Who this is for: Cambridge IGCSE Biology (0610) students who want osmosis — the net movement of water through a partially permeable membrane — to become a reliable source of marks instead of a half-remembered definition blurred with diffusion.
What query it owns: how to understand and revise osmosis in Cambridge IGCSE Biology (0610).
Why this is safe: this page owns the osmosis revision-guide angle, while Tutopiya’s Osmosis subtopic page owns the learning resource and the free Osmosis quiz owns the practice.

Osmosis is tested heavily in Cambridge IGCSE Biology (0610) — in definitions, potato cylinder experiments, and questions about plant cells in dilute versus concentrated solutions. Examiners expect you to state that only water moves, that movement is through a partially permeable membrane, and that water moves from higher water potential to lower water potential (or from dilute to concentrated solution, in syllabus wording). This guide explains the core ideas, the question types that actually appear, and where to practise each skill.

Key takeaways

• Osmosis is the net movement of water molecules through a partially permeable membrane from a region of higher water potential to lower water potential.
• It is a special case of diffusion — passive, no energy from respiration required.
• In dilute solution, plant cells become turgid; in concentrated solution, they become plasmolysed.
• Always state water only — solutes do not move through the membrane in osmosis questions at this level.

What is osmosis in Cambridge IGCSE Biology?

Osmosis is the net movement of water molecules through a partially permeable membrane from a region of higher water potential to a region of lower water potential. In Cambridge IGCSE Biology (0610) you also describe this as water moving from a dilute solution to a more concentrated solution across the membrane. The membrane allows water through but restricts many solute molecules.

Read the full explanation and worked examples on Tutopiya’s Osmosis subtopic page before attempting questions.

The core ideas you must master

Idea	What it means	How the exam uses it
Partially permeable membrane	Allows water, not all solutes	”Through a partially permeable membrane”
Water potential	Measure of tendency of water to move	”Higher to lower water potential”
Turgid / plasmolysed	Plant cell state after osmosis	”Describe what happens to the plant cell”
Potato experiment	Mass change shows water gain/loss	”Explain the change in mass”

How to answer osmosis questions — step by step

1. Confirm it is water — if the question is about glucose or ions moving, it is not osmosis alone.
2. Name the membrane — partially permeable (cell membrane or visking tubing).
3. State the direction — higher water potential → lower water potential (or dilute → concentrated).
4. Describe the cell outcome — turgid, flaccid, plasmolysed, or crenated (animal cells).
5. For experiment questions — link mass change to water entering or leaving by osmosis.
6. Check the command word — define needs precision; explain needs mechanism.

Test yourself with the free Osmosis quiz once you have worked through a few stems.

Dilute vs concentrated: what happens to plant and animal cells?

Solution	Water movement	Plant cell	Animal cell (e.g. red blood cell)
Dilute (high water potential)	Water enters cell	Turgid — vacuole swells, membrane against wall	Haemolysis — may burst (no cell wall)
Same concentration	No net movement	No change	No change
Concentrated (low water potential)	Water leaves cell	Plasmolysed — membrane pulls away from wall	Crenated — shrivelled

Osmosis in past-paper wording: command words that matter

Command word / phrase	What the question wants	Typical osmosis stem
Define	Full osmosis definition	”Define osmosis.”
Explain	Why mass or length changed	”Explain why the potato cylinder increased in mass.”
Describe	What you observe	”Describe the appearance of the plant cell in concentrated solution.”
Suggest	Predict outcome	”Suggest what happens to a red blood cell in distilled water.”
Compare	Diffusion vs osmosis	”Compare diffusion and osmosis.”

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

1. “Define osmosis.” Net movement of water molecules through a partially permeable membrane from a region of higher water potential to a region of lower water potential. Reward: water only, partially permeable, correct direction.
2. “A potato cylinder is placed in distilled water. Explain why its mass increases.” Distilled water has higher water potential than cell cytoplasm → water enters potato cells by osmosis through partially permeable membranes → cylinder gains mass. Reward: water potential gradient + osmosis named.
3. “Describe and explain what happens to a plant cell placed in a concentrated salt solution.” Water leaves by osmosis → cytoplasm shrinks → cell membrane pulls away from cell wall → plasmolysis. Reward: water leaves + plasmolysed described.

Work the full set on the Movement topical past paper questions and the Osmosis quiz.

How osmosis connects to the rest of Biology (0610)

Osmosis explains support in plants (turgidity), water uptake by roots, and kidney function in later topics. It pairs with Diffusion in compare questions and contrasts with Active Transport. The Cambridge IGCSE Biology resource hub links all Movement subtopics.

Common mistakes students make

• Defining osmosis as movement of solute instead of water.
• Omitting partially permeable membrane in definitions.
• Saying water moves to the more dilute solution without linking to water potential.
• Confusing flaccid and plasmolysed — plasmolysis is membrane away from wall.
• Applying osmosis when the question is about active transport of mineral ions.

When you need more support

If osmosis experiments or plasmolysis diagrams keep costing marks, use the Movement topical past paper questions and Osmosis quiz, then book a Cambridge IGCSE Biology tutor.

Frequently asked questions

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

Is osmosis active or passive? Passive — no energy from respiration is required for osmosis.

Why do plant cells not burst in distilled water? The cell wall prevents bursting; the cell becomes turgid instead.

How do I revise osmosis for Paper 6? Practise describing potato or visking tubing experiments and drawing plasmolysed cells; use the Osmosis quiz and Diffusion and Osmosis flashcard.

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