What would happen if guard cells in a plant stopped working? a. diseases would quickly invade the plant. b. photosynthesis would occur more slowly. c. stomata would not open and close. d. chloroplasts would change color

C. Stomata would not open and close.

Explanation: 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.