Who this is for: Cambridge IGCSE Biology (0610) students who want diffusion — the net movement of particles down a concentration gradient — to become a reliable source of marks instead of a vague idea mixed up with osmosis.
What query it owns: how to understand and revise diffusion in Cambridge IGCSE Biology (0610).
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 one of the most frequently tested processes in the Movement into and out of cells unit of Cambridge IGCSE Biology (0610). Whenever a question involves particles spreading from high to low concentration — in gases, liquids or through a partially permeable membrane — examiners expect a precise definition and a clear explanation of the factors that change the rate. This guide explains exactly what diffusion covers, how to handle the question types that actually appear, and where to practise each skill.

Key takeaways

• Diffusion is the net movement of particles from a region of higher concentration to a region of lower concentration, down a concentration gradient.
• It is a passive process — no energy from respiration is required.
• Temperature, concentration difference and surface area affect the rate; state each with a biological reason in explain questions.
• Always separate diffusion from osmosis (water only) and active transport (against the gradient, uses energy).

What is diffusion in Cambridge IGCSE Biology?

Diffusion is the net movement of particles from an area of higher concentration to an area of lower concentration, as a result of the random movement of particles. In Cambridge IGCSE Biology (0610) it applies to gases such as oxygen and carbon dioxide, to dissolved substances such as glucose, and to any situation where particles spread until equilibrium is approached. It does not require energy from the cell.

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

These four ideas appear again and again. Learn what each one means and the exam phrasing that signals it.

Idea	What it means	How the exam uses it
Concentration gradient	Difference in concentration between two regions	”Down a concentration gradient”
Net movement	More particles move one way than the other	”Define diffusion”
Passive process	No ATP / no respiration energy needed	”Explain why diffusion does not need energy”
Factors affecting rate	Temperature, SA, distance, concentration difference	”Explain how temperature affects diffusion”

How to answer diffusion questions — step by step

The safest method works for define, describe and explain questions.

1. Identify what is moving — particles, molecules or ions (not always water).
2. State the direction — from higher to lower concentration.
3. Name the process — net movement due to random motion of particles.
4. Add energy note — passive; no energy from respiration for simple diffusion.
5. For explain questions — link the factor to particle kinetic energy or collision frequency.
6. Check you have not described osmosis — if only water moves across a membrane, that is osmosis.

Once you have worked through a few, test yourself with the free Diffusion quiz — it tells you fast whether the definition has actually stuck.

Diffusion vs osmosis vs active transport: which process does the question want?

Students lose marks by applying the wrong process name. Use the stem to decide.

Situation	What to do	Typical signal words
Any particles down a gradient	Diffusion	”spread”, “higher concentration”, “gas exchange”
Water only across membrane	Osmosis	”water potential”, “partially permeable”, “dilute solution”
Against the gradient, uses energy	Active transport	”low concentration to high”, “root hair”, “requires energy”
Alveoli / villi adaptation	Link SA to diffusion rate	”large surface area”, “thin walls”

Diffusion in past-paper wording: command words that matter

Most lost marks in diffusion questions come from misreading the command word or swapping in osmosis vocabulary. These are the command words you will see and what each one demands.

Command word / phrase	What the question wants	Typical diffusion stem
Define	Precise biological meaning	”Define diffusion.”
Describe	What happens, no why	”Describe how oxygen reaches the blood in the lungs.”
Explain	Reason or mechanism	”Explain why diffusion is faster at higher temperature.”
Suggest	Apply knowledge to a new context	”Suggest why alveoli have thin walls.”
Compare	Similarities and differences	”Compare diffusion and active transport.”

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

Practising the wording — not just the definition — is what method marks reward. Here is how three real-style stems are answered.

1. “Define diffusion.” Net movement of particles / molecules / ions from a region of higher concentration to a region of lower concentration (down a concentration gradient). Mark-scheme reward: “net movement”, concentration gradient, correct direction.
2. “Explain how oxygen moves from the alveolar air into the blood.” Oxygen concentration is higher in alveolar air than in deoxygenated blood → net movement down the concentration gradient across the thin alveolar wall by diffusion. Reward: gradient + thin wall / large SA mentioned.
3. “Explain why increasing temperature increases the rate of diffusion.” Particles gain kinetic energy → move faster → more collisions → faster net movement down the gradient. Reward: link to particle movement, not just “it speeds up”.

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

How diffusion connects to the rest of Biology (0610)

Diffusion feeds directly into gas exchange in humans (alveoli) and plants (stomata), and into nutrition (absorption in the small intestine). It contrasts with Osmosis and Active Transport, which examiners often bundle in compare questions. When you are ready to mix topics, the Cambridge IGCSE Biology resource hub lets you move straight from a weak subtopic into the next.

Common mistakes students make

• Defining diffusion as “movement of water” — that is osmosis.
• Omitting “net movement” in definitions.
• Saying diffusion needs energy from respiration — it is passive.
• Confusing concentration with amount — a large volume can still be low concentration.
• Forgetting to mention concentration gradient in explain answers.

When you need more support

If diffusion questions keep tripping you up — especially compare questions with osmosis and active transport — work through the Movement topical past paper questions and the Diffusion quiz to pinpoint the exact gap, then get focused help from a Cambridge IGCSE Biology tutor to fix it quickly.

Frequently asked questions

Is diffusion hard in Cambridge IGCSE Biology? The idea is straightforward. Marks are lost when students give vague definitions, confuse diffusion with osmosis, or omit the concentration gradient.

What is the quickest way to define diffusion in an exam? Net movement of particles from higher to lower concentration down a concentration gradient — passive, no energy required.

Does diffusion only happen in liquids? No — it happens in gases and liquids; exam questions often use oxygen and carbon dioxide in the lungs.

How do I revise diffusion effectively? Read the subtopic notes, practise define and explain stems, then take the Diffusion quiz. Use the Diffusion and Osmosis flashcard to separate processes.

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