Module 3 - Mass transport in animals

Question 1

3 marks

The oxygen dissociation curve for heamoglobin shifts right during vigorous exercise. Explain the advanatge of this shift

Answer 1

1. Low pH due to increased CO2/ increased respiration
2. Increased dissociation of haemoglobin
3. Oygen diffuses from r.b.c to tissues

Question 2

3 marks

How does exposure to CO affect loading and unloading of oxygen by haemologlobin

Answer 2

1. A low Po2 Hb exposed to CO has a higher affinity for oxygen than normal Hb
2. In respiring tissue its unloading less oxygen than it should
3. At high Po2 (lungs) it has a lower affinity for oxygen than normal Hb- only 50% saturation of the no CO Hb (less oxygen loaded at lungs)

Question 3

3 marks

Explain why the thickness of the aorta wall changes all the time during each cardiac cycle

Answer 3

1. Aorta wall stretches because ventricle contracts (pressure increases)
2. Aorta wall recoils because ventricle relaxes (pressure falls)
3. Maintain smooth flow / pressure

Question 4

What does atheroma lead to

Answer 4

Atheroma leads to blockage of coronary artery

Question 5

Name the type of blood vessel that controls blood flow to muscles and explain how these blood vessels change blood flow during exercise.

Answer 5

1. Arteriole;
2. (Circular/smooth) muscle relaxes;
3. Widens/dilates (lumen of) blood vessel so increases blood flow;

Question 6

2 marks

There is a small increase in pressure and in rate of blood flow in the aorta.
Explain how this happens and its importance.

Answer 6

1. Elastic recoil of the aorta wall
2. Smooths the blood flow

Question 7

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

Answer 7

Diameter of red blood cell

Question 8

2 marks

How is the pressure in the ventricle related to the thickness of ventricle wall

Answer 8

• Thickness of wall increases because ventricle wall contracts
• Contraction caused by increase in pressure

Question 9

3 marks

Explain why high blood pressure leads to the accumulation of tissue fluid

Answer 9

• High blood pressure (as ventricle contracts)= high hydrostatic pressure
• Increase in outward pressure from arteriole end of capillary
• So more tissue fluid formed

Question 10

3 marks

Why does venule end of capillary have lower blood plasma water potential

Answer 10

1. Water has left capillary
2. Proteins in blood too large to leave
3. Higher concentration of blood plasma proteins

Question 11

Why does carbonmonoxide kill people. Use loading and unloading of O2.

Answer 11

At low pO2, Hb exposed to CO has higher affinity for O2 than normal Hb
In respiring tissues it is unloading less O2 than it should
At high PO2, it has lower affinity for O2 than normal Hb- less O2 loaded to lungs

Question 12

6 marks

Explain how tissue fluid is formed and how it may be returned to the circulartory system

Answer 12

1. High hydrostatic pressure at arterial end
2. Soluble molecules pass out
3. Proteins remain - too large
4. This lower water potential at venule end
5. Water moves back into venule end via osmosis
6. Lymphatic system collects any excess tissue fluid which returns to blood

Question 13

2 marks

High absorption of salt from the diet can result in a higher than normal
concentration of salt in the blood plasma entering capillaries. This can lead to a build-up of tissue fluid. Explain how.

Answer 13

1. Higher salt results in higher blood pressure–> higher hydrostatic pressure
2. So more fluid forced out of arteriole end of capillary
   OR
3. Higher salt results in lower water potential of tissue fluid
4. So less water returns to capillary by osmosis at venule end

Question 14

6 marks

Explain how the structures of the walls of arteries, veins and capillaries are related to their functions.

Answer 14

Artery
1. thickest wall, enabling it to carry blood at high pressure / withstand pressure surges
2. most elastic tissue, which evens out pressure
3. most muscle which maintains pressure
4. muscle in wall to control blood flow
Vein
5. thin wall does not have to withstand high pressure
Capillary
6. thin wall, allowing diffusion
7. only endothelium present, allowing short diffusion pathway
All vessels
8. have endothelium that reduces friction

Question 15

Does artery or vein have larger lumen

Answer 15

Arteries have smaller lumens than veins

Question 16

3 marks

Explain how oxygen in a RBC is made available for respiration in active tissues

Answer 16

• Low pH due to increased CO2 due to increased respiration;
• Increased dissociation of haemoglobin
• Oxygen diffuses from r.b.c. to tissues

Question 17

2 marks

A decrease in the pH of blood plasma reduces the affinity of haemoglobin for oxygen.
Explain how aerobic respiration in cells leads to a change in the pH of blood plasma.

Answer 17

1. CO2 is produced
2. Forms carbonic acid
3. Hydrogen ions released

Question 18

2 marks

What is the advantage to tissue cells of a reduction in the affinity of haemoglobin for oxygen when the plasma pH decreases?

Answer 18

1. Low pH due to high rates of respiration
2. Cells need more oxygen
3. More oxygen released

Question 19

4 marks

Describe how oxygen in the air reaches capillaries surrounding alveoli in the lungs.
Details of breathing are not required.

Answer 19

1. Trachea and bronchi and bronchioles
2. Down pressure gradient
3. Down diffusion gradient
4. Across alveolar epithelium
5. Across capillary endothelium

Question 20

2 marks

The oxygen dissociation curve of the fetus is to the left of that for its mother. Explain the advantage of this for the fetus.

