Question 1
Paper 1A style
Fenestrated capillaries are found in the glomerulus of the kidney. What is the advantage of fenestrations?
- They prevent blood cells from leaving the capillary
- They allow particularly rapid exchange of fluid and solutes
- They increase blood pressure in the capillary
- They prevent backflow of blood
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Answer: B [1]
Question 2
Paper 2A style
Distinguish between the structure of arteries and veins, relating each difference to function.
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- arteries have thicker walls relative to the lumen / veins thinner walls [1]
- artery walls withstand high pressure [1]
- arteries have more elastic fibres which stretch and recoil to maintain pressure/even out flow [1]
- arteries have more smooth muscle to narrow the lumen/maintain pressure [1]
- veins have valves to prevent backflow at low pressure [1]
- veins have wider lumen / flexible walls compressed by skeletal muscle to push blood to heart [1]
- max 4
Question 3
Paper 2A style
A student counted her radial pulse for 20 s three times and got 24, 26 and 25 beats. Calculate her mean heart rate in beats per minute and state why she should use her fingertips rather than her thumb.
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- mean = 25 beats per 20 s, so 25 × 3 = 75 beats per minute [1]
- the thumb has its own pulse, which could be counted by mistake [1]
Question 4
Paper 1B style
A study recorded mean daily saturated fat intake and deaths from coronary heart disease (CHD) in six populations. The correlation coefficient was r = +0.98. (a) Describe the relationship shown. (b) Explain how a high saturated fat intake could lead to occlusion of a coronary artery. (c) Evaluate whether the data show that saturated fat causes CHD.
| Population | Saturated fat / % of energy intake | CHD deaths per 100 000 per year |
|---|---|---|
| 1 | 7 | 60 |
| 2 | 9 | 95 |
| 3 | 11 | 140 |
| 4 | 13 | 150 |
| 5 | 15 | 230 |
| 6 | 17 | 240 |
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- (a) positive correlation: as saturated fat intake increases, CHD deaths increase [1]
- (a) strong correlation, as r is close to +1 [1]
- (b) raises blood cholesterol which forms fatty deposits/plaque in coronary artery walls, narrowing lumen [1]
- (b) plaque rupture leads to a blood clot that blocks the artery [1]
- (c) correlation does not prove causation [1]
- (c) other factors could differ between populations, e.g. smoking, exercise, genetics, age / only six populations [1]
- max 5
Question 5
Paper 2B style
Explain how water is transported from the roots to the leaves of a plant during transpiration.
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- water evaporates from (spongy mesophyll) cell walls and diffuses out through stomata [1]
- water drawn from xylem/through cell walls by capillary action/adhesion to cellulose [1]
- generates tension/negative pressure potential in xylem [1]
- tension pulls water up xylem [1]
- cohesion between water molecules due to hydrogen bonding [1]
- keeps a continuous column of water [1]
- adhesion of water to xylem walls [1]
- xylem has no cell contents/end walls so flow is unimpeded [1]
- lignified walls prevent collapse under tension [1]
- pits allow water to enter/leave xylem [1]
- passive process / energy from evaporation (sun), not ATP [1]
- max 6