3.2

Osmosis

Cambridge IGCSE Biology (0610)  · Unit 3: Movement into and out of cells  · 12 flashcards

Osmosis is topic 3.2 in the Cambridge IGCSE Biology (0610) syllabus , positioned in Unit 3 — Movement into and out of cells , alongside Diffusion and Active transport.  In one line: 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.

This topic is examined in Paper 1 (multiple-choice) and Papers 3/4 (theory), plus Paper 5 or Paper 6 (practical / alternative to practical).

The deck below contains 12 flashcards — 5 definitions, 3 key concepts, 1 process card and 3 application cards — covering the precise wording mark schemes reward.  Use the 5 definition cards to lock down command-word answers (define, state), then move on to the concept and application cards to handle explain, describe and compare questions.

Key definition

Osmosis

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.

Example: water moves into root hair cells from the soil via osmosis.

What the Cambridge 0610 syllabus says

Official 2026-2028 spec

These are the exact learning objectives Cambridge sets for this topic. Match the command word (Describe, Explain, State, etc.) in your answer to score full marks.

  1. Describe Describe the role of water as a solvent in organisms with reference to digestion, excretion and transport
  2. State State that water diffuses through partially permeable membranes by osmosis
  3. State State that water moves into and out of cells by osmosis through the cell membrane
  4. Investigate Investigate osmosis using materials such as dialysis tubing
  5. Investigate Investigate and describe the effects on plant tissues of immersing them in solutions of different concentrations
  6. State State that plants are supported by the pressure of water inside the cells pressing outwards on the cell wall
  7. Describe Describe osmosis as 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 Supplement
  8. Explain Explain the effects on plant cells of immersing them in solutions of different concentrations by using the terms: turgid, turgor pressure, plasmolysis, flaccid Supplement
  9. Explain Explain the importance of water potential and osmosis in the uptake and loss of water by organisms Supplement
Definition Flip

What is osmosis?

Answer Flip

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.

Example: water moves into root hair cells from the soil via osmosis.
Key Concept Flip

Describe the role of water as a solvent in digestion.

Answer Flip

Water acts as a solvent in digestion, dissolving substances to facilitate their transport and chemical reactions.

Example: water dissolves digested food molecules like glucose to be absorbed into the bloodstream.
Key Concept Flip

Describe the role of water as a solvent in excretion.

Answer Flip

Water acts as a solvent in excretion, dissolving waste products to facilitate their removal from the body.

Example: urea is dissolved in water to form urine, which is then excreted by the kidneys.
Key Concept Flip

Describe the role of water as a solvent in transport.

Answer Flip

Water acts as a solvent in transport, carrying dissolved substances throughout the organism.

Example: blood plasma, which is mostly water, transports nutrients, hormones, and waste products throughout the body.
Definition Flip

What does it mean for a plant cell to be turgid?

Answer Flip

A turgid plant cell is swollen and firm due to water entering by osmosis, causing the cytoplasm to push against the cell wall. This provides support to the plant.

Example: turgid cells in leaves help keep them firm and upright.
Definition Flip

What is turgor pressure?

Answer Flip

Turgor pressure is the pressure exerted by the cell contents against the cell wall in a plant cell. It is caused by the osmotic uptake of water. Turgor pressure is essential for plant support and rigidity, such as keeping stems erect.

Definition Flip

What does it mean for a plant cell to be plasmolysed?

Answer Flip

A plasmolysed plant cell has lost water by osmosis and the cytoplasm has pulled away from the cell wall. This occurs when the cell is in a solution with a lower water potential.

Example: plant cells in salty soil may become plasmolysed.
Definition Flip

What does it mean for a plant cell to be flaccid?

Answer Flip

A flaccid plant cell is limp and lacks turgor pressure. This occurs when there is no net movement of water into or out of the cell because the water potential inside and outside the cell is equal. Flaccid plant stems droop over.

Key Concept Flip

How does osmosis contribute to plant support?

Answer Flip

Water enters plant cells by osmosis, creating turgor pressure that pushes the cytoplasm against the cell wall. This makes the cells turgid, providing support and rigidity to the plant. Lack of water will result in wilting.

Key Concept Flip

Why is water potential important for organisms?

Answer Flip

Water potential affects the direction of water movement in and out of cells. Organisms must maintain appropriate water potential gradients to ensure water balance for essential processes like nutrient uptake, waste removal, and cell function.

Key Concept Flip

Describe an experiment to investigate osmosis using dialysis tubing.

Answer Flip

Fill dialysis tubing with a sugar solution, seal the ends, and weigh it. Immerse it in distilled water for a set time. Reweigh the tubing; an increase indicates water entered by osmosis due to a higher water potential outside.

Key Concept Flip

Explain the importance of osmosis in the uptake of water by root hair cells.

Answer Flip

Root hair cells have a lower water potential than the surrounding soil. This difference in water potential causes water to move from the soil into the root hair cells via osmosis, allowing the plant to absorb the water it needs.

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3.1 Diffusion 3.3 Active transport

Key Questions: Osmosis

What is osmosis?

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.

Example: water moves into root hair cells from the soil via osmosis.
What does it mean for a plant cell to be turgid?

A turgid plant cell is swollen and firm due to water entering by osmosis, causing the cytoplasm to push against the cell wall. This provides support to the plant.

Example: turgid cells in leaves help keep them firm and upright.
What is turgor pressure?

Turgor pressure is the pressure exerted by the cell contents against the cell wall in a plant cell. It is caused by the osmotic uptake of water. Turgor pressure is essential for plant support and rigidity, such as keeping stems erect.

What does it mean for a plant cell to be plasmolysed?

A plasmolysed plant cell has lost water by osmosis and the cytoplasm has pulled away from the cell wall. This occurs when the cell is in a solution with a lower water potential.

Example: plant cells in salty soil may become plasmolysed.
What does it mean for a plant cell to be flaccid?

A flaccid plant cell is limp and lacks turgor pressure. This occurs when there is no net movement of water into or out of the cell because the water potential inside and outside the cell is equal. Flaccid plant stems droop over.

More topics in Unit 3 — Movement into and out of cells

Osmosis sits alongside these Biology decks in the same syllabus unit. Each uses the same spaced-repetition system, so progress in one informs the next.

3.1 Diffusion

10 flashcards
3.3 Active transport

10 flashcards

Cambridge syllabus keywords to use in your answers

These are the official Cambridge 0610 terms tagged to this section. Mark schemes credit responses that use the exact term — weave them into your answers verbatim rather than paraphrasing.

osmosis water potential partially permeable membrane selectively permeable dilute solution concentrated solution turgid plasmolysis flaccid turgor pressure water movement visking tubing

Key terms covered in this Osmosis deck

Every term below is defined in the flashcards above. Use the list as a quick recall test before your exam — if you can't define one of these in your own words, flip back to that card.

Osmosis
What does it mean for a plant cell to be turgid
Turgor pressure
What does it mean for a plant cell to be plasmolysed
What does it mean for a plant cell to be flaccid

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