Who this is for: Cambridge IGCSE Biology (0610) students who want osmosis — net movement of water through a partially permeable membrane — to become reliable marks instead of a vague “water moves” answer.
What query it owns: how to understand and revise osmosis in Cambridge IGCSE Biology.
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 the net movement of water molecules from a region of higher water potential (dilute solution) to a region of lower water potential (concentrated solution) through a partially permeable membrane. Cambridge IGCSE Biology (0610) tests precise definitions, predictions about plant and animal cells in different solutions, and explanations of turgidity and plasmolysis. This guide covers what examiners expect and how to answer real paper stems.

Key takeaways

• Osmosis is diffusion of water only, through a partially permeable membrane.
• Water moves from dilute to concentrated solution (higher to lower water potential).
• In plant cells, water enters by osmosis → cell becomes turgid; water leaves → plasmolysis.
• Solute concentration and water potential are inversely related — more solute means lower water potential.
• Potato cylinder and red blood cell questions test whether you can predict direction of water movement.

What is osmosis in Cambridge IGCSE Biology?

Osmosis is the net movement of water molecules from a region of higher water potential to a region of lower water potential through a partially permeable membrane. A partially permeable membrane allows some molecules (like water) to pass but not others (like large solute molecules). Because solute particles lower water potential, water net-moves into solutions that are more dilute when separated by such a membrane.

Read the full explanation 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, blocks many solutes	”Define osmosis”
Water potential	Measure of tendency of water to move	”State the direction of water movement”
Turgid plant cell	Full vacuole pushes against cell wall	”Describe a plant cell in pure water”
Plasmolysis	Membrane pulls away from cell wall	”Describe a plant cell in strong salt solution”
Haemolysis / crenation	Animal cell in dilute vs concentrated solution	”Explain what happens to red blood cells”

Predicting water movement — comparison table

Solution outside cell	Water movement	Plant cell	Animal cell (e.g. RBC)
Pure water / dilute	Into cell	Turgid	Swells — may burst (haemolysis)
Isotonic	No net movement	Normal	Normal shape
Concentrated / strong solution	Out of cell	Plasmolysed	Shrinks (crenation)

Osmosis in past-paper wording: command words that matter

Command word / phrase	What the question wants	Typical osmosis stem
Define	Full osmosis definition with membrane	”Define the term osmosis.”
Explain	Direction + reason (water potential)	“Explain why the potato cylinder increased in mass.”
Describe	Observable change	”Describe what you would see in the epidermal cells.”
Predict	Outcome in a named solution	”Predict the effect of 10% salt solution on the cell.”
Suggest	Apply osmosis to a new context	”Suggest why wilting occurs in dry soil.”

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

1. “Define the term osmosis.” Osmosis is the net movement of water molecules from a region of higher water potential to a region of lower water potential through a partially permeable membrane. Mark-scheme reward: water molecules, water potential, partially permeable membrane.
2. “A potato cylinder is placed in distilled water for 30 minutes. Explain why its mass increases.” Distilled water has higher water potential than the potato cell cytoplasm → net movement of water into the cells by osmosis → cylinder gains mass. Reward: direction linked to water potential gradient.
3. “Describe what happens to a plant cell placed in a concentrated salt solution.” Water leaves the cell by osmosis → vacuole shrinks → cytoplasm pulls away from the cell wall (plasmolysis). Reward: sequence of events, named plasmolysis.

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

How osmosis connects to the rest of the syllabus

Osmosis links to Diffusion (general particle movement) and Active Transport. It explains root water uptake, kidney function, and why plants wilt. Use the Cambridge IGCSE Biology resource hub to move between subtopics.

Common mistakes students make

• Defining osmosis without mentioning partially permeable membrane.
• Saying water moves to the “stronger solution” without linking to water potential.
• Confusing plasmolysis (plant) with haemolysis (animal).
• Describing solute particles moving when only water moves in osmosis.
• Forgetting the cell wall prevents bursting in plant cells in pure water.

When you need more support

If osmosis predictions keep failing — especially potato practical stems — use the Movement topical past paper questions and Osmosis quiz, then book a Cambridge IGCSE Biology tutor.

Frequently asked questions

Is osmosis just diffusion of water? Yes — osmosis is the net movement of water molecules down a water potential gradient through a partially permeable membrane.

Why do plant cells not burst in pure water? The rigid cell wall prevents excessive expansion; the cell becomes turgid instead.

What is plasmolysis? When a plant cell loses water by osmosis and the cell membrane pulls away from the cell wall.

How do I revise osmosis effectively? Learn the definition precisely, practise predicting cell changes in dilute vs concentrated solutions, then take the Osmosis quiz.

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