2(g) Gas exchange
Pearson Edexcel International GCSE Biology · 4BI1
Paper 2 | Whole paper: All content including bold B statements
How gases move in and out of plants and humans, and the surface adaptations that make it fast enough.
Specification coverage
Topic 2 Structures and functions in living organisms (g) Gas exchange — statements 2.42–2.52B (includes bold B statements assessed on Paper 2 only)
Assessment objectives: AO1, AO2, AO3. Suggested learning time: 70 minutes.
Required knowledge
- Gas exchange in flowering plants, including the role of stomata and the effect of light
- The structure of the human thorax and the mechanism of ventilation
- The adaptations of the alveoli for gas exchange: large surface area, thin walls, moist surface, good blood supply
- The differences in composition between inspired and expired air
- Bold B statements: the effect of exercise on breathing in greater depth
Required skills
- Explain an adaptation by linking structure to rate of diffusion
- Describe ventilation as a pressure-driven process
- Interpret data comparing inspired and expired air
- Describe and evaluate the required practical: Investigate the effect of exercise on breathing rate, and the composition of inhaled and exhaled air.
How it is examined
- Multiple-choice and short-answer recall
- Application of the content to an unfamiliar context
- Extended open-response, marked on the quality of a connected explanation
- Practical questions on method, variables, data and sources of error
Common mistakes
- Saying air is 'sucked in'. The diaphragm and intercostal muscles change the volume of the thorax, which changes the pressure, and air moves down the pressure gradient.
- Claiming expired air contains no oxygen. It contains about 16%.
- Listing alveolar adaptations without saying what each one does to the rate of diffusion.