DP Biology (first assessment 2025)

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Question 20N.2.SL.TZ0.b

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Date November 2020 Marks available [Maximum mark: 3] Reference code 20N.2.SL.TZ0.b
Level SL Paper 2 Time zone TZ0
Command term Suggest Question number b Adapted from N/A
b.
[Maximum mark: 3]
20N.2.SL.TZ0.b

Sea otters are considered keystone species in this environment. Suggest how the presence of sea otters could affect the algae population.

[3]

Markscheme

a. sea otters (feeding on sea urchins) limit sea urchin population;

b. the largest sea urchins are eaten;

c. shown by low biomass/small size (of sea urchins);

d. fewer/smaller sea urchins allow for increase in algae population;

e. sea otters have a top down effect;

Allow converse reasoning.

Examiners report

The majority of candidates could suggest that the sea algae population could be affected by sea otters feeding on sea urchins; most nevertheless did not use the graphs or mention that a top down effect was present.

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