Fig. 2.1 is a photomicrograph showing a transverse section through a bronchus and the surrounding lung tissue. [Figure 2.1]

Mark scheme

Marking points from the official mark scheme (May/June 2019). The mark or mark type is shown in brackets.

1. [2] correctly stated formula ;
2. e.g. actual diameter = image length / magnification
3. magnification = image length / actual diameter
4. allow a magnification triangle
5. 1750 (µm); (for 70 mm) credit also measurements made to 0.5 mm
6. Α 1700 (μm) (for 68 mm)
7. Α 1725 (μm) (for 69 mm)
8. A 1775 (μm) (for 71 mm)
9. Α 1800 (μm) (for 72 mm)
10. [1] squamous epithelial (tissue); A pavement epithelial (tissue)
11. [2] any two from:
12. (alveoli have) thin wall / wall is one cell thick; A wall composed of thin cells
13. idea of short diffusion distance;
14. R thin membrane R thin cell wall
15. in context of between alveolar space and, blood / capillary
16. elastic tissue, qualified; A elastin / elastic fibres
17. e.g. stretch and recoil for, ventilation / inhalation and exhalation
18. maintaining steep, diffusion / partial pressure, gradient
19. (many) alveoli provide a large surface area (for diffusion) ;
20. I idea that a single alveolus has a large surface area
21. AVP; surfactant, prevents alveolar collapse / maintains inflation
22. I ref. to moist lining
23. [3] any three from:
24. 1 loosely packed spongy mesophyll cells / spongy mesophyll cells surround air spaces / air spaces between spongy mesophyll cells ;
25. 2 large, surface / area, for evaporation (of water to air space) ;
26. In context of spongy mesophyll cells, surfaces / cell walls
27. 3 (cells arranged so that), air spaces above the stomata / sub-stomatal air spaces;
28. 4 ref. to evaporation creates saturated air spaces / water vapour collects in air spaces;
29. 5 idea of creates water potential gradient between air in air spaces and air in external environment;
30. 6 AVP; e.g. guard cells situated in epidermis to form stomatal pore
31. ref. to xylem, close proximity to spongy mesophyll cells for passage of water / passes on water to spongy mesophyll cells
32. [3] accept au for arbitrary units and first hour etc. for 08.00 etc.
33. any three from:
34. 1 between 08.00 and 09.00, steep increase / increase from 2.5 au to 5 au ;
35. 2 highest rate / peak, at 09.00 ; A maximum rate is at 09.00
36. 3 fluctuates / AW, between 10.00 and 15.00 ;
37. 4 (continued) decrease between 15.00 and 19.00;
38. A steep /steepest, decrease between 15.00 and 16.00
39. A less steep (than 15.00 to 16.00) decrease between 16.00 and 19.00
40. 5 comparative data quote for decrease; e.g.
41. 3.8 au at 15.00 to 0.5 au at 19.00
42. or
43. 3.8 au at 15.00 to 2.00 au at 16.00
44. or
45. 2.0 au at 16.00 to 0.5 au at 19.00
46. [2] any two from:
47. change in external environmental factor
48. decrease in light intensity / AW ; A (less sunlight because it was) cloudy
49. decrease in temperature / AW ; temperature decreased because it was cloudy is mp2 only
50. decrease in, wind speed / air movement / AW ;
51. increase in humidity / raining / AW ;
52. stomata, decrease in (aperture) size / open less wide ;
53. decreased evaporation (rate);
54. water vapour diffuses out less rapidly / less steep water potential gradient ; AW
55. AVP; e.g. suggestion of xerophytic feature occurring in response to increased, temperature / light intensity (to 09.00)