O-LevelBiologyEcology & Environment5090/12 · Oct/Nov 2016 · Q321 Mark

Why does the oxygen concentration in a river decrease when sewage is discharged into it?

ALess oxygen is absorbed from the air.

BThere is a decrease in the number of plants.

CThere is an increase in the number of bacteria.

DThere is an increase in the number of fish.

✓ Correct answer

C: There is an increase in the number of bacteria.

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Topic: Ecology & Environment, O-Level Biology (syllabus 5090). Multiple choice, 1 mark.
Source: O-Level Biology, Oct/Nov 2016 Paper 1 Variant 2, question 32.

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