Human gas exchange

Question 1

Explain why ventilation of the lungs increases the efficiency of gas exchange.

Answer 1

Brings more oxygen/removes carbon dioxide;

Maintains diffusion/concentration gradients;

Between alveoli and blood/capillaries;

Question 2

Data like these are often given as percentages of people dying from each cause.

Explain the advantage of giving these data as percentages.

Answer 2

easier to compare if sample size effectively the same;
different numbers of people in each group;

Question 3

Risk Factor

Probability (P value)

Obese

< 0.001

Burned wood indoors

= 0.06

Lived with a cat or dog

< 0.05

A student who looked at these results concluded that all three risk factors are linked with asthma. Evaluate this conclusion.

Answer 3

In support

1. (Link/risk with asthma and) living with cat or dog is (statistically) significant;
2. (Link with) obesity is most/highly significant;

Reject ‘results are significant’

Not supported

3. (Link/risk with asthma and) burned wood (indoors) is not (statistically) significant;

Accept ‘due to chance’ for ‘not significant’ and converse

Question 4

Particulate matter is solid particles and liquid particles suspended in air. Polluted air contains more particulate matter than clean air.

A high concentration of particulate matter results in the death of some alveolar epithelium cells. If alveolar epithelium cells die inside the human body they are replaced by non-specialised, thickened tissue.

Explain why death of alveolar epithelium cells reduces gas exchange in human lungs.

Answer 4

Reduced surface area;

2. Increased distance for diffusion;

Accept description of efficient gas exchange in healthy alveolar epithelium as long as reference made to the damaged tissue changing this.

3. Reduced rate of gas exchange;

Question 5

Do the data in the graph above show a linear relationship between concentration of particulate matter and percentage of dead cells?

Use suitable calculations to justify your answer.

Answer 5

(No)

EITHER

1. 9 (percent per 5 µg cm–3);
2. 1.42/1.8 (percent per 5 µg cm–3);

Question 6

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

Answer 6

(Across) alveolar epithelium;

2. Endothelium / epithelium of capillary;