O-LevelBiologyPlant Nutrition5090/22 · Oct/Nov 2016 · Q59 Marks

Sweet clover is a member of the pea and bean family (leguminous plants) that grows amongst grass in fields used for cattle feed.

(a)Explain how sweet clover can improve the soil in which it grows.[2]
(b)As sweet clover dries, fungi that grow on it produce a chemical (dicoumarol) that prevents blood from clotting. Suggest a protein that cattle which eat sweet clover affected by such fungi might be unable to produce.[1]
(c)(i)Dicoumarol has been used for many years as a constituent in a form of rat poison. Fig. 5.1 shows the change in the LD50 for dicoumarol in rats from 2000 to 2015. The LD50 is a measure of the amount of poison that will kill 50% of the rats that consume it. [Figure 5.1] Describe the change in the LD50 for dicoumarol in rats from 2000 to 2015.[2]
(c)(ii)Suggest an explanation for the change you have described.[4]

This question uses a diagram from the original paper, which isn't shown here. Open the full paper from the past papers archive to see it.

Mark scheme

Marking points from the official mark scheme (Oct/Nov 2016). The mark or mark type is shown in brackets.

[2] bacteria (or correctly named) + roots/nodules ;
fix/convert/turn + nitrogen ;
ploughing/digging into soil;
decay/decompose ;
(which produces) nitrates/nitrites/ammonium ;
[1] fibrinogen/fibrin ;
[2] increase;
no change + (from 2000) to 2002/3/4/ first 2 years/first 3 years/first four years;
exponential or described/more quickly AW ;
[4] mutation/change/variation ;
reference to genes/DNA ;
resistance (to poison)/better adapted;
survival;
breeding/reproduction/produce offspring;
natural selection/evolution;
greater amount (of dicoumarol) now required to kill/used to kill/the LD50 must be increased;

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