1. 1
   An environmental scientist is studying the carbon cycle around a power station that burns coal, a fossil fuel formed millions of years ago from the remains of ancient plants. Nearby, a forest of growing trees absorbs carbon dioxide from the atmosphere.

   (a)

   A power station burns coal, a fossil fuel formed from the remains of ancient plants, releasing carbon dioxide into the atmosphere. Which process in the carbon cycle does this represent?

   [1 mark]

   • APhotosynthesis
   • BCombustion
   • CDecomposition
   • DNitrogen fixation

   (b)

   The nearby forest of growing trees absorbs carbon dioxide from the atmosphere and uses it to build organic molecules such as glucose and cellulose. Which process is responsible for this?

   [1 mark]

   • ARespiration
   • BCombustion
   • CPhotosynthesis
   • DDenitrification

   (c)

   Explain how the coal being burned at the power station was originally formed, and describe two other processes (besides combustion and photosynthesis) that move carbon between organisms and the atmosphere in the carbon cycle.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A farmer applies a nitrate-based fertiliser to a field of crops to improve their growth. Some of this nitrate is absorbed by the crop plants, but some also leaches into a nearby stream, where certain bacteria in the waterlogged, oxygen-poor stream sediment convert some of the nitrate back into nitrogen gas.

   (a)

   Which process allows plants to make use of this fertiliser to build proteins?

   [1 mark]

   • AAbsorption of nitrate ions by plant roots, used to make amino acids and proteins
   • BDenitrification of nitrate ions into nitrogen gas
   • CNitrogen fixation by lightning
   • DDecomposition of the fertiliser by fungi

   (b)

   In the waterlogged sediment of the nearby stream, bacteria convert some of the nitrate that has leached from the field back into nitrogen gas, which is released into the atmosphere. What is this process called?

   [1 mark]

   • ANitrification
   • BNitrogen fixation
   • CAssimilation
   • DDenitrification

   (c)

   State the roles of microorganisms in two other processes of the nitrogen cycle: the decomposition of proteins and the conversion of ammonium ions into nitrate ions.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   An agricultural scientist is comparing two farming practices that affect the nitrogen cycle in soil: growing a leguminous crop such as clover, which has root nodules containing nitrogen-fixing bacteria, and applying large amounts of artificial nitrate fertiliser directly to the soil, some of which is later found to have washed into a nearby river.

   (a)

   A species of leguminous plant (such as clover) is grown in a field alongside cereal crops because it has root nodules containing nitrogen-fixing bacteria. Describe the process of nitrogen fixation carried out by these bacteria, and explain why growing legumes can improve the nitrogen content of the soil for other crops.

   [3 marks]

   (b)

   Some of the nitrate fertiliser applied to the field is found to have washed (leached) into a nearby river. Explain, using the term eutrophication, the sequence of events that could occur in the river as a result of this nitrate entering the water.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   An environmental science course is studying two interconnected nutrient cycles, the carbon cycle and the nitrogen cycle, both of which have been significantly affected by modern human activity, including the burning of fossil fuels and the widespread use of artificial nitrogen fertilisers in agriculture.

   (a)

   Explain fully how carbon is cycled between the atmosphere, living organisms and fossil fuels, referring to photosynthesis, respiration, feeding, decomposition, the formation of fossil fuels and combustion. Include in your answer how human activities such as burning fossil fuels have disturbed the natural balance of this cycle.

   [6 marks]

   (b)

   Explain fully how nitrogen is cycled between the atmosphere, soil and living organisms, referring to nitrogen fixation, absorption of nitrate ions by plants, feeding and digestion of proteins, deamination, decomposition, nitrification and denitrification. Include in your answer the roles of microorganisms at each stage.

   [6 marks]

   Total for question 4: 12 marks

End of questions