Question

The primary osmolyte, which causes an opening and closing of stomata is
A. Sugars
B. Starch
C. K-malate
D. Water

Answer 1

Hint:The word stomata refers to the tiny pores found in the epidermis of leaves, stems, and other organs. The function of stomata is to control the rate of gas exchange. The opening and closing of stomata are controlled by a specialized cell called guard cells.

Complete answer: Microscopic openings on the upper surface of the leaves and other parts of the body are called stomata. These stomata are surrounded by a pair of specialized parenchyma cells known as guard cells. These guard cells regulate the function of opening and closing of the stomata. The excess amount of water is evaporated in the form of vapors from the stomata. The stomatal movement during day time converts the starch into organic acids like malic acid. As a result of the production of malic acid, the proton concentration in the guard cell increases. Exchange of protons takes place for potassium ions from the surrounding cells. The opening of the stomata is caused by the influx of potassium ions which lead to the inflow of water into guard cells making it turgid. Therefore, K-malate is the primary osmolyte responsible for the opening and closing of stomata.

So, option C is the correct option.

Note: Stomatal frequency means the number of stomata present per unit area of a leaf surface. The stomatal frequency within a plant is not constant. It keeps changing according to the surrounding environment. The highest stomatal frequencies are often found in those leaves that occur on the top of the plant. The stomatal frequency varies even within a leaf. For example, in grass leaf, the highest stomatal frequency is observed at the point of insertion of the leaf where the cells are still developing and the smallest and lowest at the tip.