Mass Transport in Humans

Question 1

Explain how an arteriole can reduce the blood flow into capillaries.

Answer 1

1. Muscle contracts

2. Constricts/narrows arteriole/lumen

Question 2

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

Answer 2

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

Question 3

Describe how the movement of the diaphragm leads to air movement into the lungs.

Answer 3

1. Diaphragm contracts and flattens.
2. Volume of lungs increases.
3. Pressure inside the lungs is lower than atmospheric pressure.
4. Air moves into the lungs.

Question 4

Describe and explain how the lungs are adapted to allow rapid exchange of oxygen between air in the alveoli and blood in the capillaries around them.

Answer 4

• Many alveoli/alveoli walls folded provide a large surface area
• Many capillaries provide a large surface area (so) fast diffusion
• Alveoli or capillary walls/epithelium/lining are thin/one cell thick/short distance between alveoli and blood;
• Flattened/squamous epithelium (so) short diffusion distance/pathway/fast diffusion
• Ventilation/circulation maintains a diffusion/concentration gradient so fast diffusion

Question 5

Describe the gross structure of human gas exchange system and how we breathe in and out.

Answer 5

-Named structures: trachea, bronchi, bronchioles, alveoli
-Above structures named in correct order
Breathing in: diaphragm contract and external intercostal muscles contract
-Volume increases and pressure decreases in thoracic cavity.
-Breathing out: diaphragm relaxes and internal intercostal muscles contract
-Volume decrease and pressure increase in thoracic cavity

Question 6

Describe the pathway taken by an oxygen molecule from an alveolus to the blood.

Answer 6

1. (Across) alveolar epithelium

2. Endothelium of capillary

Question 7

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. (6)

Answer 7

Elastic tissue:
1. Elastic tissue stretches under pressure/when heart contracts
2. Recoils/springs back
3. Evens out pressure/flow;
Muscle:
4. Muscle contracts
5. Reduces diameter of lumen/vasoconstriction/constricts vessel
6. Changes flow/pressure
Epithelium:
7. Epithelium smooth
8. Reduces friction/blood clots/less resistance

Question 8

The thickness of the aorta wall changes all the time during each cardiac cycle.
Explain why. (5)

Answer 8

1. (Aorta wall) stretches
2. Because ventricle/heart contracts/systole/pressure increases
3. (Aorta wall) recoils
4. Because ventricle relaxes/heart relaxes/diastole/pressure falls
5. Maintain smooth flow/pressure

Question 9

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

Answer 9

Formation:
1. High blood/hydrostatic pressure/pressure filtration
2. Forces water/fluid out
3. Large proteins remain in capillary
Return:
4. Low water potential in capillary/blood 
5. Due to (plasma) proteins
6. Water enters capillary/blood
7. (By) osmosis
8. Correct reference to lymph

Question 10

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

Answer 10

1. Smaller mammal has greater surface area to volume ratio
2. Smaller mammal/larger SA:Vol ratio, more heat lost (per unit body mass)
3. Smaller mammal/larger SA:Vol ratio, has greater rate of respiration/metabolism
4. Oxygen required for respiration
5. (Haemoglobin) releases more oxygen/oxygen released more readily/haemoglobin has lower affinity