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1. (a) Figure 1 shows the sources of pollution and different levels of water pollution in a river - Edexcel - GCSE Biology - Question 1 - 2020 - Paper 1
Question 1
1. (a) Figure 1 shows the sources of pollution and different levels of water pollution in a river. (i) Which part of the river will have the largest number of blood... show full transcript
Worked Solution & Example Answer:1. (a) Figure 1 shows the sources of pollution and different levels of water pollution in a river - Edexcel - GCSE Biology - Question 1 - 2020 - Paper 1
Step 1
Step 2
Give the names of the two indicator species from the box which provide evidence for clean water.
Answer
The two indicator species that provide evidence for clean water are 'freshwater shrimp' and 'stonefly.' These species are sensitive to pollution and indicate a healthy aquatic environment.
Step 3
Explain why sewage pollution in the river can decrease the oxygen levels in the water.
Answer
Sewage pollution introduces organic matter and bacteria into the water. As bacteria decompose this organic material, they consume oxygen in the process. This higher demand for oxygen can lead to decreased levels of dissolved oxygen, which is harmful to aquatic life.
Step 4
Step 5
State why the build-up of nitrates is less likely to affect a river than a lake.
Answer
The build-up of nitrates is less likely to affect a river than a lake because water in rivers is moving continuously. This movement helps to disperse and wash away the nitrates, preventing significant accumulation. In contrast, lakes have still water, leading to a higher concentration of nitrates and a greater potential for eutrophication.