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A-Level Biology
Revision notes 2015
Contents
A-Level Biology
...
0
Biological Molecules and Enzymes
...
6
Classification
...
13
Photosynthesis
...
17
Transport
...
24
Transport
...
31
Nervous and Hormonal Control
...
37
Homeostasis
...
44
Ecological Concepts
...
50
Health and Disease
...
57
DNA and the Genetic Code
...
60
Genetic Engineering
...
64
Applications of Genetic Engineering
...
67
These notes cover the main areas of this subject
...
They are provided “as is” and S-cool do not guaranteed the suitability, accuracy or completeness of this
content and S-cool will not be liable for any losses you may incur as a result of your use or non-use of this
content
...
s-cool
...
uk)
...
Carbon (C)
2
...
Oxygen (O)
Carbohydrates are found in one of three forms:
1
...
Disaccharides (both sugars)
3
...
One monosaccharide loses an H atom
from carbon atom number 1 and the other loses an OH group from carbon 4 to form the bond
...
Examples of Disaccharides
Sucrose: glucose + fructose,
Lactose: glucose + galactose,
Maltose: glucose + glucose
...
Substrate for respiration (glucose is essential for cardiac tissues)
...
Intermediate in respiration (e
...
glyceraldehydes)
...
Energy stores (e
...
starch, glycogen)
...
Structural (e
...
cellulose, chitin in arthropod exoskeletons and fungal walls)
...
Transport (e
...
sucrose is transported in the phloem of a plant)
...
Recognition of molecules outside a cell (e
...
attached to proteins or lipids on cell surface membrane)
...
The most common type of lipid is the triglyceride
...
Fats and oils are very similar in structure (triglycerides)
...
Functions of lipids
1
...
2
...
3
...
4
...
5
...
6
...
7
...
Oestrogen requires lipids for its formation, as do other
substances such as plant growth hormones
...
Buoyancy - as lipids float on water, they can have a role in maintaining buoyancy in organisms
Phospholipids
A phosphate-base group replaces one fatty acid chain
...
Due to this arrangement, phospholipids form bilayers (the main component of cell and organelle membranes)
...
g
...
Despite this, each
one is made up of amino acid subunits
...
Hence, stringing them together in different combinations produces very
different proteins
...
The bond formed is called a peptide bond
...
Fibrous proteins are made of long molecules arranged to form fibres (e
...
in keratin)
...
Globular proteins are made of chains folded into a compact structure
...
Although these folds are less regular than in a helix, they are highly specific and a particular
protein will always be folded in the same way
...
If a protein is made up of several polypeptide chains, the way they are arranged is called the quaternary
structure
...
g
...
Virtually all enzymes are proteins
...
Structural: e
...
collagen and elastin in connective tissue, keratin in skin, hair and nails
...
Contractile proteins: actin and myosin in muscles allow contraction and therefore movement
...
Hormones: many hormones have a protein structure (e
...
insulin, glucagon, growth hormone)
...
Transport: for example, haemoglobin facilitates the transport of oxygen around the body, a type of
albumin in the blood transports fatty acids
...
Transport into and out of cells: carrier and channel proteins in the cell membrane regulate movement
across it
...
Defence: immunoglobulins (antibodies) protect the body against foreign invaders; fibrinogen in the blood is
vital for the clotting process
...
Enzymes are proteins and
thus have a specific shape
...
The site of the reaction occurs in an area on the surface of the protein called the active site
...
However, most substrates require an input of energy to get the reaction going, (the reaction is not
spontaneous)
...
When the substrate(s) react, they need to form a complex called the transition state before the reaction actually
occurs
...
4
Factors Affecting the Rate of Reaction
1
...
pH
3
...
Substrate Concentration
Cofactors
Most enzymes require additional help from cofactors, of which there are 2 main types:
1
...
2
...
g
...
Inhibitors
Inhibitors slow down the rate of a reaction
...
Reversible Inhibitors:
Competitive reversible inhibitors
Non-competitive reversible inhibitors
Irreversible Inhibitors:
These molecules bind permanently with the enzyme molecule and so effectively reduce the enzyme
concentration, thus limiting the rate of reaction, for example, cyanide irreversibly inhibits the enzyme cytochrome
oxidase found in the electron transport chain used in respiration
...
Chromatography
This technique separates out mixtures of chemicals by using their different solubilities in certain solvents
...
It can be seen with a light microscope (LM) but many of the structures within a cell - organelles - can only be
seen clearly with an electron microscope (EM)
...
Prokaryotic and eukaryotic cells
There are 2 basic cell types:
Prokaryotic: bacteria and cyanobacteria (which used to be called blue-green algae)
...
Organelles
Much of what you will need to know applies to the structure of eukaryotic cells
...
Cytosol and Endoplasmic Reticulum (ER)
Cytoplasm refers to the jelly-like material with organelles in it
...
It consists mainly of
water with dissolved substances such as amino acids in it
...
Running through
the cytosol is endoplasmic reticulum (ER), a system of flattened cavities lined by a thin membrane
...
The cavities also function as a transporting system whereby substances can move through them from one
part of the cell to another
...
Ribosomes are made of RNA and protein and are the site of protein synthesis
Smooth (SER): obviously looks as though it has a smooth surface
...
Golgi apparatus
6
The Golgi apparatus is a series of flattened layers of plate-like membranes
...
The whole structure is called a vesicle
...
In the cavity of the Golgi apparatus, the vessel proteins are modified for export - for example, by having a
carbohydrate added to the protein
...
The vesicle will fuse with this membrane and so release the secretory product
...
Lysosomes may be used inside the cell during endocytosis, or to break-down
old, redundant organelles
...
