ .
So, the chemical energy in food, ends up being stored in _____. The
production of ATP from ____ and ____ is called PHOSPHORYLATION,
which can be summarised by the following equation:
ADP + Pi
ATP
When cells require an _______________ source of energy, the “high energy”
bond between the last two _____________ molecules breaks and energy is
released for cellular processes that include:
 muscle ________________
 _________ transport
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



mitosis/meiosis (to separate the chromosomes)
DNA ________________
protein synthesis
phagocytosis (to allow membrane to move and engulf bacteria).
Cells need a constant supply of ATP, so it is re-synthesised as quickly as it is
broken down. All living things respire - this is often referred to as “chemical”
or “tissue” respiration (to distinguish it from the common use of the word
“respiration” to mean “breathing”).
ATP acts as a link between aerobic respiration and other cell processes which
require ATP to drive them e.g. protein synthesis as shown in the diagram below.
Food +
oxygen
CO2 +
H 2O
Amino
acids
ADP + Pi
Proteins
OXIDATION AND REDUCTION
Oxidation is the _______ of _____________ atoms, and when this
happens, energy is _______________. (Remember “OIL” = oxidation is
loss).
Reduction is the _______ of _____________ atoms, and when this
happens, energy is _______________. (Remember “RIG” = reduction is
gain).
[Respiration is often referred to as a process involving the “oxidation of
foodstuffs”. This is because during respiration, hydrogen atoms are removed
from the respiratory substrate (e.g. glucose) and used to produce energy
(ATP)].
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INTERNAL STRUCTURE OF A MITOCHONDRION
The diagram below shows the internal structure of a mitochondrion. This cell
organelle is the site of ___________ ________________.
1μm (micrometer or micron) = 1000th of a millimetre.
A typical cell contains around 1000 mitochondria, but those cells which have a
high __________ requirement, e.g. _________ and ___________ cells
have many more.
The central matrix contains the enzymes that are involved in the _________
_________; the cristae contains the enzymes that are involved in the
_____________ system (also called the hydrogen transfer system).
THE CHEMISTRY OF RESPIRATION
Respiration can be divided into 3 separate but continuous processes:
1.
________________
2.
The ________ Cycle (sometimes called the citric acid cycle).
3.
The ________________ system (sometimes called the
_______________ transfer system).
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GLYCOLYSIS
Glycolysis takes place in the ___________________ of a cell. No
____________ is needed for glycolysis to occur. Glycolysis involves the
splitting of ___________ (6C) into two molecules of _____________
acid (2 X 3C). This produces ________ molecules of ATP, but since
_______ molecules of ATP are needed to split the glucose in the first
place, the NET GAIN is 2 molecules of ATP.
So, whether oxygen is available or not, the end products of glycolysis
are:


2 molecules of _____________ _______
a net gain of _______ molecules of ATP
In order for glycolysis to occur in the first place, both ______ and
____________ must be available to the cell.
If oxygen is not available to the cell - in other words if conditions are
______________, then the anaerobic phase of respiration occurs.
The pyruvic acid remains in the ________________ of the cell and is then
respired anaerobically as follows:
During anaerobic respiration, the only source of ATP comes from
_______________. Note that plant cells include fungus (like yeast) and
animal cells include bacteria.
THE KREB’S CYCLE
If oxygen is available, the pyruvic acid diffuses from the _______________
into the central matrix of the mitochondrion. It is here that the Kreb’s Cycle
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occurs. Unlike glycolysis, ____________ is needed for this stage. The
diagram below outlines the Kreb’s Cycle.
Each molecule of pyruvic acid loses a ___________ atom (as carbon dioxide).
This produces a 2-carbon compound called __________. (This joins with an
enzyme called CoA, forming a compound called Acetyl CoA).
This newly formed 2C compound then joins with a 4C compound already present
in the central matrix of the ____________________. This produces a ___carbon compound called _________ acid. Each molecule of citric acid then
loses a carbon atom (as __________ _____________) to produce a 5carbon compound which in turn loses a carbon atom to produce a _____ carbon
compound. It is this 4C compound that joins with the 2C acetyl compound and
the cycle begins
again. _____ molecules of ATP are produced as a direct result of the Kreb’s
cycle.
