Figure 2.1 shows the amount of bean seeds harvested from fields where varying amounts of a nitrogen-containing fertiliser had been applied. Bean plants use nitrogen for making proteins. The yield rises from about 1.3 tonnes per hectare with no fertiliser to a peak of about 3.4 at 170 kg per hectare, then falls to about 2.9 at 250 kg.

1. aDescribe the effects of the fertiliser on the yield of beans. [2]
2. bSuggest an explanation for your answer. [3]
3. cState two signs of nitrogen deficiency in plants. [2]

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