AI-generated practice question — model-generated for extra practice, not a previous-year CBSE board question.
Guard cells regulate the opening and closing of stomata, thereby controlling gaseous exchange (CO₂ and O₂) and transpiration (water loss) in the leaf.
Examiners expect two functions in one line: stomatal regulation and what that controls (gas exchange + water loss). Mentioning only "open and close stomata" without stating why it matters may cost half the mark. The source passages do not directly describe guard cells, so use standard NCERT Life Processes knowledge here.