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OCR AS Level Biology A
By
Mo Awe

MODULE 2
...

Maximum magnification = x1,500
Maximum resolution = 200nm
Scanning electron microscope:
We can see 3D structures and surface of the cell as electron are bounced of the surface
Maximum magnification = x100,000
Maximum resolution = 10nm
Transmission electron microscope:
We can see the internal structures as electrons are passes through
Maximum magnification = x500,000
Maximum resolution = 0
...
Therefore, multiple images can be combines to form a 3D structure
...

Making a permanent slide involves:
1
...

3
...


Fix using formadelyde
Dehydrate with ethanol
Impregnate with paraffin wax
Slice using a microtome

The use of staining in light microscopy
The main objective in staining is:
•
•
•

Make the object visible
Increase contrast so object can be seen more clearly
Use of differential staining to identify parts of tissue

Stains used in differential staining are eosin which stains the cytoplasm, sudan red which stains lipids,
iodine which stains cellulose cell wall yellow
...

The interrelationships between organelles in the role of protein production and secretion
1
...

3
...


The nucleus contains the gene for protein
Ribosomes is the site of protein synthesis
The sent to the Golgi apparatus in vesicles where it is further processed and packaged
Sent to plasma membrane where vesicle fuses in exocytosis

The similarities and differences between prokaryotic and eukaryotic cells
Similarities:
• Presence of plasma membrane, cytoplasm, ribosomes, DNA and RNA
Differences:
• Prokaryotes have no centrioles, nucleus, membrane bound organelles unlike eukaryotes
• Prokaryotes have smaller ribosomes known as 70s and cell wall is made from peptidoglycan
The ultrastructure of eukaryotic cells and the functions of the different cellular components + the
importance of the cytoskeleton
STRUCTURE
Nucleus, nuclear envelope and nucleolus
•

This is surrounded by a double
membrane known as the nuclear
envelope

Rough endoplasmic reticulum
•

Ribosomes are embedded in the
structure

Smooth endoplasmic reticulum

FUNCTION
• The nucleolus is the site where
ribosomes are made
• The pores allow mRNA to leave the
nucleus to be involved in translation
• The job of the nuclear membrane is to
separate the contents of the nucleus
from the rest of the cell
• Synthesis protein
• Cisternae transport substances from one
area of a cell to another area
•

Contain enzymes that are involved in
lipid metabolism

OCR AS Level Biology A
By
Mo Awe
• Lack of ribosomes on structure
Golgi apparatus
•

This is a series of cisternae but unlike
the endoplasmic reticulum, they are not
interconnected
Mitochondrion
•
•

A membrane bound organelle
Inner membrane is folded into cristae

•
•
•
•
•
•

Chloroplasts
•
•

A membrane bound organelle
Contain loops of DNA and starch
granules
• Stacks of thylakoids form grana which
are joined together by lamellae,
surrounded by the stroma
• Only found in plant cells
Vacuole

Lysosomes

•
•
•

•

They are formed from centrioles and
each contain microtubules
Ribosomes
•
•

Produced from ribosomal RNA
Synthesised in the nucleolus as two
subunits
• Present attached to RER or free in the
cytoplasm
Centrioles
•
•

Produced from bundles of microtubules
Microtubules are made of protein called
tubulin

Cytoskeleton
•

This is a series of protein threads made
from micro tubulin and microfilaments

Has own genetic material therefore can
replicate
The site of ATP production in aerobic
respiration
Common in cells that have a high
metabolic rate e
...
liver cells
The site for photosynthesis
Light dependent stage occurs in the
grana and light independent stage takes
place in the stroma
Common in leaf cells e
...
palisade
mesophyll layer

•

Important in maintaining turgidity as it
is filled with water and solutes as
pushes against cell wall

•

Responsible for keeping hydrolytic
enzymes separate from rest of cell

•

Cilia are found in airways to beat and
move mucus
Undulipodium present in sperm to allow
it to move
Ribosomes that are attached to the RER
are predominantly exported out of cell
Ribosomes free in cytoplasm are
usually for cell’s own use

•

Contain powerful hydrolytic enzymes
therefore abundant in neutrophils and
macrophages
• Formed from the Golgi apparatus
Cilia and Undulipodia

