Syllabus Edition

First teaching 2023

First exams 2025

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Neural Signalling (HL IB Biology)

Exam Questions

3 hours35 questions
1a
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3 marks

The image shows a representation of a neurone.uqsE6XvR_e-1a

Identify structures X-Z in the image.

1b
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1 mark

Branching from structure X of the neurone in part a) are structures known as dendrites.

State the role of dendrites in the nervous system.

1c
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2 marks

Describe the structure of from the image in part a).

1d
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2 marks

It has been estimated that a neurone without structure Y present can conduct nerve impulses at speeds of 0.5 m s-1 whereas a neurone with structure Y present can conduct impulses at speeds of 150 m s-1.

Calculate how many times faster impulse conduction is in the presence of structure Y than without structure Y.

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2a
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3 marks

The graph below shows changing membrane potential in an axon within a human leg.

action-potentials-sq

At 0.5 ms:

(i)

Identify the type of membrane potential present in the axon.

[1]

(ii)

Explain how this membrane potential has been achieved.

[2]

2b
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1 mark

At 1 ms in the graph in part a) the membrane is stimulated.

State what happens within the membrane at 1 ms as a result of this stimulation.

2c
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3 marks

Explain the shape of the curve between 1 - 1.8 ms in the graph in part a).

2d
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2 marks

Assuming the intensity of stimulation remains constant, calculate how many complete action potentials will occur in 1 second in the graph shown in part a). Note that there are 1000 ms in a second.

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3a
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2 marks

The graph below shows the changes in membrane potential that take place in a neurone during a single action potential.

action-potential-sq

Stages 1 and 5 can be identified as the neurone in its resting state, and during stage 4 the neurone is said to be hyperpolarised.

Identify stages 2 and 3 in the graph.

3b
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2 marks

Explain the change in membrane potential taking place during stage 3 in the graph in part a).

3c
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3 marks

The table below contains a series of statements that describe the propagation of a nerve impulse a long an axon.

  Sodium ions diffuse along the inside of the axon from an area of high concentration to an area of low concentration
  A new action potential is generated in the neighbouring section of the axon
  The recent influx of sodium ions creates a sodium gradient between the stimulated part of the axon and the neighbouring section.
  If a depolarisation threshold is reached new sodium ion channels open

Identify the correct sequence of events by writing the numbers 1-4 in the blank boxes. The first event should be number 1, and so on.

3d
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1 mark

State the role of the refractory period in the propagation of action potentials.

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4a
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3 marks

The image below shows a representation of a junction between two neurones.

synapse-sq

Identify structures A-C.

4b
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2 marks

Part a) shows that the junctions between neurones contain molecules known as neurotransmitters.

Outline how neurotransmitters interact with the structures labelled D to bring about an action potential in the new neurone.

4c
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1 mark

Once its role is complete the neurotransmitter needs to be broken down and recycled in order for the junction between neurones to continue functioning.

Identify an enzyme that is involved with the breakdown of neurotransmitter molecules.

4d
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1 mark

Neonicotinoids are chemicals used in some types of pesticide. Neonicotinoids have a similar function to certain neurotransmitters in the nervous systems of insects, with one major difference being that the enzyme in part c) cannot break them down.

Suggest why the enzyme in part c) cannot break down neonicotinoids.

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5a
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3 marks

Outline the role of the myelin sheath in nerve transmission.

5b
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5 marks

Draw a labelled diagram of a neurone.

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1a
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1 mark

Describe and explain one way in which an axon may be adapted to conduct impulses at a faster rate in the nervous system.

1b
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3 marks

The presence of myelin around an axon can help speed up a nerve impulse.

Explain how.

1c
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2 marks

Pacinian corpuscles are one of many receptors found in the skin. They detect changes in pressure.

A scientist wanted to research the effects of different pressures on the magnitude of membrane potentials generated. They investigated this effect by connecting multiple microelectrodes to the end of a toe and applying different pressures to the toe. The microelectrodes measured the maximum membrane potential of the pacinian corpuscle and its associated neurone, called a sensory neurone, when different pressures were applied.

The diagram below shows the structure of the Pacinian corpuscle, along with its sensory neurone and the position of the microelectrodes.

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The table below shows the results.