Generally, they are
sausage-shaped organelles whose walls consist of 2 membranes
...
Inside this is the matrix
...
Cell wall and chloroplasts
These are only found in plant cells
...
They have pairs of membranes called thylakoids arranged in stacks, each stack being called a granum
...
Surrounding the internal membranes, inside the
envelope is thestroma
...
Nucleus
The nucleus is separated from the surrounding cytoplasm by the double membrane around it, the nuclear
envelope
...
Other organelles
Vacuole: fluid-filled space in the cytoplasm surrounded by a membrane called the tonoplast; contain a solution
of sugars and salts called the cell sap
...
Provide the structural support of cells and
can aid transport through the cell
...
Again, like microtubules, provide support and
aid movement
...
They are involved
in the formation of spindle fibres used in mitosis
...
They move fluid, which is outside the cell - for example,
ciliated cells lining the respiratory tract move mucus, away from the lungs
...
Used in the movement of the whole cell
...
The Cell Membrane
Much of the membrane is made up of a 'sea' of phospholipids with protein molecules 'floating' in between the
phospholipids
...
Because the membrane is fluid, and because of the mosaic arrangement of the protein molecules, the structure
of the membrane is called the fluid mosaic model
...
The phosphate heads are polar molecules and so are
water-soluble
...
Functions of a membrane it's:
1
...
2
...
Allows communication with other cells
4
...
Allows mobility in some organisms, e
...
amoeba
6
...
Movement
It is important that the cell is supplied with all the substances it needs (e
...
oxygen) and that waste substances
(e
...
carbon dioxide), or substances for export, leave the cell
...
Diffusion
This is the process that is used in oxygen entering a cell, and carbon dioxide leaving
...
i
...
they diffuse down a concentration gradient
...
Osmosis
This is a special case of diffusion in which we are concerned only with the movement of water
...
The movement of water molecules from a region of higher water potential to a region of lower water potential
through a semi-permeable membrane
...
Osmosis in animal and plant cells
If the water potential surrounding an animal cell is higher than that of the cell, it will gain water, swell and burst
...
This is
why it is so important to maintain constant water potential inside the bodies of animals
...
They move through protein-lined pores
...
Different channels allow different substances to pass through (the channels are selective)
...
Carrier proteins: In this case, the substance actually combines with a protein and is carried from one side of
the membrane to the other
...
) These proteins are specific for a
particular substance
...
Active transport
9
Sometimes substances need to be moved from where they are at a lower concentration to where they are at a
higher concentration - against the concentration gradient
...
Because molecules are moved against the concentration gradient, it requires energy
...
Endocytosis and exocytosis
If very large molecules or groups of molecules need to enter or exit a cell, they do so using vesicles
...
The vesicle will fuse with the cell
surface membrane and the contents leave
...
Materials entering the cell can do so when the plasma membrane invaginates to surround the material
...
This is endocytosis
...
This type of endocytosis is called pinocytosis
...
This occurs in white blood cells that ingest bacteria and other foreign bodies
...
Tissues may contain only one type of cell, or several types
...
Two tissues that you need to know
about are squamous and ciliated epithelia
...
The
cells rest on a basement membrane which is a network of collagen and glycoproteins that is secreted by cells
underneath the epithelial tissue
...
They are
packed closely together like tiles on a roof and provide a low friction surface over which fluids can move
...
Ciliated epithelia: This tissue is made up of cells with cilia and so is often found in areas where it is needed to
transport something - for example, lining the oviducts and bronchioles of the lungs
...
If the cells are tall and narrow, it is referred
to as columnar ciliated epithelia
...
Xylem has the dual function of support of the plant and transport of water and dissolved
10
mineral salts
...
Phloem tissue is
responsible for translocation which is the transport of soluble organic substances - for example, sugar
...
The cells are tall and
thin and are tightly packed together
...
Organs: An organ is part of the body which, forms a structurally and functionally separate unit and is made up
of more than one type of tissue
...
Examples of animal
organs are the liver, brain, heart and kidney
...
Classification
Kingdoms
All living organisms are classified into different groups
...
Monera (also known as 'Prokaryota')
2
...
Fungi
4
...
Animalia
The way the kingdom is broken down is as follows:
A number of species make up a genus
...
A number of families make up an order
...
A number of classes make up a phylum
...
Species
The species is the lowest level of classification within each Kingdom
...
They have a particular set of characteristics
...
The Animalia Kingdom
Some examples of classifications within the Animalia Kingdom:
Kingdom e
...
Animalia
Phylum e
...
g Mammalia
Order e
...
Primates
Family e
...
Homindae
Genus e
...
g
...
It does not show any detail, such as the position of the internal organs
...
The classification of one member species
...
Diffusion is required to supply all organisms with oxygen
...
A large surface area over which exchange can take place
...
A concentration gradient without which nothing will diffuse
...
A thin surface across which gases diffuse
...
The larger the area and difference in concentration and the thinner the surface, the quicker the
rate
...
Instead gases diffuse in through the
cell membrane
...
Multicellular organisms
Multicellular Organisms are bigger than Unicellular organisms
...
However, if they are small, or large but very thin (like the flatworms, Platyhelminths), the outer surface of the
body is sufficient as an exchange surface because the surface area to volume ratio is still high
...
They require oxygen for respiration and carbon
dioxide for photosynthesis
...
From these spaces they will diffuse into the cells that require them
...
There are tiny holes called spiracles along the side of the insect
...
The ends of these tubes, which are in contact with individual cells, contain a small amount of fluid in which the
gases are dissolved
...
This increases the surface area of
air in contact with the cells
...
Ventilation movements of the body during exercise may help this diffusion
...
