Question 21N.2.HL.TZ0.c
| Date | November 2021 | Marks available | [Maximum mark: 3] | Reference code | 21N.2.HL.TZ0.c |
| Level | HL | Paper | 2 | Time zone | TZ0 |
| Command term | Explain | Question number | c | Adapted from | N/A |
Explain the propagation of nerve impulses along the membrane of a neuron.
[3]
a. depolarization of part of axon/membrane triggers/causes depolarization of next part;
b. local currents;
c. diffusion of sodium ions between depolarized part and next/polarized part (of axon);
d. resting potential reduced/polarization of membrane becomes less /change from -70 to -50mV;
e. sodium channels open when -50mV/threshold potential reached;
f. entry of sodium ions causes depolarization;
g. saltatory conduction in myelinated neurons/axons;
Allow answers in an annotated diagram
This was a more difficult question with a much higher correlation coefficient. Many candidates did not understand what is meant by propagation of an impulse along the membrane of a neuron and answers tended to include accounts of the whole sequence of events in an action potential or in synaptic transmission. The mark most frequently awarded was for the mechanism of saltatory conduction.
