Guard cells are paired cells that are found in the leaves of plants. What is the role of guard cells in a plant?

Explanation:

Guard cells are located in the leaf epidermis and pairs of guard cells surround and form stomatal pores, which regulate CO2 influx from the atmosphere into the leaves for photosynthetic carbon fixation. Stomatal guard cells also regulate water loss of plants via transpiration to the atmosphere.

i am going to guess that it is co2.