These help keep humidity around the
opening, ensure there is a lower concentration gradient of water vapour, and so less is lost from the insect by
evaporation
...
Gills have numerous folds that give them a very large surface area
...
The folds are kept supported and moist by
the water that is continually pumped through the mouth and over the gills
...
There are numerous alveoli - air sacs, supplied with gases via a system of tubes (trachea, splitting into two
bronchi - one for each lung - and numerous bronchioles) connected to the outside by the mouth and nose
...
These gases diffuse a very short
distance between the alveolus and the blood because the lining of the lung and the capillary are both only one
cell thick
...
Ventilation movements also maintain the concentration gradients because air is regularly moving
in and out of the lungs
...
Both the intercostal muscles (in between the ribs) and the diaphragm receive impulses from the respiratory
centre
...
Chemoreceptors
14
There are also chemoreceptors in the medulla and certain blood vessels that are sensitive to changes in
carbon dioxide levels in the blood
...
chlorophyll a
chlorophyll b
chlorophyll c
bacteriochlorophyll (found in photosynthetic bacteria!)
There are also other families of pigments, such as the carotenoids
...
Photosystems
The pigments are arranged in funnel shaped photosystems that sit on the thylakoid membranes in the
chloroplasts
...
The various accessory pigments absorb light of different wavelengths and pass the energy down the
photosystem
...
There are 2 types of photosystem:
Photosystem One - PS I:
Its primary pigment is a molecule of chlorophyll a with an absorption peak at 700nm
...
It is called P680
Light Dependant Reactions
15
The first reactions of photosynthesis require light energy, and are called light dependant reactions
...
The production of ATP using light is called
photophosphorylation
...
They need ATP for energy to drive the reactions, and they
need NADPH for reducing power
...
16
Nutrition and Digestion
Nutrition
The whole point of nutrition is to obtain a source of energy and of carbon
...
Obtaining this energy and carbon is done in a variety of ways
by different organisms
...
e
...
Heterotrophic means that they feed on other organisms that have made their own food
...
g
...
Light is the primary source of energy
...
e
...
some bacteria
...
e
...
animals, fungi, and most protoctista
...
Within the chemoheterotrophs there may be:
Saprotrophic
nutrition:
Parasitic
nutrition:
Holozoic
nutrition:
e
...
fungi
...
Enzymes are
secreted onto the dead organism to digest the large molecules so digestion is external
...
e
...
tapeworm
...
The parasite therefore produces no enzymes and needs no gut system
...
e
...
many animals and carnivorous plants
...
They therefore will need to be able to catch or obtain and produce enzymes
to digest their food
...
The nerves regulate:
The gut movements by muscle contractions to force the food along or to mix the food with secretions in a
particular region
...
Mouth and saliva
Even before food enters the mouth the sight, smell and thought of the food stimulates a conditional reflex that
results in the release of saliva into the mouth
...
Again, releasing saliva
...
5 litres of saliva is released each day
...
Chewing mechanically breaks up the food so that there is a larger surface over which the amylase can work
...
Oesophagus
The oesophagus is a muscular tube with a squamous epithelium lining and mucus glands to lubricate the
passageway down to the stomach
...
With no food present, the sphincter remains closed so that no acid can enter and burn the oesophagus
...
The mucosais folded and the millions of microscopic projections created by this folding of the inner surface of
the wall are called villi
...
The possession of the villi and the folds in the cell surface membranes of the epithelial cells lining the villi
(microvilli) massively increases the surface area
...
Most multicellular plants and animals have too small a surface area to volume ratio so diffusion would be too
slow to provide the necessary molecules
...
The needs of a plant and animal are similar in some aspects and very different in others
...
Transport in Plants
Two main types of plant tissue are used in transport - xylem and phloem
...
Phloem transports organic molecules such as the products of photosynthesis
...
Substances are carried in a transport medium of the blood
...
Blood vessels
Blood is carried within a closed transport system that is made up of three types of vessel:
Arteries carry blood away from the heart
...
Veins take blood back into the heart
...
The rest of the blood is made
up of cells (red blood cells and white blood cells) and platelets
...
Homeostasis
Red Blood Cells
Also known as erythrocytes
...
Red blood cells are made in the bone marrow (the liver in a foetus) of many bones
...
Oxygen can therefore diffuse
very quickly into the cell and because the cell is so small, quickly bind to a haemoglobin molecule
...
There are two basic types of white blood cells; the granulocytes (they have granular cytoplasm and lobed
nuclei) and agranulocytes (the cytoplasm appears smooth and the nucleus is rounded or horseshoe in shape)
...
They have no nucleus but reactions do
take place in the cytoplasm
...
Blood groups
The most commonly required blood-grouping system is the ABO system
...
The antigens are called agglutinogens in this case and are:
agglutinogen A and agglutinogen B
...
Blood transfusions
It is important to match blood correctly so that agglutinins in the recipient don't clump the red blood cells of the
donor
...
The agglutinins in the plasma from the donor are so diluted that no harm is
done
...
Oxygen carriage
Oxygen does dissolve in plasma but the solubility is low and decreases further if the temperature increases
...
The Heart
The structure is closely related to its function
...
The oxygenated blood
then returns to the left hand side of the heart in the pulmonary vein
...
Since the right side pumps to the lungs which are situated close to the heart, the walls are much thinner than
the left side which has to pump blood out of the heart to the body
...
The cardiac cycle
One cardiac cycle consists of the atria and then the ventricles contracting so that the blood that has entered the
heart is pumped out
...
The periods of contraction are
called systole
...
Regulation of the cardiac cycle by the heart itself
The heartbeat is initiated in a specialised area of muscle in the right atrium called the sinoatrial node (SAN) or
the pacemaker
...
