3.3.4.1 Mass transport in animals

Question 1

How many oxygen molecules can each haemoglobin molecule carry?

Answer 1

Each haemoglobin molecule can carry four oxygen molecules.

Question 2

Where in the body would you find a low partial pressure of oxygen?

Answer 2

Respiring tissues

Question 3

Why are oxygen dissociation curves S-shaped?

Answer 3

• When haemoglobin (Hb) combines with the first O₂ molecule, its shape alters in a way that makes it easier for other molecules to join too.
• But as the Hb starts to become saturated, it gets harder for more oxygen molecules to join.

Question 4

Haemoglobin is a protein with a quarternary structure.
Explain what this means.
[1 mark]

Answer 4

It is composed of more than one polypeptide chain.

Question 5

Haemoglobin has a high affinity for oxygen. Explain what this means.

Answer 5

‘Affinity’ for oxygen means ‘tendency to combine with’ oxygen.

Question 6

When is oxyhaemoglobin formed?

Answer 6

Oxyhaemoglobin is formed in the lungs when oxygen joins to haemoglobin in red blood cells.

Question 7

What is partial pressure of oxygen (pO₂)?

Answer 7

A measure of oxygen concentration.

Question 8

When does haemoglobin give up its oxygen more readily?

Answer 8

Haemoglobin gives up its oxygen more readily at higher partial pressures of carbon dioxide (pCO₂).

Question 9

• When cells respire they produce __________, which raises ________.
• This increases the rate of _____ _____, so the dissociation curve ‘shifts’ _____.
• The saturation of blood with oxygen is lower for a given pO₂, meaning that _____ _____ is being released.

Answer 9

• When cells respire they produce carbon dioxide, which raises pCO₂.
• This increases the rate of oxygen unloading, so the dissociation curve ‘shifts’ right.
• The saturation of blood with oxygen is lower for a given pO₂, meaning that more oxygen is being released.

Question 10

What affects oxygen unloading?

Answer 10

Carbon dioxide concentration.

Question 11

Organisms that live in environments with a low concentration of oxygen have haemoglobin with a __________ for oxygen than human haemoglobin.

Answer 11

Organisms that live in environments with a low concentration of oxygen have haemoglobin with a higher affinity for oxygen than human haemoglobin.

Question 12

Organisms that are very active and have a high oxygen demand have haemoglobin with a __________ for oxygen than human haemoglobin.

Answer 12

Organisms that are very active and have a high oxygen demand have haemoglobin with a lower affinity for oxygen than human haemoglobin.

Question 13

Name all the blood vessels entering and leaving the heart.

Answer 13

• Pulmonary vein (oxygenated blood to the heart)
• Pulmonary artery (deoxygenated blood to lungs)
• Aorta (oxygenated blood to the body)
• Vena Cava (deoxygenated blood to the heart)

Question 14

List four types of blood vessel.

Answer 14

• Arteries
• Arterioles
• Veins
• Capillaries

Question 15

Explain why water returns to the capillary at the venule end of the capillary bed.

Answer 15

• The water potential at the venule end is lower than the water potential in the tissue fluid…
• …due to the fluid loss and an increasing concentration of plasma proteins in the capillaries.
• This means that some water re-enters the capillaries at the venule end by osmosis.

Question 16

Describe two structural features of an artery and explain how each feature relates to its function.
[4 marks]

Answer 16

• They have elastic tissue in the walls…
• …so they can stretch and recoil as the heart beats, which helps maintain the high pressure.
• The inner lining (endothelium) is folded…
• …so that the artery can expand when the heartbeat causes a surge of blood.

Question 17

At the arteriole end of the capillary bed, the hydrostatic pressure is 5.1 kPa in a capillary bed and 0.13 kPa in the space around the cells.
Explain the effect this has on the movement of fluid between the capillary and cell space.
[2 marks]

Answer 17

• The hydrostatic pressure in the capillary is greater than the hydrostatic pressure in the spaces around the cells,…
• …so fluid moves out of the capillary and into spaces around the cells.

Question 18

Describe a structural feature of a vein and explain how the feature relates to its function.

Answer 18

• Veins contain valves…

- …to stop the blood flowing backwards.

Question 19

What are arterioles?

Answer 19

Arterioles are smaller arteries that control blood flow from arteries to capillaries.

Question 20

How are capillaries adapted for efficient diffusion?

Answer 20

• They’re always found near cells in exchange tissues, so there’s a short diffusion pathway.
• Their walls are only one cell thick, which also shortens the diffusion pathway.
• There are a large number of capillaries, to increase surface area for exchange.

Question 21

Which side of the heart carries oxygenated blood?

Answer 21

The left side pumps oxygenated blood to the whole body.

Question 22

Explain the purpose of the semi-lunar valves.

Answer 22

The semi-lunar valves stop blood flowing back into the heart after the ventricles contract.

Question 23

Name the blood vessel that carries blood from the lungs to the heart.

Answer 23

Pulmonary vein

Question 24

Give three factors that can increase the risk of developing cardiovascular diseases.

Answer 24

• High blood cholesterol and poor diet
• Cigarette smoking
• High blood pressure

Question 25

The results of a study involving 168,000 people in 63 countries have shown a strong correlation between waist measurement and risk of cardiovascular disease. Analysis of the results has shown that waist circumference is independently associated with cardiovascular disease.
Give two reasons why the study provides strong evidence for a link between waist measurement and risk of cardiovascular disease.
[2 marks]

Answer 25

• A large sample size was used.

- The sample included many countries.

Question 26

The results of a study involving 168,000 people in 63 countries have shown a strong correlation between waist measurement and risk of cardiovascular disease. Analysis of the results has shown that waist circumference is independently associated with cardiovascular disease.
Suggest why waist measurement might be related to risk of cardiovascular disease.
[3 marks]

Answer 26

• A large waist measurement could indicate that someone is overweight.
• Being overweight can be linked to high blood pressure.
• High blood pressure is a risk factor for cardiovascular disease because it increases the risk of damage to artery walls.

Question 27

What is Atheroma?

Answer 27

A fibrous plaque caused by the hardening and build up of white blood cells, lipids and connective tissue.

Question 28

How does Atheroma formation affect the arteries?

Answer 28

It partially blocks the lumen of the artery and restricts blood flow, which causes blood pressure to increase.

Question 29

What are the two types of disease that affect the arteries?

Answer 29

Aneurysm and Thrombosis.

Question 30

What is an Aneurysm?

Answer 30

An aneurysm is a balloon-like swelling of the artery.

Question 31

What is Thrombosis?

Answer 31

Thrombosis is the formation of a blood clot in the artery.

Question 32

What is a cardiac cycle?

Answer 32

The cardiac cycle is an ongoing sequence of contraction and relaxation of the atria and ventricles that keeps blood continuously circulating round the body.

Question 33

Explain the role of the heart in the formation of tissue fluid.
[2 marks]

Answer 33

• Contradiction of ventricles produce high blood/hydrostatic pressure.
• (This) forces water (and some dissolved substances) out (of blood capillaries).

Question 34

Lymphoedema is a swelling in the legs which may be caused by a blockage in the lymphatic system.
Suggest how a blockage in the lymphatic system could cause lymphoedema.
[1 mark]

Answer 34

Excess tissue fluid cannot be (re)absorbed/builds up.

Question 35

Explain how changes in the shape of haemoglobin result in the S-shaped (sigmoid) oxyhaemoglobin dissociation curve for Hb.
[2 marks]

Answer 35

• First oxygen binds (to Hb) causing a change in shape.

- (Shape change of Hb) allows more O₂ to bind (easily).