Predicting Gas Exchange

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📚 Part 1: Multiple Choice (Choose one)

1. Given alveolar PO2 = 13 kPa and pulmonary capillary PO2 = 6 kPa, which best describes oxygen movement?

Oxygen diffuses from alveolus into blood (capillary).

Oxygen diffuses from blood into alveolus.

No net oxygen movement — equilibrium.

Carbon dioxide diffuses from alveolus into blood instead.

2. Muscle tissue PCO2 = 6.5 kPa and nearby systemic capillary PCO2 = 5.0 kPa. What happens to carbon dioxide?

CO2 diffuses from muscle into the capillary.

CO2 diffuses from capillary into the muscle.

CO2 movement depends only on blood flow, not partial pressure.

No net CO2 movement because of active transport mechanisms.

3. During intense exercise, which change increases oxygen unloading to muscles?

Muscle PO2 decreases, increasing the diffusion gradient for O2 into muscle.

Arterial PO2 increases, reducing oxygen unloading to muscle.

Alveolar PO2 rises, causing O2 to move out of blood into alveoli.

Capillary PCO2 falls, which forces CO2 into muscle cells.

4. If a person travels to high altitude where alveolar PO2 is lower, which is a likely immediate effect on gas exchange?

Reduced diffusion of O2 from alveoli to blood; potential hypoxia in tissues.

Increased O2 diffusion into blood because capillaries adapt instantly.

CO2 diffusion reverses direction at the alveolar surface.

No change in gas exchange unless temperature falls below 0 °C.

✏️ Part 2: Short Answer — Data interpretation

Use the data below for Questions 5–7.

Dataset: Alveoli — PO2 13.0 kPa, PCO2 5.0 kPa. Pulmonary (incoming venous) capillary — PO2 5.0 kPa, PCO2 6.0 kPa. Muscle tissue — PO2 2.0 kPa, PCO2 7.0 kPa.

5. Between alveoli and pulmonary capillary: Predict the direction of O2 and CO2. Briefly justify using partial pressures (one sentence each).

6. Between systemic capillary (after oxygenation) and muscle tissue: Predict the direction of O2 and CO2. Write your prediction and a short explanation referencing diffusion gradients.

7. Explain in 2–3 sentences how the concept of partial pressure and diffusion explains gas exchange in both examples above. Use at least two scientific terms from the word bank.

8. Challenge: How would intense exercise (muscle PO2 falls to 1.0 kPa and PCO2 rises to 9.0 kPa) change the directions and rates of gas exchange? Give one physiological reason for the change.

✅ Success Criteria, Scaffolds & Extension

Success criteria (I can...):

- interpret PO2 and PCO2 values to predict gas movement between compartments; _________

- justify predictions using the terms diffusion, partial pressure, alveoli, capillary; _________

- explain how exercise or altitude affects gas exchange. _________

Scaffolding & Differentiation strategies

- Sentence starters: "Oxygen will move from ______ to ______ because the PO2 is higher in ______ (value) than in ______ (value)." / "Carbon dioxide moves ______ because the PCO2 gradient is ______."

- Word bank: diffusion, partial pressure, gradient, alveoli, capillary, oxygenated, deoxygenated, equilibrium.

- For students needing more support: work with a simplified dataset (two values) or use peer pairing. Teachers may read data aloud or allow oral answers.

- For typical learners: complete this worksheet independently and justify each answer in one or two sentences.

Extension activities (advanced learners)

- Use simulation software to model how changing alveolar PO2, ventilation rate or blood flow alters exchange; record and compare three runs.

- Calculate percentage change in diffusion gradient if alveolar PO2 falls from 13.0 kPa to 9.0 kPa and discuss likely physiological effects.

- Design a brief investigation: propose how to measure changes in arterial PO2 during light vs intense exercise (include variables and expected results).

Teacher checklist for formative assessment: Look for correct direction predictions, use of scientific terms, and clear reasoning referencing partial pressures.