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1 Communication 2 Nerves 1
Cells communicate by cell signalling ­ one cell Sensory receptors (e.g. rods and cones in the retina)
produces a chemical that is detected by another convert one form of energy (e.g. light) into electrical
cell. energy in a nerve impulse.
Cell signalling can be nervous (i.e. a Neurones carry impulses: sensory (from receptors to
neurotransmitter at a synapse) or hormonal (i.e. a CNS) motor (from CNS to effectors) and relay
hormone carried in blood). (connect sensory and motor).
It coordinates responses to stimuli from internal More Na+ ions pumped out of nerve membrane than
(e.g. temp and pH) and external (e.g. light, temp, K+ in, using ATP . Negative ions trapped inside, so
humidity) environments. inside of neurone membrane is negative .
A response to stimuli is a change in behaviour or A negative resting potential (voltage ) of ­60 mV
physiology to cope with the change in environment. compared with outside ­ known as polarised .
3 Nerves 2 4 Nerves 3
Nerve membranes have voltagegated channels Na+ diffuses sideways and creates local currents that
for Na+
and K+ ions ­ closed during resting potential depolarise the next piece of membrane ­ the
so it stays at ­60 mV.
depolarisation travels along the neurone.
A generator potential or other stimulation can open Mammalian neurones have a myelin sheath
the channels. Na+ diffuses in and depolarises the (electrical insulation) formed by Schwann cells.
membrane to +40 mV inside cell.
Gaps in the myelin insulation are called nodes of
Na+ channels close and more K+ channels open so Ranvier which allow impulses to jump from node to
+
K diffuses out of the cell. The inside becomes node.
negative (­60 mV) again i.e.
repolarised . This jumping is called saltatory conduction and
Depolarisation followed by repolarisation in a section makes the speed of impulse much faster (120 m/s)
of nerve membrane is called an action potential. than in unmyelinated neurones (30 m/s).
5 Synapses and signals 6 Hormones 1
Depolarisation (nerve impulse) travels at a fixed Hormones are chemicals secreted by endocrine
speed ­ a stronger stimulus gives more frequent glands . They travel to all cells via the blood but only
impulses not faster ones. affect cells in target tissues .
A synapse is a junction between two nerve cells: The adrenal gland produces adrenaline which prepares
presynaptic membrane ­ synaptic cleft (gap) ­ the body for activity ­ e.g. increases heart rate,
postsynaptic membrane. glycogen conversion to glucose, etc.
An impulse causes release of a neurotransmitter Adrenaline is an example of a first messenger and
(acetylcholine ) from vesicles, which fuses with the cyclic AMP is an example of a second messenger .
presynaptic membrane. An exocrine gland is one that secretes molecules into
Acetylcholine diffuses across the cleft and a duct, which then carries the molecules to where they
depolarises the postsynaptic membrane of the next are used.
neurone ­ a new impulse starts.

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Hormones 2 8 Hormones 3
The pancreas secretes enzymes into the gut Type I diabetes (insulin dependent) ­ not enough
(exocrine gland) and hormones into blood (endocrine insulin produced. Type II (noninsulindependent ) ­
gland). liver and muscle cells not responding to insulin.
Pancreatic cells detect high blood glucose ­ Bacteria can be genetically modified to produce
hormone insulin secreted. cells detect
l ow blood human insulin. Pancreatic stem cells could produce
glucose ­ hormone glucagon secreted. new cells in diabetics.…read more

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Kidney 4 14 Temperature regulation
Kidney failure is the inability to (i) remove excess Endotherms (birds and mammals) can produce heat
water urea and salts and (ii) regulate water and salt (e.g. from metabolism in the liver/muscles) to maintain
levels. body temperature.
It can be treated by dialysis ­ timeconsuming use of The hypothalamus thermoregulatory centre detects
an artificial, partiallypermeable membrane to filter the blood temperature and negative feedback is used to
blood. control changes.…read more

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Photosynthesis 5 ­ lightindependent (Calvin 20 Photosynthesis 6 ­ factors affecting
cycle) photosynthesis
CO 2 (via stomata) combines with Ribulose
A limiting factor (e.g. temperature) is the one in the least
bisphosphate ( RuBP ) (5C) to make 2 molecules of supply compared with the other factors and can
glycerate 3phosphate ( GP ) (2 x 3C). Enzyme determine the rate of photosynthesis.
rubisco catalyses this reaction.…read more

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Respiration 5 ­ oxidative phosphorylation and 26 Respiration 6 ­ anaerobic/ATP yield/respiratory
chemiosmosis substrates
All reduced NAD and reduced FAD become oxidised The total yield o f ATP per glucose should be 30 ­ not
­ H atoms split into electrons and protons. Electrons reached because ATP i s used in some stages and
go down electron transport chain . protons leak .
Electron flow gives energy to pump protons into Some ATP is produced directly in respiration reactions.…read more

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Variation and genetics 2 32 Variation and natural selection
The position of a gene on a chromosome is its Natural selection is when the variant best suited to
locus . If a gene locus is on ( carried on ) the X or Y the environment reproduce more and increase in
chromosome it is known as sexlinkage . frequency within the population.
If two genes (loci) are on the same chromosome If environment changes (e.g.…read more

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Gene technologies 1 ­ genome sequencing 36 Gene technologies 2 ­ genetic engineering
35
and recombinant DNA Sections of DNA containing a desired gene (e.g. for
Chromosomes are first broken into short sections. human insulin) can be cut by restriction
These act as templates to get DNA pieces that only endonuclease enzymes and isolated .
differ from each other by a single base. These enzymes cut the DNA at a specific base
DNA pieces are separated by gel electrophoresis . sequence (e.g.…read more

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Ecosystems 3 42 Ecosystems 4
Limiting factors (e.g. space, food, light) create a Preservation is the protection of an area by restricting
carrying capacity ­ maximum population of a or banning human exploitation or contact ­ nature
species that an environment can support. reserves/preserves/parks.
Predatorprey cycle : increased prey numbers Conservation is maintaining biodiversity but allowing
predator numbers increase as more food leads to sustainable production ­ replanting mixed tree species
decrease in prey predator numbers fall increase after felling for timber.…read more

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Animal responses 3 48 Animal responses 4
Voluntary muscle is striated and multinucleate. For Learning is a change in behaviour from experience ­
example, attached to bones for conscious movements e.g. habituation (not responding to a constant stimulus),
such as at leg joints for walking. imprinting and conditioning.
Cardiac (myogenic heart) muscle is striated not Imprinting is learning during a certain life phase (e.g. a
multinucleate. Involuntary muscle is neither striated chick recognising a parent). Conditioning is learning
nor multinucleate ­ e.g.…read more

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Terms to Define Terms to Define
Genetic Code: Consists of a Triplet Base Sequence Recessive: Alleles that have to occur in homozygous
which codes for specific Amino Acids. form in order to be expressed in the phenotype.
Allele: Different versions of the same genes. Linkage: When two genes are located on the same
Locus: The location of a gene on a chromosome. chromosome.
Phenotype: The characteristics expressed in an Sex Linkage: When the genes expressed are derived
organism. from the X or Y chromosome.…read more

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