IGCSE Biology glossary
Partially permeable membrane
Biology editorial review is supported by the named review panel. Reviewer participation may vary by guide. Checked against Cambridge IGCSE Biology 0610 (2026–2028); last reviewed August 2026.
Definition
A membrane that allows some molecules to pass through but not others, depending on their size or other properties. The cell membrane is partially permeable, allowing small molecules like water to pass through while blocking larger solute molecules.
What to include in an exam answer
Always write 'partially permeable', never 'semi-permeable'. Cambridge mark schemes penalise the older term. This phrase is essential in osmosis definitions.
Example in context
Explain the role of a partially permeable membrane in osmosis (2 marks): The partially permeable membrane allows water molecules to pass through but prevents larger solute molecules from crossing, so water moves from higher water potential to lower water potential.
Related syllabus topic
Movement into & out of cells