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, controlling the exchange of gases (CO₂ and O₂) and the loss of water vapour (transpiration) in a leaf.
Examiners expect mention of stomata regulation and at least two functions — gas exchange and transpiration control. The guard cells change shape by altering their water content, but for a 1-mark answer, simply stating their role in opening/closing stomata with the outcome is sufficient.