Question 21M.2.HL.TZ2.b
| Date | May 2021 | Marks available | [Maximum mark: 2] | Reference code | 21M.2.HL.TZ2.b |
| Level | HL | Paper | 2 | Time zone | TZ2 |
| Command term | Outline | Question number | b | Adapted from | N/A |
Cholinergic synapses use acetylcholine as their neurotransmitter. They are widespread in the body, passing on signals to muscle cells. These synapses are affected by neonicotinoid pesticides.
The diagrams, which are not drawn to scale, show the synapse between two neurons and a detail of the synaptic cleft.
Outline how depolarization of the membrane of an axon occurs.
[2]
a. (local depolarization) causes ion / sodium / voltage gated channels to open ✔
b. altering membrane permeability to sodium ions/Na+/positive ions / Na+ diffuses into the cytoplasm ✔
c. membrane potential (of the axon) changes from negative to positive ✔
d. a threshold potential is reached and an action potential is generated ✔
Do not accept sodium pumps.
Mp b requires evidence that the student recognizes sodium is an ion.
Numerical values indicating change from −70 to +30/+40/+55 can be accepted.
In many exams, candidates seemed to confuse the voltage gated ion channels with sodium-potassium pumps.
