Question

Cacti grow slowly due to the fact that they keep their stomata closed for much of the day. Why would closing their stomata during the day be an advantage for the cacti?
A. it limits water loss through transpiration
B. it conserves oxygen produced in photosynthesis
C. it recycles carbon dioxide within plant systems
D. it protects plant tissues from predators

Answer 1

The answer is A. Stomata are used for gas exchange - CO2 in and O2 out, but when they are open there will also be water loss through transpiration. This is a major problem if a plant is in a desert environment and has to conserve water. The cactus is conserving water by keeping its stomata closed for part of the day but since CO2 is needed for photosynthesis this will have the side effect of slowing growth.

Answer 2

B is wrong because oxygen is a waste product to a plant.
C is wrong because although CO2 is produced during plant metabolism, any recycling of CO2 is a consequence of closing the stomata rather than a cause, since open stomata would allow diffusion of CO2 from the atmosphere.
D -This is wrong because the stomata are only a few tens of microns across - bacteria might be able to enter but nothing bigger like an insect.

Answer 3

thank you soo much

Answer 4

You're welcome :)