Describe how the nitrogen cycle makes nitrogen in the air available for both plant and animal protein.

Mark scheme

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

1. [max 5] fix/convert/change/turn (nitrogen in air) ;
2. reference to lightning;
3. reference to bacteria;
4. legumes (peas/beans)/root nodules;
5. to ammonium ;
6. to nitrates;
7. (nitrates) absorbed + by plants ;
8. reference to amino acids (in either plants or animals);
9. plants + eaten by animals;
10. protein digested (in animals);
11. [max 5] production of crops: increases/increased yield;
12. (due to) improved growth ;
13. increased profit/AW;
14. environment: reference to positive effect on environment e.g. more photosynthesis reduces CO2/increases O2/more wild plants for insects ;
15. growth of weeds ;
16. leaching (into water sources) AW;
17. eutrophication or process described;
18. death of aquatic life;
19. possible contamination/pollution of (drinking) water ;