AI-generated practice question — model-generated for extra practice, not a previous-year CBSE board question.
Answer: B – Guard cells
Guard cells control the opening and closing of the stomatal pore by changing their turgidity.
Guard cells are specialised cells that surround each stoma. When they absorb water and become turgid, the pore opens; when they lose water and become flaccid, the pore closes. Examiners expect the direct answer "Guard cells" for 1 mark — no elaboration is strictly necessary, but one supporting line shows understanding.