Which of the plant systems is most like the cardiovascular system in animals?

The plant systems that is comparable to the cardiovascular system in animals would be the vascular tissue system. It is responsible for transporting food, water and other nutrients throughout the plant which can be compared to the cardiovascular system which is responsible of transporting blood, oxygen and other nutrients to the animal's body.

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.