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THE CYTOCHROME SYSTEM
The cytochrome system is sometimes called the _______________ transfer
system - this is because it consists of a series of _____________ carriers
(called cytochromes). The cytochrome system occurs in the ___________ of
the mitochondria. Oxygen is needed. 34 molecules of ATP are produced from
one molecule of ____________ during the cytochrome system.
During glycolysis and the Kreb’s cycle, carbon and _________________
atoms are removed from the original ___________ molecule. After hydrogen
atoms have been removed, they are picked up by a single hydrogen carrier
molecule called ______ , which is reduced to NADH2.
NAD is used to transfer the hydrogen atoms from the cytoplasm or the
central matrix to the ___________ of the mitochondria. On arriving at the
cristae, they are released by NAD and then pass through the cytochrome
system.
ADP
NADH2
CARRIER 1
Pi
ADP
CARRIER 2
Pi
ADP
CARRIER 3
Pi
CARRIER 4
OXYGEN
WATER
NAD
ATP
ATP
ATP
As the hydrogen atoms pass through the cytochrome system, the most
important compound that is produced is _____. ___________ function is to
act as the final hydrogen acceptor. When oxygen combines with hydrogen at
the end of the cytochrome system, __________ is produced.
Apart from glucose (a carbohydrate) other respiratory substrates include fats,
fatty acids, glycerol and proteins. Cell proteins (like the body’s muscles e.g. the
heart) are only ever used as a respiratory substrate in times of acute
____________________.
Handout 4 on page 23 shows a more detailed outline of chemical respiration.
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ENZYME INHIBITORS
An enzyme inhibitor is a substance that can either _____________ an
enzyme or block it’s active site. This means that the enzyme can no longer join
with it’s ______________. The diagram below illustrates how an inhibitor can
stop an enzyme’s activity by blocking it’s active site. (DO NOT ATTEMPT TO
MEMORISE NAMES!)
Because the inhibitor mimics the shape of the enzyme’s substrate, the inhibitor
can block the active site by fitting into it. This results in the enzyme becoming
inactive i.e. it can no longer function. Inhibitors can therefore a affect a
metabolic pathway as shown in the diagram below.
compound A
enzyme 1
compound B
enzyme 2
compound C
If an enzyme inhibitor affects enzyme 2, then this would result in compound B
_______________ and compound C ________________. Although the
inhibitor affects enzyme 2, it does not affect the activity of enzyme 1.
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DNA AND PROTEIN SYNTHESIS
THE STRUCTURE OF DNA
DNA =
________________________
________
Chromosomes are found in the _____________ of a cell. Each chromosome
consists of many _________. These genes contain the _____________
information which determines an organism’s characteristics. Genes are made
of _______.
DNA is an example of a _______________ acid. Nucleic acids like DNA are
made from millions of repeating units called _______________. The
structure of a single nucleotide is shown below.
A SINGLE NUCLEOTIDE OF DNA
There are _______ different bases in DNA. Their names are:
1.
______________ (A)
2.
_______________ (T)
3.
_______________ (G)
4.
_______________ (C)
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It is only the ________ which makes one nucleotide different from another.
So, since there are only four different bases, there can only be four different
_________________ in DNA .
DNA is a double stranded structure. It’s two strands are twisted like a spiral
staircase. This structure is called a ___________ _________. The
phosphate and _______________ sugar molecules form it’s backbone. The
bases pair off and are held together by weak ________________ bonds.
Adenine always pairs with ______________ and vice versa, and guanine always
pairs with _____________ and vice versa. For this reason they are referred
to as __________________ base pairs. The diagram below shows the DNA
double helix.
DNA REPLICATION
A huge coiled and folded strand of DNA makes up one chromosome.
Chromosomes are found in the _____________ of cells. Before cells divide,
an exact copy of the DNA must be made. This process is called DNA
________________ and it is important because it ensures that each new cell
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receives the correct amount of ____________ information for it to grow and
___________ properly. DNA replication occurs at the very end of mitosis
just before the _______________ divides the parent cell into two
genetically identical daughter cells
In order for DNA replication to occur, the following four things must be
present in the cell.
1.
2.
3.
4.
many of the four free _________________ in DNA
the original DNA molecule (which acts as a template to copy)
the correct ______________
_____ which provides the energy needed for this process.
Stages of DNA Replication
DNA replication occurs as follows:
1.
2.
3.
4.
5.
6.
