When organic waste is released into aquatic ecosystems like rivers and lakes, it leads to pollution. Under aerobic conditions, microorganisms break down this organic material, which removes dissolved oxygen from the water. The amount of oxygen required for this biological decomposition is known as the Biological Oxygen Demand (BOD).
The table below shows BOD values for some potential pollutants:
| Pollutant | BOD (mg of O2\text{O}_2O2 per litre of pollutant) |
|---|---|
| Treated municipal sewage | 15−4515 - 4515−45 |
| Untreated municipal sewage | 250−400250 - 400250−400 |
| Dairy processing effluent | 4,000−8,0004,000 - 8,0004,000−8,000 |
| Poultry farm waste | 15,000−25,00015,000 - 25,00015,000−25,000 |
| Waste fruit juice concentrate | 120,000120,000120,000 |
Explain which pollutant is likely to have the most severe effect on the organisms in a river.
A quantity of pollutant is released into a river. The overall effect on the aquatic organisms will depend on the BOD value of the pollutant and other factors. Suggest one of these other factors.
Waste fruit juice concentrate is one of these pollutants. Name one biological molecule found in fruit juice that microorganisms could feed on.
Suggest a reason for the difference between the BOD of untreated municipal sewage and the BOD of treated municipal sewage.
44 exam-style questions on Edexcel IGCSE Biology Human influences on the environment. Each one has a worked solution and a mark scheme showing where the marks go.