The systems that make up life have many levels of organization. From smallest to biggest, they are: molecule, cell, tissue (group of cells with a common purpose), organ (part of the body with a purpose), organ system (group of organs that work together), organism, population (group of organisms of the same species), community (all of the organisms that interact in an area), ecosystem (all of the organisms in an area and the non-living surroundings), and biosphere (all parts of the Earth that have life).