Which of the following essential nutrients plays an essential role in theopening and closing of the stomatal aperture?a) ABAb) Mgc) Hd) K

The correct answer is d) K. Potassium (K) plays an essential role in the opening and closing of the stomatal aperture.

Here's a step-by-step explanation:

1. Stomata are tiny openings or pores in plant tissue that allow for gas exchange. They are crucial for photosynthesis, as they let in carbon dioxide (CO2), which is needed for the process, and let out oxygen (O2), which is a byproduct of the process.

2. The opening and closing of these stomata are controlled by the turgor pressure in the surrounding guard cells.

3. Potassium ions (K+) play a key role in regulating this turgor pressure. When the plant needs to open its stomata (usually during the day, when photosynthesis can occur), potassium ions are pumped into the guard cells. This causes water to also flow into the cells (due to osmosis), making them turgid and causing the stomata to open.

4. Conversely, when the plant needs to close its stomata (usually at night, or when the plant is under stress and needs to prevent water loss), potassium ions are pumped out of the guard cells. This causes water to also flow out of the cells (again due to osmosis), making them flaccid and causing the stomata to close.

So, while ABA (a plant hormone), Mg (magnesium), and H (hydrogen) all play important roles in plant physiology, it is K (potassium) that is directly involved in the opening and closing of the stomatal aperture.