In biological organization, the most complex level includes those life forms with organ systems. When considering the organization of all known ecological forms, the universe is the most complex.
In a standard biological system, the lowest or least complicated organization level is the atom, which is the smallest unit of measurement for chemical elements. Each subsequent layer is made up of atoms and groups of atoms to create the sub-cellular and cellular levels. Cells form tissues, which form organs that make up organisms. The ecosystem is made up of living and dead organisms as well as the material generated by them and the substances in which they thrive and grow.
The ecosystem itself comprises the most complex level of organization for individual biological systems. However, the ecosystem includes the interaction of many biological systems and exists within an environment known as the biosphere or ecosphere. The biosphere is the largest ecosystem and encompasses all organizational systems on the planet. The Earth itself stands as the next level of organization and is part of a solar system. Solar systems and galaxies form the universe, which is the most complex level of organization that includes all forms of life and the emergent properties from which it is created.