NEET BIOLOGY

Detailed explanation-1: -K+ ion theory (potassium pump theory)was proposed by Levitt in 1974. He states that:-During light:-Starch is converted to PEP ( phosphoenol pyruvic acid) which combines with CO to form oxaloacteic acid (OAA) and ánally to malic acid. This malic acid dissociates into malate anions and H ions in guard cells.

Detailed explanation-2: -According to Levitt theory, during day time starch is converted to organic acids. This causes increase in proton concentration. These protons are exchanged for potassium ions from surrounding subsidiary cells. The influx of potassium ions leads to inflow of water into guard cells, which become turgid and stomata open.

Detailed explanation-3: -Active potassium transfer theory was observed by Fujino (1967) that opening of stomata occurs due to the influx of K+ ions into the guard cells. The source of K+ ions are the neighbouring subsidiary and epidermal cells, thereby increasing the concentration from 50mM to 300mM in guard cells.

Detailed explanation-4: -Due to turgor, the guard cells become more arched outwards and the aperture between them widens, thereby opening the stoma. At night or when there is a shortage of water in the leaf, the guard cells turn flaccid and their inner rigid walls become straight, thus closing the stomatal aperture.