Answer:
They increase the rate of photosynthesis by increasing the amount of water in the plant.
Explanation:
It is hot and dry when these openings close, so the Sun has to be out. Photosythesis is caused when the Sun and water are used by a plant to make food.
The answer to the question should be they increase the rate of photosynthesis by increasing the amount of water in the plant.
A diagram of photosynthesis is below.