SuccessionAQA A-Level Biology: Subtopic test

1. 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.

   (a)

   What term describes the first species to colonise the bare lava rock?

   [1 mark]

   • AClimax species
   • BIndicator species
   • CKeystone species
   • DPioneer species

   (b)

   What is the name given to the stable community that eventually forms on the island?

   [1 mark]

   • APioneer community
   • BSeral community
   • CClimax community
   • DFounder community

   (c)

   Explain how the lichens make conditions on the bare rock more suitable for mosses.

   [2 marks]

   Total for question 1: 4 marks

2. 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.

   (a)

   Which feature makes marram grass a successful pioneer on the shifting dunes?

   [1 mark]

   • AIt needs deep, fertile soil
   • BIt tolerates salt spray, drought and shifting sand
   • CIt grows only in shade
   • DIt needs high concentrations of nitrate

   (b)

   Which abiotic change is most likely to occur as the dunes become older, moving inland?

   [1 mark]

   • AMore organic matter and greater water retention in the soil
   • BHigher wind speed at ground level
   • CGreater exposure to salt spray
   • DShallower soil

   (c)

   Suggest why there are more plant species on the older dunes inland than on the dunes near the sea.

   [2 marks]

   Total for question 2: 4 marks

3. 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.

   (a)

   Explain how the alder shrubs made the environment more suitable for spruce seedlings.

   [3 marks]

   (b)

   Explain why the alder are eventually replaced by spruce, and suggest the effect of this on biodiversity.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A disused slate quarry in Wales has areas that were abandoned at different times. The oldest area, abandoned about 250 years ago, is now oak woodland. The youngest area, abandoned 5 years ago, is bare rock with thin patches of lichen.

   (a)

   Explain how a woodland community could develop from the bare rock in the quarry.

   [6 marks]

   (b)

   Species richness (the number of plant species in 100 m²) was measured in five areas: 4 in the 5-year-old area (soil 0.5 cm deep), 15 at 20 years (3 cm), 34 at 50 years (9 cm), 21 at 120 years (25 cm) and 17 at 250 years (40 cm). Explain the pattern in species richness and evaluate whether these data show that biodiversity is lower in the climax community than at an intermediate stage.

   [6 marks]

   Total for question 4: 12 marks

End of questions