Agroup of snails (of the same species) lives in a garden that also includes beetles and tomato plants. what level(s) of ecological organization does the group of snails belong to?

The group of snails would represent the "population" level of ecological organization. A single snail would represent and Individual. The snails and beetles would represent a community, and the garden itself with the various creatures would represent and ecosystem.

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.