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Which of the following facilitates opening of stomatal aperture?

1. Decrease in turgidity of guard cells
2. Radial orientation of cellulose microfibrils in the cell wall of guard cells
3. Longitudinal orientation of cellulose microfibrils in the cell wall of guard cells
4. Contraction of outer wall of guard cells

Correct answer: Radial orientation of cellulose microfibrils in the cell wall of guard cells

Solution

Radially arranged cellulose microfibrils make the guard-cell wall expand unevenly, so turgor pressure bends the cells apart and opens the pore. The other options either reduce turgor or describe wall behavior that would not promote opening.

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