revision notes and exam tips.

a concise set of notes on various topics, with exam tips.

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  • Created on: 21-04-10 11:53
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based on common characteristics, either physical or genetic
`Life' has MRS GREN in common.
Classification is hierarchical, large groups are divided up into
nonoverlapping smaller groups.
Phylogenetic organisation is based on the order in which
organisms evolved, generally going from simple to complex.
There are 5 kingdoms ­ prokaryotes, protocists, fungi, plants
and animals. You need to know each kingdom's common
The normally accepted hierarchy is Kingdom, Phylum, Class,
Order, Family, Genus, species (always written lower case).
Questions usually involve definitions or identifying information about
an organism given in a passage of information.
can be continuous or discontinuous
may have genetic and/or environmental causes.
Genetic causes may be mutation, crossing over in first prophase
of meiosis, independent assortment of chromosomes, or random
fertilization. You may need to explain how each of these produce
Environmental effects may be temperature, food availability (light
for plants), water etc. Again, you may need to explain.
Natural selection
Darwin described a sequence of events to produce evolution by
natural selection:
Organisms overproduce offspring
Resources are finite
Offspring compete for the finite resources
The offspring will be varied, so some will compete more
successfully than others.
The best suited to the environment are more likely to survive.
They will pass on the genetic features that have made them more
successful to the next generation.
This is described as the survival of the fittest.
Questions usually give you a written description and ask you to apply
the above ideas to explain a change in a population or species.

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This definition is frequently the start of
a question on speciation.
Species are produced from existing species by isolation and
mutations in the isolated populations until the populations are no
longer compatible. This may be genetically or behaviourally.
Questions will usually be similar to those for natural selection.
the stages in meiosis are crucial, it is not essential to know the
names, but it makes answering questions a lot easier.…read more

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The intensity of a stimulus is signalled by how many times a
neuron `fires' in a second.
The impulse is passed from one neuron to another at a synapse
When the impulse arrives Ca2+ ions enter the presynapse.
Neurotransmitter has already been synthesised and stored in
Energy is required so many mitochondria in the nerve.
Ca2+ signals to the vesicles to fuse with the presynaptic
Neurotransmitter diffuses rapidly across the synaptic cleft down
the diffusion gradient.…read more

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Cones are found in the area directly behind the pupil (the fovea),
away from the fovea the proportion of rods increases.
No cells are found where the optic nerve leaves the eye, this is
called the blind spot.…read more

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The blood glucose level decreases, and insulin production stops.
If the glucose level falls due to respiration in the cells, the
pancreas detects the fall.
The cells of the Islets secrete glucagon into the blood.
This signals to cells with a glycogen store that they must
hydrolyse the glycogen to glucose and return it to the blood.
The glucose level rises and stops further production of glucagon.…read more

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The increased heat production combined with the increased
insulation raises the body temperature.
Osmoregulation maintains the water balance so reactants are in
the correct concentrations to maintain metabolism at the correct
It also serves an excretory function (removal of waste products)
as urea passes out with the excess water.
Excess amino acids are deaminated in the liver, and the urea
enters the bloodstream.
Blood that travels to the kidney along the renal artery eventually
enters a ball of capillaries called a glomerulus.…read more

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When it reaches the 2nd convolution, it increases the permeability
to water, and more water is reabsorbed making the urine even
more concentrated, and an even smaller volume.
This reduces water loss even further, so it can be more easily
restored by drinking, eating, and respiration.
This consists of the brain and spinal cord.
Functions are localised within the brain, then association areas
link these functions together (you must know especially the areas
involved with vision and speech).…read more


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