Pearson Edexcel International A Level Biology: Neurones, Reflexes and Synapses (YBI11) – Practice Questions

These are original questions written for Marlbridge, for revision and practice on this content. They are not reproduced past-paper questions, and they do not replicate the exam’s exact structure, question count or mark tariffs – examination boards hold copyright in their own papers. Use these alongside the official past papers from your board or school.

These questions follow the Pearson Edexcel International Advanced Subsidiary/Advanced Level Biology (YBI11) specification, Issue 2, statements 8.1 to 8.7 of Topic 8. Topics 5 to 8 are International A2 content, and there are no tiers. Read the study guide first and keep the revision notes beside you. The course hub, the checklist and the free diagnostics help with planning. Show working in every calculation.

Questions

1. (a) State three differences between a sensory neurone and a motor neurone. [3] (b) Describe how Schwann cells produce a myelin sheath. [2]

2. A person touches a sharp object and pulls their hand away before feeling pain. (a) Name, in order, the structures that the impulse passes through from receptor to effector in the spinal reflex arc. [3] (b) State where in the spinal cord the cell bodies of relay neurones are found, and what the white matter contains. [2] (c) Explain why a reflex is protective. [2]

3. An impulse travels 0.35 m along a myelinated axon in 7.0 ms. An unmyelinated axon of the same length takes 0.28 s. (a) Calculate the speed in the myelinated axon, in m/s. [2] (b) Calculate how many times faster the myelinated axon conducts. [2] (c) Explain why the myelinated axon conducts faster. [2]

4. The table shows the membrane potential at one point on an axon after a stimulus.

Time (ms)	0.0	0.5	1.0	1.5	2.0	2.5	3.0	3.5	4.0	5.0
Potential (mV)	−70	−70	−55	+20	+40	+10	−40	−75	−78	−70

(a) State the resting potential and the peak potential, and calculate the change between them. [2] (b) Explain the change in potential between 1.0 ms and 2.0 ms. [3] (c) Explain the change in potential between 2.5 ms and 3.5 ms. [2] (d) The axon cannot fire for 2.5 ms after an action potential begins. Calculate the maximum number of action potentials per second. [2]

5. (a) Explain how myelination increases the speed of conduction along an axon. [4] (b) A disease destroys the myelin on part of a sensory neurone. Suggest the effect on the person. [2]

6. (a) Describe how an action potential in a presynaptic neurone leads to an action potential in the postsynaptic neurone at a cholinergic synapse. [6] (b) Explain why transmission across a synapse is in one direction only. [2]

7. The table shows the mean depolarisation of the postsynaptic membrane at a synapse bathed in different calcium ion concentrations.

Calcium ions (mmol dm⁻³)	0.5	1.0	2.0	4.0
Depolarisation (mV)	0.8	2.4	5.6	6.0

(a) Describe the relationship shown. [2] (b) Calculate the percentage increase in depolarisation when the concentration rises from 1.0 to 2.0 mmol dm⁻³. [2] (c) Explain how calcium ions affect the depolarisation. [2]

8. In dim light a pupil has a diameter of 8.0 mm. In bright light the diameter is 3.0 mm. (a) Describe the changes in the iris muscles in bright light. [3] (b) Calculate the percentage decrease in diameter. [2] (c) Calculate how many times larger the area of the dilated pupil is than the area of the constricted pupil. [2]

9. Explain the effect on a cholinergic synapse of: (a) nicotine, [2] (b) cobra venom alpha toxin, [2] (c) lidocaine applied to an axon. [2]

10. (a) Explain why people with Parkinson’s disease are given L-DOPA rather than dopamine. [3] (b) Describe how MDMA increases the effect of serotonin at synapses. [2]

11. An isolated axon has a stimulating electrode and three recording electrodes. R1 is nearest the stimulus. Lidocaine is applied to the membrane at R2. R3 is beyond R2. After a stimulus, R1 records a peak of +40 mV. R2 records a rise from −70 mV to −62 mV only. R3 records no change from −70 mV. (a) Calculate the amplitude of the response at R1 from the resting potential. [1] (b) Calculate the rise at R2 as a percentage of the amplitude at R1. [2] (c) Explain the result at R2. [3] (d) Explain the result at R3. [2] (e) Explain why R1 shows a full response. [1]

Answers

1. (a) Any three: sensory carries impulses towards the CNS, motor away from it [1]; sensory cell body lies off to the side of the fibre, motor cell body is at the end with dendrites [1]; sensory cell body is outside the cord, motor cell body is in the CNS [1]. (b) A Schwann cell wraps its membrane round the axon many times [1], forming layers of lipid-rich membrane (myelin), with gaps between cells being nodes [1]. [5] Examiner insight: Differences need both sides stated; “sensory is long” alone is weak because both are long.

2. (a) Sensory neurone [1], relay neurone [1], motor neurone, ending at the effector muscle [1]. (b) Cell bodies of relay neurones are in the grey matter [1]; white matter contains myelinated axons running up and down the cord [1]. (c) Short pathway with few synapses [1], so the response is fast and avoids damage before the brain is involved [1]. [7] Examiner insight: Answers tend to gain more when they name the sequence in the right order and use “neurone” with its type.

3. (a) Speed = distance / time = 0.35 / 0.0070 [1] = 50 m/s [1]. (b) Unmyelinated speed = 0.35 / 0.28 = 1.25 m/s [1]; 50 / 1.25 = 40 times [1]. (c) Action potentials occur only at the nodes of Ranvier [1] because myelin insulates the axon, and local currents carry depolarisation between nodes [1]. [6] Examiner insight: Convert milliseconds to seconds before dividing, and write the unit on the final line.

