What would happen if guard cells in a plant stopped working?

Photosynthesis would occur more slowly.

Chloroplasts would change color.

Stomata would not open and close.

Diseases would quickly invade the plant.

ok not the last one

The answer is C

Explanation:

Guard cells usually keep stomata open during the day and closed at night. If the stomata were open at night, very little gas exchange would occur, but water loss would still continue.

well, that's easy; the answer's c, "it reduces contamination of the water and substrate of the estuary."