Question Constellation Sign up for free AQA · GCSE · Biology · Higher
Tadpole mortality factors
Students investigated the number of tadpoles in a pond for 8 weeks. After 0 weeks, no more tadpoles hatched in the pond.
After 4 weeks many of the tadpoles had died. Suggest two reasons why the tadpoles died.
Write your answer first. You can study the marking guidance whenever you need it.
Study the marking See what earns credit and compare it with a full-mark answer.
Marking points
- 1 Gives disease/pathogens as one reason.
- 2 Gives predation as one reason.
- 3 Gives lack of food/competition for food as one reason.
- 4 Gives low oxygen/eutrophication as one reason.
- 5 Gives temperature change as one reason.
- 6 Gives pH change as one reason.
- 7 Gives drying/lack of space as one reason.
- 8 Gives a toxic chemical or accepted named example as one reason.
Full-mark answer
1. Some tadpoles may have been eaten by predators. 2. The oxygen concentration in the pond water may have fallen too low.
Why this answer loses marks
Pollution and competition killed the tadpoles.
Both ideas are unqualified; name the toxic input or the resource being competed for.