1. 1
   An agricultural scientist is studying energy transfer on a cattle farm. She measures the energy stored in the grass eaten by a herd of cattle and compares it with the energy stored as new biomass gained by the cattle over the same time period, in order to work out how efficiently energy is transferred from the grass (producer) to the cattle (primary consumer).

   (a)

   On a cattle farm, an agricultural scientist measures the energy stored in the grass eaten by a herd of cattle and compares it with the energy stored in the biomass gained by the cattle over the same period. She finds that only a small fraction of the energy in the grass is converted into cattle biomass. Which of the following is a major reason why most of the energy in the grass is not transferred into cattle biomass?

   [1 mark]

   • AEnergy is released as heat through respiration in the cattle
   • BEnergy is destroyed and disappears completely
   • CEnergy is transferred into biomass at 100% efficiency, so none is lost
   • DGrass does not contain any stored energy

   (b)

   The scientist calculates that the grass in a field stores 100,000 kJ of energy, and the cattle that graze on it gain only 10,000 kJ of energy as new biomass. What is the percentage efficiency of energy transfer from the grass to the cattle?

   [1 mark]

   • A1%
   • B10%
   • C50%
   • D90%

   (c)

   Using the low percentage efficiency of energy transfer you calculated, explain why food chains on the farm, and food chains in general, rarely contain more than four or five trophic levels.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A coal-fired power station burns coal, which formed over millions of years from the compressed and fossilised remains of ancient plants, in order to generate electricity. This process releases large amounts of carbon dioxide, which had been locked away in the coal, back into the atmosphere as part of the carbon cycle.

   (a)

   A coal-fired power station burns coal, which formed from the compressed remains of plants that died millions of years ago, to generate electricity. This burning process releases large amounts of carbon dioxide into the atmosphere. What is the name of this process, in which stored carbon is released as carbon dioxide by burning a fuel?

   [1 mark]

   • ATranspiration
   • BPhotosynthesis
   • CNitrogen fixation
   • DCombustion

   (b)

   The coal being burned at the power station formed over millions of years from plant material that did not fully decompose before being buried and compressed underground. What is the name of the process by which this ancient plant material became coal (a fossil fuel) rather than being broken down by decomposers?

   [1 mark]

   • ARespiration
   • BDenitrification
   • CFossilisation
   • DCondensation

   (c)

   Describe the journey of a carbon atom from the carbon dioxide released by burning coal at the power station, through to it eventually becoming part of a new plant, referring to the relevant carbon cycle processes.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A farmer grows a field of pea plants, a type of legume, which have small swellings called root nodules containing nitrogen-fixing bacteria. These bacteria convert nitrogen gas from the air into nitrogen-containing compounds that the pea plants can absorb and use, and other soil bacteria carry out further steps of the nitrogen cycle in the same field.

   (a)

   A farmer grows a field of pea plants (a legume), which have small swellings called root nodules containing bacteria. These bacteria convert nitrogen gas from the air into nitrogen-containing compounds that the pea plants can absorb and use to build proteins. Describe this process and explain why it is important for the nitrogen cycle and for soil fertility.

   [3 marks]

   (b)

   In the same field, other soil bacteria convert ammonium compounds released by decomposers (from dead plant and animal material) into nitrate ions, which plant roots can absorb; meanwhile, a different type of bacteria living in waterlogged, poorly aerated parts of the field convert nitrate ions back into nitrogen gas, which is lost to the atmosphere. Name and describe these two further processes occurring in the field, and explain why the second process can reduce the nitrogen available to the farmer's crops.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A tropical rainforest experiences very high rainfall throughout the year. Water evaporates from the leaves of the dense forest canopy through transpiration and from the surface of rivers and soil through evaporation, rises into the atmosphere, cools and condenses to form clouds, and later falls back to the forest as heavy rain (precipitation), where it is absorbed by plant roots or flows into rivers, before the cycle repeats continuously.

   (a)

   Explain, using the terms evaporation, transpiration, condensation and precipitation, how water is continuously cycled through this rainforest ecosystem, and describe what is likely to happen to local rainfall patterns if a large area of the forest is cut down (deforested).

   [6 marks]

   (b)

   A conservation organisation is comparing the energy efficiency of two food production systems near the rainforest: one in which local people grow and eat crops such as maize directly, and another in which the same land is used to grow crops that are fed to cattle, which are then eaten as beef. Using your knowledge of energy transfer between trophic levels, explain why growing crops for direct human consumption is generally a more energy-efficient way of feeding a population than growing crops to feed livestock, and evaluate why, despite this, many people still choose to eat meat.

   [6 marks]

   Total for question 4: 12 marks

End of questions