Fig. 2.1 is a diagram of the circulation in a mammal. [Figure 2.1] Fig. 2.2 is a transmission electron micrograph of a cross-section of an arteriole. Blood flows from muscular arteries through arterioles into capillary networks. The lining of the arteriole is folded because the arteriole has constricted. This constriction causes the blood pressure to decrease from 12.7 kPa in the muscular artery to 2.7 kPa at the end of the arteriole. [Figure 2.2]

Mark scheme

Marking points from the official mark scheme (May/June 2024). The mark or mark type is shown in brackets.

1. [3] any three from:
2. [3] 1 water is a, good / universal / AW, solvent ; A dissolves many substances / description of solvent action A solvent for / dissolves, (named) ions and (named) polar molecules
3. [3] 2 transport of one named substance for a correct reason ; e.g. urea for excretion
4. [3] 3 high specific heat capacity; A a full description e.g. the amount of heat that must be added to, one unit of mass of the substance / 1 gram or 1 cm³ of water, to increase the temperature by, one unit / 1 °C
5. [3] 4 so temperature of blood remains (fairly) constant / heat is dispersed throughout the body; must be linked to mp3 I temperature of water is constant
6. [3] AVP; e.g. water is (di)polar
7. [1] P - aorta A dorsal aorta
8. [1] Q - vena cava ; I superior and inferior
9. [2] 1 aorta / P, transports / delivers / AW, oxygenated blood to the, organs / body / respiring tissues / systemic circulation or aorta / P, transports / AW, blood at high pressure to, organs / body / respiring tissues / systemic circulation ;
10. [2] 2 vena cava / Q, transports / returns / AW, deoxygenated blood to the, right atrium / heart (from systemic circulation) or vena cava / Q, transports / AW, blood at low pressure to the, right atrium / heart ; A vena cava / Q, collects blood from, veins / systemic circulation
11. [2] alternative 3 aorta / P, transports oxygenated blood and, vena cava / Q, transports deoxygenated blood ;
12. [2] 4 blood in aorta to, organs / body / respiring tissues / systemic circulation, and blood in vena cava to, right atrium / heart ;
13. [2] closed blood is contained within vessels ; A at least three from heart, arteries / arterioles, veins / venules, capillaries
14. [2] double blood flows twice through the heart in, one / each, (complete), circuit/circulation (of the body) ; A pulmonary circulation and systemic circulation A described
15. [2] any two from:
16. [2] (blood at high pressure) will, burst / damage, capillaries ; A cannot withstand high pressure
17. [2] capillaries have thin walls / capillary walls are composed of one (thin) layer of (endothelial) cells ; A capillary walls are one cell thick R capillaries have cell walls
18. [2] idea that at low pressure blood flows slowly to allow, exchange / diffusion, of substances (in capillaries); A efficient exchange (of substances)
19. [2] AVP; e.g. idea that pressure will be low at venous end of capillaries so that tissue fluid is reabsorbed
20. [3] any three from: I functions
21. [3] similarities 1 (both have) endothelium / tunica intima; A tunica interna 2 (both have) tunica media / smooth muscle ;
22. [3] differences muscular artery – accept ora for arteriole 3 smaller lumen to wall thickness / ratio of wall thickness to lumen width is smaller ; A thicker wall ; I artery is 'bigger / thicker / wider', unqualified
23. [3] 4 wider lumen ;
24. [3] 5 more smooth muscle (layers) / thick (layer) v thin (layer), smooth muscle ; A thicker tunica media
25. [3] 6 more / presence of, elastic, fibres / tissue ; A no elastic lamina
26. [3] 7 more / presence of, collagen (fibres) ;
27. [3] 8 AVP; e.g. ref. to blood vessels in wall of artery (vasa vasorum) e.g. no vesicles in endothelium e.g. artery has, tunica externa / adventitia A tunica externa not (clearly) visible in arteriole