The document discusses the basic building blocks of living things. It introduces cells as the smallest unit of life and notes that all cells are made of macromolecules. It defines macromolecules as large molecules formed by joining many smaller molecules together. The four main types of macromolecules are carbohydrates, lipids, proteins, and nucleic acids. These macromolecules are synthesized from simple precursor molecules called monomers that join together in chains to form larger polymer molecules.