Match each pollutant to its source and effect, read BOD and eutrophication, explain biomagnification and heavy-metal disease, and compare pesticide classes.
Unit 8 carries 2 of the 40 Zoology marks; averaged over its four chapters that is half a mark per chapter (MEC publishes weights by unit, not by chapter). MEC scope: "Environmental pollution: Air pollution, Water pollution, Soil pollution, Pesticides."
Pollution is any undesirable change in the physical, chemical or biological character of air, water or soil that harms living things. A primary pollutant is emitted as such (CO, SO2); a secondary pollutant forms in the environment (ground-level ozone, PAN). Biodegradable pollutants (sewage, vegetable waste) are broken down by microbes; non-biodegradable ones (plastics, DDT, mercury) persist.
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