A2 Biology Chapter 10:
Common Exam Questions and Mark-schemes
10.3+4+5
Nerve Impulses
Question
How is resting potential
made?
How is an action
potential made?
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Sodium ion channels open
Sodium ions enter axon quickly (these 2 for a 2 marker)
Membrane depolarised
Threshold reached
Even more Na+ channels open
In repolarisation phase; K+ channels open/K+ leaves axon
How is the axon
repolarised?
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Sodium ion channels close
potassium ion channels open
Potassium ions diffuse out of axon
No (new) action potential/nerve impulse be produced in
this time;
What is meant by the
refractory period?
Explain the effect of
myelinatation
10.6+7
Synapses
Mark Scheme
 Membrane relatively impermeable/ less permeable to
sodium ions / gated channels are closed/ fewer
channels;
 sodium ions pumped / actively transported out;
 by sodium ion carrier / intrinsic proteins;
 higher concentration of sodium ions outside the neurone;
 inside negative compared to outside / 3 sodium ions out
for two potassium ions in;
How does information
pass across a synapase?
How do synapses ensure
impulse is sent in one
direction only?
 Myelin prevents movement of ions
 Impulses jump from node to node / salutatory
conduction
 Calcium ions enter pre-synaptic neurone
 Vesicles containing neurotransmitter fuse with the presynaptic membrane
 Neurotransmitter released
 Movement by diffusion;
 Binding to receptors on (post-synaptic) membrane;
 Neurotransmitter only produced in pre-synaptic neuone
 Receptors for neurotransmitter only in post-synaptic
neurone