SuccessionAQA A-Level Biology: Mind map

Exam questions on Succession

1. A volcanic eruption created a new island of bare lava rock. Over several decades the island was colonised, first by lichens, then by mosses and grasses, followed by shrubs and finally by woodland.
   Explain how the lichens make conditions on the bare rock more suitable for mosses.2 marks
2. On a coastal sand dune system, marram grass grows on the shifting dunes closest to the sea. Further inland, older and more stable dunes support other grasses, then shrubs such as gorse, and finally woodland. The depth of soil and the amount of humus increase with distance inland.
   Suggest why there are more plant species on the older dunes inland than on the dunes near the sea.2 marks
3. After a glacier retreated, bare gravel was exposed. The first plants to establish were low-growing mat plants, followed by alder shrubs and then spruce trees. Alder roots have nodules containing nitrogen-fixing bacteria, and alder leaf litter makes the soil more acidic. Spruce grow taller than alder and eventually replace them.
   Explain how the alder shrubs made the environment more suitable for spruce seedlings.3 marks