Synthesises lipids
Modify lipids and proteins delivered by
the endoplasmic reticulum
Manufacture lysosomes

•
•
•

•

Involved in making spindle required
during metaphase of mitosis and
meiosis
• Also, responsible for producing cilia
and undulipodia
• Centrioles are absent in plants
Extracellular Movement
Cilia and flagella moves cells
Intracellular Movement
Thread from tracks so organelles can move
Strengthening and support

OCR AS Level Biology A
By
Mo Awe
Strengthens and support organelles
• Prevents plant cells from bursting as
provides strength and support

Cellulose cell wall
•

Present in plants and made from
cellulose fibres

MODULE 2
...

Polar substances are attracted to each other by hydrogen
bonding
...

Lower density
Ice is less dense than water therefore floats which is useful as ice forms an insulating layer on
top of water so living things can survive below ice as temperature remains constant
Cohesion
Hydrogen bonds pull water molecule towards each other therefore water flows
...

Adhesion
Hydrogen bonds causes water molecules to be attracted to surfaces so water can move up
tubes with the help of cohesion
Tension
Hydrogen bonds pull water molecules inwards e
...
insects can skate
High specific heat capacity
This is the energy required to raise the temperature of 1g by 1 degree
...
Living things
needs a stable temperature for enzyme controlled reactions
High latent heat vaporisation

OCR AS Level Biology A
By
Mo Awe
A lot of energy is required to break hydrogen bonds so suitable coolant e
...
sweat evaporates
so cools the body
The concept of polymers and monomers and importance of condensation and hydrolysis
reactions
Monomers: small molecules that join together to from polymers
Polymers: large molecule made from smaller molecules known as monomers
A condensation reaction occurs when two molecules are joined together by the removal of
water
...

TYPE OF MOLECULE
Carbohydrates
Proteins
Nucleic acids

MONOMER
Monosaccharides
Amino acids
Nucleotides

POLYMER
Polysaccharides
Polypeptides or protein
DNA or RNA

The chemical elements that make up biological molecules
TYPE OF MOLECULE
Carbohydrates
Lipids
Proteins
Nulcleic acids

ELEMENTS PRESENT
C, H, O
C, H, O (lower proportion of oxygen than
carbohydrates)
C, H, O, N , S
C, H, O, N, P

The ring structure and properties of glucose as an example of a hexose monosaccharide
and the structure of ribose as an example of pentose monosaccharide

Glucose is known as a hexose
sugar as contains 6 carbons
...
The chemical bond
also contains a lot of energy

This is an example of a pentose sugar
as contains 5 carbons known as ribose

OCR AS Level Biology A
By
Mo Awe

The synthesis and breakdown of a disaccharide and a polysaccharide by the formation and
breakage of glyosidic bonds
Disaccharides are made by two
monosaccharides:
Alpha Glucose + Alpha Glucose à Maltose
Alpha Glucose + Fructose à Sucrose
Beta Galactose + Alpha glucose à Lactose
Beta Glucose + Beta Glucose à Cellobiose
When they join together in a condensation
reaction a bond known as a glycosidic bond is
created
...

The hydroxyl group is hidden inside the coil so less soluble, so does not affect water
potential
...

Amylopectin
This is a branched chain of alpha glucose joined by 1,4 and 1,6 glycosidic bonds
...
As the chain is branched, glucose can be
released quickly
...
The hydroxyl groups are exposed so can
form hydrogen bonds with adjacent molecules
...

Glycogen
This is a branched chain of alpha glucose
...

The structure of a triglyceride and a phospholipid as example of macromolecules
Macromolecules: A chain of small molecules formed from different monomer units

OCR AS Level Biology A
By
Mo Awe
Examples of lipids include triglycerides, phospholipids, waxes,
resin and steroids
Triglycerides are formed from glycerol and three fatty acids
called an ester bond, which results in the loss of three waters
...

The properties of triglycerides include:
•
•
•
•
•

Protects major organs
Provides insulating layer
Provides buoyancy as less dense than water
Energy source
When triglycerides are oxidized, they release hydrogen which bonds to oxygen to
from water known as metabolic water, which is useful for desert animals when there
is limited water
...
g
...
g
...
The part
hydrophilic heads and part hydrophobic tails leads to
an effective membrane barrier
Cholesterol
Cholesterol is small and hydrophobic which means it can bind to hydrophobic tails of the
phospholipid bilayer and therefore control fluidity
...

