At resting potential the inside of the cell membrane is negatively charged. Why?

When the membrane is at rest, K+ ions accumulate inside the cell due to a net movement with the concentration gradient. The negative charge within the cell is created by the cell membrane being more permeable to potassium ion movement than sodium ion movement.

There would be one bar shorter than the bar for peaches.

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.