GCSE / O Levels Chemistry

Nitrogenous fertilisers can cause eutrophication to occur in rivers. Eutrophication involves the five
stages listed.
1
The fertiliser is washed into the river.
2 Oxygen levels become depleted in the river.
3
Plants die.
4
Plants begin to decay.
5 Plants in the river grow at an increased rate.
In which order do these five stages occur during eutrophication?
first
last
A
1
2
4
В
1
2
4
1
2
3
4
D
1
3
4
2
3.
3.


Choice D is correct because:

In the process of eutrophication, the sequence of events should be:

The fertiliser is washed into the river: The process begins when fertiliser runoff from agricultural fields makes its way into a body of water like a river.

Plants in the river grow at an increased rate: The fertiliser, being rich in nutrients (such as nitrogen), stimulates the overgrowth of plants and algae.

Plants die: After a quick growth spurt, the overcrowded plants and algae begin to die off.

Plants begin to decay: As the dead plants and algae decompose, decomposition bacteria multiply and consume the remaining oxygen in the water.

Oxygen levels become depleted in the river: Due to the decomposition process, oxygen in the water gets depleted, which can harm or kill aquatic life.

Therefore, the correct order is: 1 → 5 → 3 → 4 → 2.

Choices A, B, and C are incorrect because they do not state the correct order of the stages during the process of eutrophication.

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