Polymerization and the break down of a polymer are two opposite reactions. what role does a water molecule play in both of them?
a water molecule is released during polymerization, which in the formation of a bond, and it is added during the break down of a polymer, which in breaking the bond.
a water molecule is added during polymerization, which in the formation of a bond, and it is released during the break down of a polymer, which in breaking the bond.
a water molecule is added during polymerization, which in the formation of a bond, but it does not play any role during the breaking down of a polymer.

1.When a water molecule is released during polymerisation, it's called a condensation reaction. What this means is that 2 molecules come together, but release water as a by-product. A water molecule needs to be introduced for the polymer to break apart (hydrolysis).

2.When a water molecule is needed during polymerisation, it's something called hydrolysis. What this means is that a when a water molecule is introduced, it causes 2 molecules to join. When the polymer breaks, water is released (condensation reaction).

3.Hydrolysis takes place to join 2 molecules together. When the polymer is broken down, water isn't released as a by-product.
(sorry that I couldn't help much on the last one).

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.

You should never redesign your experiment. try and see what in your experiment you made a mistake on or try and test your experimemt with somebody else. see if they get the right results.