Explain how an increase in temperature and an increase in surface area each affect the rate of diffusion.

Cambridge International IGCSE Biology (0610) — 3.1 Diffusion · Explain · 4 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Model answer (4 marks)

Increasing temperature increases the rate of diffusion because the molecules gain kinetic energy and move faster.
Increasing surface area increases the rate of diffusion because there is more space / more sites available for particles to diffuse through the membrane.

Examiner tips

Use the exact phrases: "increasing temperature increases the rate of diffusion" and "increasing surface area increases the rate of diffusion". Explain the cause: "molecules gain kinetic energy and move faster" and "more space / more sites available for particles to diffuse through the membrane". Keep the answer concise – one sentence for each effect – to match the 4‑mark structure.

Common mistakes

Writing the effects in the wrong order, or omitting the cause. Using vague terms like "more movement" instead of "gain kinetic energy". Adding unnecessary words such as "in this essay" or restating the question.

Mark scheme (4 marks)

Increasing temperature increases the rate of diffusion
Because molecules gain kinetic energy and move faster
Increasing surface area increases the rate of diffusion
Because there is more space / more sites available for particles to diffuse through (the membrane)

Key terms in this question

diffusion · surface area