The general structure of an amino acid
Function of a protein:
•
•
•
•
•

enzyme
hormone
antibodies
structural e
...
collagen
functional e
...
amylase

Peptide bond:
When two amino acids join together via condensation reaction

OCR AS Level Biology A
By
Mo Awe
The levels of protein structure
Primary structure
Sequence type and number of amino acids and position of disulphide bond
Secondary structure
Particular shape by coiling or folding as a result of bonds which can lead to an alpha helix or
a beta pleated sheet
Alpha helix - Hydrogen bonds held between the NH and CO groups weak but a number of
them make them stable
Beta pleated sheet - Folds in concertina way with hydrogen bonds connecting adjacent
pleated sheets
Tertiary structure
3D shape of protein when secondary structure undergoes further coiling and folding
...
If protein twists into a long structure then
it is called a fibrous structure
Globular shape allows enzymes to have specifically shape active site
Fibrous protein plays structural roles e
...
keratin
What bonds are present in protein
•
•
•
•

Hydrogen bonds
Ionic bonds
Disulphide bonds formed between the R groups of two cysteine ---> strong covalent
Hydrophobic and hydrophilic interactions

Quaternary structure
When some proteins are made up of more than one polypeptide chain
The structure and function of globular protein
Haemoglobin has quaternary structure with haem group containing inorganic ion
4 polypeptide chains, two alpha chains and two beta chains
Haem is a prosthetic group (non-protein part that is permanently attached)
Haemoglobin is a conjugated protein as has a prostatic group attached to a globular protein
The structure and function of fibrous proteins

OCR AS Level Biology A
By
Mo Awe
Collagen
Provides strength e
...
in artery walls collages prevents vessels from bursting and present in
tendon that connect muscle to bone
...
Keratin is found in
fingernails, hair and horns
...

Elastin
Elastin is found in skin as well as in lungs to help deflate and inflate
...
3: NUCLEIC ACIDS

The structure of a nucleotide as the monomer of nucleic acids
Contains a pentose sugar which can be either ribose or deoxyribose, an organic nitrogenous
base (A,T,G,C) and a phosphate group
...
Purines are larger
than pyrimidines as have 2 carbon-nitrogen rings compare to one in pyrimidines
...

A and T form 2 bonds
G and C form 3 bonds
They synthesis and break down of polynucleotides and breakage of phosphodiester bonds
Nucleotides are joined together by a condensation reaction to form a polynucleotide
...

The structure of DNA

•
•
•

OCR AS Level Biology A
By
Mo Awe
Two polynucleotides are joined together by hydrogen bonds to from a double helix
Strands are anti parallel as run in different directions
Molecules is stable and integrity of coded information is protected

Semi-conservative replication

DNA helicase
unzips DNA
and therfore
breaks
hydrogen
bonds

Two separate
strands act as
a template for
a new strand

Free floating
nucleotides
join to
exposed bases
catalyses by
DNA
polymerase in
a
condensation
reaction

Hydrogen
bonds and
sugar
backbone
reforms

The nature of the genetic code
Degenerate: This means there are different codes for the same amino acids therefore if a
mutation occurs then it may still code for the same amino acid
...
4: ENZYMES
The role of enzymes
Catalyst is a substance that increases the rate of a chemical reaction without being altered,
and enzyme is an example of a catalyst
...
g
...
Some are free in solution or
on cell surface membrane
Extracellular enzymes – Catalyse reactions outside cells e
...

amylase starch --> maltose
trypsin protein --> amino acids
The mechanism of enzyme action
Specificity
The relationship between the enzyme and the only type of molecule that fits which is
determined by R group of amino acids
...

Activation energy
The energy needed to overcome the energy barrier to allow a reaction to occur
...

Induced fit hypothesis
Active site does not have a complementary shape to substrate until it has moulded
...
However, if the temperature increases
too much then the kinetic energy breaks hydrogen and ionic bonds that stabilise the tertiary
structure so active site changes
...

