Explain why osmosis is important for plant cells when the concentration of water molecules outside the cell is higher than inside the cell.

Edexcel GCSE Biology (1BI0) — 1.5 Transport in cells · Explain · 4 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Plant cells contain a large central vacuole filled with cell sap. The movement of water into and out of plant cells affects how firm or flaccid the cell becomes.

Model answer (4 marks)

Osmosis is the movement of water molecules from a region of higher water concentration to a region of lower water concentration.
The movement occurs through a partially permeable membrane.
Water moves into the plant cell by osmosis because the water concentration outside is higher than inside.
This causes the cell to become turgid, which supports the plant.

Examiner tips

Use the definition of osmosis first, then mention the membrane, then explain the direction of movement, finally state the effect on the cell.
Show the logical sequence: concentration difference → membrane → water influx → turgidity.
Use the word "turgid" and link it to plant support.

Common mistakes

Confusing osmotic pressure with osmosis, or stating that water moves from inside to outside.
Using the wrong direction of water movement (e.g., saying water leaves the cell).
Omitting the role of the partially permeable membrane.

Mark scheme (4 marks)

Osmosis is the movement of water molecules from a region of higher water concentration to a region of lower water concentration
The movement occurs through a partially permeable membrane
Water moves into the plant cell by osmosis because the water concentration outside is higher than inside
This causes the cell to become turgid, which supports the plant

Key terms in this question

osmosis