This document discusses the four main types of organic molecules that make up living cells: carbohydrates, lipids, proteins, and nucleic acids. It explains that carbohydrates like sugars are a major source of fuel for cells and are made up of monomers like glucose. Lipids including fats and steroids function in energy storage, insulation, and as chemical messengers. Proteins are made through linking amino acid monomers and perform most functions in cells, such as structure, storage, defense. Enzymes, a type of protein, act as catalysts to speed up chemical reactions by lowering their activation energy. The document provides details on the structures, functions, and reactions of these essential biomolecules that make up living organisms.