Short answers, pulled from the story.
Metabolism describes the set of chemical reactions that occur within organisms to convert food into energy, build tissues, and eliminate waste. This process functions as the fundamental engine of life that allows organisms to grow, reproduce, and respond to their environments.
The first controlled experiments in human metabolism were published by Santorio Santorio in 1614 in his book Ars de statica medicina. He described how he weighed himself before and after eating, sleeping, working, and excreting to measure food loss.
Adenosine triphosphate serves as the energy currency of cells and acts as a bridge between catabolism and anabolism. The human body uses about its own weight in adenosine triphosphate per day as it is continuously regenerated to power every cellular process.
Most structures that make up animals, plants, and microbes are made from four basic classes of molecules: amino acids, carbohydrates, nucleic acids, and lipids. Proteins are made of amino acids, carbohydrates store energy, nucleic acids store genetic information, and lipids form biological membranes.
Eduard Buchner discovered enzymes at the beginning of the 20th century and separated the study of chemical reactions of metabolism from the biological study of cells. This discovery marked the beginnings of biochemistry and allowed scientists to study metabolic reactions independently of whole cells.