Biological organisation
![A population of bees shimmers in response to a predator.](/Images/godic/202501/10/-Shimmering_bees_drive_hornet_away.ogg4139.jpg")
![The simplest unit of life is the atom, like oxygen. Two or more atoms is a molecule, like dioxide. Many molecules is a macromolecule, such as a phospholipid. Multiple macromolecules form a cell, like a club cell. A group of cells functioning together is a tissue, for example, Epithelial tissue. Different tissues make up an organ, like a lung. Organs work together to form an organ system, such as the Respiratory System. All of the organ systems make a living organism, like a lion. A group of the same organism living together in an area is a population, such as a pride of lions. Two or more populations interacting with each other form a community, for example, lion and zebra populations interacting with each other. Communities interacting not only with each other but also with the physical environment encompass an ecosystem, such as the Savanna ecosystem. All of the ecosystems make up the biosphere, the area of life on Earth.](/Images/godic/202501/10/Levels_of_Organization.svg4140.png")
Biological organization is the hierarchy of complex biological structures and systems that define life using a reductionistic approach. The traditional hierarchy, as detailed below, extends from atoms to biospheres. The higher levels of this scheme are often referred to as a ecological organization concept, or as the field, hierarchical ecology.