DP Biology (first assessment 2025)

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Question 21N.2.HL.TZ0.2d

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Date November 2021 Marks available [Maximum mark: 2] Reference code 21N.2.HL.TZ0.2d
Level HL Paper 2 Time zone TZ0
Command term Explain Question number d Adapted from N/A
d.
[Maximum mark: 2]
21N.2.HL.TZ0.2d
(d)

Explain the mechanism that prevents polyspermy during fertilization.

[2]

Markscheme

a. cortical reaction (after first sperm nucleus enters the egg);
b. vesicles/cortical granules release their contents/enzymes (from the egg/zygote);
c. zona pellucida/glycoprotein coat/outer coat hardened / fertilization membrane formed;
d. enzymes of sperm/acrosome cannot digest (hardened coat)
OR
glycoproteins/ZP3 (in zona pellucida) altered so sperm cannot bind;

Examiners report

Answers were mixed. Most knew that there is a mechanism that prevents more sperm fusing with the egg after the first one and some gave accurate and detailed accounts of it.

Syllabus sections