This is the answer because guard cells play an important function of controlling stomata. The ensures that stomata are open during the day and closed during the night for the purposes of photosynthesis. The stomata are the pores that are found on the under surface of a plant leave,whose role is gaseous exchange.
The main function of guard cells is to regulate the opening and closing of the pore formed between the gap of two guard cells, termed as stomata.
Option A is incorrect as stomata are the least susceptible area from where pathogens can enter the plant cell.
Option B is incorrect because photosynthesis is not directly and much affected by guard cells.
Option D is incorrect as chloroplasts are not associated with the guard cells.
Stomata are directly linked with movement of guard cells, so correct answer is option C. Through stomata, exchange of gases and water vapor takes place.
"Down" is simply the direction gravity is pulling you, and "up" is just the opposite direction. ... Gravity is a centrally attractive force, so "going down" means falling or being pulled towards the center of the nearest massive object.
