Question

Influx of $K^+$ ions into guard cells and efflux of $H^+$ ions from guard cells leads to
A. Exosmosis
B. Plasmolysis
C. Closing of stomata
D. Opening of stomata

Answer 1

Hint: The closing and opening of stomata is governed by increases or decreases of solutes in the guard cells, which cause them to lose water or loss, respectively. When the guard cells take in potassium ions, water diffuses into the cells by osmosis.

Complete answer:
Guard cells are specific plant cells in the leaf's epidermis, stems and other organs that are utilized to control gas exchange. They occur in pairs with a gap between them that produces a stomatal pore. The stomatal pores are vast whilst water is freely available and the guard cells turgid and close when less water is available and the guard cells become flaccid.

Now, let us find the solution from the option.
The stomata are open and close because of water and ion moves. When the light falls on the plant, chloroplast performs photosynthesis. ATP comes from photosynthesis, sodium and potassium pumps. Then the $K^+$ ions are transferred into the guard cells, by forming a dense gradient. For this absorption of $K^+$ ions it needs protons ($H^+$) ions then, $K^+$ ions are replaced for the protons $H^+$. Absorption of $K^+$ ions is called the influx of $K^+$ ions into guard cells and forward movement of $H^+$ ions is called the efflux of $H^+$ ions.

This is an active ionic exchange and requires ATP energy and cytokinin (a plant hormone). In this way, the concentration of $K^+$ ions increases in guard cells and at the same time, the concentration of $H^+$ ions decreases in guard cells. As a result of this, guard cells swell and stomata open.

Thus, the correct option is D. i.e. Opening of stomata.

Note: Guard cells are cells enclosing every stoma. They support altering the value of transpiration via closing and opening the stomata. Light is the major instigator for the opening or closing. Every guard cell has a thick cuticle part and thin one against it. As water enters the cell, the thin part bulges externally like a balloon and draws the thick part along with it, developing a crescent; the combined crescents produce the opening of the pore.