A Level Biology: Control and coordination — Practice Questions (Cambridge 9700)

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 — Cambridge International holds copyright in its own papers. Use these alongside the official past papers available from your board.

Each question practises a skill tested in the June 2024 Paper 42. After each answer there is an examiner insight or a tip and, where one matches, the real question to try next.

---

Questions

1. A person touches a hot pan and pulls their hand away in a reflex action.

(a) Name the type of cell that carries impulses from the spinal cord to the muscles of the arm.

(b) Name the type of cell that wraps around the axons of these cells to form the myelin sheath.

(c) Name the short gaps in the myelin sheath along the axon. [3]

2. Explain why action potentials travel faster along a myelinated axon than along an unmyelinated axon of the same diameter. [4]

3. An action potential travels along a myelinated motor neurone that is 0.84 m long in 12 ms. Calculate the speed of conduction in m s⁻¹. [2]

4. At a cholinergic synapse, ion channels in the presynaptic membrane and ion channels in the postsynaptic membrane both open during transmission. For each type of channel, state which ion passes through it and what causes it to open. [2]

5. Some insecticides inhibit the enzyme acetylcholinesterase at the cholinergic synapses between an insect’s motor neurones and its muscles. Suggest and explain the effects of these insecticides on transmission across the synapse and on the insect’s muscles. [4]

6. In an experiment, the fluid around a neurone was changed so that its resting potential fell from −70 mV to −80 mV. The threshold potential of the neurone stayed at −55 mV. Suggest how this change affects the ability of the neurone to produce action potentials when it is stimulated. [3]

---

Answers

1. (a) Motor neurone [1].

(b) Schwann cell [1].

(c) Nodes of Ranvier [1].

Examiner insight (Cambridge 9700 June 2024 examiner report, Paper 42, Question 8(a)): When a question asks for a type of cell, name a whole cell. Answers such as “axon” or “dendrite” came from not focusing on the word “cell”. Most candidates knew that Schwann cells form the myelin sheath.

Source for the examiner insights on this page: Cambridge International AS & A Level Biology 9700 June 2024 Principal Examiner Report for Teachers, Paper 9700/42 section, paraphrased.

Try the real question next: Cambridge International AS & A Level Biology 9700, June 2024, Paper 42, Question 8(a).

2. Any four: the myelin sheath insulates the axon, so ions cannot move across the membrane where it is covered [1]; voltage-gated channels are found at the nodes of Ranvier, so ions can move across the membrane only there [1]; depolarisation (action potentials) happens only at the nodes [1]; local circuits form between one node and the next, so they are much longer than in an unmyelinated axon [1]; the action potential jumps from node to node (saltatory conduction), instead of travelling along every part of the membrane [1].

Examiner insight (Cambridge 9700 June 2024 examiner report, Paper 42, Question 8(b)): Good answers linked the insulating myelin to action potentials occurring only at the nodes and to longer local circuits. Writing that “impulses jump” was a common error, although credit could still be gained by naming saltatory conduction.

Try the real question next: Cambridge International AS & A Level Biology 9700, June 2024, Paper 42, Question 8(b).

3. Time = 12 ms = 0.012 s. Speed = distance ÷ time = 0.84 ÷ 0.012 [1] = 70 m s⁻¹ [1].

Tip: Convert milliseconds to seconds (divide by 1000) before dividing, or your answer will be 1000 times too small.

4. Presynaptic membrane: calcium ions (Ca²⁺) pass through voltage-gated channels, which open when an action potential arrives and depolarises the membrane [1]. Postsynaptic membrane: sodium ions (Na⁺) pass through ligand-gated channels, which open when acetylcholine binds to them [1].

Examiner insight (Cambridge 9700 June 2024 examiner report, Paper 42, Question 8(c)(i)): Many answers only described where the channels are. Credit came from naming the correct ion for each channel and comparing how each one opens. Write the calcium ion as Ca²⁺, not Ca⁺.

Try the real question next: Cambridge International AS & A Level Biology 9700, June 2024, Paper 42, Question 8(c)(i).

5. Any four: acetylcholine is not hydrolysed (broken down) in the synaptic cleft [1]; so acetylcholine stays bound to the receptors on the postsynaptic membrane [1]; the sodium ion channels stay open, so the postsynaptic membrane stays depolarised (or action potentials keep being generated) [1]; the muscles keep contracting and cannot relax (spasms or paralysis), which can kill the insect [1]; choline is not recycled to the presynaptic knob, so less new acetylcholine can be made [1].

Examiner insight (Cambridge 9700 June 2024 examiner report, Paper 42, Question 8(c)(ii)): Credit depended on naming the specific membrane: say presynaptic membrane or postsynaptic membrane, not just “membrane” or “neurone”.

Try the real question next: Cambridge International AS & A Level Biology 9700, June 2024, Paper 42, Question 8(c)(ii).

6. The inside of the neurone is now more negative (hyperpolarised) than before [1]. A bigger depolarisation is needed to reach the threshold: 25 mV (from −80 mV to −55 mV) instead of 15 mV (from −70 mV to −55 mV) [1]. So stimuli that would normally be strong enough no longer produce an action potential, and fewer (or no) action potentials are produced [1].

Examiner insight (Cambridge 9700 June 2024 examiner report, Paper 42, Question 8(c)(iii)): A common error was to say the inside becomes “negative”; it is already negative at rest, so you must say it becomes more negative. Strong answers then linked this to the threshold being harder to reach.

Try the real question next: Cambridge International AS & A Level Biology 9700, June 2024, Paper 42, Question 8(c)(iii).

---

Where marks are usually lost

• Naming part of a cell (axon, dendrite) when the question asks for a type of cell.
• Saying “impulses jump” without naming saltatory conduction or action potentials at the nodes.
• Describing where ion channels are instead of how they open and which ions pass through.
• Writing “membrane” or “neurone” without saying presynaptic or postsynaptic membrane.
• Saying the inside becomes “negative” rather than “more negative”.