AP BIOLOGY

Detailed explanation-1: -Potassium is transported across the apical membrane by an electroneutral transporter that tightly binds one sodium and potassium ion to two chloride ions. A second component of potassium reabsorption involves paracellular transport mediated by the lumen positive transepithelial potential difference.

Detailed explanation-2: -Potassium channels function to conduct potassium ions down their electrochemical gradient, doing so both rapidly (up to the diffusion rate of K+ ions in bulk water) and selectively (excluding, most notably, sodium despite the sub-angstrom difference in ionic radius).

Detailed explanation-3: -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-4: -Potassium channels are also stimulated by depolarization, but open about one millisecond later and are responsible for the repolarizing phase of the action potential. Potassium channels open just as the sodium channels are closing.