23
Nutrition and Digestion
Nutrition
The whole point of nutrition is to obtain a source of energy and of carbon
...
Obtaining this energy and carbon is done in a variety of ways
by different organisms
...
e
...
Heterotrophic means that they feed on other organisms that have made their own food
...
g
...
Light is the primary source of energy
...
e
...
some bacteria
...
e
...
animals, fungi, and most protoctista
...
Within the chemoheterotrophs there may be:
Saprotrophic
nutrition:
Parasitic
nutrition:
Holozoic
nutrition:
e
...
fungi
...
Enzymes are
secreted onto the dead organism to digest the large molecules so digestion is external
...
e
...
tapeworm
...
The parasite therefore produces no enzymes and needs no gut system
...
e
...
many animals and carnivorous plants
...
They therefore will need to be able to catch or obtain and produce enzymes
to digest their food
...
The nerves regulate:
The gut movements by muscle contractions to force the food along or to mix the food with secretions in a
particular region
...
Mouth and saliva
Even before food enters the mouth the sight, smell and thought of the food stimulates a conditional reflex that
results in the release of saliva into the mouth
...
Again, releasing saliva
...
5 litres of saliva is released each day
...
Chewing mechanically breaks up the food so that there is a larger surface over which the amylase can work
...
Oesophagus
The oesophagus is a muscular tube with a squamous epithelium lining and mucus glands to lubricate the
passageway down to the stomach
...
With no food present, the sphincter remains closed so that no acid can enter and burn the oesophagus
...
The mucosais folded and the millions of microscopic projections created by this folding of the inner surface of
the wall are called villi
...
The possession of the villi and the folds in the cell surface membranes of the epithelial cells lining the villi
(microvilli) massively increases the surface area
...
Most multicellular plants and animals have too small a surface area to volume ratio so diffusion would be too
slow to provide the necessary molecules
...
The needs of a plant and animal are similar in some aspects and very different in others
...
Transport in Plants
Two main types of plant tissue are used in transport - xylem and phloem
...
Phloem transports organic molecules such as the products of photosynthesis
...
Substances are carried in a transport medium of the blood
...
Blood vessels
Blood is carried within a closed transport system that is made up of three types of vessel:
Arteries carry blood away from the heart
...
Veins take blood back into the heart
...
The rest of the blood is made
up of cells (red blood cells and white blood cells) and platelets
...
Homeostasis
Red Blood Cells
Also known as erythrocytes
...
Red blood cells are made in the bone marrow (the liver in a foetus) of many bones
...
Oxygen can therefore diffuse
very quickly into the cell and because the cell is so small, quickly bind to a haemoglobin molecule
...
There are two basic types of white blood cells; the granulocytes (they have granular cytoplasm and lobed
nuclei) and agranulocytes (the cytoplasm appears smooth and the nucleus is rounded or horseshoe in shape)
...
They have no nucleus but reactions do
take place in the cytoplasm
...
Blood groups
The most commonly required blood-grouping system is the ABO system
...
The antigens are called agglutinogens in this case and are:
agglutinogen A and agglutinogen B
...
Blood transfusions
It is important to match blood correctly so that agglutinins in the recipient don't clump the red blood cells of the
donor
...
The agglutinins in the plasma from the donor are so diluted that no harm is
done
...
Oxygen carriage
Oxygen does dissolve in plasma but the solubility is low and decreases further if the temperature increases
...
The Heart
The structure is closely related to its function
...
The oxygenated blood
then returns to the left hand side of the heart in the pulmonary vein
...
Since the right side pumps to the lungs which are situated close to the heart, the walls are much thinner than
the left side which has to pump blood out of the heart to the body
...
The cardiac cycle
One cardiac cycle consists of the atria and then the ventricles contracting so that the blood that has entered the
heart is pumped out
...
The periods of contraction are
called systole
...
Regulation of the cardiac cycle by the heart itself
The heartbeat is initiated in a specialised area of muscle in the right atrium called the sinoatrial node (SAN) or
the pacemaker
...
30
Reproduction
The Cell Cycle
Interphase
DNA replicates as mitosis
...
The chromatids become coiled around each
other
...
These
breakage points result in "cross-overs" or Chiasmata
...
Which pair of chromosomes orientates to which pole is completely
random (called random assortment
...
Note: Unlike mitosis, there is no division of the centromeres at this stage
...
Prophase II
New spindle is formed and the centrioles have replicated
...
Metaphase II
The pairs of chromatids line themselves up on the equator as in mitosis, with sister chromatids orientated toward
opposite poles
...
Telophase II
The cell divides
...
The chromosomes uncoil and go into interphase
...
31
Sexual Reproduction in Flowering Plants
Most exam boards only require knowledge about reproduction in Angiosperms - the flowering plants
...
Within a flower, there are usually structures that
produce both male gametes and female gametes
...
Each ovule begins life as a small projection into the
cavity of the ovary
...
At the start, the ovule is a group of similar cells called the nucellus
...
At the centre of the ovule is an embryo sac containing the haploid egg cell (the female gamete)
...
Many pollen grains develop inside each pollen sac
...
All are diploid
...
The surface pattern is different on pollen grains from different species
...
Pollination
Many plants favour cross-pollination, so pollen must be transferred to the stigma of another plant if sexual
reproduction is to take place
...
Self-pollination is where the pollen is transferred to the stigmas of the same flower or the stigma of another
flower on the same plant
...
Fertilisation
If the pollen grain lands on a compatible stigma, a pollen tube will grow so that eventually the egg cell, hidden
away in the embryo sac, can be fertilised
...
