mass transport in animals

Question 1

(a) What was the range of the resting heart rates in males after the exercise programme?
(b) Calculate the percentage decrease in the mean resting heart rate of females after the exercise programme. Show your working.

Answer 1

(a) 53−70 / 70-53 / 17 (beats per minute)
(b) 13.6 / 13.58 / 14;

Question 2

The scientists used the percentage change in the mean resting heart rate after the exercise programme to compare the results for males and females. Explain why they used percentage change in the resting heart rate.

Answer 2

1. Allows comparison;
2. (Initial / resting) heart rates different (between males and females).

Question 3

The scientists calculated the cardiac output of the volunteers before and after the exercise programme. In some volunteers, their cardiac output stayed the same, even though their resting heart rate decreased. Explain how their cardiac output could stay the same even when their resting heart rate had decreased.

Answer 3

1. Cardiac output = stroke volume × heart rate
2. (So) stroke volume increases / increased size or volume of ventricles.

Question 4

What is the function of the coronary arteries?

Answer 4

1. (Carry) oxygen / glucose;
2. (To) heart muscle / tissue / cells / myocytes.

Question 5

The rise and fall in blood pressure in the aorta is greater than in the small arteries.Suggest why.

Answer 5

1. (is) close / directly linked to the heart / ventricle / pressure is higher / is very high;
2. (Aorta has) elastic tissue;
3. (Aorta has) stretch / recoil.

Question 6

Although the speed of blood flow in an arteriole is greater than speed of blood flow in a capillary, blood does not accumulate in the arterioles. Explain why.

Answer 6

1. Many / more capillaries (than arterioles);
2. (Cross-sectional) area of capillaries (much) greater (than of arterioles).

Question 7

Other than causing slow blood flow, explain one advantage of capillaries being narrow.

Answer 7

1. Short pathway / short distance between blood and outside of capillary;
2. Large surface area (of blood) in contact with walls of capillaries;
3. Fast exchange / fast diffusion / fast osmosis.

Question 8

What factor limits the minimum internal diameter of the lumen of a capillary?

Answer 8

Width / size / diameter of blood cell.

Question 9

A principle of homeostasis is the maintenance of a constant internal environment. An increase in the concentration of carbon dioxide would change the internal environment and blood pH. Explain the importance of maintaining a constant blood pH.

Answer 9

(Maintaining constant pH to avoid)

1. Named protein / enzyme (in blood) sensitive to / affected by change in pH;
2. (Resultant) change of charge / shape / tertiary structure;

The change in charge idea relates to the enzyme / protein and not the blood (plasma) or red blood cells.

3. Described effect on named protein or enzyme. e.g. less oxygen binds with haemoglobin / less transport across membranes / fewer substrates can fit active site / fewer enzyme-substrate complexes.

Question 11

Use the information in the figure above to explain how tissue fluid is formed.

Answer 11

1. (Overall) outward pressure of 3.2 kPa;
2. Forces small molecules out of capillary.

Question 12

(b) The hydrostatic pressure falls from the arteriole end of the capillary to the venule end of the capillary. Explain why.
(c) High blood pressure leads to an accumulation of tissue fluid. Explain how.

Answer 12

(b) Loss of water / loss of fluid / friction (against capillary lining).
(c) 1. High blood pressure = high hydrostatic pressure;
2. Increases outward pressure from (arterial) end of capillary / reduces inward pressure at (venule) end of capillary;
3. (So) more tissue fluid formed / less tissue fluid is reabsorbed.

Question 13

The water potential of the blood plasma is more negative at the venule end of the capillary than at the arteriole end of the capillary. Explain why.

Answer 13

1. Water has left the capillary;
2. Proteins (in blood) too large to leave capillary;
3. Increasing / giving higher concentration of blood proteins (and thus wp).

Question 14

(a) Use information from the figure to explain how the pressure in the dog’s ventricle is related to blood flow into the aorta.
(b) Use information from the figure to explain how the pressure in the dog’s ventricle is related to the thickness of the ventricle wall.

Answer 14

(a) 1. Ventricle pressure rises then blood starts to flow into aorta because pressure causes (aortic / semilunar) valve to open;
2. Ventricle pressure starts to fall so blood flow falls; Idea of sequence is essential
(b) 1. Thickness of wall increases because ventricle (wall) contracts;
2. Contraction causes the increase in pressure;

Question 15

Use the figure to calculate the heart rate of the dog in beats per minute. Show your working.

Answer 15

1. Between 120 ± 5;

Length of cycles varies slightly

2. Length of cardiac cycle correct but final answer wrong;

Length of cardiac cycle = 0.45 - 0.52