Carbon dioxide is a waste product in most things that can move.

The importance of carbon dioxide is that many organisms that take in energy from sunlight use it as a way to store that energy in the form of sugars. This becomes the food that other organisms eat, and serves as the energetic basis for virtually all ecosystems. I think an interesting thought is that at some point in history, every atom of carbon in your body was a molecule of carbon dioxide.

But the importance of carbon dioxide is ecological, not just with single animals. So the answer to your question is basically yes plants need it to make food, and we need it so that plants can make food.

Warning to left wingers-----> don't try and breathe pure CO2, that will cause you to asphyxiate. somebody explain that to stupid62 please.

It's all so clear to me now!  Damn that Al Gore!