Guard cells are involved in the process of:

Correct option is D

The correct answer is (D) transpiration.

• Guard cells play a crucial role in the process of transpiration, which is the loss of water vapor from the leaves of a plant through the stomata.
• Guard cells regulate the opening and closing of the stomatal pores, thereby controlling the rate of transpiration.

Explanation of other options:

• Transport of food : This is carried out by the phloem, not guard cells.
• Tropic movements : These are directional growth movements in response to stimuli, such as light or gravity, and are not directly related to guard cells.
• Circulation : Plants do not have a circulatory system like animals; instead, they rely on xylem and phloem for transport of water and nutrients.

Key Role of Guard Cells:

• Guard cells surround each stomatal pore and control its size by swelling (opening) or shrinking (closing) in response to environmental conditions like light, humidity, and carbon dioxide concentration.
• This regulation not only facilitates transpiration but also helps in gas exchange during photosynthesis.