7.2 Organisation of an ecosystem

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Question 7
Medium

Agricultural run-off containing high concentrations of nitrates can enter river systems, causing significant ecological changes downstream.

The graph below shows the changes in nitrates, green algae, decomposer bacteria, and dissolved oxygen downstream from where fertilizer runoff entered a river.

Line graph showing the relative levels of nitrates, green algae, decomposer bacteria, and dissolved oxygen in a river plotted against distance downstream. An arrow on the horizontal x-axis indicates where the 'Fertilizer enters river'. The nitrate curve spikes immediately at this point and declines. The green algae curve rises to a high peak shortly downstream, then falls. The decomposer bacteria curve starts to rise as the green algae curve falls, peaking further downstream. The dissolved oxygen curve decreases to a minimum where the bacteria curve peaks, then gradually recovers to its original level.

a.

Which group of organisms had the most rapid increase in population size shortly after the nitrates entered the river?

  • Green algae
  • Decomposer bacteria
[1]
b.

Describe two ways the graph shows a relationship between the green algae population and the decomposer bacteria population.

[3]
c.

What biological process carried out by the decomposer bacteria causes the concentration of dissolved oxygen to decrease?

[1]
d.

Explain why the concentration of dissolved oxygen begins to increase again further downstream as the green algae population stabilizes and decomposer bacteria numbers fall.

[2]

7.2 Organisation of an ecosystem Questions

  1. GCSE
  2. /Biology
  3. /7.2 Organisation of an ecosystem