Question

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

Answer 1

The percentage of Oxygen in the atmosphere will decrease. This will make it more difficult for organisms to get enough Oxygen to carry on cellular respiration needed for life.

Explanation:

Photosynthesis takes Carbon Dioxide `CO_2` and water `H_2O`
and turns the compounds into Oxygen and Glucose.

If the number of photosynthetic organisms decrease the amount of Oxygen in the atmosphere will also decrease.

This is why the deforestation of the earth is of such great concern. The forest, especially the rain forest are the greatest producers of Oxygen on the land.

Pollution of the Ocean is of even greater concern. The photosynthetic organisms in the ocean are the earth's greatest source of Oxygen. If pollutions kills significant numbers of these microscopic organisms other life will become much more difficult and impossible for some species.