Question

Opening and closing of pores is a function performed by
A. Stomata
B. Chlorophyll
C. Chloroplast
D. Guard cell​

Answer 1

Stomata, or plant pores, are required for life. When they first appeared around 400 million years ago, they aided plants in their conquest of the land. Plants absorb carbon dioxide through their stomata and expel oxygen and water vapor as part of the carbon and water cycles on Earth.

Complete answer:
Stomata are the small openings found on the leaf epidermis. Stomata can be seen beneath the light microscope. Stomata can be found on stems and other plant parts.

Stomata Structure:
- Two guard cells surround each stoma.
- The kidney-shaped guards contain chloroplasts.
- In each stoma, there is a respiratory chamber.

Mechanism of stomatal closure and reopening:
- The mechanism of stomatal closure and opening is dependent on the presence of sugar and starch in the guard cells.
- The guard cells of the stomata contain sugar, which is synthesized by their chloroplasts in the presence of light.
- Because sugar is soluble, it raises the concentration of guard cells.
- Due to the higher concentration of cytoplasm in guard cells, water enters these cells via osmosis from neighboring cells. As a result, the stomata remain open.

Hence the correct answer is Option D: Guard Cell.

Note: In the absence of light, the sugar in guard cells is converted into starch. Because starch is insoluble, the guard cells have a lower concentration than the neighboring cells, and the neighboring cells take out the water from the guard cells via osmosis, making them flaccid and the stomata close.