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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
- Stonefly. These species are sensitive to pollution and their presence indicates a clean aquatic environment.
Step 3
Explain why sewage pollution in the river can decrease the oxygen levels in the water.
Answer
Sewage pollution introduces organic waste into the water, which bacteria break down. This process, known as decomposition, consumes oxygen dissolved in the water, leading to decreased oxygen levels. A lower oxygen concentration can harm aquatic life, such as fish and invertebrates, which rely on oxygen for survival.
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 rivers have flowing water, which moves the nitrates downstream. This movement dilutes the concentration of nitrates, whereas in lakes, the still water allows for a higher concentration to accumulate, leading to more severe effects such as algal blooms.