A-LevelBiologyControl and coordination9700/43 · May/June 2022 · Q96 Marks

(a) [Figure 9.1] shows a cross-section through a myelinated neurone.

(a)Identify structures A and B. A B[2]
(b)With reference to voltage-gated sodium ion channels, explain the difference in speed of transmission of an action potential along a myelinated neurone and a non-myelinated neurone.[4]

This question uses a diagram from the original paper, which isn't shown here. Open the full paper from the past papers archive to see it.

Mark scheme

Marking points from the official mark scheme (May/June 2022). The mark or mark type is shown in brackets.

A – axon / axoplasm ;
B – Schwann cell nucleus ;
1 myelinated has faster speed (of transmission of action potential);
plus any three from: 2 (myelinated) Na+ channels only occur at nodes of Ranvier or (non-myelinated) Na+ channels occur along length of neurone ;
3 (myelinated) depolarisation only occurs at nodes or (non-myelinated) depolarisation occurs along length of neurone ;
4 (myelinated) long local circuits or (non-myelinated) short local circuits ;
5 (myelinated) saltatory conduction / described ;
6 AVP; e.g. 100 ms-¹ v 2 ms-1

On Oracle Prep you can write or photograph your own answer and have it marked by AI against this mark scheme, with feedback on what you missed.