5 original questions · Application and evidence

Gas exchange and circulation: linking measurements

Use the context and data to draft a response, then compare your reasoning with an explanatory example.

Context and data

A healthy adult model has the heart measurements below. A separate illustrative haemoglobin dataset gives oxygen saturation at selected oxygen partial pressures under one fixed set of conditions. These datasets do not directly measure oxygen consumption by an individual muscle.

Heart measurements
Measurement	Rest	Exercise
Heart rate / beats min⁻¹	72	144
Stroke volume / cm³ beat⁻¹	70	110

Illustrative haemoglobin dissociation data
Oxygen partial pressure / kPa	Haemoglobin saturation / %
4	50
6	75
10	94
13	97

Original illustrative data. Use the stated assumptions and units; these are not examination-board questions.

This worksheet includes questions and data, with space for your responses. Answers are omitted.

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Five questions

1. Calculate cardiac output at rest and during exercise, in dm³ min⁻¹.

2. Compare the fall in saturation from 13 to 6 kPa with the fall from 13 to 4 kPa. Express the differences in percentage points.

3. Explain how increased carbon dioxide in an active tissue can promote oxygen unloading at a given oxygen partial pressure.

4. Predict how doubling gas-exchange barrier thickness would affect diffusion rate if area and partial-pressure difference remain unchanged in a simple inverse-distance model.