WGU C190 Intro to Biology Guaranteed
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1. Levels of Biological Organization
Biology often studies life through a hierarchy of complexity.
Abiotic: Non-living; may be within or made by a living organism.
Biotic: Living. Matter is considered biotic if it was ever alive at some point in time.
Atom: The smallest level and basic unit of matter.
Molecule: Two or more atoms held together by chemical bonds.
Macromolecule: Large, biologically important polymers (e.g., DNA).
Organelle: Compartments inside a cell (like the nucleus) that carry out specific
functions.
Cell: The fundamental unit of life; the smallest entity possessing all characteristics of
life.
Microorganism: A single-celled life form (e.g., bacteria).
Tissue: A group of similar cells working together for a detailed function.
Organ: Collections of tissues carrying out a common general function.
Organ System: A group of functionally related organs.
Organism: Individual living entities that survive and reproduce as a unit.
Population: All individuals of a species living within a specific area.
Community: All the interacting populations in a specific area.
Ecosystem: All living things in an area combined with the abiotic (non-living)
environment.
Biosphere: The highest level; the collection of all ecosystems on Earth.
