Question

What happens to pH, when the stomata of guard cells opens? It
A. Decreases
B. Increase
C. Does not change
D. Anything happens on state of plant

Answer 1

Hint: Stoma in the leaves is surrounded by the guard cells. Opening and closing of stomata can occur due to change in the turgidity of the cells. There is a huge change in the pH of the cells. It can also help in gaseous exchange.

Complete answer:
The tiny pores present in the leaves are called stomata. Guard cells are present around the stoma. They have a very important function in regulating the rate of the transpiration. Opening and closing of the stomata checks the rate of transpiration. When the guard cells are turgid and swollen and the stomata opening is also large. The accumulation of K+ ions (potassium ions) caused the turgidity of the cell.
Levitt inn 1974, proposed the malate or potassium ion pump hypothesis. According to this, decrease in carbon dioxide and photosynthesis increases the pH of the guard cells. It is caused due to the hydrolysis of starch to form phosphoenol pyruvate(PEP). The organic acids like oxalic acids are formed when PEP combines with carbon dioxide. This in turn causes the ionization of the organic acids and proton passes out of guard cells and potassium ion is actively absorbed and accumulated. It passes to the small vacuoles when combined with malate.
Absorption of chloride ions also occurs to maintain electroneutrality. Guard cells become turgid and stomata open due to decrease in the water potential.
From the above information we have found that when the stomata of guard cells open pH will increase.

Hence, the correct answer is option (B).

Note: Opening and closing of the stomata also helps in the gaseous exchange. Absorption of CO2 and removal of O2 occurs by these structures. Large number of stomata is present in the lower portion of the leaves. It is also said that sucrose is produced from the guard cells. It also contains several metabolites. Temperature and light also affects opening and closing of the stomata.