DP Biology (last assessment 2024)

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Question 20N.3.HL.TZ0.24

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Date November 2020 Marks available [Maximum mark: 6] Reference code 20N.3.HL.TZ0.24
Level HL Paper 3 Time zone TZ0
Command term Explain Question number 24 Adapted from N/A
24.
[Maximum mark: 6]
20N.3.HL.TZ0.24

Explain how steroid and peptide hormones exert their effect.

[6]

Markscheme

a. endocrine glands secrete hormones directly into the bloodstream;

Steroid hormones:
b. pass through the plasma membrane (of target cells);

c. bind to receptor proteins in the cytoplasm
OR
form a receptor–hormone complex;

d. (receptor–hormone complex) enters the nucleus;

e. promotes the transcription of specific genes;

Peptide hormones:
f. bind to receptors in the plasma membrane (of the target cell);

g. (binding of hormones to membrane receptors) activates a cascade of reactions;

h. (cascade of reactions) mediated by a second messenger (inside the cell);

i. (cascade results in) activation of enzymes;

Examiners report

The majority of candidates provided complete explanations, even if they did not specify plasma membrane; there are nevertheless some candidates having difficulty over the role of second messengers, the effect of peptide hormones on enzyme action or being able to outline the events in a correct sequence.

Syllabus sections