7.
the DNA double helix __________ from one end only
the weak _______________ bond between the complementary
bases __________.
the two strand of DNA ____________ exposing their bases
free ________________ find their complementary nucleotide on
the open DNA strands
weak hydrogen bond form between the _________
bonds then form between the phosphate of one nucleotide to the
_________________ of the next
each new DNA molecule coils to form a double __________.
HANDOUT 5 on page 28 shows the process of DNA replication.
One half (i.e. one of the strands) of each new DNA double helix comes from the
original DNA molecule. The other half has been made from free DNA
________________ joining together. Since 50% or half of the original DNA
molecule ends up in the new DNA molecule, DNA replication is referred to as
being semi -_____________________.
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DNA Content of Cells
Not all cells in our body contain the same amount of DNA. Since
____________ (sex cells) eggs and __________ in animals; pollen grains and
__________ in plants, contain ________ the number of chromosomes as
somatic (non-sex) cells, they contain half the amount of DNA as somatic cells.
Mature red blood cells do not have a nucleus therefore they have no
chromosomes and in turn will have no DNA. The table below summarises the
DNA content of some human cells.
CELL TYPE
liver
sperm
UNITS OF DNA
6.0
mature red blood cell
muscle
gamete mother cell
egg (ovum)
young red blood cell
skin cell (just before
cell completely divides)
12.0
If a DNA molecule contains 1000 bases, and 200 of these bases are adenine,
then _______ bases will be thymine. This leaves 600 bases which will be
divided equally between cytosine and ____________. So, in this particular
molecule of DNA 300 bases will cytosine and 300 will be guanine.
The Genetic Code
The sequence of _______ in our DNA contains a “code” or recipe for making
cell _____________ e.g. enzymes, hormones etc. Proteins are made from
single units called ________ ________ . There are approximately ____
different amino acids which need to be “coded” for. If only one base coded for
1 amino acid, we could only code for ____ different amino acids (1 per base)
leaving _____ amino acids that will not be “coded” for. If two bases “coded”
for 1 amino acid, _____ different amino acids could be “coded” for, leaving
____ amino acids that will not be “coded” for. If three bases “code” for 1
amino acid, _____ different amino acids could be “coded” for which is more
than enough.
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So, THREE BASES CODE FOR 1 AMINO ACID - this makes the genetic
code a triplet code. Each triplet of _________ , only codes for one specific
amino acid and no other. Each amino acid however may have more than one
triplet of bases “coding” for it. For example the triplet CAA will only code for
the amino acid called __________ and only ___________ , but the triplet
CAC also codes for valine (and only valine).
The diagram below shows the genetic code. DO NOT ATTEMPT TO LEARN
ANY OF THIS CODE .
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The Role of RNA in Protein Synthesis
RNA stands for _________________ _________ and as the name suggests,
like DNA it is also a ______________ acid. There are two types of RNA.
These are:
1.
2.
mRNA
tRNA
(messenger RNA)
(transfer RNA)
The Structure of mRNA
Like DNA, mRNA is made from many single ________________. However
the sugar in mRNA is called __________. In mRNA, the base
____________ does not exist - it is replaced by a base called
____________. mRNA is single-stranded unlike DNA which is doublestranded. The table below summarises the structural differences between
DNA and mRNA.
DNA
mRNA
SUGAR
BASES
STRANDS
DNA is only found in the _____________ of a cell, whereas mRNA is found in
both the ______________ and the ________________ of a cell.
TRANSCRIPTION (of DNA into mRNA)
During the process of transcription, the genetic code in our DNA is transferred
to mRNA. This needs to happen because this code is going to provide the recipe
for making a ____________ and proteins are synthesised in the
_____________. This is the only way that the genetic code (in our DNA) can
get to the ribosomes.
During transcription, a section of the DNA molecule unwinds and unzips. (This
section represents one gene) This allows mRNA complementary bases (A-U; TA; C-G and G-C) to bind temporarily (via the formation of weak
______________ bonds) with the exposed bases on this section of one of the
DNA strands.
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Once a single complementary strand of mRNA has been synthesised, the weak
hydrogen bonds between the bases _________. This then allows the mRNA
strand to peels off. It then leaves the _____________ through a pore in the
______________ membrane and makes its way to a ______________ .
Ribosomes are found free in the cytoplasm or attached to the rough
________________ ________________. A diagram showing the
transcription of DNA into mRNA is shown below.