4. (a) Resting −70 mV, peak +40 mV [1]; change = 40 − (−70) = 110 mV [1]. (b) Voltage-gated sodium channels open [1], and sodium ions diffuse into the axon [1]; once threshold (about −55 mV) is reached, more channels open, so depolarisation is rapid (positive feedback) [1]. (c) Sodium channels close and voltage-gated potassium channels open [1]; potassium ions diffuse out, repolarising the membrane [1]. (d) Maximum frequency = 1 / 0.0025 [1] = 400 per second [1]. [9] Examiner insight: Explanations tend to gain credit when the ion, the direction and the type of channel are all named.

5. (a) Myelin is an insulator, so ions cannot cross the membrane where it is present [1]; action potentials occur only at nodes of Ranvier [1]; local currents carry the depolarisation between nodes, so the impulse jumps (saltatory conduction) [1]; fewer places need to be depolarised, so conduction is faster [1]. (b) Impulses slow or fail to reach the CNS [1], so sensation is reduced or lost [1]. [6] Examiner insight: Say that the action potential occurs at nodes only; “insulation speeds it up” alone is too vague.

6. (a) Action potential arrives at presynaptic knob [1]; voltage-gated calcium channels open and Ca²⁺ diffuses in [1]; vesicles fuse with the presynaptic membrane and release acetylcholine by exocytosis [1]; acetylcholine diffuses across the cleft [1] and binds to receptors on the postsynaptic membrane, opening sodium channels [1]; Na⁺ enters, depolarising the membrane to threshold and starting an action potential [1]. (b) Only the presynaptic knob contains vesicles of transmitter [1]; only the postsynaptic membrane has receptors [1]. [8] Examiner insight: Sequence questions tend to reward every link in the chain, so do not skip the calcium step.

7. (a) Depolarisation increases as calcium concentration rises [1]; the increase slows at higher concentrations, from 5.6 to 6.0 mV between 2.0 and 4.0 mmol dm⁻³ [1]. (b) (5.6 − 2.4) / 2.4 × 100 [1] = 133% [1]. (c) More Ca²⁺ entering means more vesicles fuse and release acetylcholine [1], so more sodium channels open and the membrane depolarises more [1]. [6] Examiner insight: Quote figures from the table when describing a trend, and show the subtraction in a percentage calculation.

8. (a) Circular muscle contracts [1]; radial muscle relaxes [1]; pupil constricts, reducing light entering the eye [1]. (b) (8.0 − 3.0) / 8.0 × 100 [1] = 62.5% [1]. (c) Areas: π × 4.0² = 50.3 mm² and π × 1.5² = 7.07 mm² [1]; 50.3 / 7.07 = 7.1 times [1]. [7] Examiner insight: Use radius, not diameter, in the area formula; the ratio (8.0 / 3.0)² is a quicker check.

9. (a) Nicotine binds to acetylcholine receptors, mimicking acetylcholine and opening sodium channels [1]; it is not broken down by acetylcholinesterase, so stimulation is prolonged [1]. (b) Alpha toxin binds to the acetylcholine receptors and blocks them [1], so acetylcholine cannot depolarise the postsynaptic membrane and the muscle is paralysed [1]. (c) Lidocaine blocks voltage-gated sodium channels [1], so action potentials are not generated or conducted and sensation is lost [1]. [6] Examiner insight: Name the target (receptor or channel) and the outcome in each case; “it blocks nerves” is too vague.

10. (a) Parkinson’s disease involves a shortage of dopamine in the brain [1]; dopamine does not cross from the blood into the brain easily, but L-DOPA does [1]; in the brain L-DOPA is converted to dopamine, which relieves symptoms [1]. (b) MDMA causes serotonin to be released from presynaptic neurones [1] and blocks its reuptake, so more serotonin remains in the cleft [1]. [5] Examiner insight: Explain why L-DOPA works as a precursor, not that it “is dopamine”.

11. (a) 40 − (−70) = 110 mV [1]. (b) Rise = −62 − (−70) = 8 mV [1]; 8 / 110 × 100 = 7.3% [1]. (c) Lidocaine blocks voltage-gated sodium channels [1], so no positive feedback occurs and threshold (−55 mV) is not reached [1]; the small rise comes from local current spreading from R1 [1]. (d) The action potential is not regenerated at R2, so no depolarisation reaches threshold at R3 [1]; no sodium ions enter at R3 [1]. (e) R1 is not under lidocaine, so its sodium channels work normally [1]. [9] Examiner insight: In data questions, link each recording to a mechanism: blocked channels, no threshold, no regeneration.

Where marks are usually lost

• Writing “sodium goes in” without saying it diffuses through voltage-gated channels.
• Leaving out potassium ions in repolarisation.
• Forgetting calcium ions in the synapse sequence.
• Naming acetylcholine as the cause of the next action potential without describing the sodium channels.
• Dividing by milliseconds without converting to seconds.
• Using diameter in place of radius in the area formula.
• Confusing nicotine (mimics) with alpha toxin (blocks).
• Giving lidocaine as a synapse drug when it acts on axons.

Next steps

• Review the revision notes and re-read the study guide.
• Plan from the course hub and the checklist.
• Try all the free 10-minute diagnostics.
• Book a free trial class.

Official syllabus

Pearson Edexcel International Advanced Subsidiary/Advanced Level in Biology (YBI11), Specification, Issue 2, Pearson Education Limited. Statements 8.1 to 8.7 of Topic 8.