If your asking if you can prove everything by science then no but people will try they will give out theories and try to find solutions that they can't. And if your asking if your able to prove all things that happen/the explanations scientifically then the answer is no. Take how the world was made for example nobody knows how it is made. The scientists are trying to prove it was created by some big bang when in reality nobody really knows that's just a theory. One of many theories.
The answer will be be that. Chemical energy can stored more efficiently as glucose than it can be as ADP .
In my opinion is A.to mark out its territory to others of its own species
You need essential amino acids in your body, because you can not make them. If you do not have any in your diet proteins break down resulting in muscle loss and problems with repair. Amino acids are building blocks of protein. So he won't be able to build protein.