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AQA GCSE · Question 04.3 · Ecology
When sewage enters a river, the concentration of dissolved oxygen decreases. The decrease in oxygen concentration is caused by organisms in the water. What process in living organisms uses oxygen?
When sewage enters a river, the concentration of dissolved oxygen decreases. The decrease in oxygen concentration is caused by organisms in the water. What process in living organisms uses oxygen?
How to approach this question
Recall the fundamental life processes. There is a key process that occurs in the cells of most living organisms to release energy from food, and this process requires oxygen. What is it called?
Full Answer
Respiration
The large population of bacteria that grows in response to the sewage uses dissolved oxygen from the water for aerobic respiration. Respiration is the process by which organisms break down glucose to release energy, and the aerobic form of this process requires oxygen. The high rate of respiration by the huge number of bacteria rapidly depletes the oxygen in the water.
Common mistakes
✗ Answering "breathing". Breathing is the physical act of moving air in and out of lungs; respiration is the chemical process in cells.
✗ Answering "photosynthesis". Photosynthesis produces oxygen, it does not use it (although plants also respire).
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