Changes in ecosystemsEdexcel A-Level Biology B: Mind map

Exam questions on Changes in ecosystems

1. A new volcanic island has formed from cooled lava, leaving bare rock with no soil. Over the following two centuries, ecologists have recorded the sequence of organisms that have become established, from the first coloniser to a stable woodland.
   Explain how the early colonisers make conditions suitable for later species.2 marks
2. A heathland nature reserve supports a population of rabbits that are preyed on by foxes. Reserve staff have counted both populations every year for 20 years. Rabbit numbers rise and fall in cycles, with each peak in fox numbers occurring shortly after a peak in rabbit numbers. After one unusually severe winter, both populations fell sharply.
   Explain why each peak in the fox population follows a peak in the rabbit population, and why rabbit numbers then fall.2 marks
3. A student investigated the effect of light intensity on the morphology of ivy (Hedera helix). She compared leaves from ivy growing on the floor of a shaded woodland with leaves from ivy growing on an open, sunny hedgerow. She measured the surface area of 30 leaves from each site. Mean leaf surface area was 38.4 cm² in the shade and 21.6 cm² in the sun.
   Describe how the student should collect the leaves and measure the abiotic factor so that the comparison is valid.3 marks