A2 biology unit 5 notes

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A2 Biology Unit 5 page 1
AQA A2 Biology Unit 5
Specification 2
Human Nervous system Nerve Cells 4
The Nerve Impulse 6
Synapses 0
Receptors 14
Muscle 17
Animal Responses 24
Control of Heart Rate 28
The Hormone System 30
Homeostasis 33
Temperature Homeostasis 34
Blood Glucose Homeostasis 38
Control of Mammalian Oestrus 42
Plant Responses 44
Molecular Genetics The Genetic Code 48
Protein Synthesis 50
Gene Mutations 54
Stem Cells 57
Control of Gene Expression 63
Biotechnology 66
DNA sequencing 71
Southern Blot 76
In vivo cloning 80
Genetically Modified Organisms 85
Gene Therapy 89
Genetic Screening and Counselling 92
These notes may be used freely by A level biology students and teachers,
and they may be copied and edited.
Please do not use these materials for commercial purposes.
I would be interested to hear of any comments and corrections.
Neil C Millar ([email protected])
Head of Biology, Heckmondwike Grammar School
High Street, Heckmondwike, WF16 0AH
Jan 2010
HGS Biology A-level notes NCM 8/09

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Biology Unit 5 Specification
Control Systems are substances that stimulate their target cells via the blood
Organisms increase their chance of survival by responding system. This results in slow, long-lasting and widespread
to changes in their environment. responses. The second messenger model of adrenaline and
glucagon action. Histamine and prostaglandins are local
The Nerve Impulse chemical mediators released by some mammalian cells that
The structure of a myelinated motor neurone. The affect only cells in their immediate vicinity.…read more

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Genetics · Small interfering RNA (siRNA) as a short, double-strand
The Genetic Code of RNA that interferes with the expression of a specific
The genetic code as base triplets in mRNA which code for gene. Interpret data provided from investigations into
specific amino acids. The genetic code is universal, non- gene expression.
overlapping and degenerate. The structure of molecules of
messenger RNA (mRNA) and transfer RNA (tRNA).…read more

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The Human Nervous System
Humans, like all living organisms, can respond to changes in the environment and so increase survival.
Humans have two control systems to do this: the nervous system and the endocrine (hormonal) system.
We'll look at the endocrine system later, but first we'll look at the nervous system. The human nervous
system controls everything from breathing and standing upright, to memory and intelligence.…read more

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Nerve Cells dendrites
The nervous system composed of nerve cells, or neurones. A neurone has a
cell body with extensions leading off it. Several dendrons carry nerve impulses
Sensory Neurone
towards the cell body, while a single long axon carries the nerve impulse away
from the cell body.…read more

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The Nerve Impulse
Neurones transmit simple on/off signals called impulses (never talk about nerve signals or messages). These
impulses are due to events in the cell membrane, so to understand the nerve impulse we need to revise
some properties of cell membranes.
The Membrane Potential
All animal cell membranes contain a protein pump called the Na+K+ATPase. This uses the energy from
ATP splitting to simultaneously pump 3 sodium ions out of the cell and 2 potassium ions in.…read more

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an electrical pulse at one end of an axon and measure the voltage changes at the other end, using an
stimulating recording
stimulator oscilloscope
electrodes electrodes
squid giant axon isotonic bath
The normal membrane potential of these nerve cells is ­70mV (inside the axon), and since this potential
can change in nerve cells it is called the resting potential. When a stimulating pulse was applied a brief
reversal of the membrane potential, lasting about a millisecond, was recorded.…read more

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How do Nerve Impulses Start?
In the squid experiments the action potential was initiated by the stimulating electrodes. In living cells they
are started by receptor cells. These all contain special receptor proteins that sense the stimulus. The
receptor proteins are sodium channels that are not voltage-gated, but instead are gated by the appropriate
stimulus (directly or indirectly).…read more

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How can Nerve Impulses convey strength?
How do impulses convey the strength of the stimulus? Since nerve impulses are all-or-nothing, they cannot
vary in size. Instead, the strength of stimulus is indicated by the frequency of nerve impulses. A weak
stimulus (such as dim light, a quiet sound or gentle pressure) will cause a low frequency of nerve impulses
along a sensory neurone (around 10Hz).…read more

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The junction between two neurones is called a synapse. An action potential cannot cross the gap between
the neurones (called the synaptic cleft), and instead the nerve impulse is carried by chemicals called
neurotransmitters. These chemicals are made by the cell that is sending the impulse (the pre-synaptic
neurone) and stored in synaptic vesicles at the end of the axon.…read more


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