Ascientific hypothesis

can be based on personal beliefs or opinions
can be tested by experiments or observations
does not have to be tested to be accepted as correct
is a proven fact with much evidence to support it

A scientific hypothesis can be tested by experiments or observations

Photo means light and synthesis means combination so combination of light

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.