1. What features does a good exchange surface have? 4

2. Large sa
Thin barrier
Fresh supply of molecules
Removal of molecules

3. How are the lungs adapted for gas exchange? 5

4. Large sa
Permeable plasma membrane of cells in alveoli
Thin barrier- alveoli wall one cell thick
Thin capillary wall
Diffusion gradient maintained by breathing and blood movement to and from lungs

5. How is a diffusion gradient maintained in the lungs? 2

6. Breathing replenishes oxygen concentration in alveoli
Heart pumps blood away from lungs lowering oxygen content in capillaries

7. Describe the role of cartilage, smooth muscle, elastic fibres, goblet cells and ciliated epithelium 5

8. Cartilage: structural, prevents collapse with pressure changes
Smooth muscle: contracts to make lumen narrower
Elastic fibres: elastic recoil after smooth muscle has contracted
Goblet cells: secrete mucus
Ciliated epithelium: move in synchronised pattern to waft mucus up airway

9. Explain how size, surface area to volume ratio and level of activity affect the need for a transport system 3

10. Size: bigger = more need for exchange surface
Sa: smaller = more need for exchange surface
Level of activity: more = more need for exchange surface

11. Explain the differences between single and double circulatory systems 3

12. Single = blood goes through heart once with each circuit of the body
Double = systemic and pulmonary circulation.
Blood visits heart twice with each circuit through the body

13. Describe the advantages of a double circulatory system 2

14. Increased pressure, so blood flows faster
Systemic circulation can carry blood at higher pressure than pulmonary circulation

15. Explain the role of the valves and the septum 2

16. Valves prevent backflow
Septum prevents oxygenated and non-oxygenated blood from mixing

17. Outline the stages in the cardiac cycle 3

18. Filling phase: diastole, all parts are relaxed, atrioventricular valves are open
Atrial systole: atria contract pushing blood into ventricles, semi lunar valves are closed
Ventricular systole: ventricles contract, atrioventricular valves close, semi-lunar valves open

19. Describe how valves work 3

20. Pressure in ventricles drops below atria
Atrioventricular valves open
Ventricle fills with blood and increase in blood pressure fills the valve pockets and closes atrioventricular valves

21. Explain how heart action is co-ordinated 5

22. SAN generates electrical activity
Spreads over atrial walls causing contraction
AVN delays the signal
Passes it down purkyne tissue
Up from the base of the heart causing ventricles to contract

23. Explain the differences between open and closed circulatory systems 2

24. Open: blood is not contained in vessels, in insects it enters heart through ostia and blood is pumped by peristalsis
Closed: blood is contained in vessels

25. Describe the structure of arteries, veins and capillaries 3

26. Arteries: small lumen, thick wall, elastic fibres, smooth muscle, contains collagen
Veins: large lumen, inner layers of collagen, smooth muscle, elastic tissue, no stretch or recoil, valves
Capillaries: thin walls, single layer of cells, narrow lumen

27. Outline the role of blood, tissue fluid and lymph 3

28. Blood: transport oxygen, hormones and carbon dioxide
Tissue fluid: plasma with dissolved nutrients and oxygen, speeds up diffusion
Lymph: contains lymphocytes and filter bacteria and foreign materials for destruction

29. Explain how tissue fluid and lymph are formed 2

30. Tissue fluid: high hydrostatic pressure pushes blood fluid out of the capillaries through tiny gaps
Lymph: some tissue fluid is drained into lymphatic vessels

31. Describe the role of haemoglobin in carrying oxygen 4

32. 4 subunits
Haem contains one iron atom
Haem has affinity for oxygen
Oxyhaemoglobin releases oxygen= dissociation

33. Explain the oxygen dissociation curve and explain why the curve for fetal haemoglobin is different 2

34. Oxygen dissociation: S shaped curve, as oxygen tension rises, more haemoglobin is saturated, then curve levels off
Fetal haemoglobin has a higher affinity so that it can absorb oxygen from mothers blood

35. How are hydrogencarbonate ions formed? 3

36. CO2 combines with water to make carbonic acid
Carbonic acid dissociates to release hydrogen ions and hydrogencarbonate ions
They diffuse out of the red blood cells into the plasma

37. What is the chloride shift? 1

38. Chloride ions (negative) move from plasma into the red blood cells, to maintain the charge as negative hydrogencarbonate ions have left

39. Outline the Bohr effect 3

40. Hydrogen ions released from dissociation of carbonic acid
Hydrogen ions displace the oxygen in haemoglobin
Oxyhaemoglobin releases more oxygen to tissues

41. Describe the distribution of xylem and phloem in the root, stem and leaf 3

42. Root: x shaped xylem
Stem: xylem and phloem in circles near outside of stem
Leaf: xylem above phloem

43. Outline the structure of xylem and phloem

44. Xylem: continuous column, dead cells, lignified, pits
Phloem: sieve tube elements, companion cells, perforated sieve tubes

45. Describe the meaning of water potential and how it affects a plant cell

46. Water potential is the movement of water down a concentration gradient: affected by pressure and solutes
Plasmolysed, turgid, flaccid

47. Outline how water can move between cells

48. Apoplast: between cell walls
Symplast: through plasma membrane
Vacuolar: through cytoplasm and vacuole

49. Explain how water moves up the stem

50. Cohesion-tension theory
Transpiration pull and capillary action

51. Outline the factors that affect the rate of transpiration (8)

52. Number of leaves
Number of stomata
Cuticle,
Light
Temp
Humidity
Air movement
Water availability

53. How do plants cope in arid conditions (how are they adapted?)

54. Rolled leaf
Thick cuticle
Trapped air inside rolled leaf
Hairs on lower surface
Stomata in pits

55. Explain how sugars are transported along the phloem tissue 2

56. Translocation
from source to sink

57. Explain the meaning of sources and sinks with examples of each

58. Source: loads sucrose
Sink: uses/stores sucrose
Leaf/root