The mRNA now holds the genetic code which provides the recipe to make
a ______________ e.g. amylase, ADH etc. Three bases in a row (one
after the other) on the mRNA strand “code” for one specific _________
________. A triplet of three bases on an mRNA strand is called a
_________. If there are 549 nucleotides (or bases) on a single strand
of mRNA, it will provide the recipe to synthesise a protein molecule that
consists ____ amino acids (i.e. 549 ÷ 3 = ____ ).
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The diagram below shows the 64 mRNA codons and the amino acids that
they “code” for.
Amino acids need to be carried to the ______________ where they will
be joined together to form a protein. tRNA molecules act as the amino
acid carriers.
The Structure of Transfer RNA (tRNA)
tRNA is not a strand – it is a molecule on its own. One such tRNA
molecule is drawn below.
The exposed triplet of bases on a tRNA molecule is called an
_______________ of which there are _____ different ones. Each
anticodon “codes” for one specific amino acid. It is this _____________
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that will determine the amino acid that the tRNA molecule will carry to
the ribosome. The above tRNA molecule will carry the amino acid called
___________.
Functions of tRNA



to transfer amino acids to the _______________
to allow codon/ _____________ links to form
to bring amino acids side by side (to allow _____________ bonds to
form between them
TRANSLATION
Translation refers to the process when mRNA is translated into a protein.
Translation therefore takes place at the _______________, because
these are the organelles that are responsible for protein synthesis.
It is the sequence of the _________ in mRNA that will determine
the sequence of the _______ _______ in the protein that will be
synthesised. It is this sequence of amino acids that makes one protein
different from another. Once the protein has been synthesised, it is
then _________________ by the rough endoplasmic reticulum to the
_________ ___________ where it is packaged and processed ready
for secretion.
HANDOUT 6 which follows shows the process of translation.
MUTATIONS
If a gene mutates, this will alter the sequence of the _______ in the
DNA that the gene is made from. This in turn, will alter the sequence of
the amino acids of the _____________ that this particular gene holds
the recipe to make. As a result a different protein will be synthesised.
Depending on the circumstances this may give the organism and advantage
or a disadvantage -see unit 2.
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Proteins
Proteins are organic* compounds composed of atoms of carbon,
______________ , oxygen and ____________. They are large, complex,
three-dimensional molecules. There are thousands of different proteins. Each
protein molecule is composed of a large number of building blocks called
_______ _______ which are linked together by __________ bonds.
Proteins have many important roles to play in both plants and animals. These
roles include:






all ___________ are proteins and they control metabolic pathways e.g.
respiration and photosynthesis
many hormones are proteins
______________ which protect our body from disease and infection,
are proteins
the plasma membrane consists of ________________ and protein
molecules – see page 13.
muscle tissue is composed mainly of protein
our red blood cells contain ________________ which is the protein
that transports oxygen around the body
Proteins can be classified as FIBROUS or GLOBULAR.
A)
FIBROUS PROTEINS
These proteins are ______________ in water. They are
structural proteins that can resist being pulled or stretched and so they
are quite strong. Fibrous proteins are arranged in long parallel strands as
shown in the diagram below.
B)
GLOBULAR PROTEINS
These proteins are not completely soluble in water. They are usually
involved in some type of metabolic reaction. Globular proteins are roughly
spherical in shape as shown in the diagram below.
Examples of each type of protein are given in the table below.
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*organic compounds contain the element carbon
FIBROUS PROTEINS
collagen (found in bone, tendons and
ligaments)
actin and myosin (found in muscles)
keratin (found in hair, nails and skin)
elastin (another protein found in
ligaments)
GLOBULAR PROTEINS
enzymes (e.g. amylase which breaks down
starch to maltose)
hormones (e.g. ADH which controls the
level of water in the blood)
antibodies (e.g. immunoglobulin which
defends the body against
infection)
plasma membrane proteins (e.g. like the
ones in the cell membrane that are
involved in active transport).
Remember, it is the sequence (order) of amino acids in a protein that makes
one protein molecule different from another (not only in function but in shape),
and it is the sequence of ______ in DNA that will determine what the
sequence of amino acids will be.
