Botany - Photosynthesis in Higher Plants Question with Solution | TestHub

In CAM plants stomata open at night. In these plants night acidification occurs. i.e., malic acid is synthesised during night due to incomplete oxidation of carbohydrates.
In night,$2{\text{C}}_6{\text{H}}_{12}{\text{O}}_6+3{\text{O}}_2\to 3{\text{C}}_4{\text{H}}_6{\text{O}}_5+3{\text{H}}_2\text{O}$
$\underset{\underset{\text{leads to opening of stomata}}{\downarrow }}{\left(\text{malic acid}\right)}$

At night malic acid formed in guard cells dissociates into H⁺and malate ions. K⁺ion exchange from subsidiary cells with H⁺ions. Thus due to accumulation of K⁺ions osmotic pressure of guard cells increases, endosmosis occurs and guard cells become turgid due to which stomata opens. The malic acid at day time breaks into CO₂and pyruvic acid thus increasing the concentration of CO₂in mesophyll cells. This is utilised in Calvin cycle to form sugar which is finally converted into starch.