Question

Stomata open during the daytime because the guard cells:

• A. Photosynthesize and produce osmotically active sugars
• B. Are thin-walled
• C. Are bean-shaped
• D. Have to help in gaseous exchange

Answer 1

The correct option is A

Photosynthesize and produce osmotically active sugars

The correct option is A:

Explanation of the correct option:

1. Guard cells are the cells that surround the stomata and guard the opening and closing of the stomata.
2. They contain chloroplasts and carry out photosynthesis, and form sugars when sunlight is available.
3. The presence of sugars will increase the osmotic concentration inside the cell, and thus the guard cells absorb water and become turgid or swollen.
4. The stomata open due to swelling of guard cells and vice versa.

Explanation of the incorrect options:

Option B:

Only the outer walls of the guard cells are thin, but the inner walls that lie towards the stomatal pore are thick.

Option C:

1. Guard cells are bean-shaped in dicots, but these are dumbbell-shaped in monocots.
2. The shape of the guard cells has no significant role in the opening and closing of guard cells.

Option D:

Guard cells help in the exchange of gases by regulating the opening and closing of stomata.

Final answer: Stomata open during the daytime because the guard cells photosynthesize and produce osmotically active sugars.