The shape of a protein molecule is very important to its function, especially
enzymes that are specific to their ___________ and antibodies that are
produced in response to specific _____________.
36
CELLULAR DEFENCE IN PLANTS AND ANIMALS
VIRUSES
Viruses are extremely small, and are capable of causing disease. Antibiotics
don’t affect them, and we therefore have to rely on our own body’s defence
systems to deal with them. Viruses also attack other animals, plants and even
bacteria.
STRUCTURE OF A VIRUS
All viruses contain either DNA or ________ that is surrounded by a
____________ coat like the one shown in the diagram below.
VIRAL REPLICATION
As the name suggests, viruses are able to make __________ copies of
themselves. In doing so, they interfere with the host cells biochemistry, and
use compounds supplied by the host cell to replicate. In doing so, they destroy
the host cell.
In order for viruses to replicate, four things must be supplied by the host cell
for replication to be possible. The four things are:

______ which supplies the energy needed for replication

free __________________ (to make copies of it’s DNA or RNA)

_______ _________ to make the protein coat that surrounds the
virus

___________ involved in replication and protein synthesis
37
STAGES OF VIRAL REPLICATION
Using ATP, free nucleotides, amino acids and enzymes supplied by the host cell,
viruses replicate. The diagram below shows the stages of viral replication.
____________________________________________________
____________________________________________________
____________________________________________________
____________________________________________________
____________________________________________________
____________________________________________________
____________________________________________________
____________________________________________________
____________________________________________________
____________________________________________________
____________________________________________________
____________________________________________________
____________________________________________________
____________________________________________________
____________________________________________________
____________________________________________________
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____________________________________________________
____________________________________________________
____________________________________________________
____________________________________________________
____________________________________________________
____________________________________________________
____________________________________________________
____________________________________________________
____________________________________________________
____________________________________________________
____________________________________________________
____________________________________________________
CELLULAR DEFENCE MECHANISMS IN ANIMALS
___________ blood cells help us to defend our body against disease and
infection. There are two types of white blood cells:
1.
_________________
2.
_________________
PHAGOCYTES
These types of white blood cells work by ______________ foreign particles
e.g. bacteria. This is a process called ___________________ which is shown
in the diagram below. Once ingested, the bacteria are destroyed by the
39
powerful digestive enzymes contained in special cell organelles inside the
phagocytes called ______________.
Phagocytic white blood cells like the one drawn above, is a good example of a
cells whose structure is related to it’s function:
1. phagocytes are able to change their _________, and this allows them to
surround and engulf bacteria.
2. phagocytes contain many _____________. The powerful digestive
___________ inside these organelles destroy the bacteria and render
them harmless.
LYMPHOCYTES
These types of white blood cells produce globular proteins called
________________ in response to foreign proteins called
______________. (Viruses and bacteria have a distinctive protein coat which
is individual to them). Antibodies are said to be _____________ because
different antibodies are produced in response to different antigens. Only one
specific type of ____________ can attack a specific type of
____________, so we have thousands of different _______________ , each
one designed to produce a ___________ antibody.
40
REJECTION OF TRANSPLANTED TISSUES OR ORGANS
When a tissue or an organ (e.g. a kidney) is transplanted from one person to
another there is the possibility that it may be _______________ (unless the
donor is an identical twin). This is because the transplant patient’s immune
system regards the transplanted tissue or organ as a collection of foreign
_____________, and attempts to destroy it - this is known as tissue
rejection.
Phagocytes and lymphocytes treat the transplanted tissue or organ like any
other antigen, but rejection can be minimised in two ways:
1.
By matching a donor who is ________________ as similar as possible
to the recipient. This is why family members make good donors.
2.
Using special drugs called ______________________ drugs which
unfortunately weaken the body’s immune system, and these drugs must be
taken for the rest of their life. An advantage of taking these drugs is
that the transplanted tissue or organ is not “attacked” by our own
phagocytes and lymphocytes, but a disadvantage is that the transplant
patient is open to attack from other pathogens (disease-causing microorganisms).
