Question

Stomata open and close due to

• A. Turgor pressure change.
• B. Hormonal change.
• C. Temperature change.
• D. All of the above.

Answer 1

The correct option is D All of the above.

There are many factors that affect stomatal movement such as:

1. Turgor pressure change: During day time photosynthesis occurs in the guard cells because they contain chloroplasts. The soluble sugar which is formed by this process decreases the water potential of guard cells and this results in uptake of water by the guard cells from the adjacent subsidiary or epidermal cells. Thus, the guard cells become turgid and stomata open. During the night, the reverse process occurs and leads to closing of stomata as the turgor pressure of guard cells decrease.

2. Hormonal change: Cytokinins are essential for the opening of stomata while abscisic acid takes part in the closing of stomata. Plants respond to water deficiency by producing more abscisic acid which causes potassium ions to move out of guard cells and stomata close.

3. Temperature change: Increase in temperature results in the increased stomatal opening. Stomata in some plants, for example, Camellia do not open at a very low temperature (below 0°C) even in strong light whereas in some plants stomata remain close at high temperature (above 30°C).

Hence, all the options given in the question are correct.