Question

Opening and closing of stomata is due to:

• A. pressure of gases inside leaves
• B. changes of turgor pressure in guard cells
• C. effect of hormones
• D. their genetic constitution

Answer 1

The correct option is B

changes of turgor pressure in guard cells

The correct option is B.

Explanation for correct option:

1. Opening and closing of stomata take place due to turgor pressure that changes in guard cells.
2. As the solute particles enter the guard cells from the epidermal and mesophyll cells, both the osmotic potential and the water potential of the guard cells get lowered.
3. This creates a water potential gradient which makes the water move towards the guard cells and thus become turgid and swell in size which causes stomatal opening.
4. With a decline in guard cells solutes, water moves out of the guard cells, making them flaccid, so stomata closes.

Explanation for incorrect option:

Option A

1. Pressure of gases outside leaves causes exchange of oxygen and carbon dioxide in the leaf.
2. This occurs through pores called stomata but opening and closing of stomata is not due to gaseous pressure.

Option C

Opening and closing of stomata is not due to effect of hormones, hormones can induce opening but it cannot help alone in the process.

Option D

Genetic constitution of stomata cannot let it open or close, opening and closing of stomata take place due to turgor changes in guard cells.

Final answer: Opening and closing of stomata is due to changes of turgor pressure in guard cells.