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Levels of Organization
(Cells to Organisms)

by Greg Crowther


Virtually all anatomy and physiology classes cover the following definitions: a group of related cells is a tissue; a group of related tissues is an organ; a group of related organs is an organ system; and the organ system collectively constitute an organism. The Holt Science and Technology short course textbook on Cells, Heredity, and Classification (2005) includes a figure whose labels are so nicely concise that, with minimal adjustments, they can be rapped. The first verse below can be done as a call-and-response; the second verse provides examples of a tissue, an organ, and an organ system; students could be given the exercise of substituting other examples.


Cells form tissues! (Cells form tissues!)
Tissues form organs! (Tissues form organs!)
Organs form organ system! (Organs form organ systems!)
Organ systems form YOU! (Organ systems form YOU!)

Cells form tissues! (Myocardium!)
Tissues form organs! (A beating heart!)
Organs form organ systems! (Cardiovascular!)
Organ systems form YOU! (Organ systems form YOU!)

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