Catherine is an environmentalist studying water pollution in the stream shown in the diagram - Edexcel - GCSE Biology - Question 1 - 2011 - Paper 1

Location C is the most polluted.

This conclusion is drawn from the fact that only 1 freshwater shrimp was found at location C, which indicates a significantly lower population compared to locations A and B, where 14 shrimps were present. Freshwater shrimps are commonly considered indicator species, meaning their presence is directly linked to the quality of water.

The absence of shrimps at location C implies that the water there is likely contaminated. Freshwater shrimps can only survive in clean water and cannot thrive in polluted conditions. Therefore, the drastic reduction in shrimp population at location C suggests that this area is experiencing high levels of pollution.