When water enters the guard cells, they swell and the opening of the stomata becomes _____.

Correct option is A

The correct answer is (a) open.

Guard cells control the opening and closing of stomata, which are tiny pores on the surface of leaves that regulate gas exchange and water loss. When water enters the guard cells, the following occurs:

Mechanism:

• Turgor Pressure: The influx of water increases turgor pressure within the guard cells.
• Swelling of Guard Cells: The guard cells swell, and their inner walls (thicker and less flexible) are pulled apart, leading to the stomatal opening.
• Opening of Stomata: This allows gas exchange for processes like photosynthesis and transpiration.

Key Points:

1. Water Entry:

   • Water enters guard cells via osmosis when potassium ion (K⁺) concentration increases inside the guard cells.
   • This process is triggered by light or other stimuli that activate the transport of K⁺ ions into the guard cells.

2. Stomatal Opening:

   • Occurs during the day to facilitate photosynthesis by allowing carbon dioxide (CO₂) to enter the leaf.

3. Stomatal Closing:

   • When water leaves the guard cells, they lose turgor pressure, become flaccid, and the stomata close to prevent water loss during drought or nighttime.

Additional Information:

• Close: Stomata close when guard cells lose water, not when they gain water.
• Shrink: Shrinking occurs when guard cells lose water and become flaccid.
• Burst: Guard cells do not burst when they swell; they are adapted to handle increased turgor pressure.