Transpiration: Factors and Mechanism · NCERT Biology

The immediate cause of the opening or closing of the stomata is a change in the:

  1. Turgidity of the guard cells
  2. Number of chloroplasts in guard cells
  3. Thickness of the outer walls of guard cells
  4. Orientation of xylem vessels
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Correct answer: Turgidity of the guard cells

Stomatal movement is driven by turgor changes in guard cells. When water flows into guard cells, they become turgid and the stomatal pore opens; when they lose water, they become flaccid and the pore closes.

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