6 exam-style questions with full mark schemes and model answers. Write your own answer and the AI examiner marks it against the mark scheme.
Only a small fraction of the energy that enters a food chain at the producer level reaches the top consumers. This is why food chains rarely have more than four or five trophic levels.
Explain how energy is transferred along a food chain and why so much energy is lost between one trophic level and the next. In your answer, refer to where the energy originally comes from and the main processes that cause the losses. (6 marks)
A student investigated the number of dandelion plants growing in a large rectangular field of total area 800 m². They placed a 0.25 m² quadrat at five random positions and counted the dandelions in each.
| Quadrat | 1 | 2 | 3 | 4 | 5 |
|---|---|---|---|---|---|
| Number of dandelions | 8 | 5 | 9 | 6 | 7 |
(a) Calculate the mean number of dandelions per quadrat. (1 mark)
(b) Use your answer to estimate the total number of dandelions in the whole field. Show your working. (2 marks)
(c) State one way the student could improve the reliability of their estimate. (1 mark)
In a grassland food chain, the producers (grass) store 40 000 kJ of energy per square metre per year. The energy stored in the biomass of the primary consumers (rabbits) that feed on the grass is 3200 kJ per square metre per year.
(a) Calculate the percentage of the energy in the grass that is transferred to the rabbits. Show your working. (2 marks)
(b) Suggest one reason why the percentage of energy transferred is less than 100 %. (1 mark)
The carbon cycle continuously recycles carbon between the atmosphere, living organisms and the soil.
Describe how carbon from the air becomes part of the body of an animal, and how that carbon is later returned to the air. In your answer, name the key processes involved. (3 marks)
A gardener placed two identical piles of grass cuttings in a garden. Pile A was left in a warm, damp, sheltered corner. Pile B was kept in a cold, dry, exposed spot. After three weeks, pile A had rotted down much more than pile B.
Explain, in terms of decomposition, why pile A rotted down faster than pile B. (2 marks)
In an ecosystem, a biotic factor and an abiotic factor can both affect the size of a population.
State what is meant by an abiotic factor, and give one example. (1 mark)