Substrate concentration
Low substrate concentration, there are fewer substrate molecules so fewer will collide and
form enzyme substrate complexes, therefore low rate
Higher substrate concentration, the number of enzymes present limit the reaction as enzyme
sites are all occupied therefore rate of reactions stays constant
Enzyme concentration
When enzyme concentration increases there are more active sites available, therefore rate of
reaction increases until other factors are limiting
pH
As pH increases some of the bonds that determine the active site break therefore active site
shape changes as charges on R groups affect the ability for active site to bind successfully
with substrate
Temperature coefficient
Ratio between rate of reaction at two different temperatures
The need for coenzymes, cofactors, prosthetic groups in enzyme controlled reactions
Coenzymes are larger cofactors that help an enzyme carry out a reaction
...

Chloride ion cofactor for amylase
Zinc ion cofactor for carbonic anhydrase
Many coenzymes are derived from water soluble vitamin:
B12 - Cobalamin coenzymes
Folic acid –Tetrahydrofolate
Nicotinamide B3 - NAD and NADP important in respiration and photosynthesis respectively
Pantothenate B6 - Coenzyme A
The effect of inhibitors on rate of enzyme controlled reactions
Competitive inhibitor - Molecules that have a similar shape to substrate therefore compete
with substrate
...
Increasing substrate concentration will increase rate of reaction as
substrate will out compete the inhibitor
...

Inhibitor attaches to allosteric site of enzyme causing active site to change and therefore rate
of reaction slows down, once all allosteric sites are occupied the reaction stops
...
5: BIOLOGICAL MEMBRANES

The fluid mosaic model
•
•

7nm
Phospholipids naturally form a bilayer when in contact with water as hydrophilic head
and hydrophobic tails

•

Bilayer is fluid as constantly moving

•

Protein scattered across bilayer like mosaic

Glycoprotein - Protein with short carbohydrate form hydrogen bonds with water therefore
stabilises the structure
...

A messenger molecule that binds to a receptor has a complementary shape and can cause
three things to happen:
•
•
•

Release 2nd messenger
Open or close channel protein
Activate an enzyme

Factors affecting membrane structure and permeability
Temperature - As temp rises the lipid component becomes more fluid as phospholipid bilayer
has more kinetic energy so reduces effectiveness as a barrier
...

Ethanol increases permeability of membrane
...
Passive so no energy required
Factors that increase diffusion rate:
• Large SA
• Thin surface
• High concentration gradient
• Temperature
Active transport - Carried out by carrier proteins
...
Respiratory inhibitors stop active transport e
...
cyanide
Facilitated diffusion - assist larger molecules and polar molecules
...

Water potential outside higher than cell therefore burst in animals or turgid in plants
(hypersonic solution)
Water potential outside lower the inside the cell therefore plasmolysis in plant cells or
crenates in animals (hypertonic solution)

MODULE 2
...
Cytoplasm and cell wall form a bulge
2
...
The bud breaks off and there is uneven distribution of cytoplasm
Mitosis in plants
Plants do not have centrioles and during cytokinesis the vesicles from the Golgi apparatus
form the plasma membrane and the cell wall
...
More common in plants as cannot move
The significance of meiosis in life cycles
Meiosis is a type of nuclear division that results in half the number of chromosomes of the
parent cell
The significance of meiosis:
•
•

Increases genetic diversity
This means that it increases survival as some organisms would have characteristics
that enable them to be better adapted

OCR AS Level Biology A
By
Mo Awe
How does meiosis increase genetic diversity?
•
•
•
•

Crossing over during prophase I shuffles allele
Independent assortment chromosomes in anaphase 1 leads to random distribution of
genetic material
Independent assortment of chromatids in anaphase 2
There is random fusion of gametes

Centrioles moves to
opposite poles

Bivalents attach to
spindle fibres by their
centromere

Chromosomes pull to
opposite poles by
contraction of
spindle fibres

Telophase 1

Homologous
chromosomes pair up
to form bivalents
chiasmata hold
chromosomes
together

Bivalents move to
equator

Anaphase 1

Chromosome
condense and
therefore become
visible

Metaphase 1

Prophase 1

The main stages of meiosis
Nuclear envelope
forms around each
set of chromosomes
Cytokinesis occurs 2
haploid cells

chromatids are
randomly arranged

Centromere divide by
contraction of
spindle fibres
Chromatids are
randomly segregated

