If a person commutes just a few miles to school, which of the following would be the most practical and most energy-efficient method of transportation - based on the reason given?
a. a bike would be practical for more than 10 miles in cold climate.
b. public transportation is always available in every metropolitan area.
c. if the commute is only a few miles, an electric car would be practical.
d. walking is always the most practical.

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.