DP Biology (first assessment 2025)

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Question 21N.2.SL.TZ0.1d

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Date November 2021 Marks available [Maximum mark: 3] Reference code 21N.2.SL.TZ0.1d
Level SL Paper 2 Time zone TZ0
Command term Suggest Question number d Adapted from N/A
d.
[Maximum mark: 3]
21N.2.SL.TZ0.1d
(d)

Some scientists predict that, if humans continue to produce carbon dioxide at the current rate, the pH of the oceans will become more acidic. Suggest possible effects on the coral reefs.

[3]

Markscheme

a. corals would not be able to maintain their skeletons;
b. (if coral reefs are lost) habitat will be lost;
c. some organisms/coral can decline if the water becomes too acidified;
d. coral bleaching could occur/become worse
OR
coral could expel their mutualistic alga/zooxanthellae;
e. enzymes could be denatured;

Examiners report

In 1d weaker students incorrectly wrote about the sea becoming acidic as the pH was increasing (sic). Indeed, it is becoming more acidic, as the pH is decreasing slightly, leading to more bleaching and the decrease in population of some creatures.

Syllabus sections