O-LevelBiologyEcology & Environment5090/11 · May/June 2011 · Q321 Mark

If high levels of nitrates are washed into rivers, the following changes may occur, causing fish to die. 1 Water plants die and fall to the bottom. 2 Bacteria multiply rapidly. 3 Concentration of oxygen in the water decreases. 4 Increased growth of single-celled water plants makes the water green. In which order do these changes take place?

A1→4→3→2

B2→3→1→4

C3→2→4→1

D4→1→2→3

✓ Correct answer

D: 4→1→2→3

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Topic: Ecology & Environment, O-Level Biology (syllabus 5090). Multiple choice, 1 mark.
Source: O-Level Biology, May/June 2011 Paper 1 Variant 1, question 32.

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