Fertilisers and eutrophicationAQA A-Level Biology: Subtopic test

1. 1
   A farmer grows wheat on the same field every year. At harvest the grain is sold off the farm and the straw is baled and removed. Soil tests show that the concentrations of nitrate ions and phosphate ions in the field fall each year.

   (a)

   Which of the following is a natural fertiliser?

   [1 mark]

   • AAmmonium nitrate granules made in a factory
   • BPellets of NPK compound fertiliser
   • CRotted farmyard manure
   • DSuperphosphate made from treated rock

   (b)

   The farmer replaces the lost minerals using an artificial fertiliser. Which statement about the nitrate in an artificial fertiliser is correct?

   [1 mark]

   • AIt is in a soluble form that plants can absorb straight away
   • BIt must first be broken down by saprobionts before plants can absorb it
   • CIt is insoluble so it stays in the soil for years
   • DIt is absorbed by plants only after nitrogen fixation by bacteria

   (c)

   Explain why nitrate and phosphate concentrations fall in this field but would not fall in an undisturbed woodland.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A freshwater lake lies next to arable fields. In spring the farmer spread fertiliser on the fields and there was heavy rain the following week. Over the next month, a green layer of algae spread across the lake surface. By midsummer, submerged plants had died and many fish were found dead.

   (a)

   Which term describes the washing of soluble nitrate ions out of the soil and into the lake?

   [1 mark]

   • ADenitrification
   • BLeaching
   • CNitrification
   • DEutrophication

   (b)

   Which is the direct reason that the submerged plants in the lake died?

   [1 mark]

   • ANitrate ions are directly toxic to plant roots
   • BThe algae released oxygen that poisoned them
   • CPhosphate ions prevented the plants absorbing water
   • DThe algal layer blocked light so they could not photosynthesise

   (c)

   Explain why the fish died after the submerged plants and the surface algae died.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A farmer grows potatoes in a field that slopes down towards a stream. She is deciding how much nitrogen fertiliser to apply. In a trial she applied ammonium nitrate at four rates and recorded the mean yield of potatoes: no fertiliser gave 28 tonnes per hectare, 100 kg per hectare gave 41 tonnes per hectare, 200 kg per hectare gave 47 tonnes per hectare and 300 kg per hectare gave 48 tonnes per hectare. She can also spread manure from a neighbouring farm.

   (a)

   Suggest why a heavy downpour is more likely to cause nitrate to leach into the stream if she has just applied ammonium nitrate than if she has just applied manure.

   [3 marks]

   (b)

   The farmer says, "I should apply 300 kg per hectare because that gives the highest yield." Evaluate her statement using the data and the environmental effects of fertiliser use.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A dairy farm borders a freshwater lake. The farmer cuts silage from his fields and sells milk and cattle, so nitrate and phosphate are removed from the farm. He can spread slurry from his own cattle or buy ammonium nitrate and superphosphate. The water authority has recorded an algal bloom on the lake in each of the last two summers.

   (a)

   Describe and explain how the use of fertilisers on the farm could lead to the death of fish in the lake.

   [6 marks]

   (b)

   Evaluate the use of slurry and of artificial fertiliser to replace the nitrate and phosphate lost from this farm, and make a justified recommendation.

   [6 marks]

   Total for question 4: 12 marks

End of questions