Which one is responsible for opening and closing of stomata?
Correct answer: D. All of the above.
- A. Rise in pH of guard cells causes hydrolysis of starch.
- B. Cytokinins and cAMP are required.
- C. Absicisic acid promotes closure.
- D. All of the above.
Explanation
Correct option is D. Abscisic acid (ABA) stimulates closure of stomata in the epidermal tissue of the leaves. Auxin and cytokinins are positive regulators of stomatal opening. In the guard cells in the presence of light, starch is broken down into malic acid, which dissociates to form protons. The protons are pumped out of the guard cells, and in exchange K+ ions are pumped in. Thus, the pH is raised and the potassium ions lower the osmotic potential, which results in endosmosis. This makes the guard cells turgid resulting in the opening of the stomata. So the D option is correct.
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The human respiratory system includes the air passages, lungs, alveoli and breathing muscles, while gaseous exchange explains how oxygen enters blood and carbon dioxide leaves it by diffusion. The effects of smoking include damage to cilia and alveoli, reduced gas exchange, chronic bronchitis, emphysema and increased risk of lung cancer.
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