CELLULAR DEFENCE MECHANISMS IN PLANTS
Plants too can be attacked by pathogens, but they don’t have an immune
system like us and so don’t produce phagocytes or lymphocytes (and
therefore do not produce _______________ ). Many plants defend
themselves against infection and disease by producing chemicals that are
either _______________ , or are enzyme ______________ . For
example: NICOTINE
 TANNINS
 RESINS
Resins are sticky chemicals. They help to prevent the spread of infections by
________________ holes in the bark of trees for example.
41
PHOTOSYNTHESIS
During photosynthesis, the energy change is from ________ to
______________. Photosynthesis can be summarised by the following
equation.
light energy
CARBON DIOXIDE
+
WATER
FOOD
chlorophyll
+
OXYGEN
(e.g. glucose)
So, photosynthesis is the process by which plants with chlorophyll manufacture
carbohydrates (e.g. glucose) from carbon dioxide and __________ using
_______ energy from the Sun. Oxygen is released as a by-product.
The Fate of Light Energy
Three things can happen to the light that strikes a leaf. It can either be
absorbed, ______________ or transmitted, as shown in the diagram below.
B _______________ (12%)
A ______________ (5%)
C ______________ (83%)
Visible light is made from 7 different colours. Each colour is determined by it’s
wavelength. In Biology, we refer to these colours of light as the
_________________ spectrum (R O Y G B I V).
Red
700
Orange
Yellow
Green
600
Blue
Indigo
500
wavelength
42
Violet
400
Absorption of Light
Light energy is absorbed by “chlorophyll” which is found in the
________________. Not all plant cells have chloroplasts e.g. the cells in the
roots of plants. This is because these cells never see the light of day!
The diagram below shows the internal structure of a chloroplast.
So, chloroplasts are the organelles found in plants cells where the process of
___________________ occurs. The “chlorophyll” whose function is to absorb
light energy is found in the __________ (pleural = grana) of the chloroplasts.
The synthesis of glucose takes place in the __________ of the chloroplasts,
during the Calvin Cycle (see page )
The Role of Chlorophyll in Photosynthesis
Apart from chlorophyll (a and b), plants also contain other ________absorbing pigments. These are referred to as ____________ pigments. They
can be extracted from leaves and then separated using a simple technique
called ________________.
43
Chromatography
Leaves are firstly ground up using a mortar and pestle, and _______ which
helps to rupture the cells. __________ (or propanone) is the solvent that is
used to extract these pigments from the leaves.
The resulting green liquid is then spotted repeatedly onto chromatography
paper. When a _________________ green spot has been produced, the
paper is dipped in another solvent and left for a few minutes.
Chromatography works on the basis of _______________. Some of the lightabsorbing pigments are more soluble than others. The ______ soluble the
pigment, the further up the paper it travels. The pigments always appear in the
same order as shown in the diagram below.
MOST SOLUBLE
CAROTENE ( ___________ )
XANTHOPHYLL ( ____________ )
CHLOROPHYLL a ( _____________ )
CHLOROPHYLL b ( _____________ )
LEAST SOLUBLE
Function of Having Different Pigments
The advantage to the plant of having more than one light-absorbing pigment is
that it EXTENDS THE ___________ OF WAVELENGTHS OF LIGHT
THAT THE PLANT CAN ___________ FOR PHOTOSYNTHESIS.
This additional ________ energy absorbed by the accessory pigments is
passed on from chlorophyll b, xanthophyll and _____________ to
chlorophyll a molecules which carry out photosynthesis.
44
Absorption Spectrum and Action Spectrum
The wavelengths of light absorbed by a pigment can be displayed as a graph
called the ______________ ___________. Because “chlorophyll” absorbs
mainly _____ and _____ wavelengths of light and ________ green
wavelengths of light, “chlorophyll” appears green to our eyes. The absorption
spectrum for chlorophyll a is shown in the graph below.
If an absorption spectrum graph peaks at the green wavelength of light, this is
not due to absorption by chlorophyll a or b (which reflects green), but will in
fact be due to light being absorbed by either ____________ or
_______________.
If a plant lacks magnesium, it will not be able to absorb as much light as a plant
that is not deficient in this element. This is because magnesium is needed by
plants to make _______________ . The less chlorophyll a plants make, the
less light they are able to absorb.
Is absorbed light actually used by the plant for photosynthesis? This can
be checked by growing plants in different _________ of light using different
coloured light bulbs and noting how well they grow. If the results of such an
experiment are plotted, a graph called an _________ _________ is
obtained. The action spectrum for a plant is drawn on the following page.
