GCSE Biology revision

Osmosis

Transport in cells

AQA 4.1.1.1

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AQA student objectives

Learning pathway

All · Most · Some

ALL 🎯

Identify and describe What is Osmosis?, How Osmosis Works and Osmosis and Animal Cells — Gaining Water in the context of osmosis.

MOST 🎯🎯

Explain the relationships between What is Osmosis?, How Osmosis Works and Osmosis and Animal Cells — Gaining Water and how they contribute to osmosis.

SOME 🎯🎯🎯

Apply and analyse knowledge of What is Osmosis?, How Osmosis Works and Osmosis and Animal Cells — Gaining Water to interpret unfamiliar information about osmosis.

Revision summary

Key knowledge

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What is Osmosis?

Osmosis is the diffusion of water from a dilute solution to a concentrated solution through a partially permeable membrane.
A dilute solution contains a high concentration of water, whereas a concentrated solution contains a low concentration of water.
A partially permeable membrane allows some molecules (such as water) to pass through, but not others (such as sugar molecules).

1. What is Osmosis?AQA

Notes

Osmosis is the diffusion of water from a dilute solution to a concentrated solution through a partially permeable membrane.
A dilute solution contains a high concentration of water, whereas a concentrated solution contains a low concentration of water.
A partially permeable membrane allows some molecules (such as water) to pass through, but not others (such as sugar molecules).

How Osmosis Works

Water molecules move from an area of higher water concentration (dilute solution) to an area of lower water concentration (concentrated solution).
Osmosis is essentially a special type of diffusion, but it only refers to the movement of water molecules.
The net movement of water continues until the concentrations on both sides of the membrane are equal.

2. How Osmosis WorksAQA

Notes

Water molecules move from an area of higher water concentration (dilute solution) to an area of lower water concentration (concentrated solution).
Osmosis is essentially a special type of diffusion, but it only refers to the movement of water molecules.
The net movement of water continues until the concentrations on both sides of the membrane are equal.

Osmosis and Animal Cells — Gaining Water

The cytoplasm of cells is a relatively concentrated solution, meaning it contains a relatively low concentration of water.
When an animal cell is placed in water (or a dilute solution), water moves into the cell by osmosis, causing it to expand.
If too much water enters, the animal cell can burst, as it has no cell wall to contain the swelling.

3. Osmosis and Animal Cells — Gaining WaterAQA

Notes

The cytoplasm of cells is a relatively concentrated solution, meaning it contains a relatively low concentration of water.
When an animal cell is placed in water (or a dilute solution), water moves into the cell by osmosis, causing it to expand.
If too much water enters, the animal cell can burst, as it has no cell wall to contain the swelling.

Osmosis and Animal Cells — Losing Water

When an animal cell is placed in a concentrated solution, the solution outside has a lower concentration of water than the cytoplasm inside.
Water moves out of the animal cell by osmosis, causing the cell to shrink.

Osmosis and Plant Cells — Gaining Water

When a plant cell is placed in water or a dilute solution, water moves into the cell by osmosis, causing it to expand.
Unlike animal cells, the cell wall prevents the plant cell from bursting when water enters.
A plant cell that has absorbed water and become swollen is described as turgid.

5. Osmosis and Plant Cells — Gaining WaterAQA

Notes

When a plant cell is placed in water or a dilute solution, water moves into the cell by osmosis, causing it to expand.
Unlike animal cells, the cell wall prevents the plant cell from bursting when water enters.
A plant cell that has absorbed water and become swollen is described as turgid.

Osmosis and Plant Cells — Losing Water

When a plant cell is placed in a concentrated solution, water moves out of the cell by osmosis, causing it to shrink.
A plant cell that has lost water and become limp and shrunken is described as flaccid.

Key Vocabulary Summary

Osmosis: the diffusion of water from a dilute solution to a concentrated solution through a partially permeable membrane.
Turgid: the state of a plant cell that has gained water by osmosis and become swollen and firm.
Flaccid: the state of a plant cell that has lost water by osmosis and become soft and limp.