It may grow downwards in response to chemicals made by the ovary (a
response known as chemotropism)
...
This triggers the
beginning of the growth of the seed
...
With the addition of water, large molecules of carbohydrate, protein and fat
can be hydrolysed (broken down) to produce substances for respiration
...
The female gamete is
fertilised and develops inside the mother's body so the reproductive systems of both males and females are
highly adapted for this
...
It takes place in the gonads of the male - the testes
...
It is in the walls of these tubules
that sperm production actually takes place
...
Hormonal control of spermatogenesis
The control centres are the pituitary gland and the hypothalamus in the brain
...
This is released into the blood and
stimulates the anterior lobe of the pituitary gland
...
ICSH: this stimulates the leydig cells that produce testosterone
...
They produce sperm in response
...
Female reproductive system and egg production
The production of eggs is called oogenesis
...
The outer layer of the ovary (the germinal epithelium) produces primary oocytes
...
33
Nervous and Hormonal Control
Nervous and Hormonal Control
Hormones
Hormones are just one of the tools used to send messages to the various parts of the body
...
They are secreted following a suitable stimulus and transported in the blood
...
The behaviour of the target will then change,
bringing about the right response
...
There are two structural types of hormone: protein and steroid
Protein hormones
Examples: insulin, glucagon, and adrenaline (try and remember these)
...
This starts off a chain
reaction inside the cell
...
Steroid hormones are different to protein hormones in that they cross the cell surface membrane and bind to
receptors in the cytoplasm
...
The 'neurone'
The nervous system carries messages around the body using specialised cells called neurones
...
The central nervous system and the peripheral nervous system
The nervous system (NS) is made up of two parts:
Central nervous system comprising the brain and spinal cord
...
The somatic (voluntary) and autonomic (involuntary) nervous
system
34
Different areas of the nervous system are used for different types of nervous reaction:
Conscious control
Non-conscious control
Sensory neurones and motor neurones
Receptors are cells that detect stimuli - for example, heat, pressure, light
...
From there, the impulse may pass on to a motor neurone to be taken to a muscle or gland (the effector)
...
Formation and Transmission of Impulses
Resting potential
In the surface membrane of a cell there are protein carriers
...
At the same time,
K+(Potassium) ions are pumped from the outside in
...
This is caused by a change in the concentrations of Na+ and K+ ions in the cell and happens in a number of
steps
...
This
means that the ions can only flow through unprotected cell-surface membrane
...
Because of this, the action potential will 'jump' from one node to the next; a process called saltatory
conduction, and so will travel much faster than in an unmyelinated neurone
...
The two neurones will not be in direct contact and action potentials cannot jump across the gap, called
a synapse (or synaptic cleft), so another method is employed
...
It diffuses
across the synapse, binds with the second neurone on the postsynaptic membrane and generates an action
potential
...
They are synthesised in
vesicles, which requires energy, so the synaptic knobs have many ATP-producing mitochondria in them
...
Your body recognises the antigens on your cells as your own (self); anything with different antigens to you (nonself) stimulates an immune response
...
Infection and disease
Your immune system is made up of cells that work with the body's physical and chemical barriers
...
Note: Harmful bacteria are an example of a pathogen
...
Physical and chemical barriers
The first line of defence is made up of physical and chemical barriers
...
e
...
These barriers occur at the skin or any other openings to the outside world
...
Nose, throat and digestive tract: the membrane lining these secretes sticky mucus to trap microbes
...
Chemical Barriers
Eyes: tears have lysozyme enzyme in them
...
Ear: your wax has antimicrobial properties
...
37
Large intestine, urethra and vagina: resident harmless bacteria use the nutrients that any harmful microbes
would need to survive (i
...
harmless bacteria out-compete the harmful bacteria)
...
The Second Line of Defence
The second line of defence is also a non-specific response (i
...
the response is the same for any pathogen)
...
Attack no 1: Inflammation
Inflammation happens because cells damaged by invading pathogens and particular white blood cells release
'alarm' chemicals which makes blood vessels enlarge (vasodilate) and the capillaries more 'leaky'
...
The three types of white blood cell you need to know for your exam are neutrophils, macrophages (these are
both phagocytes, which are engulfing cells), and lymphocytes
...
Attack no 3: Macrophages and Interferon
Other than direct 'hand-to-hand' combat, some killing is done at a distance
...
They can punch holes in the bacteria and parasites so that they die
...
Or the proteins can stick to the outside of the bacteria to make them more appealing for the phagocytes to eat!
If a virus or an intracellular parasite (one that lives inside a cell) has invaded a cell, the cell will make a chemical
called interferon
...
Lymphocytes
The third line of defence depends on lymphocytes
...
T Cells: mature after having first migrated from the bone marrow to the thymus gland
...
Involved in the
humoral response
...
A clone of identical T cells is formed, all with the correct shaped receptor
...
These are:
Killer T cells
Helper T cells
Suppressor T cells
Memory cells
Humoral response (B cells)
As with T cells, a B cell will form a clone if it comes into contact with a complementary shaped antigen
...
Antibodies
The plasma cells are highly developed and are able to make several thousand antibody molecules every
second
...
However, the memory B cells and a few memory T
cells survive
...
So they wait in the lymph nodes in case re-infection occurs, in which case they are ready to attack
...
Artificial immunity - vaccines
Vaccine is small quantities of the antigen attached to the offending organism
...
Because in response to the antigens, Band T cells have gone into action and a memory has been produced, it is
also termed active immunity
...
Antibiotics
These are drugs used to treat or cure infections and to be effective they must kill or disable the pathogen,
leaving host cells unharmed
...
A few antibiotics are synthetic but most are derived from living
organisms
...
