Detailed Explanation:

Stomatal opening and closing is regulated by the turgor pressure in guard cells.

When guard cells absorb water, they become turgid and the stomata open; when they lose water, they become flaccid and the stomata close.

✅ Option 3 – Correct: The amount of water in cells directly controls the opening and closing of stomata through changes in turgor pressure.
❌ Option 1 – Incorrect: Position of nucleus does not affect stomatal movement.
❌ Option 2 – Incorrect: While proteins are involved in water transport mechanisms, the immediate cause is water content, not protein composition change.