Telophase 2

Chromosomes attach
by their centromere
to the equator of the
spindle

Anaphase 2

Chromosome
condense and
therefore become
visible

Metaphase 2

Prophase 2

OCR AS Level Biology A
By
Mo Awe

Nuclear envelope
form around each set
of 4 haploid nuclei

How cells of multicellular organisms are adapted to their function
Erythrocytes
•
•
•

They have a large surface area to volume therefore more oxygen can diffuse through
Flexible so can twist and through narrow capillaries
Few organelles so more space for haemoglobin

Neutrophils
•
•
•

Flexible shape allows them to form pseudopodia
Many lysosomes so can digest pathogens
Lobed nucleus so can squeeze through capillaries

Sperms cells
•
•
•
•

Tail provides propulsion
Many mitochondria to carry out aerobic respiration
Reduced cytoplasm therefore reduces mass from swimming
Acrosome contains enzymes to digest egg

Palisade cells
•
•
•

Many chloroplasts to trap as much light
Contain cytoskeleton to move chloroplast neat upper leaf
Tall and thin so light can penetrate further

Root hair cells
•
•
•

Many carrier proteins to actively transport minerals
Extra mitochondria
Many hairs for greater surface area for absorption

OCR AS Level Biology A
By
Mo Awe
Xylem
•
•
•

Pits allow lateral movement of water
Lignin strengthens
Wide lumen so little resistance to flow of water

Phloem
•
•
•

Reduced cytoplasm and organelles so more space for solutes
Lots of mitochondria in companion cells, important in active loading in phloem
Parenchyma provides support

The production of xylem vessels and phloem sieve tubes from meristem cells
Phloem cells always divide on the outside and xylem cells on the inside
...
Phloem loses cytoplasm and organelles then
develops sieve plates
...
g
...
1: EXCHANGE SURFACES AND BREATHING

The need for specialised surfaces
•

Some cells are too deep in body due to big distance, so diffusion would be too slow to
reach these innermost cells before they die
...
g
...
g
...

Insects – Insect makes pumping movement with thorax
...
At the end of a tracheal there is tracheal fluid which dissolves the
oxygen and diffuses into the tissue
...


MODULE 3
...
Diffusion is slow so cells in the
innermost part of the body may end up dying before oxygen gets there
...
g
...
g
...
g
...

Also lower pressure in the pulmonary side reduces damage to capillaries in lungs
The structure of arteries, capillaries and veins
VEINS
ARTERIES
• Pulse absent
• Tunica intima endothelium has a
• Tunica media thinner
smooth surface
in veins than arteries
which reduces
as blood is at a lower
friction
pressure
•

•

Large lumen
compensates for
absence of pulse also
reduces friction as
less blood in contact
with walls
Veins have valves to
prevent back flow

•

Tunica media smooth muscle and
elastic tissue

•

Elastic fibres allows
the blood pressure to
stretch and recoil to
maintain pressure

•

Smooth muscle
strengthen artery +
resists high blood
pressure

•

Tunica adventitia consists of collagen
which is tough and
prevents vessel from
overstretching and
withstands high
pressure

CAPILLARIES
• Small lumen causes
friction with blood
and slows down so
longer time to
exchange materials
•

One cell thick so
minimises the
distance cells travel

Formation of tissue fluid
1
...
In the capillaries because the plasma proteins are too large to pass through, they stay
in the plasma and generate oncotic pressure, making the water potential lower than
that in the tissue fluid

OCR AS Level Biology A
By
Mo Awe
3
...