They may
inhibit the synthesis of the cell wall, translation or transcription of proteins; interfere with membrane function or
enzyme action
...
They are only effective when the organism is making new cell walls, i
...
growing
...
They are caused by allergens - for example, pollen, dust, particles of animal skin, dust mites and their faeces
...
It is important for the body to have
a stable environment for cells to function correctly
...
There are basically two ways to regulate body
temperature and we use these to categorise organisms:
1
...
Their internal
body temperature is independent of the external temperature
...
2
...
Their internal
temperature fluctuates with the external temperature
...
Homoiotherms (for example, you)
In your brain is there is an area called the hypothalamus
...
You also have thermo-receptors in your skin and these detect
the temperature outside
...
As mentioned before, nitrogenous waste would be toxic if it accumulated so it must be removed from the body
...
Excess proteins (i
...
2
...
3
...
This process is called deamination
...
The urea is then transported in the blood to the kidney (where it is extracted and excreted via the bladder)
...
, is extracted from the blood in the kidney by a process called
ultrafiltration
...
This fluid is called the filtrate
...
Much of what has been filtered out needs to be returned to the blood - they are too precious to lose - so the
next process is called selective reabsorption
...
The
higher the concentration of the blood the less water there is in the blood
...
The
water levels will be brought back to normal and the impulses stop
...
If the level rises too much the normal behaviour of cells is affected and serious problems can arise
...
Insulin reduces the level of glucose in the blood plasma
Glucagon increases the level of Glucose in the blood plasma
Glucagon promotes the conversion of fatty acids
...
This process is
called Gluconeogenisis (remember, neogenesis means new formation)
...
To be able to fully understand these, the structure of the liver must first be understood
...
The liver is supplied with blood flowing in from the hepatic artery (bringing oxygen) and the hepatic portal vein
(bringing blood from the gut)
...
Liver Functions:
1
...
2
...
This is then converted
into urea and released into the blood to be taken to the kidney for excretion
...
The skeleton
may be an endoskeleton, an exoskeleton or a hydrostatic skeleton
...
g, flying, swimming, climbing, and walking)
...
Its functions are:
Support
...
Movement - a point of attachment for muscles
...
A source (sink) for calcium and phosphate
...
Cartilage cells are called chondrocytes
...
They also secrete collagen fibres that become embedded in the matrix to strengthen it
...
Muscles and Movement
Movement is made more flexible with joints
...
They limit the movement
thus preventing dislocation
...
Muscles are attached to bones by tendons that are made of collagen fibres
...
Each muscle is called a fibre
...
Each myofibril is made of myofilaments - actin and myosin
...
44
Actin: consists of 2 threads wrapped around each other
...
In a
relaxed state, a molecule called tropomyosin covers these sites
...
Each molecule has a tail and a double globular head
...
If it is stronger than a threshold stimulus contraction will occur
...
The boundaries of the ecosystem studied are dictated by the individual carrying out the study
...
Understanding ecological terms
The following are important terms which are frequently used in ecology
...
Population: A group of organisms, all of the same species, and all of whom live together in a particular habitat
...
Niche: The position occupied by an organism in a particular ecosystem, dependent upon the resources it uses
...
Ecosystem: The biotic community together with the abiotic environment
...
These relationships are the biotic factors of the ecosystem
...
These are the abiotic
factors
...
Abiotic factors: these are the physical factors that affect an ecosystem
...
Pioneer species to climax communities
Pioneer species: These are the first species to occupy a new habitat, starting new communities
...
Many have an asexual stage
to their reproduction
...
Climax community: This is the stable community that is reached, beyond which, no further succession occurs
...
g, following a volcanic eruption or a landslide)
...
They are able to penetrate the bare surface, trap organic
material and begin to form humus
...
The soil can be used by a more diverse range of plants with deeper
root systems
...
Finally a climax community is reached and the species present do not change unless the environment changes in
some way
...
g, following a fire, flood or human intervention)
...
Populations
The factors affecting population growth and how populations increase in numbers are important concepts in
ecology as they are necessary in order to successfully study how ecosystems work
...
The population density can be affected by a number of factors:
47
1
...
Immigration: The number of new individuals joining a population
...
Death: The number of individuals within a population that die
...
Emigration: The number of individuals leaving a population
Population size can also be affected by the following:
Density dependent factors: These are any factors, dependent on the density of the population in question
...
Density independent factors: These are any factors, not dependent upon the density of the population in
question
...
Competition
Competition is often considered to be the most important biotic factor controlling population density
...
Competition Types:
Intraspecific competition
Scramble competition
Contest competition
Interspecific competition
Trophic levels
This describes a specific level in a food chain
...
There are four important levels in most food chains:
Producers: Organisms which convert some of the energy from the sun into stored chemical energy (usually
plants)
...
They are herbivores
...
They are
carnivores
...
They are bacteria or fungi that obtain
their energy by breaking down dead organisms from the other trophic levels
...
Organisms may occupy
more than one trophic level, (e
...
Transfer of energy between trophic levels
Transfer of energy between trophic levels is relatively inefficient
...
Pyramids in ecology
Ecological pyramids are used as a tool to illustrate the feeding relationships of the organisms, which together
make up a community
...
Nutrient cycle types:
The carbon cycle
The nitrogen cycle
Nitrifying bacteria will produce nitrates from these organic nitrogen compounds
...
Deforestation
Deforestation is the rapid destruction of woodland
...
49
Evolution
Types of variation
For each characteristic, the population may show either continuous or discontinuous variation
...
This gene pool can change in content (new alleles arriving, existing alleles being lost) or the ratio
of alleles altering due to the following:
1
...
natural selection,
3
...
immigration,
5
...
