Answer : The correct option is, the biochemical reactions that occur in an organism.
Explanation :
Metabolism : It is defined as the biochemical processes or reaction that occur within a living organism to maintain the life.
In the metabolism process, the food converted into the energy that means in this process what you eat or drink that is converted into the energy.
For example : When a person eats a spoonful of sugar then inside the body the sugar molecule are broken down into simple molecules with release of some energy. This energy is used by the body for another purposes.
Hence, the most complete definition of metabolism is the biochemical reactions that occur in an organism.