Question

Which is not true regarding stomata?

• A. They are turgor operated valves
• B. Have differentially thickened walls of guard cells
• C. They open when OP of guard cell decreases
• D. Show scotoactive opening in CAM plants

Answer 1

The correct option is C They open when OP of guard cell decreases

Stomata and guard cells are called turgor operated valves because each stomata consists of a minute pore called stoma surrounded by two guard cells. The stoma acts as a turgor operated valve which closes and opens according to the turgidity of guard cells.

Stomata are composed of two guard cells. These cells have walls that are thicker on the inner side than on the outer side. This unequal thickening of the paired guard cells causes the stomata to open when they take up water and close when they lose water. When guard cells are turgid, stomata opens and closes when guard cells are flaccid.

CAM plants open stomata during night and close during the day. This type of stomata are called scotoactive stomata.

DPD is the amount by which the diffusion pressure of water or solvent in a solution is lower than that of pure water or solvent. It is equal to the difference between osmotic pressure and turgor pressure. During stomatal opening water moves into the guard cells and they swell and become turgid. This movement of water into the guard cells is made possible due to an increase in DPD (increase in OP and decrease in TP).

So, the correct answer is "option C"