A group of students investigated two habitats: dense woodland and open grassland. • Trees are the dominant plants in woodland. The trees form a canopy under which flowering herbs, small shrubs and grasses grow. • Grasses are the dominant plants in grassland. The grasses and small flowering plants form a continuous ground cover with only a few small shrubs present. [Figure 1.1] shows photographs of the two areas. The students decided to compare the adaptations for reducing water loss in the plants growing in each area. The students suggested the following hypothesis: The density of stomata will be higher in plants found in the woodland habitat than in the grassland habitat.

Mark scheme

Marking points from the official mark scheme (May/June 2022). The mark or mark type is shown in brackets.

1. [2] independent variable: (type of) habitat / described ;
2. dependent variable: density / number / AW, of stomata;
3. [2] Radius / diameter (of field of view / image / circle / Fig 1.2);
4. number of stomata ;
5. [2] 2 marks for density range: 0.014-0.019;;
6. if outside this range one mark for: stomatal number: 61 (full) - 69 (all);
7. area: 4069-4301;
8. [6] any six from:
9. 1 ref. to method of, random / systematic sampling of plants;
10. 2 (take leaves) from same species, that is present in both habitats ;
11. 3 collect a minimum of 5 leaf samples (in both habitats);
12. 4 same position / age, of leaf (on plant);
13. 5 impressions to be taken from, lower / upper / both / same, surface(s) (of leaves) ;
14. 6 (impressions viewed using) same, magnification / lens / size of field of view ;
15. 7 count stomata (in field of view);
16. 8 details of systematic counting / count only whole stomata / take a photograph and mark ;
17. 9 repeat, (same) experiment (both habitats) minimum of twice, and calculate a mean;
18. 10 safety: hazard and risk and mitigation ;
19. [1] 73 (%);
20. [3] support – max 2 marks:
21. 1 stomatal density on upper surface is higher in plants grown in high light intensity ora ;
22. 2 difference in (mean) stomatal density on upper surface (between the two light intensities) is greater than the difference between the lower surfaces ora ;
23. 3 stomatal density on lower surface is similar / very close;
24. 4 leaf 1 stomatal density on lower surface is less than in plants grown in low light intensity ora ;
25. 5 calculate pair of stomatal densities (for 1 to 4);
26. doesn't support – max 2 marks:
27. 6 mean stomatal density, on lower / both, surface(s) is higher in plants grown in high light intensity ora ;
28. 7 for 2 out of 3 leaves / leaf 2 and 3, stomatal density is not higher only on the upper surface/ is higher on lower / both, surface(s);
29. 8 calculate pair of stomatal densities (for 6/7); ecf
30. 9 no statistical analysis done ;
31. 10 data only, for one species / L. esculentum ;