DP Biology (first assessment 2025)

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Question 19M.2.SL.TZ1.10c

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Date May 2019 Marks available [Maximum mark: 3] Reference code 19M.2.SL.TZ1.10c
Level SL Paper 2 Time zone TZ1
Command term Outline Question number c Adapted from N/A
c.
[Maximum mark: 3]
19M.2.SL.TZ1.10c
(c)

With respect to this food chain, outline what is meant by a keystone species.

[3]

Markscheme

a. keystone species have a disproportionate effect on the biological community ✔ 

b. removal of the sea bream «due to fishing» ✔

c. results in more sea urchins ✔

d. which significantly reduce the producers/seagrass ✔

Do not accept first trophic level for mpd

Examiners report

The syllabus definition of a keystone species was not often given, so alternative wording had to be judged on merit. The keystone species was not always recognized as the sea bream, but if it was, three marks were easily achieved.

Syllabus sections