Stomata is one of the critical parts of gaseous exchange. The surface of the leaves is full of thousands of stomata. Most are on the lower side of the leaves.
What are Stomata?
Stomata are the small openings that are present on the leaf epidermis. Beneath the light microscope we can see stomata. Stomata are found on stems and other parts in some plants.
Structure of Stomata
- Each stoma is surrounded by two guard cells.
- The guards are of kidney shaped and contain chloroplasts.
- There is a respiratory chamber present in each stoma.
Mechanism of the closing and opening of the stomata
- The mechanism of the closing and opening of the stomata depends upon the presence of sugar and starch present in the guard cells.
- In the presence of light, the guard cells of the stomata contain sugar which is synthesized by their chloroplasts.
- The sugar is soluble and increases the concentration of guard cells.
- Due to higher concentration of the cytoplasm of guard cells, the water enters into these cells from the neighbouring cells by osmosis. Hence, the stomata remains open.
In the absence of light the sugar present in guard cells converts into the starch. The starch is insoluble, and this way the guard cells remains in lower concentration than the of neighbouring cells, and the neighbouring cells take out the water from the guard cells by osmosis making them flaccid and the stomata closed.