4
...
As lymph
passed through the lymph nodes lymphocytes, antibodies and plasma cells are added to the
fluid
Tissue fluid does not contain red blood cells or large proteins
The cardiac cycle
Atria fill with blood
from the vena cava
and the pulmonary
vein

Pressure higher in
ventricles so blood
forced through
semilunar valves
into aorta and
pulmonary artery

Short delay to allow
ventricles to
completely fill then
ventricles contract

Higher pressure in
the atria than
ventricles

So blood is forced
out through the
atriventricular
valves by
contraction of atria

How the heart is initiated and coordinated
1
...
Non-conductive tissue between atria and ventricles prevents spread of the impulse to
ventricles except AVN
3
...
AVN sends impulse to ventricles, then Bundle of His and up Purkyne fibres

OCR AS Level Biology A
By
Mo Awe
The use and interpretation of electrocardiogram
Bradycardia – slow heart rate
Tachycardia - fast heart rate
Ectopic heart beat – heart beats early
Fibrillation – irregular heart beat with so sinus rhythm
The role of haemoglobin in transporting oxygen and carbon dioxide
How is carbon dioxide transported?
• Dissolved carbon dioxide
• Hydrogen carbonate ions formed in red blood cells
• Bound to haemoglobin as carbaminohaemoglobin

carbon dioxide
diffuses into red
blood cells

Chloride ions diffue
into red blood cells to
maintain
electrochemical
neutrality

Hydrogen ions bind
to haemoglobin

Carbon dioxide
converted to carbonic
acid by enzyme
carbonic anhydrase

This is sodium
hydrogen carbonate

This forms
haemoglobinic acid

Carbonic acid
dissociated to
hydrogen ion and
hydrogen carbonate
ion

hydrogen carbonate
ion diffuses out of
red blood cell and
binds with sodium

This is known as a
buffering effect

The oxygen dissociation curve of fetal and adult haemoglobin
Fetal haemoglobin has a higher affinity for oxygen than adult as by the time blood reaches
the placenta, the oxygen saturation has decreased
...

Bohr affect
In strenuous exercise, lots of carbon dioxide is released which lowers the affinity of Hb for
oxygen so more oxygen is released
...
3: TRANSPORT IN PLANTS
The need for transport system in multicellular plants
•

Multicellular plants have a small SA/V ratio so diffusion would be slow

• They are relatively big therefore have a higher metabolic rate
Xylem
•
•
•
•
•

Transports water upwards
Dead cells no cytoplasm so water moves more freely
Cell thickened with lignin therefore support and waterproof
Pits allow water to move transversely
End wall is lost to allow free passage of water

Phloem
•
•
•
•
•

Transport solutes up and down
Living cells
Many plasmodesmata for easy flow
No nucleus, little cytoplasm and few organelles
Many mitochondria to produce ATP

The process of transpiration
Transpiration is a result of gaseous exchange as plants need to open stomata for carbon
dioxide to produce glucose but also let out water as high-water potential in leaf than outside
...
Air current removes water molecules therefore increases
concentration gradient
Humidity - As humidity increases, water potential rises so diffusion gradient between leaf
and surrounding air decrease so equilibrium is finally reached
Light intensity - In the dark stomata close once there is enough light stomata open
The transport of water in plants
Water movement up a plant
1
...

3
...


Root pressure pushes some water upwards
Water evaporates from surface of leaf by transpiration
Creates tension
Water molecules are attracted together by cohesion creating continuous column of
water
5
...
g
...
Active transport of hydrogen ion out of companion cell which creates diffusion
gradient
2
...
Sucrose moves in with hydrogen ion by cotransport protein
4
...
1: COMMUNICABLE DISEASE

The different type of pathogens that cause communicable disease
Non-communicable disease – disease not causes by a pathogen
Communicable disease – Disease caused by a pathogen
Parasite – Lives in host and obtains nutrition form host
Pathogen – An organism that causes disease
Bacteria in animals
•
•

Virus in animals

Bacteria in plants
•

•
•

Tuberculosis
Bacterial
meningitis

Influenza
HIV

Virus in plants

Ring rot in
tomatoes and
potatoes

•

Tobacco
mosaic virus

Protoctista in
animals
• Malaria

Fungi in animals
•

Athlete’s
foot
Ringworm

•
Protoctista in
plants
• Potato and
tomato
blight

Fungi in plants
•

Black
sigatoka

The means of transmission
Indirect transmission - Transmitted via vector that transfers pathogen such as tomato/potato
blight and malaria
Direct transmission - When a disease is directly transmitted from an organism to another via
physical contact or droplet infection such as coughing and sneezing
...

