mass transports 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;
   Points 1, 3, 5, and 7 must be comparative: eg higher
6. Semilunar valve opens;
   Marks 2, 4, 6, 8 given in the correct sequence can gain 4 marks
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
  o OR
  o 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

the flow of the heart

Answer 9

deoxygenated blood
vena cava
right atrium
atrioventricular valve
right ventricle
semi lunar valve
pulmonary artery

oxygenated blood
pulmonary vein
left atrium
atrioventricular valve
left ventricle
semi lunar valve
aorta