1. 1
   A city has a large coal-fired power station and heavy road traffic. Local health officials have recorded rising rates of respiratory illness among residents living close to the main road, and doctors have noted that some patients have reduced oxygen-carrying capacity in their blood.

   (a)

   Which pollutant, released mainly by burning fossil fuels containing sulfur impurities, combines with water vapour in the air to form acid rain?

   [1 mark]

   • ACarbon monoxide
   • BSulfur dioxide
   • CMethane
   • DNitrous oxide

   (b)

   Which pollutant reduces the oxygen-carrying capacity of blood by binding to haemoglobin more strongly than oxygen does?

   [1 mark]

   • ASulfur dioxide
   • BCarbon dioxide
   • CCarbon monoxide
   • DNitrous oxide

   (c)

   Explain why residents living close to the main road, where vehicle exhaust fumes are concentrated, are at greater risk of the respiratory and blood problems described.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A river flows past a farm that has recently applied large amounts of nitrate fertiliser to its fields, and past a village where untreated sewage occasionally enters the water. Over the following weeks, biologists observe a dense growth of algae covering the surface of the river, followed by the deaths of large numbers of fish.

   (a)

   What is the name of the process, beginning with excess nutrients entering water and ending in oxygen depletion, that has caused the fish deaths?

   [1 mark]

   • AEutrophication
   • BDenitrification
   • CBioaccumulation
   • DFermentation

   (b)

   Which of the following directly causes the fish to die during this process?

   [1 mark]

   • AToxins produced by the fertiliser
   • BAn increase in water pH
   • CAn increase in water temperature
   • DA decrease in dissolved oxygen in the water

   (c)

   Explain how the leaching of nitrate fertiliser into the river leads to the death of fish.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A large area of tropical rainforest is cleared and burned to create land for cattle grazing. In the following rainy season, local residents notice that the cleared soil washes away much more readily than it did when the forest was present, and that a nearby stream becomes clouded with soil particles.

   (a)

   Explain why the cleared soil erodes more readily and washes into the stream compared with when it was covered by forest.

   [3 marks]

   (b)

   Describe two further biological consequences of clearing this forest, other than soil erosion, referring to both local water cycling and the global carbon cycle.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   Scientific records show that since the start of the Industrial Revolution, the concentration of carbon dioxide and other gases in the atmosphere has increased steadily, alongside a rise in average global temperatures. Governments are now debating international measures to limit further increases in these gases.

   (a)

   Explain, using named greenhouse gases and named human activities, how human activity since the Industrial Revolution has increased the greenhouse effect and led to global warming.

   [6 marks]

   (b)

   Describe three consequences of continued global warming caused by the enhanced greenhouse effect.

   [6 marks]

   Total for question 4: 12 marks

End of questions