1. 1
   In a deciduous woodland, oak seedlings grow in the shade beneath mature oak trees. Ecologists notice that very few seedlings survive to become tall trees, while bramble shrubs growing at the woodland edge, where light is more freely available, grow quickly and densely.

   (a)

   Which resource are the oak seedlings most likely competing for with the mature trees above them?

   [1 mark]

   • ALight
   • BOxygen
   • CTerritory
   • DMates

   (b)

   The brambles at the woodland edge also spread rapidly by sending out long horizontal stems that root at intervals, allowing new bramble shoots to occupy bare ground before other plant species can establish there.
   
   Which statement best explains why occupying bare ground quickly gives the brambles a competitive advantage?

   [1 mark]

   • AIt prevents pollination of the oak trees
   • BIt increases the rate of photosynthesis in nearby oak trees
   • CIt reduces the amount of carbon dioxide in the atmosphere
   • DIt increases the brambles' access to space, water and mineral ions before competitors arrive

   (c)

   The woodland also contains a species of fungus that grows only in a close relationship with the oak trees' roots, helping the trees absorb mineral ions from the soil in exchange for sugars produced by photosynthesis. Explain, using the idea of interdependence, what would happen to the oak trees and to the fungus if this fungus species were removed from the woodland.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   On a grassland reserve, ecologists have recorded rabbit and fox populations for ten years. Rabbit numbers rise in spring when food is abundant, then fall each winter, and fox numbers rise a few months after each rise in rabbit numbers before also falling. Last year, a new pathogen affecting rabbits arrived on the reserve.

   (a)

   Which term describes the new pathogen as a factor affecting the rabbit population?

   [1 mark]

   • AA producer
   • BAn abiotic factor
   • CA biotic factor
   • DA decomposer

   (b)

   Which statement best explains why fox numbers rise a few months after rabbit numbers rise, rather than at exactly the same time?

   [1 mark]

   • AFoxes cause rabbit numbers to rise by providing shelter for rabbits
   • BMore rabbits means more food available for foxes, so fox numbers increase shortly afterwards as foxes reproduce and survive better
   • CRabbits and foxes do not interact, so the changes are coincidental
   • DFox numbers rise because of changes in soil pH caused by rabbits

   (c)

   Explain how the arrival of the new pathogen is likely to affect the fox population over the following year, and why this shows that a stable community depends on its species and environmental factors remaining in balance.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A species of fox living in a hot, dry desert has unusually large ears compared with foxes living in cooler climates, is most active at night, and produces very small amounts of concentrated urine. A species of bacteria found in a nearby hot spring survives and reproduces at water temperatures close to boiling point.

   (a)

   (a) Using the terms structural, behavioural and functional, classify each of the desert fox's three features described above as an adaptation, and explain briefly why each one helps the fox survive in its hot, dry environment.

   [3 marks]

   (b)

   (b) The hot spring bacteria are described as extremophiles. Define the term extremophile, and explain two ways in which studying organisms adapted to extreme environments, such as the desert fox and the hot spring bacteria, can improve scientific understanding of how organisms survive environmental change.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A group of students used quadrats placed at regular intervals along a transect running from the edge of a lake into dry grassland, to record the abundance of a reed species and a grass species at each point. Reeds were abundant near the lake edge, where soil moisture was very high, but were absent more than five metres from the water. The grass species showed the opposite pattern, being rare near the lake edge and abundant in the drier grassland.

   (a)

   (a) Explain how abiotic factors could account for the distribution pattern of the reeds and the grass species observed along the transect, and describe how using a transect with quadrats at regular intervals allows ecologists to investigate this kind of pattern reliably.

   [6 marks]

   (b)

   (b) The following year, a small population of grazing animals moved into the grassland and began eating large amounts of the grass species close to the lake edge, but avoided the wetter soil directly next to the reeds. Evaluate how the arrival of these grazing animals, as a biotic factor, might change the distribution of the reed and grass species along the transect over several years, and explain how repeating the transect and quadrat survey in future years would help ecologists assess this change.

   [6 marks]

   Total for question 4: 12 marks

End of questions