If a plant has xylem and phloem, then the plant is best described as A.) Nonflowering.
B.) Vascular.
C.) Flowering.
D.) Nonvascular.

I believe that B. Vascular is the correct optionz

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.