Explain why a circular system is important in meeting the needs of all cells throughout an animals body

The circular system is important because it touches every organ and system in your body. when a human breathes the circular system carries oxygen to your cells and carries dissolved carbon dioxide back to the lungs. all the cells in your body that needs oxygen accsess to the fluids in your circulatory system.

Atp is is our little "pocket" of energy. of course, if you have too little, then it means you have too little energy, and you'll pass out. the way to not have enough, is to have no energy sources (glucose, fats, proteins). you can't have too many atp molecules. cycles like the krebs cycle produce it, but if you have too much of any substrate (or too little for that matter), the cycle stops and atp is no longer made (it stops until substrate levels are such that the process can go on). in any case, this is unlikely since atp is constantly hydrolyzed and remade, even while you're asleep. you won't have too much. if you have zero, you are dead or dying.