To explain scientific biological phenomena, scientists use a technique called A~ the scientific method
B~ the scientific law
C ~ conclusions
D~ measurements

Only algae, oak trees, and bermuda grass produce atp by photosynthesis i am almost positive

Mitochondria produce atp, a high energy compound. atp is used for all sorts of enzyme-mediated reactions, such as making proteins/nucleotides/etc, certain compounds cross the cell membrane, muscles move, etc.  without this source of energy, a cell will die. it will not be able to repair itself, defend against pathogens, etc.