What physiological change in leaf stomatal guard cells triggers the opening of the stomatal pore during daylight?
Answer and explanation
Correct answer: A. influx of potassium ions followed by water uptake that increases guard cell turgidity
- Step 1: In light, active proton-pumping drives an influx of potassium (K⁺) and chloride ions into guard cells. Step 2. Increased osmotic concentration causes water to enter by osmosis, increasing turgor pressure. Step 3. Because inner cellulose walls are thicker and less elastic than outer walls, guard cells bow outward, opening the pore. Answer: influx of potassium ions followed by water uptake that increases guard cell turgidity. Why not the others: Efflux causes closure at night; starch converts to malate/sugars, not cellulose; cuticular contraction is not the mechanism.
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