Plants, through the process of photosynthesis, use solar energy to produce the end product glucose. since energy is used here, what type of reaction is photosynthesis?
endergonic reaction
exergonic reaction
reversible reaction

The answer is Endergonic reaction.

In the endergonic reactions, energy is used. In the exergonic reactions, energy is released. Since energy is used in photosynthesis, it is the endergonic reaction. 

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.