1. 1
   A factory discharges untreated sewage, containing large amounts of organic waste and nutrients, directly into a nearby river. Downstream, local fishermen report a sudden decline in fish numbers over the following weeks.

   (a)

   A factory discharges untreated sewage into a river. This sewage contains large amounts of organic waste and nutrients. What process is this discharge most likely to trigger in the river?

   [1 mark]

   • ANitrogen fixation
   • BEutrophication
   • CPhotosynthesis inhibition only
   • DBioaccumulation of plastics

   (b)

   Fishermen downstream report a sudden decline in fish numbers over the following weeks. Which of the following best explains why the fish died?

   [1 mark]

   • AIncreased algal growth followed by decomposition used up dissolved oxygen in the water, suffocating the fish
   • BThe sewage directly poisoned the fish with heavy metals
   • CThe sewage increased the water's salinity to lethal levels
   • DThe sewage caused the water temperature to rise sharply

   (c)

   Explain the process of eutrophication that leads to fish deaths in this river, describing the sequence of events from the sewage entering the water to the death of the fish.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A coastal clean-up team finds large quantities of discarded plastic bottles and bags washed up on a beach, some of which have broken down over many years into smaller pieces known as microplastics. Marine biologists studying the same coastline have also found evidence that local seabirds and fish frequently mistake these plastic fragments for food.

   (a)

   What is the main problem with this type of plastic pollution?

   [1 mark]

   • APlastic is biodegradable and breaks down harmlessly within a few days
   • BPlastic pollution has no known effect on wildlife
   • CPlastic pollution only affects producers, never consumers
   • DPlastic is non-biodegradable and persists in the environment for a very long time, harming aquatic and terrestrial organisms

   (b)

   Marine biologists find evidence that local seabirds and fish frequently mistake small plastic fragments for food and ingest them. What is a likely consequence of this for the affected animals?

   [1 mark]

   • AImproved nutrition, since plastic provides additional energy
   • BIncreased reproduction rate
   • CBlockage of the digestive system, reduced feeding and potential starvation
   • DNo effect, since plastic passes through the body unnoticed

   (c)

   Explain why non-biodegradable plastic pollution is a persistent problem in both aquatic and terrestrial ecosystems, and describe one effect of this plastic pollution on wildlife in each environment.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   An environmental agency is investigating two sources of air pollution in a region: a large cattle farm identified as a major source of atmospheric methane, and a coal-burning power station identified as a major source of atmospheric carbon dioxide. The agency is also monitoring a nearby lake that has recently undergone severe eutrophication due to fertiliser runoff from surrounding farmland.

   (a)

   A large cattle farm is identified as a major source of methane gas released into the atmosphere, while a nearby power station releases large quantities of carbon dioxide from burning coal. Explain how these two gases contribute to the enhanced greenhouse effect and climate change.

   [3 marks]

   (b)

   The agency is also monitoring a nearby lake that has recently undergone severe eutrophication due to fertiliser runoff from surrounding farmland. Explain the full process of eutrophication in this lake, from the increased availability of nutrients through to the death of oxygen-dependent organisms.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   An environmental impact review is assessing an industrial river estuary polluted simultaneously by untreated sewage, agricultural fertiliser runoff, and discarded plastic waste, alongside a separate regional concern about rising atmospheric methane and carbon dioxide emissions from nearby livestock farms and power stations contributing to climate change.

   (a)

   An industrial river estuary receives pollution from three sources simultaneously: untreated sewage from a nearby town, excess fertiliser runoff from surrounding farmland, and large quantities of discarded non-biodegradable plastic waste. Explain fully the combined effects that these three sources of pollution are likely to have on the estuary ecosystem, referring to eutrophication and the specific problems caused by non-biodegradable plastic.

   [6 marks]

   (b)

   The same regional review raises separate concerns about rising atmospheric methane emissions from livestock farms and rising carbon dioxide emissions from power stations in the area, both of which are contributing to the enhanced greenhouse effect. Explain fully how these emissions cause climate change, and evaluate why reducing air pollution from methane and carbon dioxide is generally considered a more challenging problem to solve than reducing water pollution from sewage or fertiliser in a single estuary.

   [6 marks]

   Total for question 4: 12 marks

End of questions