Mass Transport in Mammals (Haemoglobin & Cardiac Cycle) 3.4.1

Question 1

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

Answer 1

1. Higher affinity so associates/loads more oxygen;
2. At low/same/high partial pressure/pO2;
3. Oxygen moves from mother to foetus.

Question 2

Describe how haemoglobin normally loads oxygen in the lungs and unloads it in a tissue cell.

Answer 2

• Oxygen combines (reversibly) to form oxyhaemoglobin;
• Each haemoglobin molecule can transport 4 molecules of oxygen/8 atoms of oxygen;
• High partial pressure of O2 in lungs;
• Haemoglobin 95% saturated/almost 100%;
• Dissociates/Unloads at low partial pressure of O2 in tissues;
• Presence of CO2 displaces curve further to the right/increases oxygen dissociation;
• Allows more O2 to be dissociated;
• Increase in temperature/acidity allows more O2 to be dissociated;
• Low pO2/increased CO2 in respiring tissue.

Question 3

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

Answer 3

1. Presence of CO2 increases respiration;
2. Increased oxygen dissociation from haemoglobin;
3. (Because of) low partial pressure in tissues/plasma;
4. Oxygen diffuses from red blood cell to (respiring) tissues (high affinity)

Question 4

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 4

1. Higher affinity so associates/loads more oxygen (than Mother);
2. At low/same/high partial pressure;
3. Oxygen moves from mother to foetus (dependent on O2 from placental blood)

Question 5

Explain how oxygen is loaded, transported and unloaded in the blood (5)

Answer 5

1. Haemoglobin carries oxygen/has high affinity for O2;
2. Hb in red blood cells;
3. Association/loading in lungs at high partial pressure;
4. Unloads/dissociates to respiring tissues at low pO2;
5. Unloading linked to higher carbon dioxide concentration.

Question 6

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

Answer 6

Cooperative Loading:
1. Binding of first O2 molecule changes tertiary/quaternary structure of Hb (causes conformational change);
2. Leads to/uncovers second/another binding site
OR uncovers another iron/Fe/haem group to bind to.
(2nd, 3rd & 4th molecule associates more readily)

Question 7

Describe and explain the effect of increasing carbon dioxide concentration on the dissociation of oxyhaemoglobin (2)

Answer 7

1. Increases/more oxygen dissociation/decreases haemoglobin’s O2 affinity;
2. (By) decreasing (blood) pH/increasing acidity (carbonic acid)

Question 8

Describe how an arteriole can reduce the blood flow into capillaries

Answer 8

1. Muscle contracts;
2. Constricts/narrows lumen

Question 9

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

Answer 9

1. Atrium has higher pressure than ventricle (due to filling/contraction);
2. (so) Atrioventricular valve opens;
3. Ventricle has higher pressure than atrium (due to filling/contraction);
4. (so) Atrioventricular valve closes;
5. Ventricle has higher pressure than aorta;
6. (so) Semilunar valve opens;
7. Aorta has higher pressure than ventricle;
8. (so) Semilunar valve closes;
9. (Muscle/atrial/ventricular) contraction causes increase in pressure.

Question 10

Name 3 common features of the mammalian circulatory system (3)

Answer 10

1. Suitable medium for transport, water-based to allow substances to dissolve;
2. Means of moving the medium and maintaining pressure throughout the body, such as the heart;
3. Means of controlling flow so it remains undirectional, such as valves.

Question 11

Relate the structures of the chambers to their function (2)

Answer 11

1. Atria - thin-walled and elastic - stretch when filled with blood;
2. Ventricles - thick muscular walls - pump blood under high pressure, thicker than right to pump blood around the body.

Question 12

Relate the structures of vessels to their function

Answer 12

1. Arteries have thick walls to handle high pressure without tearing, and are muscular and elastic to control blood flow;
2. Veins have thin walls due to lower pressure, therefore requiring valves to ensure blood doesn’t flow backwards, less muscular and elastic tissue.

Question 13

Why are two pumps (left and right) needed instead of one?

Answer 13

• To maintain pressure around the body
• Blood passes through narrow capillaries of the lungs and causes pressure drop, returned to heart to be pumped around the body.

Question 14

Describe what happens during cardiac diastole

Answer 14

• Heart is relaxed;
• Increase in pressure as blood enters atrium;
• Atrioventricular valves open;
• Blood flows into ventricles;
• Pressure in heart lower than in arteries, so semilunar valves stay shut.

Question 15

Describe what happens during atrial systole

Answer 15

• Atria contract
• Blood is pushed into the ventricles

Question 16

Describe what happens during ventrical systole

Answer 16

• Ventricles contract;
• Pressure increases;
• Atrioventricular valves close to prevent backflow;
• Semilunar valves open;
• Blood flows into arteries

Question 17

Name the nodes involved in heart contraction and where they are situated (2) !!

Answer 17

1. Sinoatrial node (SAN) = wall of right atrium;
2. Atrioventricular node (AVN) = between the two atria.

Question 18

Describe what myogenic means (1)

Answer 18

Heart contraction is initiated by muscles, not nerves

Question 19

Explain how the heart contracts (3) !!

Answer 19

1. Sinoatrial node (SAN) initiates and sends impulse to atria to contract;
2. Atrioventricular node (AVN) recieves, delays and sends impulse down ‘bundle of his.’
3. Impulse travels to Purkinje fibres (branched across ventricles) so they contract (bottom-up)

Question 20

How are the structures of the capillaries suited to their function?

Answer 20

• Walls are one cell thick - short diffusion pathway;
• narrow - capillaries can permeate tissues and deliver oxygen;
• many capillaries and highly branched - large surface area.

Question 21

What is tissue fluid? (1)

Answer 21

A liquid containing glucose, amino acids, oxygen and nutrients - it is supplied to cells and removes waste materials.

Question 22

Describe how tissue fluid is formed and how it is returned to the circulatory system (6)

Answer 22

FORMED
1. Hydrostatic/high pressure of blood (in small vessels);
2. Forces tissue fluid out of capillary;
3. Large proteins remain in capillary;
RETURN
1. Low water potential in capillary
2. Due to plasma proteins;
3. Fluid enters capillary BY OSMOSIS;
4. Lymph fluid collects excess tissue fluid and deposits back into bloodstream (for recirculation).

Question 23

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

Answer 23

Elastic Tissue
1. Elastic tissue stretches under pressure/when heart contracts;
2. Recoils;
3. Evens out pressure/flow;

Muscle
1. Muscle contracts;
2. Reduces diameter of lumer/VASOCONSTRICTION;
3. Changes pressure/flow;

Epithelium
1. Smooth surface;
2. Reduces friction/blood clots/less resistance.

Question 24

The thickness of the aorta wall changes all the time during each cardiac cycle. Explain why (4)

Answer 24

1. Aorta wall stretches;
2. Because ventricle/heart contracts (systole) pressure increase;
3. Aorta wall recoils;
4. Because ventricle/heart relaxes (diastole) pressure decrease;
5. Maintains smooth flow/pressure

Question 25

Heat from respiration helps mammals to maintain a constant body temperature. Explain the relationship between the surface area to volume ratio of mammals and the oxygen dissociation curves of their haemoglobins (5)

Answer 25

1. Smaller mammal has greater SA:V ratio;
2. Larger mammal with smaller SA:V loses more heat;
3. Larger mammal has greater rate of respiration;
4. More oxygen required for respiration so O2 dissociates more readily.