Free Pollution questions for IGCSE Biology (0610), part of Ecology & human influence. Each question has the answer and the marking points an examiner would look for.
Generate a full Pollution worksheet →All Ecology & human influence questionsWhich sequence describes eutrophication after fertiliser runs into a lake?
Answer: A
Excess fertiliser can run into rivers and cause eutrophication.
Describe the sequence of events in eutrophication.
Suggest one way farmers can reduce eutrophication.
| Part | Answer and marking points | Marks |
|---|---|---|
| (a) | nitrates → algal growth → light blocked → plants die → decomposers use oxygen → fish die fertiliser (nitrate) runs into water B1 algae grow rapidly (algal bloom) B1 algae block light so plants below die B1 decomposers break down dead plants and use up oxygen B1 fish and other organisms die from lack of oxygen B1 | 5 |
| (b) | apply fertiliser carefully; buffer strips use less fertiliser / not before rain / leave strips of land by rivers B1 | 1 |
Untreated sewage enters a river at a point 0 m. Samples are taken upstream and at distances downstream. Table 3.1 shows the results.
| distance from sewage outlet / m | 100 upstream | 50 | 200 | 400 | 800 | 1500 |
|---|---|---|---|---|---|---|
| dissolved oxygen / mg per dm³ | 9.6 | 4.0 | 2.2 | 4.2 | 6.8 | 9.0 |
| number of invertebrate species | 14 | 5 | 3 | 4 | 9 | 13 |
Calculate the percentage decrease in dissolved oxygen between 100 m upstream and 200 m downstream.
Explain why the concentration of dissolved oxygen falls downstream of the sewage outlet.
Suggest why the dissolved oxygen concentration rises again further downstream.
Describe the relationship between dissolved oxygen and the number of invertebrate species.
Some species, such as sludge worms, are found only where dissolved oxygen is low. Explain how such species can be used to monitor pollution.
Fertiliser running into a lake can have a similar effect. Describe the sequence of events that follows.
| Part | Answer and marking points | Marks |
|---|---|---|
| (a) | 77.1 % (9.6 − 2.2) ÷ 9.6 × 100 C1 77.1 % A1 | 2 |
| (b) | bacteria decompose sewage; respire aerobically; use oxygen sewage provides organic matter / food for bacteria B1 bacteria (decomposers) increase in number B1 their aerobic respiration uses dissolved oxygen B1 | 3 |
| (c) | sewage broken down; fewer bacteria; oxygen dissolves from air / photosynthesis most of the sewage has been decomposed so fewer bacteria / less respiration B1 oxygen dissolves from the air / is released by photosynthesis of plants and algae B1 | 2 |
| (d) | more oxygen, more species the higher the dissolved oxygen concentration, the more invertebrate species (positive correlation) B1 | 1 |
| (e) | indicator species; presence shows low oxygen / pollution they are indicator species B1 their presence (and absence of sensitive species) shows that the water is polluted / low in oxygen B1 | 2 |
| (f) | algal bloom; light blocked, plants die; decomposers increase; oxygen used, animals die nitrate / phosphate causes rapid growth of algae (algal bloom) B1 algae block light so plants below die B1 decomposers / bacteria increase and decompose dead plants B1 their respiration uses oxygen so fish and other animals die (eutrophication) B1 | 4 |
This question is about the effects of humans on ecosystems.
Fertiliser washes into a lake. Describe the sequence of events that leads to the death of fish.
Give two effects of large-scale deforestation on the environment.
Explain why deforestation can lead to an increase in flooding.
Describe two methods used to conserve fish stocks.
Explain why seed banks and captive breeding are used to conserve endangered species.
| Part | Answer and marking points | Marks |
|---|---|---|
| (a) | nutrients cause algal bloom; blocks light; plants die; decomposers multiply, respire; oxygen used up; fish die nitrates / phosphates increase growth of algae (algal bloom) B1 algae block light so plants below die B1 bacteria decompose the dead material B1 bacteria use oxygen in aerobic respiration B1 oxygen concentration falls so fish die B1 | 5 |
| (b) | more CO₂ (less photosynthesis, burning); soil erosion; loss of habitat; flooding Any 2 of: less carbon dioxide absorbed / more released by burning; loss of habitats / extinction; soil erosion; flooding / disrupted water cycle B2 | 2 |
| (c) | fewer roots, soil eroded; less transpiration / water uptake, more run-off fewer trees take up water / less transpiration B1 more water runs off the soil into rivers / soil is eroded into rivers B1 | 2 |
| (d) | quotas; net mesh size; closed seasons; protected areas Any 2 of: fishing quotas; minimum net mesh size so young fish escape; closed seasons / protected areas; restocking B2 | 2 |
| (e) | maintain genetic variation; reintroduce into the wild to prevent extinction and maintain genetic variation B1 so organisms can be reintroduced into restored habitats B1 | 2 |
Acid rain damages ecosystems.
Name the gas mainly responsible for acid rain and its source.
Describe two effects of acid rain.
| Part | Answer and marking points | Marks |
|---|---|---|
| (a) | sulfur dioxide; burning fossil fuels sulfur dioxide B1 from burning fossil fuels (coal) B1 | 2 |
| (b) | kills trees; acidifies lakes; damages buildings Any 2 of: damages trees/leaves; acidifies lakes, killing fish; damages buildings/statues B2 | 2 |
Non-biodegradable plastics damage ecosystems.
Describe two effects of plastics on aquatic animals.
Explain how sewage pollution reduces oxygen in rivers.
| Part | Answer and marking points | Marks |
|---|---|---|
| (a) | entanglement; ingestion animals get entangled B1 animals eat plastic and starve/are poisoned B1 | 2 |
| (b) | decomposers respire aerobically bacteria decompose the sewage B1 their aerobic respiration uses up dissolved oxygen B1 | 2 |
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Meet Riyaz →Original Cambridge-style practice questions written for mentorriyaz.in. These are not Cambridge past paper questions, and this site is not affiliated with or endorsed by Cambridge University Press & Assessment. Updated 2026-11-04. Paper generator · mentorriyaz.in