Question

A transverse section of a leaf is represented in the diagram above. Transpiration in the leaf depends on the transport of potassium ions

• A. into O
• B. into P
• C. from M to L
• D. from M to Q

Answer 1

The correct option is B into P

Stomatal opening and closing is caused by the absorption and removal of water into and from the guard cells (P) respectively. K+ ions have a huge role to play in this.
Opening is regulated by huge amounts of potassium ions which gets accumulated in the guard cells which increase the solute potential and hence the water potential drops. This causes water from neighbouring cells to enter the guard cell and they become turgid or swollen. In this condition, the stomatal pore is opened.
While closing is the opposite phenomenon of opening as it occurs when water is removed from the guard cells and they become flaccid. K+ ions move out of the cell. This causes the stomatal pore to close. This occurs in the absence of light or when rates of photosynthesis are low. In this condition the stomatal pore is closed.
So the correct answer is P - guard cell.