45
ACTION SPECTURM GRAPH
(measures the rate of photosynthesis at each wavelength of light)
The rate of photosynthesis can be measured as:

volume of ____ absorbed, or

volume of ____ released, or

increase in dry mass
}
all measured over a period of time
If an absorption spectrum graph and an action spectrum graph follow a similar
pattern, then we could conclude that the light being absorbed by the pigment is
actually being used for _________________.
If the graphs do not follow a similar pattern, then it is likely that other
pigments are involved in absorbing different wavelengths of light.
46
THE CHEMISTRY OF PHOTOSYNTHESIS
Photosynthesis can be divided into two stages. The products of the first stage
however, are required for the second stage to occur. These two stages are:
Stage 1
the ________-dependent stage (photolysis and
photophosphorylation)
Stage 2
the __________ Cycle or the ___________ fixation stage
Stage 1
This stage (which requires light energy) takes place in the __________
of the chloroplast. The light energy which is absorbed by
______________ can either be used to:
1. split __________ molecules into ______________ atoms and oxygen
gas which is then released by the plant as a by-product. This process of
using light energy to split water molecules is called PHOTOLYSIS.
The hydrogen atoms are picked up by a “hydrogen carrier” molecule
called NADP which is reduced to NADPH2. NADP carries the hydrogen
atoms to the _________ of the chloroplast where they are needed for
the Calvin Cycle.
2. make ATP. Light energy is used to join _____ and _____ together to
make ATP. This process is called PHOTOPHOSPHORYLATION. ATP is
also needed for the Calvin Cycle to occur.
The two processes of the light-dependent stage ( ________________ and
_______________________ ) are outlined in the diagram on the next page.
47
THE LIGHT-DEPENDENT STAGE
(occurs in the ___________ of a chloroplast)
light energy
NADPH2
NADP
hydrogen atoms
CHLOROPHYLL
energy
energy
WATER (H20)
ADP + Pi
ATP
oxygen gas
(released as a by-product)
When light energy splits a molecule of water into ______________ atoms
and __________ gas, the hydrogen atoms are picked up and carried by NADP
(as NADPH2) from the ___________ to the stroma of the chloroplast.
The source of the oxygen released during photosynthesis is therefore
____________.
BOTH NADPH2 AND ATP ARE NEEDED FOR STAGE 2. WITHOUT THEM,
THE CALVIN CYCLE CANNOT OCCUR.
48
Stage 2
The second stage of photosynthesis (i.e. the Calvin Cycle), does not
require light energy. In simple terms, during this stage, carbon dioxide is
______________ by the hydrogen atoms which have come from
__________ to make carbohydrates (CHO’s) e.g. ____________.
The Calvin Cycle is a series of metabolic pathways, each controlled by a
different ____________ . The Calvin Cycle takes place in the
___________ of the chloroplast.
49
Carbon dioxide is picked up by the carbon dioxide acceptor molecule called
_____________ __________________ (RuBP). When they combine,
glycerate phosphate (GP) is produced. GP is then reduced using hydrogen
atoms supplied by _________. This requires energy which comes from
______. The end product is glucose. The glucose is broken down by the plant
during respiration to produce ATP. The plant however, might join some of
these glucose molecules together to form either:
1.
2.
__________ for storage or
_____________ which is the structural carbohydrate that plant
_______ ________ are composed of.
Limiting Factors
Three factors can limit the rate at which a plant can photosynthesise. The
three limiting factors are:
1.
_________________ (which affect enzyme activity)
2.
light _______________
3.
___________ ______________ concentration
Below shows a typical limiting factors graph that often appears in higher exam.
50
IMPORATANT EXAM INFORMATION
You will often be asked to name the compounds in both RESPIRATION and the
CALVIN CYCLE. Not only do you need to know their names, you need to know
how many CARBON ATOMS these compounds contain. These tables should help
you to do this!!
RESPIRATION
Name of compound
Number of carbon atoms
(in a single molecule)
GLUCOSE
PYRUVIC ACID
ACETYL (Co A)
CITRIC ACID
CARBON DIOXIDE (CO2)
PHOTOSYNTHESIS
Name of compound
Number of carbon atoms
(in a single molecule)
GLYCERATE PHOSPHATE (GP)
RIBULOSE BIPHOSPHATE (RuBP)
GLUCOSE
CARBON DIOXIDE (CO2)
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Handout 1
52
Handout 2
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