The end result of metabolism is a cellular energy unit called
an enzyme.
a carbohydrate.
a glucose molecule.
atp.

The best answer is ATP (Adenosine triphosphate).

Metabolism is a term referring to the overall processes by which  energy is obtained by an organism. In man it begins with the digestion process, and ends with cellular respiration.

Food molecules are broken down into their monomer units through the digestive process. Carbohydrates are broken into glucose units. Glucose is taken in by cells and used in cellular respiration to produce ATP, which is the form of energy that cells use.

Cellular respiration involves three stages namely glycolysis , Krebs cycle and electron transport chain.  From one molecule of glucose, the number of ATP molecules generated through cellular respiration  is 36 to 38 molecules.