Why are animals important to an ecosystem? select one: a. they produce carbon dioxide for food b. they produce carbon dioxide to with photosynthesis c. they produce oxygen to with photosynthesis d. they produce oxygen for food is it a or b? i know this is an easy question, but i'm not so sure : l animals breathe out carbon dioxide for the plants. (which is their food) but in b it says animals release carbon dioxide to with photosynthesis involves with carbon dioxide.