Rice, maize and wheat plants are the main carbohydrate source for more than 60% of the human population.

Mark scheme

Marking points from the official mark scheme (May/June 2021). The mark or mark type is shown in brackets.

1. [1] photosynthesis ;
2. [1] in leaves / green parts of plants / in mesophyll / chloroplasts / using chlorophyll;
3. [1] using light energy;
4. [1] water + soil / irrigation / roots / root hair cells ;
5. [1] carbon dioxide + air / through stomata ;
6. [1] produce glucose / C6H12O6;
7. [1] starch;
8. [1] magnesium + from soil + to make chlorophyll ;
9. [1] greater demand for food;
10. [1] not enough land available for farming;
11. [1] land being used for e.g. building / biofuels / deforestation;
12. [1] increase in greenhouse gases ;
13. [1] (leads to) climate change;
14. [1] droughts / floods / salinisation AW ;
15. [1] lack of nutrients in soils monoculture / overcrowding AW ;