[Campbell Biology P.847] Which of the following statements correctly describes a mechanism o... | Practice Question

Which of the following statements correctly describes a mechanism of stomatal regulation?

  • A: Light stimulates guard cells to accumulate Na+, leading to stomatal opening.
  • B: Depletion of CO2 within leaf air spaces causes stomata to close.
  • C: Abscisic acid (ABA) promotes stomatal opening under water deficiency.
  • D: Blue-light receptors activate proton pumps, promoting K+ absorption and stomatal opening.

Explanation

Light, specifically blue light, activates receptors in guard cell plasma membranes. This stimulates proton pumps, leading to an influx of K+ ions. The accumulation of K+ causes water to enter the guard cells by osmosis, making them turgid and opening the stomata. CO2 depletion also leads to opening, and ABA leads to closing.