DP Biology (first assessment 2025)
Question 21M.2.SL.TZ2.2b
| Date | May 2021 | Marks available | [Maximum mark: 2] | Reference code | 21M.2.SL.TZ2.2b |
| Level | SL | Paper | 2 | Time zone | TZ2 |
| Command term | Outline | Question number | b | Adapted from | N/A |
b.
[Maximum mark: 2]
21M.2.SL.TZ2.2b
(b)
Outline how depolarization of the membrane of an axon occurs.
[2]
Markscheme
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.
Examiners report
In many exams, candidates seemed to confuse the voltage gated ion channels with sodium-potassium pumps.
