Question

When would the stomata be open?

Answer 1

Stomata generally remain open when there is bright sunlight and plant is actively engaged in photosynthesis.

Explanation:

Stomata are used to exchange gases. CO2 required for photosynthesis is received through stoma but there is also loss of moisture. So dry weather or windy condition may lead to closure of stoma. You may note that many desert plants, xerophytes, open their stomata only in night to collect CO2 and fix the carbon temporarily in the form of malic acid.

Underlying mechanism of stomatal opening and closure is a complex phenomenon controlled by level of sugar and movement of ions in surrounding guard cells.