A-LevelBiologyControl and coordination9700/43 · May/June 2024 · Q1010 Marks

(a) Fig. 10.1 is a diagram of part of a neurone membrane while the resting potential is maintained. [Figure 10.1]

(a)On Fig. 10.1, use label lines and letters to label: K - potassium ions A – ATP.[2]
(b)Describe the sequence of events that occur during an action potential.[4]
(c)Table 10.1 shows the axon diameter, myelination and transmission speed of impulses of motor neurones for three animals: squid, cockroach and cat. [Table 10.1] Describe and suggest explanations for the results shown in Table 10.1.[4]

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Mark scheme

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[2] K; A;
[4] any four from:
[4] 1 sodium (ion) channels open or Na+ enters (axon);
[4] 2 (so) membrane depolarised ;
[4] 3 ref. to threshold (potential) reached (for action potential to occur) ;
[4] 4 potassium (ion) channels open or K+ moves out (of axon);
[4] 5 (causes) repolarisation (of membrane);
[4] 6 ref. to hyperpolarisation (of membrane);
[4] 7 return to resting potential ;
[4] 8 AVP; e.g. entry of sodium ions causes more sodium channels to open
[4] any four from:
[4] description 1 myelinated axon / myelination, produces faster transmission speed (than unmyelinated);
[4] 2 a larger the diameter (for unmyelinated) results in a faster transmission speed ; ora
[4] 3 myelination has a greater effect on transmission speed than axon diameter ;
[4] explanation 4 (myelinated faster due to) saltatory conduction or action potential jumps from node (of Ranvier) to node ;
[4] 5 axons with wider diameter have, less ion leakage / larger surface area / lower resistance ;

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