Mass transport in animals

Question 1

Give the pathway a red blood cell takes when travelling in the human circulatory system from a kidney to the lungs. (3)

Answer 1

• through renal vein
• into vena cava to right atrium
• into right ventricle and up pulmonary artery

Question 2

Describe the advantage of the Bohr effect during intense exercise. (2)

Answer 2

1. Increases dissociation of oxygen; / unloading of O2
2. For aerobic respiration at the tissues/muscles/cells

Question 3

What is the consequence of having too high haematocrit in blood? (4)

(too many RBC’s)

Answer 3

• thickens blood
• slows blood flow
• could cause clots
• could block coronary arteries

Question 4

Why is the O2 dissasociation curve an S shape?

Answer 4

• It is difficult for the haemoglobin to pick up the first O2 molecule.
• Binding of the first O2 changes the tertiary structure of the haemoglobin.
• This uncovers another heam group for O2 to binding to.
• So hemoglobin’s affinity for oxygen increases.
• This makes it easier to pick up the next two oxygen molecules.
• This is called cooperative binding.

Question 5

Gas exchange for the fetus occurs in the placenta.
Describe how the composition of blood in the pulmonary artery of a fetus is different from the composition of blood in the pulmonary artery of its mother.
Give one reason for this difference. (2)

Answer 5

1. Fetal blood has more oxygen
   ..
2. (Because) gas exchange occurs in the placenta
   OR
   Gas exchange does not occur in (fetal) lungs;

Question 6

Explain how water from tissue fluid is returned back to the circulatory system: (4)

Answer 6

1. (Plasma) proteins remain;
2. Reduces water potential (of blood);
3. Water moves (to blood) by osmosis;
4. Returns (to blood) by lymphatic system;

Question 7

cardiac output

Answer 7

heart rate x stroke volume

Question 8

The rise and fall in blood pressure in the aorta is greater than in the small arteries. Suggest why. (3)

Answer 8

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

Question 9

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. (2)

Answer 9

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

Question 10

Other than causing slow blood flow, explain one advantage of capillaries being narrow. (3)

Answer 10

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 11

Explain how blood in a vein in the leg is returned to the heart (6)

Answer 11

1. Muscles (surrounding veins) contract and press on (walls of) vein and squeezes blood along veins;
2. Valves prevent backflow
3. contraction of heart pumps blood (through arteries) into veins
4. Recoil of heart muscle during diastole / after contraction;
5. Draws blood from veins into atria;
6. Wide lumen little resistance / friction

Question 12

Species A and B live in the same place but B is more active.
Suggest an advantage to B of having an oxygen haemoglobin dissociation curve to the right of that for A.

Answer 12

• fish B has greater rate of respiration
• so more o2 supplied