Levels of Organization of Living Things (1)

Levels of Organization of Living Things Living things are highly organized and structured. The atom is the smallest and most fundamental unit of matter. It consists of a nucleus surrounded by electrons. Atoms form molecules. A molecule is a chemical structure consisting of at least two atoms held together by a chemical bond. Many biologically important molecules are macromolecules. A macromolecule is a large molecule that is typically formed by combining smaller molecules. For example, nucleotides are small molecules linked together to form the macromolecule, DNA (deoxyribonucleic acid). DNA contains the instructions necessary for cells and organisms to maintain homeostasis.