If the number of photosynthetic organisms on the earth decreased drastically, what would happen?

There would be no life on earth.

Explanation:

Photosynthetic organism provides life to other life forms on earth by providing food. Basic is the basic need for all the living organism on earth.

Only photosynthetic organisms have the ability to synthesize food by the help of carbon dioxide and water in presence of sunlight.

This food( glucose) is used by the consumers to sustain life on earth. This energy is used by the organism to perform various tasks of the body. All the food chains starts by photosynthetic organism.

So, ultimately all the other organism would die without photosynthetic organisms.

im not intirely sure but i think the anwser is d relative humidity