Key Concepts: Levels of Biological Organization

Hierarchy of Life

Life is organized in a hierarchy from simple to complex levels:

• Atom → Molecule → Organelle → Cell
• Tissue → Organ → Organ System → Organism
• Population → Community → Ecosystem → Biosphere

Key Definitions

• Population: All members of a species in one area
• Community: All populations in an area
• Ecosystem: Community plus the physical environment
• Biosphere: All ecosystems on Earth