What features does a good exchange surface have? 4

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