Gas Exchange Practice Questions

Question 1

5 marks

The diagram shows an alveolus in a human lung and a blood capillary next to it. Gas A and gas B move between the air in the alveolus and the blood in the capillary.

(a)

Name gas A and gas B.

/ 2

(b)

Name the process by which gases A and B move between the alveolus and the blood.

/ 1

(c)

The wall of the alveolus is only one cell thick. Explain how this helps gas exchange.

/ 2

Question 2

4 marks

The alveoli in the lungs are adapted for efficient gas exchange.

Complete the table by writing in the four missing boxes (i), (ii), (iii) and (iv).

Adaptation of the alveoli	How the adaptation increases the rate of gas exchange
Very large total surface area	(i)
(ii)	Gases only have a short distance to diffuse across
Lining of the alveoli is moist	(iii)
Covered by a dense network of capillaries	(iv)

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Question 0

6 marks

The table shows the concentration of oxygen and carbon dioxide in the air in an alveolus and in the blood in the capillary next to it.

	Oxygen concentration / arbitrary units	Carbon dioxide concentration / arbitrary units
Air in the alveolus	14.0	5.3
Blood entering the capillary	5.3	6.1
Blood leaving the capillary	13.3	5.3

(a)

Use the data in the table to explain the direction in which oxygen and carbon dioxide diffuse across the alveolus wall.

/ 2

(b)

Explain how breathing in and out (ventilation) helps to keep the rate of gas exchange high.

/ 2

(c)

Explain how the continuous flow of blood through the capillary helps to keep the rate of gas exchange high.

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Question 0

5 marks

Emphysema is a lung disease in which the walls between neighbouring alveoli break down, so the lungs contain fewer, much larger air spaces.

The table shows data for a healthy adult and for an adult with emphysema.

	Healthy adult	Adult with emphysema
Total surface area of the alveoli / m $^2$	70	28
Thickness of the gas exchange surface / µm	0.6	0.6

(a)

Calculate the percentage decrease in the total surface area of the alveoli in the adult with emphysema.

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(b)

The adult with emphysema becomes very breathless when walking upstairs. Explain why, using the data in the table.

/ 3

Question 0

6 marks

Pulmonary fibrosis is a lung disease in which scar tissue builds up in the walls of the alveoli. In one patient, the thickness of the gas exchange surface increased from 0.6 µm to 3.0 µm. The total surface area of the alveoli did not change.

(a)

Calculate how many times thicker the patient's gas exchange surface is compared with a healthy gas exchange surface.

/ 1

(b)

Explain the effect of this change on the amount of oxygen entering the patient's blood.

/ 3

(c)

In a different lung condition, fluid leaks from the capillaries and collects inside the alveoli. Suggest why this also reduces the rate of gas exchange.

/ 2

Question 0

7 marks

Scientists are developing an artificial lung to be used by patients waiting for a lung transplant. Blood is pumped continuously through the device, and oxygen is passed over a thin artificial membrane.

The table shows data for two prototypes and, for comparison, for a pair of healthy human lungs.

	Surface area of gas exchange surface / m $^2$	Thickness of gas exchange surface / µm	Oxygen transferred to blood / cm $^3$ per minute
Prototype A	1.5	10.0	55
Prototype B	4.0	3.0	190
Human lungs	70.0	0.6	250

(a)

Calculate how many times greater the surface area of the human lungs is than the surface area of prototype B.

/ 1

(b)

Using the data in the table and your knowledge of how alveoli are adapted for gas exchange, explain why prototype B transfers more oxygen to the blood than prototype A, and suggest how the artificial lung could be improved further.

/ 6

Key Concepts in Biology

Cells & Control

Genetics

Natural Selection & Genetic Modification

Health, Disease & the Development of Medicines

Plant Structures & their Functions

Animal Coordination, Control & Homeostasis

Exchange & Transport in Animals

Ecosystems & Material Cycles

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