1. 1
   A group of students is studying decomposition in a woodland. They observe that fallen leaves on the forest floor break down over several months, and carbon dioxide levels in the pockets of air within the soil are higher than in the surrounding atmosphere. The students want to understand how carbon moves between the atmosphere and living organisms in this ecosystem.

   (a)

   Which process removes carbon dioxide from the atmosphere and converts it into glucose in green plants?

   [1 mark]

   • APhotosynthesis
   • BRespiration
   • CCombustion
   • DDecomposition

   (b)

   Which group of organisms is mainly responsible for breaking down the fallen leaves in the woodland?

   [1 mark]

   • AProducers
   • BHerbivores
   • CCarnivores
   • DBacteria and fungi

   (c)

   Explain how decomposers such as bacteria and fungi contribute to the carbon cycle in the woodland.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A coastal town in an area of drought has an unreliable supply of fresh water from rainfall. To secure a reliable water supply, engineers build a desalination plant that removes salt from seawater to produce potable (drinkable) water. The plant forces seawater through a partially permeable membrane to separate the salt from the water molecules.

   (a)

   In the water cycle, which process describes water vapour turning into liquid water droplets to form clouds?

   [1 mark]

   • ATranspiration
   • BEvaporation
   • CCondensation
   • DPrecipitation

   (b)

   Which process is used in the desalination plant to remove salt from seawater using a partially permeable membrane?

   [1 mark]

   • ADiffusion
   • BReverse osmosis
   • CActive transport
   • DDistillation

   (c)

   Explain how the desalination plant produces potable water from seawater.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A farmer grows wheat on a field for several years and notices that crop yields fall as nitrate levels in the soil decrease. To restore soil fertility, the farmer decides to rotate the wheat with a crop of clover, a legume with root nodules containing nitrogen-fixing bacteria, before adding a nitrate-based fertiliser the following season.

   (a)

   Explain how nitrogen-fixing bacteria in the root nodules of the clover plant make nitrogen available for plant growth.

   [3 marks]

   (b)

   Explain how growing clover as part of crop rotation, together with the use of nitrate-based fertiliser, helps to maintain nitrate levels in the soil for the following wheat crop.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A group of environmental scientists is monitoring a river that runs past a farm and a large compost processing facility. At the compost facility, food waste is left to decompose under different conditions of temperature, water content and oxygen availability to produce compost for the farm's fields. Downstream, the scientists sample the river at several points and record which invertebrate species are present, using this information to assess the level of water pollution entering the river from the farm and compost facility.

   (a)

   Evaluate how temperature, water content and oxygen availability affect the rate of decomposition at the compost facility, and explain how the facility could adjust these conditions to produce compost more quickly.

   [6 marks]

   (b)

   Discuss how the environmental scientists could use indicator species to assess the level of pollution in the river at different points downstream of the farm and compost facility.

   [6 marks]

   Total for question 4: 12 marks

End of questions