Pressure applied to the end of the toe

Membrane potential at A (mV)

Membrane potential at B (mV)

None -70 -70
Light -45 -70
Medium +35 +40
Heavy +40 +40

 

Explain how the sensory neurone within the Pacinian corpuscle maintains a resting potential when no pressure is applied.

1d
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2 marks

The membrane potential measured at microelectrode B (from part c of question 1) was identical for both medium and heavy pressure.

Explain why.

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2a
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2 marks

Body temperature can affect the speed of an action potential. Research has found that reaction time is slower when body temperature falls. This is because nerve impulse conduction is slower.

Explain how a lower temperature leads to slower nerve impulse conduction.

2b
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3 marks

The permeability of the axon’s cell-surface membrane changes during an action potential.

The graph below shows changes in permeability of the membrane during a single action potential to both sodium (Na+) and potassium (K+) ions.

screenshot-2023-07-14-at-1-12-11-pm

Explain the steep increase in sodium ion permeability seen between 0.5 ms and 0.7 ms.

2c
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3 marks

During an action potential, the membrane potential of the axon reaches +40 mV and then falls steeply. Use the information from the graph in part (b) to explain this fall.

2d
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2 marks

After exercise, ATP is required for the resting potential to be re-established in axons. Explain how this occurs.

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3a
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2 marks

Below is a micrograph of a synapse. The arrow shows the direction of the nerve impulse.

TUl3-RWG_2

Label on the diagram the synaptic vesicles and the synaptic cleft.

3b
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3 marks

Neonicotinoids are synthetic chemicals that bind to acetylcholine receptors in cholinergic synapses in insects.  The enzyme acetylcholinesterase does not break down neonicotinoids and therefore the binding of neonicotinoids is irreversible.

Describe how this may lead to death of the insect affected by neonicotinoids.

3c
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2 marks

Dopamine is a neurotransmitter that plays a vital role in areas of the brain responsible for muscle control. It is transported back out of the synaptic cleft by a transporter protein located within the presynaptic membrane. Dopamine diffuses across the synaptic gap and binds to a receptor on the postsynaptic membrane.

Describe how this results in the depolarisation of the postsynaptic membrane.

3d
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2 marks

Explain why it is essential that neurotransmitters like dopamine are transported back out of synapses.

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4a
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2 marks

Researchers were studying the effect of different stimulation frequencies on the production of action potentials by a single neurone.

The diagram below shows a recording of the action potentials generated when the frequency of stimulation was 155 per second. At this specific frequency, each stimulus is able to produce one action potential.

screenshot-2023-07-14-at-1-34-14-pm

The time required for the completion of one action potential is X.

Calculate the value of X. Give your answer to the nearest microsecond. Show your working.

4b
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3 marks

The diagram below shows the results when the stimulation frequency was 220 per second.

screenshot-2023-07-14-at-1-42-06-pm

Not every stimulus generated an action potential.

Explain why.

4c
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1 mark

The following statements are about events that happen during an action potential.

A         Hyperpolarisation of the membrane occurs
B         Potassium ions diffuse out of the membrane of the neurone
C         Active transport of sodium ions and potassium ions restores resting potential
D         Sodium ion channels open
E          Potassium ion channels open
F          Sodium ions diffuse into the neurone

Which of the events, A - F, starts depolarisation?

4d
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1 mark

Which of the events from part (c) requires hydrolysis of ATP?

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5a
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5 marks

Describe the mechanism which allows information to pass across a synapse.

5b
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4 marks

Scientists wanted to investigate how a stimulating electrode changed the potential difference across an axon membrane.   The scientists inserted two other electrodes, P and Q, to record any potential difference produced. The experiment was repeated six times (A - F), using a different stimulus potential each time. The diagram below shows their results.

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Explain the results of experiments A - D.

5c
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6 marks

The propagation of nerve impulses is the result of local currents within the axon.

Explain how local currents are generated and how this leads to the propagation of a nerve impulse.

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1a
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2 marks

The graph below shows the changes in membrane potential that occur during a cardiac (heart) action potential.

Cardiac action potential SQ

Stage 0 occurs more quickly in a cardiac action potential than the equivalent stage in a regular action potential.

Suggest two possible explanations for the increased rate at which stage 0 takes place in a cardiac action potential.

1b
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4 marks

Compare and contrast the changes in membrane potential that occur during the cardiac action potential in part a) with the changes that occur during a regular action potential.