The factors favouring stability of the gene pool are:
1
...
No natural selection,
3
...
No gene flow (due to individuals emigrating or immigrating),
5
...
Hardy-Weinberg Equilibrium
Using the Hardy-Weinberg Equilibrium, it is possible to establish the ratio of dominant to recessive alleles
...
However, the population is limited by environmental factors and so
remains more or less constant over time
...
There are three types of selection that occur in nature:
Stabilizing selection
...
50
Disruptive selection
...
Palaeontology
The study of fossils
...
When a group of organisms all possess a structure that appears to have come from a common ancestor and
which has the same microscopic structure and body position, as well as other features, they are said to have
homologous structures
...
Examples include:
Insect wing and bird wing
...
g, squid) and the eye of a vertebrate
...
In these cases, selection pressures from the environment in which
each species lives have caused particular structures to be advantageous
...
Looking at the order of bases in the lengths of DNA and the order of amino acids in a protein, it is possible to
determine how similar they are in different species
...
A comparison of DNA sequences show that it is 99
...
51
Evolution in Action
Evolution occurs when there is a change in the environment or when there is mutation because the allele
frequencies will change as a result
...
Usually mutations are harmful, occasionally they are neutral and infrequently they are beneficial
...
Antibiotic resistance
Antibiotics are chemicals usually produced by fungi
...
There may be however, one or more bacteria in the population that are able to inactivate the chemical
making them resistant to the antibiotic
...
Definition of a species
A group of organisms with similar morphological, physiological and behavioural features, which can interbreed to
produce fertile offspring, and are reproductively isolated from other species
...
Disease is a disorder or malfunction of the mind or body, which destroys good health
...
Physical Disease
Infectious disease
Non-infectious diseases
Deficiency diseases
Inherited diseases
Degenerative diseases
Mental disorders
Social diseases
Self-inflicted diseases
Terms used to describe diseases
An infectious disease, which is always present in a population, is called endemic
...
If a disease spreads over
a continent or even the world it will be termed pandemic
...
Incidence, prevalence
and mortality for a disease may be determined
...
Smoking and Disease
53
Tobacco companies do not declare the ingredients in cigarettes, but upon analysis, they contain over 4000
different chemicals, many of which are toxic
...
Chemicals found in cigarettes
Tar
This is a mixture of aromatic substances, which settles on the airway linings and stimulates changes that may
lead to obstructive lung disease and lung cancer
...
This stops the haemoglobin from becoming fully saturated and so it carries 5-10%
less oxygen
...
This increases heart rate and blood pressure and
decreases the blood supply to the extremities - for example, the hands and feet
...
Chronic bronchitis
Tar stimulates goblet cells and mucus glands to enlarge, producing more mucus
...
Emphysema
Due to constant infection, phagocytes are attracted to the lungs where they release elastase - an enzyme that
breaks down the elastin in the alveoli walls, to enable them to reach the surface where the bacteria are
...
Large air spaces appear, reducing the surface area for gas exchange and making sufferers breath more
rapidly
...
Chronic obstructive pulmonary disease
54
This very disabling disease is the result of chronic bronchitis and emphysema occurring together
...
Britain has the highest death rate from this disease in the world
...
Links between smoking and lung disease
These can be put into two groups:
Epidemiological evidence looks for patterns in the diseases, which smokers suffer from
...
Experimental evidence attempts to prove a causal link
...
They are responsible
for 50% of deaths in developed countries and are multifactorial - smoking being one risk factor
...
An atheroma is a build-up of cholesterol, fibres, dead muscle cells and platelets and is
more likely to develop upon damage to the artery wall by high blood pressure, carbon monoxide or nicotine
...
Coronary heart disease
This is a disease of the coronary arteries, which branch from the aorta to supply the heart muscle
...
This
makes it difficult for the heart to receive the extra nutrients and oxygen it requires during exercise
...
The brain tissue becomes starved of oxygen and dies
...
Links between smoking and cardiovascular disease
Smoking increases the concentration of blood cholesterol, which is a risk factor, so smokers increase the risk of
having heart disease or a stroke
...
Being overweight increases the risk as does eating a diet high in saturated fat and salt
...
Having diabetes raises
the risks and high alcohol intake is another contributory factor
...
F1 is used for their offspring
...
Capital letters are used to denote a dominant allele
...
Incomplete dominance
This is when neither allele is dominant
...
A heterozygote has an intermediate phenotype as there is partial influence from both alleles
...
They are independent, so there is no 'blending' as in the snapdragons; instead the phenotype is a result of the
full expression of both alleles
...
For example, a disease caused by one pair of alleles may
have several or many symptoms
...
g, skin colour)
...
57
DNA and the Genetic Code
Evidence for the structure of DNA
Many observations contributed to the evidence from which the structure of DNA was eventually deduced by
Watson and Crick:
1
...
Chargaff's work on base equivalence
3
...
The chain of nucleotides is formed in exactly the same way as
in DNA, but the molecule has some very important differences:
1
...
2
...
(Think "No cup of T
for U!")
3
...
4
...
The Structure of DNA
DNA is a polymer of nucleotides
...
a sugar - deoxyribose
...
DNA is a macromolecule polymer made of subunits called nucleotides
...
DNA Replication
Since DNA forms the genetic code and that it is known that genes may be inherited, it follows that DNA must be
copied exactly before being incorporated into gametes at meiosis
...
DNA and Protein Synthesis
58
DNA is the molecule which controls the synthesis of proteins
...
Thus DNA is able to exert a controlling influence over the whole cell and ultimately, the whole organism
...