Answer 20

1. Higher affinity for oxygen at low partial pressure
2. Oxygen moves from mother to fetus

Question 21

5 marks

Explain how the heart muscle and the heart valves maintain a one-way flow of blood from the left atrium to the aorta.

Answer 21

1. Atrium has higher pressure than ventricle (due to contraction) causing atrioventricular valves to open
2. Ventricle has higher pressure than atrium (due to contraction) causing atrioventricular valves to close
3. Ventricle has higher pressure than aorta causing semilunar valve to open
4. Higher pressure in aorta than ventricle (as heart relaxes) causing semilunar valve to close
5. Contraction causes increase in pressure

Question 22

3 marks

The oxygen dissociation curve for haemoglobin shifts to the right during vigorous exercise.
Explain the advantage of this shift.

Answer 22

• Lower affinity for oxygen
• To muscles/tissues
• For high respiration

Question 23

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 23

1. Water has left the capillary
2. Proteins in blood too large to leave capillary
3. Increasing concentration of blood proteins

Question 24

2 marks

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

Answer 24

1. 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

Question 25

# 2 marks What is the function of the coronary arteries?

Answer 25

1. Carry oxygen 2. To heart muscles

Question 26

# 6 marks Arteries and arterioles take blood away from the heart. Explain how the structures of the walls of arteries and arterioles are related to their functions.

Answer 26

**Elastic tissue** 1. Elastic tissue stretches under pressure then recoils 2. Evens out pressure / flow **Muscle** 3. Muscle contracts to reduce diameter of lumen / vasoconstriction 4. Changes blood flow **Epithelium** 5. Epithelium smooth 6. Reduces friction

Question 27

# 2 marks Give two structural features of an aorta wall and explain how they are related to the function of an aorta.

Answer 27

1. Smooth muscle withstands high blood pressure 2. Elastic tissue stretches and recoils maintains/smooths blood pressure 3. Smooth endothelium reduces friction 4. Protein coat prevents artery wall splitting

Question 28

# 6 marks Explain how oxygen is loaded, transported and unloaded in the blood.

Answer 28

1) Haemoglobin carries oxygen / has a high affinity for oxygen / oxyhaemoglobin 2) In red blood cells 3) Loading/uptake/association in lungs 4) At high partial pressure of oxygen 5) Unloads/ dissociates / releases to respiring cells/tissues 6) at low partial pressure of oxygen 7) Unloading linked to higher carbon dioxide conc

Question 29

# 3 marks The oxygen dissociation curve of the foetus is to the left of that for its mother. Explain the advantage of this for the foetus.

Answer 29

1) Have a higher affinity / loads more oxygen 2) At low pO2 3) So oxygen moves from mother to fetus

Question 30

# 4 marks Explain how oxygen in a red blood cell is made available for respiration in active tissues.

Answer 30

1) Respiration increases carbon dioxide conc 2) So increases rate at which oxygen is dissociated 3) Low partial pressure of oxygen in tissues/plasma 4) So oxygen diffuses from red blood cells to tissues

Question 31

# 4 marks Describe and explain four ways in which the structure of a capillary adapts it for the exchange of substances between blood and the surrounding tissue.

Answer 31

1. permeable capillary wall 2. Thin epithelium walls, reduces diffusion distance 3. flattened endothelium cells, reduces diffusion distance 4. fenestrations, allows large molecules through 5. small diameter, gives a large surface area to volume / short diffusion distance 6. narrow lumen, reduces flow rate giving more time for diffusion 7. red blood cells in contact with wall- more time for diffusion

Question 32

# 3 marks Give the pathway a red blood cell takes when travelling in the human circulatory system from a kidney to the lungs. Do not include descriptions of pressure changes in the heart or the role of heart valves in your answer.

Answer 32

1. Renal vein 2. Vena cava to right atrium 3. Right ventricle to pulmonary artery

Question 33

# 1 mark Give one other way, besides ventillation, that helps to maintain the difference in oxygen concentration.

Answer 33

Ciculation of blood

Question 34

Equation for pulmonary ventillation

Answer 34

PV= breathing rate x tidal volume

Question 34

# 2 marks When a person starts to breathe out, the percentage of oxygen in the air first exhaled is the same as the percentage of oxygen in the atmospheric air. Explain why.

Answer 34

1. Air is dead space/ not from trachea/ bronchi 2. Gas exchange only in alveoli

Question 35

Equation for cardiac output

Answer 35

CO= breathing rate x stroke volume

Question 36

# 2 marks In healthy lungs, a gradient is maintained between the concentration of oxygen in the alveoli and the concentration of oxygen in the lung capillaries. Describe how ventilation helps to maintain this difference in oxygen concentration.

Answer 36

In alveolus 1. Brings in air containing a high(er) oxygen concentration; 2. Removes air with a low(er) oxygen concentration

Question 37

# 2 marks Binding of one molecule of oxygen to haemoglobin makes it easier for a second oxygen molecule to bind. Explain why.

Answer 37

1. Binding of first oxygen changes tertiary structure of haemoglobin 2. Creates another binding site