Older MCQs might not have the typical A, B, C,
D
choices. They
have choices 1, 2, 3, and a combination of them is the answer. Below is the key that maps such
combinations to the answer.
A
1, 2 and 3 are correct
B
1 and 2 only are correct
C
2 and 3 only are correct
D
1 only is correct
Describe the harmful effects of: (a) water pollution by untreated sewage and nitrogen-containing fertilisers leading to eutrophication, limited to: (i) increased availability of nitrate and other ions (ii) increased growth of producers (iii) increased decomposition after death of producers (iv) increased aerobic respiration by decomposers (v) reduction in dissolved oxygen (vi) death of organisms requiring dissolved oxygen in water (b) air pollution by greenhouse gases (carbon dioxide and methane), contributing to global warming and its likely effects (c) pollution due to insecticides and herbicides (d) non-biodegradable plastics in the environment, in both aquatic and terrestrial ecosystems
Explain the importance of a clean water supply, hygienic food preparation, good personal hygiene, waste disposal and sewage treatment in controlling the spread of cholera (details of the stages of sewage treatment are not required)
Describe the effects of osmosis on plant and animal tissues and explain the importance of water potential gradient and osmosis in the uptake and loss of water
