Who this is for: Cambridge IGCSE Biology (0610) students who want diffusion — net movement of particles down a concentration gradient — to become reliable marks instead of a definition they blur with osmosis.
What query it owns: how to understand and revise diffusion in Cambridge IGCSE Biology.
Why this is safe: this page owns the diffusion revision-guide angle, while Tutopiya’s Diffusion subtopic page owns the learning resource and the free Diffusion quiz owns the practice.

Diffusion is the passive movement of particles from a region of higher concentration to a region of lower concentration until equilibrium is reached. Cambridge IGCSE Biology (0610) tests whether you can define it precisely, explain where it happens in living organisms, and distinguish it from osmosis and active transport. This guide covers the syllabus definitions, the factors that change rate, and the question types that appear every year.

Key takeaways

• Diffusion is the net movement of particles from high to low concentration — it does not require energy from respiration.
• It applies to dissolved substances or gases, not just water.
• Rate increases with higher temperature, greater concentration difference, and larger surface area.
• Partially permeable membranes allow diffusion of small molecules; osmosis is diffusion of water only.
• Exam answers must name what is moving and which direction relative to concentration.

What is diffusion in Cambridge IGCSE Biology?

Diffusion is the net movement of particles from a region where they are at a higher concentration to a region where they are at a lower concentration, as a result of their random movement. The movement continues until the concentration is the same throughout — equilibrium. In living organisms, diffusion supplies cells with oxygen and removes carbon dioxide; it also moves glucose and other small molecules where concentration gradients exist.

You can read the full explanation, worked examples and notes on Tutopiya’s Diffusion subtopic page before you attempt questions.

The core ideas you must master

Idea	What it means	How the exam uses it
Net movement	More particles move one way than the other	”Define diffusion”
Concentration gradient	Difference in concentration between two regions	”State the direction of movement”
Passive process	No energy from respiration required	”Compare diffusion and active transport”
Equilibrium	Equal concentration throughout	”Describe what happens over time”
Surface area	More area → faster exchange	”Explain why root hairs are adapted”

Factors affecting the rate of diffusion

Factor	Effect on rate	Biological example
Temperature	Higher temperature → faster (more kinetic energy)	Warm water vs cold water
Concentration difference	Steeper gradient → faster	Oxygen into blood at lungs
Surface area	Larger area → faster net movement	Alveoli, root hair cells
Distance	Shorter distance → faster	Thin walls of capillaries

Diffusion in past-paper wording: command words that matter

Command word / phrase	What the question wants	Typical diffusion stem
Define	Precise syllabus definition	”Define the term diffusion.”
State	Short factual answer	”State the direction of net movement.”
Explain	Cause and effect	”Explain how oxygen reaches muscle cells.”
Describe	What happens, step by step	”Describe what happens to a crystal of dye in water.”
Compare	Similarities and differences	”Compare diffusion and osmosis.”

Worked exam-style stems (how to answer the wording)

1. “Define the term diffusion.” Diffusion is the net movement of particles from a region of higher concentration to a region of lower concentration. Mark-scheme reward: net movement, higher to lower concentration.
2. “Explain how oxygen moves from the air in the alveoli into the blood.” Oxygen concentration is higher in the alveolar air than in the blood → net movement down the concentration gradient across the thin alveolar wall and capillary endothelium. Reward: named locations + gradient direction.
3. “State two factors that increase the rate of diffusion.” Any two from: increased temperature, greater concentration difference, larger surface area, shorter diffusion distance. Reward: syllabus factors, not vague “more particles”.

When you can recognise the wording instantly, work the full set on the Movement into and out of Cells topical past paper questions and the Diffusion quiz to lock the definitions in.

How diffusion connects to the rest of the syllabus

Diffusion sits alongside Osmosis (water only) and Active Transport (against a gradient, needs energy). It underpins gas exchange, absorption in the small intestine, and transpiration. The Cambridge IGCSE Biology resource hub links every Movement subtopic.

Common mistakes students make

• Defining diffusion as “movement” without net movement or concentration gradient.
• Describing osmosis when the question asks about dissolved glucose or oxygen.
• Saying diffusion requires energy from respiration (that is active transport).
• Ignoring surface area adaptations in explain questions.
• Using “high to low pressure” instead of concentration.

When you need more support

If diffusion questions keep costing marks — especially compare questions with osmosis — work through the Movement topical past paper questions and the Diffusion quiz, then get focused help from a Cambridge IGCSE Biology tutor.

Frequently asked questions

Is diffusion hard in Cambridge IGCSE Biology? The idea is simple, but marks are lost when students blur diffusion with osmosis or omit net movement in definitions.

What is the difference between diffusion and osmosis? Diffusion is net movement of any particles down a concentration gradient; osmosis is the net movement of water molecules through a partially permeable membrane.

Does diffusion need energy? No — it is passive. Active transport moves substances against a gradient and requires energy from respiration.

How do I revise diffusion effectively? Read the subtopic notes, practise definitions from memory, compare with osmosis and active transport, then take the Diffusion quiz.

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