1. 1
   A fish farmer feeds pellets to salmon in a large aquaculture pen, and a scientist calculates how much of the energy in the fish food is eventually transferred into new salmon biomass compared with the energy lost from the salmon's waste and respiration.

   (a)

   Approximately what percentage of the biomass (energy) at one trophic level is typically transferred to the level above it?

   [1 mark]

   • A10%
   • B1%
   • C50%
   • D90%

   (b)

   Why is only around 10% of the biomass in the salmon's food transferred into new salmon biomass?

   [1 mark]

   • ABecause most of the energy is used for photosynthesis
   • BBecause the salmon cannot digest most of their food
   • CBecause energy cannot be transferred between organisms
   • DBecause some materials and energy are lost in the salmon's waste and much of the energy is used in respiration and eventually transferred to the surroundings

   (c)

   Explain why a farmer could produce more fish biomass from a given amount of fish food by reducing the number of stages (trophic levels) in the food chain leading to the salmon.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   Certain species of bacteria, called extremophiles, are found living in the boiling, mineral-rich water of hot springs, conditions in which most other organisms would die.

   (a)

   What term describes organisms, such as these bacteria, that are adapted to survive in very extreme environmental conditions?

   [1 mark]

   • AParasites
   • BExtremophiles
   • CProducers
   • DDecomposers

   (b)

   Which type of adaptation would allow the hot spring bacteria to survive high temperatures without their proteins being destroyed?

   [1 mark]

   • AA behavioural adaptation
   • BAn adaptation that increases competition for territory
   • CA structural or functional adaptation, such as heat-stable enzymes
   • DAn adaptation related only to camouflage

   (c)

   Distinguish between a structural adaptation and a behavioural adaptation, giving one example of each that could help an organism survive in an extreme environment.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A local council is deciding whether to compost or incinerate the garden waste it collects from residents, and is also investigating why a nearby river has recently turned green and has fewer fish living in it.

   (a)

   Explain, in terms of the carbon cycle, what happens to the carbon in the garden waste if it is composted rather than incinerated.

   [3 marks]

   (b)

   Suggest why the river has turned green and now has fewer fish living in it, explaining the process involved.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A large area of tropical rainforest is being assessed by conservationists before a decision is made on whether to allow it to be cleared for cattle grazing, which would replace a complex, diverse ecosystem with a much simpler one.

   (a)

   Explain, using the idea of energy transfer through trophic levels, why clearing a diverse forest ecosystem and replacing it with cattle grazing changes the amount of biomass and the number of organisms that can be supported.

   [6 marks]

   (b)

   Discuss the environmental consequences of large-scale deforestation of the rainforest, in addition to the loss of biodiversity.

   [6 marks]

   Total for question 4: 12 marks

5. 5
   An ecologist studying a freshwater lake estimates the total biomass of phytoplankton (microscopic algae), zooplankton that eat the phytoplankton, and small fish that eat the zooplankton, in a one square metre column of water.

   (a)

   If the biomass is drawn to scale as a pyramid of biomass, with phytoplankton at the bottom, what shape would the pyramid usually have?

   [1 mark]

   • AWidest at the top, narrowing towards the bottom
   • BThe same width at every level
   • CWidest at the bottom, narrowing towards the top
   • DAn irregular shape with no clear pattern

   (b)

   Which trophic level in this lake would you expect to have the smallest total biomass?

   [1 mark]

   • AThe small fish
   • BThe zooplankton
   • CThe phytoplankton
   • DAll three levels would have equal biomass

   (c)

   Suggest why the biomass of the small fish is much lower than the biomass of the phytoplankton they ultimately depend on.

   [2 marks]

   Total for question 5: 4 marks

6. 6
   On a coral reef, two species of small fish that feed on the same type of algae are often seen chasing each other away from patches of reef, while a species of goby fish is regularly seen removing parasites from the skin of a much larger reef fish.

   (a)

   What term best describes the relationship between the two fish species chasing each other away from the same food source?

   [1 mark]

   • APredation
   • BParasitism
   • CMutualism
   • DCompetition

   (b)

   What are the two fish species mainly competing for in this example?

   [1 mark]

   • AMates and light
   • BFood and space (territory)
   • CWater and minerals
   • DOxygen and shelter only

   (c)

   Explain why the relationship between the goby fish and the larger reef fish is an example of interdependence rather than competition.

   [2 marks]

   Total for question 6: 4 marks

7. 7
   A woodland has remained a stable community for many decades, with dead leaves and fallen branches constantly being broken down on the forest floor, while the populations of trees, insects and birds living there stay roughly the same size from year to year.

   (a)

   Explain what is meant by a 'stable community' in terms of the processes that remove and return materials, using the decay of dead leaves as an example.

   [3 marks]

   (b)

   Explain how the population sizes of the different species in this stable woodland community are likely to be limited and kept roughly constant, referring to interdependence between species.

   [4 marks]

   Total for question 7: 7 marks

8. 8
   Conservationists are studying an Arctic tundra food chain in which lichen is eaten by caribou, which are in turn hunted by wolves, in an environment with extremely cold temperatures and short summers.

   (a)

   Explain why the Arctic tundra food chain can only support a much smaller total biomass and number of wolves compared with the number of caribou, and compared with the biomass of lichen.

   [6 marks]

   (b)

   Describe structural and behavioural adaptations that help the wolves and caribou survive the extreme cold and the competition for resources in the Arctic tundra.

   [6 marks]

   Total for question 8: 12 marks

End of questions