The opening and closing of stomata is regulated by the:
A. Phloem cells
B. Epidermal hairs
C. Xylem vessels
D. Guard cells
Answer: Option D
Solution (By JKSSB Mock Tests)
Stomata are surrounded by two kidney-shaped guard cells in dicots (dumb-bell-shaped in grasses) that control pore opening/closing via turgor pressure changes. When guard cells absorb water and become turgid, the stomatal pore opens; when flaccid, it closes. This process is influenced by light, CO₂ concentration, and abscisic acid (ABA). Stomata are critical for gas exchange and transpiration.
Explanation:
Veins, especially in limbs, have one-way valves that prevent the backflow of blood as it returns to the heart against gravity. Arteries have thick walls to withstand pressure and lack valves. Capillaries have no valves.
Explanation:
Charles Darwin and Alfred Wallace independently proposed natural selection as the mechanism for evolution. Darwin published 'On the Origin of Species' in 1859.
Explanation:
Apical dominance is the phenomenon where the main central stem (apical bud) grows more strongly than the side stems (lateral buds). This is primarily controlled by auxin (specifically IAA), which is produced at the shoot apex and moves downwards, inhibiting the growth of lateral buds. Removal of the apical bud promotes lateral branching.
No comments yet. Be the first to start the discussion!