IB Biology HL B3.1.3 Maintaining Concentration Gradients Questions

Explore how oxygen partial pressure and ventilation or circulation determine the steep gradients that drive gas exchange in IB Biology HL B3.1.3.

Exam points

Explain how lower oxygen partial pressure at altitude reduces oxygen diffusion into blood.

[Maximum number: 3]

The graph shows the relationship between partial pressure of oxygen in air and altitude.

Altitude in metres plotted against partial pressure of oxygen in air in kPa. Labelled points mark the summit of Everest, highest human habitation, Pikes Peak, Denver and Ben Nevis.

Explain the consequence of high altitude for gas exchange in humans.

a. lower oxygen partial pressure reduces oxygen availability (for the blood);

b. less oxygen diffuses/is exchanged with the blood OR less oxygen diffuses across the alveolar membrane/alveoli;

c. less saturation of hemoglobin with oxygen;

d. more $\mathrm{CO}_{2}$ remains in the blood OR less $\mathrm{CO}_{2}$ is exhaled;

e. breathing rate/depth is increased (in the short term);

f. (to compensate for the lack of oxygen) the body will produce more erythrocytes/RBCs/hemoglobin;

Mp a: Do not accept lower oxygen concentration at high altitude. Partial pressure must be mentioned.

Mp c: Do not accept increased hemoglobin affinity for oxygen instead of saturation.

Mp d: Allow higher $\mathrm{CO}_{2}$ decreasing hemoglobin affinity for oxygen.

Marking guidance:

3 max

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IB Biology HL B3.1.3 Maintaining Concentration Gradients Questions question 1