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AQA GCSE · Question 04.6 · Ecology
The concentration of oxygen in the water at site A is much lower than at site B.
- Sludge worms live in places which have a low concentration of oxygen.
- Mayfly nymphs need a high concentration of oxygen.
Give evidence from Table 2 for the difference in oxygen concentration at sites A and B. Refer to sludge worms and to mayfly nymphs in your answer.
The concentration of oxygen in the water at site A is much lower than at site B.
- Sludge worms live in places which have a low concentration of oxygen.
- Mayfly nymphs need a high concentration of oxygen.
Give evidence from Table 2 for the difference in oxygen concentration at sites A and B. Refer to sludge worms and to mayfly nymphs in your answer.
How to approach this question
1. Look at the information given about sludge worms (live in low oxygen). Find their numbers at Site A and Site B from Table 2. Explain what these numbers suggest about the oxygen level at each site.
2. Look at the information given about mayfly nymphs (need high oxygen). Find their numbers at Site A and Site B from Table 2. Explain what these numbers suggest about the oxygen level at each site.
3. Combine these two pieces of evidence to form a conclusion about the difference in oxygen concentration.
Full Answer
Sludge worms and mayfly nymphs are indicator species for oxygen levels.
- The high number of sludge worms at Site A (80) and very low number at Site B (2) indicates that Site A has a low oxygen concentration, as these organisms are adapted to such conditions.
- The absence of mayfly nymphs at Site A (0) and their presence at Site B (15) indicates that Site B has a higher oxygen concentration, as these organisms require clean, well-oxygenated water to survive.
Together, these data strongly support the conclusion that Site A is polluted and has low oxygen, while Site B is cleaner and has higher oxygen.
Common mistakes
✗ Only referring to one of the two species. The question asks for reference to both.
✗ Stating the numbers from the table without explaining what they mean in terms of oxygen levels.
✗ Confusing which species indicates high/low oxygen.
Practice the full AQA GCSE Biology Foundation Tier Paper 2
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