Question

Which one of the following essential elements plays an important role in the opening and closing of stomata?
A) Mg
B) K
C) Mn
D) P

Answer 1

Hint: Stomata are minute openings present on the surface of the leaves. It is surrounded by specialized cells called guard cells. Its opening and closing is mediated by a macronutrient present in the soil.

Step by step answer: Potassium is an important and mobile macro element. It is functional in sugar metabolism, translocation and also enables closing and opening of stomata according to the requirement. The nutrients required by plants can be classified as micronutrient or macronutrient. Micronutrients are nutrients that are essential to plants but in trace amounts or very little amounts. Macronutrients are nutrients that are required by the plants in large amounts and are essential for plant growth. The main macronutrients required for the plant growth are Nitrogen (N), Potassium (K) and Phosphorous(P) which also make the great chemical composition of a fertiliser. Potassium is present in sufficient amounts in clay soils and is present in a soluble form. This can be found in fixed form and also in exchangeable forms. Plants acquire potassium from the soil in the form of potassium salts. It is a major important macronutrient which has a role in carbohydrate mechanism and translocation of the prepared sugar. It also maintains the turgidity of cells by maintaining osmosis. It also forms the part of enzymes and is important for the maximum activity. Potassium is also important for opening and closing of stomata. Transpiration is the process of giving out excess water to maintain water balance. The potassium ions create the water potential by accumulating in the guard cells of stomata. The increase in potassium ions makes the water enter the opening outside the guard cells. This makes the cell shrink or flaccid as water evaporates from the stomatal opening and potassium ions move outside the guard cells when there is the closing of stomata. Thus, the opening and closing of stomata is regulated by the influx and efflux of potassium ions.
Thus, the correct answer is option B.

Note: The guard cells contain phototropic proteins which sense light and the transpiration is triggered. The potassium ion channels in the guard cells are activated by calcium and not by potassium as potassium only creates a potential difference for closing and opening of stomata.