mass transport in humans

Question 1

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

Answer 1

. Muscle contracts;
. 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 / (So) fast diffusion;
. Ventilation / circulation; So 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
OR
Above structures labelled in correct positions on a diagram
. 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;