Question

The element responsible for opening and closing of stomata is

• A. boron
• B. potassium
• C. phosphorus
• D. sodium

Answer 1

The correct option is B potassium

Potassium ions play a major role in the opening and closing of stomata. Stomatal apparatus is present in the epidermis of leaves. It includes a pair of guard cells enclosing a stomatal pore. Exchange of gases and transpiration occur through these stomatal pores. Opening and closing of the stomata is controlled by the guard cells. Due to the efflux (moving out) of potassium ions from guard cells, the water potential inside the guard cells increases and the water moves out of the guard cells into the neighbouring cells. This makes the guard cells flaccid and stomatal pore closes.
Due to the influx of potassium ions into the guard cells, water potential inside guard cells decreases and water from the neighbouring subsidiary cells enters guard cells making them turgid. This causes the opening of stomatal pore.