Gas ExchangeEdexcel GCSE Biology: Revision notes
Section 1
Adaptations of the Alveoli
Alveoli: large total surface area, thin (one cell) walls, good blood supply, moist lining, good ventilation.
Key termsalveolicapillariesdiffusion
Common mistake
Millions of alveoli together create large total surface area.
Section 2
Factors Affecting Rate of Diffusion
Larger surface area, steeper concentration gradient, shorter diffusion distance all increase rate.
Key termsconcentration gradientdiffusion distance
Section 3
Fick's Law
rate of diffusion ∝ (surface area × concentration difference) ÷ thickness of membrane.
Key termsFick's law
Example
SA=4mm², concdiff=10, thickness=2: rate∝20. Doubling SA to 8: rate∝40 (doubles).
Must Know
- Alveoli: large SA, thin walls, good blood supply, moist lining.
- O2 diffuses alveoli→blood; CO2 blood→alveoli.
- Rate ∝ SA, conc gradient; ∝1/thickness (Fick's law).
That's the notes covered.
Carry on to the next subtopic.