# Osmosis

The movement of water through a partially permeable membrane from a dilute solution to a more concentrated one.

Biology (school) · Part 02: Moving materials, enzymes and energy · Card 2 of 11 · Last updated 2026-10-19

## Analogy

Water is pulled towards the side with more dissolved stuff, like a sponge pulling in water.

## Example

**Potato in water**

Start mass: 10 g
End mass: 12 g
Change: +2 g
2 / 10 x 100 = +20%
Water moved into the potato

## In practice

A potato chip put in salty water shrinks because water leaves its cells.

## Practice

### Flashcards

- **Define osmosis.** The movement of water across a partially permeable membrane from a dilute solution to a more concentrated one.

### Interview questions

**Explain the difference between diffusion, osmosis and active transport.**

- Diffusion is the spreading of particles down a concentration gradient
- Osmosis is diffusion of water through a partially permeable membrane
- Active transport moves particles against the gradient
- Active transport needs energy from respiration

## Questions people ask

### What is the difference between diffusion and osmosis?

Diffusion is the movement of any particles from high to low concentration. Osmosis is a special case that involves only water molecules moving across a partially permeable membrane. Water moves from a dilute solution, which has more water, to a concentrated solution, which has less.

### Why do plant cells not burst in pure water?

When a plant cell takes in water, it swells and presses against its stiff cell wall. The wall pushes back and stops the cell from bursting. The cell becomes firm, or turgid. This pressure supports soft plant stems. Animal cells have no wall, so they can burst.

## Related concepts

- [Diffusion](https://studyvisually.com/learn/science/biology-school/biology-school-part-2/biology-school-part-2-concept-1)
- [Active transport](https://studyvisually.com/learn/science/biology-school/biology-school-part-2/biology-school-part-2-concept-3)

Web page: https://studyvisually.com/learn/science/biology-school/biology-school-part-2/biology-school-part-2-concept-2
Study this card in the app: https://studyvisually.com/app/learn?category=biology-school&card=biology-school-part-2-concept-2