Predict and explain the effect of the dissolved oxygen concentration at X in Fig. 6.1 on the organisms in the river.
(b)[1]
Describe why it matters to humans that sewage is treated before it enters rivers.
(c)[3]
State three other factors that can lead to extinction.
Worked solution & mark scheme
This 9-mark question has a full step-by-step worked solution and mark scheme. One marking point: “at the start initially, dissolved oxygen concentration is high / stable / constant” …