(i)

The effect on crop yield of using an increasing mass of fertiliser is…

Any three of the following:

The yield is 800 (kg/10 000m2) when no fertiliser was used; [1 mark]
An increase in the mass of fertiliser results in greater crop yield; [1 mark]
With 150 (kg/10 000m2) fertiliser, the highest crop yield of 5600 (kg/10 000m2) can be seen; [1 mark]
Any further increase in the mass of fertiliser does not increase the crop yield / crop yield plateaus at 150 (kg/10 000m2); [1 mark]

Do not ignore the command word (describe) and start explaining the graph which is not required. Describe, in this context, means we just have to quote the data given in the figure. The highest and the lowest yield should be discussed along with where it stops.

Usually, 1 mark could be lost for not mentioning the data from the graph.

(ii)

Nitrogen in the fertiliser is absorbed by crop plants by…

Any three of the following:

Nitrate ions are absorbed by the root hair; [1 mark]
Through active transport / against the concentration gradient OR by diffusion / down the concentration gradient; [1 mark]
They are used to produce amino acids / proteins; [1 mark]
Which increase the growth of the plant; [1 mark]

The command word “how” means the process through which nitrogen is absorbed, so the concept of active transport should be recalled. Nitrogen is present in the form of nitrate ions which need energy to be absorbed against their concentration gradient.

(iii)

A farmer may decide to use a mass of fertiliser that is less than needed for a maximum crop yield because…

Any three of the following:

There may be runoff / leaching of fertilisers; [1 mark]
Which can lead to eutrophication; [1 mark]
(Eutrophication) can lead to the harm / death (of aquatic) organisms/animals; [1 mark]
Fertilisers are expensive; [1 mark]
The possible return might not benefit the farmer due to high cost; [1 mark]

Accept a description of eutrophication for marking point 2

[Total: 9 marks]

The command word 'explain' means to set out the reason or purpose.

High use of fertilisers can lead to land pollution as well as eutrophication. This is when fertilisers can flow off into the water bodies which results in algal blooms that can reduce dissolved oxygen in water bodies, and animals requiring oxygen may die.

You should make a point from an economical point of view: Chemical fertilisers are expensive which not all the farmers can afford.

Mineral Nutrition (Cambridge O Level Biology)

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