Photosynthesis is important to living organisms because it is
a. the foundation of most food chains
b. the source of nitrogen gas in the air
c. how animals get carbon dioxide to breathe
d. the process that occurs in most ecosystem

It is not C because animals use cellular respiration to transfer CO2 into Oxygen in the mitochondria.

It could be considered A because in food chains, plants are the primary producers of food chains. These primary food chains go through photosynthesis in order to "breathe" and make food. So the best answer to me is A.

*Though, if you dig deeper, the process that occurs in most ecosystems could be the answer because most ecosystems have plants because plants are the bottom of the food chain, without plants, there is no oxygen for the mammals to breathe. Ask your teacher/professor upon this question and be sure to include the main points in my conclusion.

Ithink it’s around 500 million or something. kinda scary honestly but that’s just my opinion.