Protein Synthesis
Protein synthesis relies on the effective communication of the coded information held in the genes to the sites
of protein manufacture, the ribosomes in the cytoplasm
...
These are messenger RNA molecules
...
While the amount of DNA for a diploid
cell is constant within a species, the differences can be great between species
...
Although transcribed, these introns are excised (cut
out) before translation
...
The importance of these sites is that they allow genes to produce various forms of the protein for in different
tissues or at different times in the development of the organisms
...
coli
The single chromosome of the common intestinal bacterium E
...
7 million base
pairs
...
The promoter is the part of the DNA to which the RNA polymerase binds before opening the segment of the DNA
to be transcribed
...
The structure and operation of an operon
Operons can either be inducible (promoters) or repressible according to the control mechanism
...
coli, seventy-five different operons have been identified
...
Gene regulation in Eukaryotic organisms
One piece of evidence suggests that the influence of the regulator genes may be thousands of base pairs away
from the promoter gene, unlike the close sequences found in E
...
Eukaryotes have a number of gene control mechanisms not found in prokaryotes
...
Human Genome Project
The structure of DNA was found by Watson and Crick in 1953, and only in 1956 was it first known that humans
had 23 pairs of chromosomes
...
In 1977, Fred Sanger invented the first DNA sequencing process
...
Sequencing the Human genome
To sequence a gene, the first difficult part is to obtain the gene
...
The manual methods involves electrophoresis; a process that separates fragments of DNA by using an electrical
current
...
"This is the end of the beginning"
One of the main project goals is to address the ethical, legal and social issues (ELSI) that may arise from the
project
...
Knowledge about the effects of DNA variations amongst individuals can lead to diagnosis and possibly treatment
of the thousands of disorders that afflict humans all over the world
...
61
Genetic Engineering
Obtaining the Gene
Genetic engineering aims to remove a desired gene and transfer it to another organism where it can be
expressed
...
Obtaining the desired gene
There are various methods that are used
...
If the amino acid sequence of the desired protein is known, the DNA code can be worked out and the DNA made
in the lab by stringing together the correct order of nucleotides
...
2
...
(The original reverse transcription enzymes were first discovered in retro
viruses
...
Isolate the gene from the entire genome
...
The enzymes used to cut the DNA are called restriction
enzymes or restriction endonucleases
...
There are several ways of getting DNA fragments into host cells:
1
...
2
...
3
...
4
...
5
...
Note: These methods only introduce DNA into the cell; they do not incorporate it into the host DNA
...
Grows fast
...
Is easily manipulated
...
Has a simple chromosome (prokaryotic cells do not have a nuclear envelope)
...
Contains naturally occurring vectors (see later)
...
Transferring the Gene
How to get the fragment into bacteria
A vector is a carrier DNA molecule into which the desired gene can be inserted
...
This is a small, extra-chromosomal, circular piece of DNA often found
in bacteria in addition to their functional DNA
...
This
genetic material integrates into the host genome, causing the production of disease or deformity such as Galls
...
PCR: Polymerase chain reaction
The purpose of this PCR is to produce huge numbers of copies of a gene
...
PCR is used as the starting point, or template, for sequencing
...
Those that have been unsuccessful have to be eliminated
...
Galls are large tumour-like growths in plants, usually produced as a response by the plant to some invasion by
microbe or insects
...
Genes coding for the tolerance to herbicides, resistance to insect pests, viral disease and other factors have been
introduced to various plant species
...
This can be split several times and each group of cells can go on to
form an individual plant (meristem tissue culture or micropropagation)
...
Germ cell therapy of sperm, egg or early embryo
...
Somatic cell therapy
...
There are 3 ways in which gene therapy can work:
1
...
2
...
3
...
Genetic fingerprinting
Much of your DNA is non - coding (i
...
it doesn't code for a protein), but rather it contains regions of highly
repetitive sequences of bases (Variable Number Tandem Repeats - VNTRs)
The number of repeats, and hence the size of the VNTRs, varies markedly between individuals
...
Only identical twins have the same number of VNTRs
...
64
Applications of Genetic Engineering
Insulin and Factor VIII
Insulin
Human insulin is a protein, normally produced by the b cells of the islets of Langerhans in the pancreas
...
Factor VIII
Haemophiliacs suffer from a defective gene that fails to produce Factor VIII, an important agent involved in
blood clotting
...
Success has been limited to somatic
(body) cells rather than sex cells (gametes)
...
The modification of germ line cells (germ line therapy) is likely to be discouraged on
moral grounds
...
The missing ADA gene is extracted from healthy bone marrow tissue
...
Chymosin
Rennet (rennin or rennilase) and cheese making:
Back in the 1960's, the world faced a severe shortage of calf rennet
...
This then separates from the liquid, whey
...
(Rennet is an enzyme found in the stomachs of young mammals, like calves, and is important in the digestion of
milk proteins
...
GE is a
new technology, and as such is met with scepticism on one hand and enthusiasm on the other
...
Genetic engineering and traditional breeding
Traditional breeding
Traditional crop and animal breeding has been practiced for thousands of years
...
Crossing takes place, usually between individuals of
the same or closely related species
...
Genetic engineering methods
These include terms such as genetic manipulation, recombinant DNA technology and gene therapy (in
humans)
...
The patient faces the
rest of their life with a cocktail of anti-suppressant drugs
...
Xenotransplantation
Organs from other animals can be used in human transplantation, but they pose a potentially greater risk of
rejection
...
You may use these for your personal use on a computer screen, print pages on paper and store such pages in
electronic form on disk (but not on any server or other storage device connected to an external network) for
your own personal, educational, non-commercial purposes
...
All copyright and publishing rights are owned by S-cool
...
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