Plant defences
Physical barrier includes:
•
•
•

Waxy cuticle
Stomata
Cellulose cell wall

OCR AS Level Biology A
By
Mo Awe
Chemical defences include:
•
•
•

Sticky resin
Compounds secreted that compete
Compounds secreted that are toxic

Active plant defences
•

Hypersensitivity - immediate death of tissue

•

Lignin deposited to reinforce cell walls and callose deposited between cell walls and
membranes at plasmodesmata which make it harder for virus to spread

•

Pathogens secrete cellulase to digest pathway, however products formed act as a
signal to stimulate phytoalexins which secrete of chitin which break down hyphae
and disrupt metabolism

Primary non-specific defences
Blood clotting and skin repair
Inflammation
Mucous membranes
The structure and action of phagocyte
Phagocytes recognise antigens on pathogen
Phagocytosis may occur which may be made easier by opsonins
So, now contained in a phagosome and lysosome fused with it therefore lytic enzymes digests
it to amino acids or APC
The structure and roles of B and T lymphocytes

OCR AS Level Biology A
By
Mo Awe
T lymphocyte activation

Surface covered
with receptors
that find to
antigens on APC

When t cell
meet
complementary
antigen -->clonal
selection occurs
leading to clonal
expansion

T helper cells release
cytokines than
bind to
receptors on B
cells

T killer cells attack and kill
body cells
T regulatory cells shut down the
immune response
to prevent
autoimmune
disease

B lymphocyte activation

Surface covered
with antibodies

When antibody
meets
complementary
antigen --> clonal
selection then
expansion

Plasma cells
produce antibodies

B cells come from stem cells and spread out throughout the lymphatic system
T cells come from stem cells but mature in thymus gland

OCR AS Level Biology A
By
Mo Awe

The primary and secondary immune response
Primary immune response - initial response caused by a first infection
Secondary immune response - more rapid and vigorous response caused by a second or
subsequent infection by the same pathogen
The structure and function of antibodies
•
•

Globular proteins
Four polypeptide chains held by disulphide bond

constant region - binding site that can be recognised by phagocytes
hinge region - some flexibility to enhance binding to pathogen
variable region - binding site specific to particular antigen
Action of antibodies
Opsonin - antibodies that bind to pathogens and help phagocytes bind
Agglutinins - antibodies that bind to two or more pathogens, forms clumps and therefore can
be easily phagocytose
Anti-toxins - antibodies that bind to the toxin making it harmless
Active and passive immunity
Active immunity - Immunity acquired by activation of the immune system which can be
artificial e
...
use of vaccination or natural e
...
an infection
Passive immunity - When someone is giving antibodies produced by someone else which
can be artificial e
...
injecting antibodies or achieved naturally e
...
breast feeding
no memory cells so no immunity therefore does not last long
Autoimmune response
This is where the body’s immune system attacks its own cells as cannot distinguish between
foreign antigens or its own antigens
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Principles of vaccination
This is the deliberate introduction of antigenic material in vaccines to stimulate production of
antibodies which would lead to memory cells being produced which will stay in the
bloodstream
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Enzyme reverse scriptase used RNA as a template for DNA
2
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DNA enters the nucleus where enzyme integrate attaches it to DNA therefore a
provirus
Opportunistic diseases - This includes diseases like thrush, TB and pneumonia which
develop due to low lymphocyte levels
Malaria
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Mosquito is a vector
Plasmodium present in salivary glands of mosquito
Infected mosquito feeds on humans therefore passes into blood

MODULE 4
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A point sampling can be used
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Animals
Small mammals such as woodlice can be trapped using a Longworth Trap
The number of population can be estimated by using this formula
T1 = T2/T3 , where T1 is number caught in the first session, T2 is the number caught in
second session and T3 is the number caught in the second session that were marked
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Biodiversity close to 1 means high biodiversity and
biodiversity close to 0 means low biodiversity
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3: CLASSIFICATION AND EVOLUTION

OCR AS Level Biology A
By
Mo Awe
The biological classification of species

Domain
Kingdom
Phylum
Class
Order
Family
Genus
Species

The binomial system
We use two Latin words to name each species
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The genus name should be written with a capital letter whereas the species should be lower
case
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Some variations are better adapted, so survive and pass on advantageous allele to
the next generation
Convergent evolution
Organisms from different taxonomic groups can become adapted to the environment by
adopting similar anatomical features e
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marsupial and placental mole
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