IGCSE Biology glossary
Guard cell
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 specialised bean-shaped cell found in pairs either side of a stoma. Guard cells control the opening and closing of stomata. When they absorb water and become turgid, the stoma opens; when they lose water and become flaccid, the stoma closes.
What to include in an exam answer
Guard cells are one of the few cells in the lower epidermis that contain chloroplasts. Their inner cell wall is thicker than the outer wall, causing them to curve when turgid, opening the pore.
Example in context
Explain how guard cells control the opening of stomata (3 marks): Guard cells absorb water by osmosis and become turgid. The inner wall is thicker and less elastic than the outer wall, so the cells curve apart, opening the stoma.
Related syllabus topic
Plant nutrition