CAIE IGCSE Biology 20.3.1 Sewage & Excess Fertiliser in Water
Practise explaining how untreated sewage and excess fertiliser alter nutrients, dissolved oxygen and aquatic populations.
- Syllabus
- 2026–2028
- Course
- Biology 0610
Exam points
- link sewage or fertiliser runoff to increased nitrate ions and producer growth
- explain how decomposition raises aerobic respiration and lowers dissolved oxygen
- interpret nitrate readings or indicator-organism distributions to locate a pollution source
20.3.1—Effects of untreated sewage and excess question 1
[Maximum number: 6]
Waste from livestock farms often pollutes water courses, such as streams and rivers, leading to a reduction in biodiversity.
Explain how the pollution of water courses by animal waste leads to a reduction in biodiversity.
any six from:
1 eutrophication ;
2 increased growth of, plants / producers / algae ;
3 plants / producers, compete with each other for light / AW ,
4 plants / producers, die or plants / producers, are decomposed ;
5 increase in, decomposers / bacteria ;
6 bacteria / decomposers, use / absorb, (dissolved) oxygen in water ;
7 decrease in concentration of (dissolved) oxygen ;
reasons for reduction in biodiversity:
8 death of, (named) animals / fish / invertebrates (due to lack of dissolved oxygen) ;
9 decrease in, food / energy, available in, ecosystem / AW ;
10 ref to, pathogens / disease / toxins / poisons ;
11 ref to aerobic respiration (in either section)
12 AVP ;
MP2 A algal bloom
MP3 A no photosynthesis as no light
MP8 A if linked to MP7
MP9 A disruption of food, chains / webs
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