Note that no credit will be given for describing the difference already noted in part a).

1c
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3 marks

A group of heart conditions known as arrhythmias involves problems with the co-ordination or speed of the heart beat. Potassium channel blockers are a group of drugs used to treat some types of arrhythmia.

(i)

Sketch on the graph in part a) the effect that you would expect a potassium channel blocker to have on the cardiac action potential.

[1]

(ii)

Suggest how potassium channel blockers have the effect predicted in part i).

[2]

1d
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2 marks

Suggest, with a reason, the type of arrhythmia that potassium channel blockers might be used to treat.

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2a
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2 marks

A study was carried out into the impact of a node of Ranvier length on nerve transmission. The graph below shows the relationship between the node of Ranvier length and the number of sodium ion channels at each node.

~6cQGJ9B_h-2a

A student concluded from the graph that there will be more sodium ion channels at longer nodes of Ranvier.

Evaluate the student's conclusion.

2b
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2 marks

The study also looked at the impact of node of Ranvier length on the speed of impulse conduction in axons. The graph below shows some of the results.

xx4QKB46_h-2b

Calculate the percentage change in impulse conduction speed when the node of Ranvier length increases from 0.5 μm to 1.5 μm. 

2c
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3 marks

Suggest an explanation for the change in conduction speed for nodes of Ranvier lengths between 0.25 and 1.75 μm.

2d
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2 marks

The study looked at nodes of Ranvier length in mice and found that an individual mouse could have some axons with longer nodes of Ranvier and some axons with short nodes of Ranvier. 

Suggest why it might be advantageous to have axons with varying nodes of Ranvier length.

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3a
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3 marks

The graphs below show the effect of applying different electrical stimuli to a neurone on its membrane potential.

stimuli-and-membrane-potential-sq

Compare and contrast the response of the membrane to the negative stimulus in trace 1 and the positive stimulus in trace 2.

3b
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2 marks

Suggest an explanation for the changes in membrane potential shown in trace 1 in part a).

3c
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2 marks

The graphs below shows the effect of changing the type of stimulus on the propagation of a nerve impulse along an unmyelinated axon.

type-of-stimulus-impulse-transmission-sq

Suggest an explanation for the difference between the transmission of the impulses shown in the top and bottom graphs.

3d
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4 marks

In an extension to the investigation shown in part c), electrodes were inserted into a fully myelinated axon of the same diameter before applying a positive stimulus at the stimulating electrode. Electrodes 1, 2, and 4 were inserted into sections of the axon surrounded by myelin while electrode 3 was inserted into a node of Ranvier.

Suggest, each with a reason, two ways in which the results would look different to those in the bottom graph shown in part c).

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4a
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3 marks

Serotonin is a neurotransmitter found in the brain. Low serotonin levels are thought to contribute to symptoms of clinical depression. One commonly used treatment for depression involves a group of drugs called SSRIs.

The diagram below shows a serotonin synapse in the brain both before (left) and after (right) treatment with SSRIs.

serotonin-neurotransmitter-ssris-sq

Suggest how SSRIs might be effective at treating the symptoms of depression.

4b
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3 marks

The image below shows the chemical structures of serotonin and an SSRI called Citalopram. Citalopram is commonly prescribed for depression due to its limited side effects, but it does sometimes cause some nausea and sleep disturbance during the first few weeks.

serotonin-citalopram-ssri-sq

Use the image to suggest how Citalopram can have the effect shown in part a) while also having some side effects.

4c
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2 marks

Although the use of SSRIs has increased significantly in recent years there is still controversy over their effectiveness in the treatment of depression, along with some concern surrounding withdrawal symptoms at the end of treatment. One group of researchers analysed the results of around 300 studies involving treatment for depression; some of their results are shown in the graph below.

treating-depression-ssri-sq

The placebo in this case was a pill identical in appearance to an SSRI but containing no active chemical ingredients.

Suggest the role of a placebo in a study of this type.

4d
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3 marks

State what can be concluded about the effectiveness of SSRIs in the treatment of depression from the information provided in part c). Note that the error bars in the graph represent standard deviation.

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5a
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5 marks

Draw an annotated diagram of an oscilloscope trace of an action potential.

5b
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8 marks

Describe how a nerve impulse is transmitted from one neurone to another.

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