ICSE Class 8 Answered

Hi Adityanshu,

Following steps takes place in the Potassium Pump Theory:

1. In the guard cells, starch is converted into malic acid in presence of light (during day time).

2. Protons formed are used by the guard cells for the uptake of K⁺ ions. This is an active ionic exchange and requires ATP energy and cytokinin.

3. The concentration of K⁺ ions increases in guard cells.

4. At the same time, the concentration of H⁺ ions decreases in guard cells. The pH of the cell sap in guard cells also increases simultaneously (pH becomes more than 7).

5. There is also an increased uptake of CI^- by the guard cells to maintain the electrical and ionic balance inside and outside the guard cells.

6. The malate anions formed in the guard cells are neutralized by the K⁺ ions. This results in the formation of potassium malate.

7. Potassium malate enters the cell sap of the guard cells thereby reducing the water potential while increasing the osmotic concentration and the osmotic pressure of the cell sap.

8. Hence, endosmosis occurs.The guard cells become turgid and kidney-shaped and the stomata opens.