Weston Middle School

Life Science Course Materials

Weston, Massachusetts
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Body Systems

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Why are there bodies and organ systems?

Single-celled organisms are generalists, needing to carry out all functions for life( G.R.I.M.M.) on their own, including:

  • Growth
  • Reproduction
  • Irritability ( communication)
  • Metabolism
  • Movement

Cells in tissues ( i.e., muscle, nervous, structural, absorptive ) can be more specialized, only needing to make a few specific proteins that enables the tissue to do its specific job for the whole organism—for example, actin/myosin ( contractile proteins), collagen and keratin( structural),hemoglobin (oxygen transport), etc.

Each organ is composed primarily of one type of tissue, performing its function on behalf of each cell in the entire body.

Organs work together in organ systems-

  • Cardiovascular system
  • Digestive System
  • Skeletal system
  • Nervous system
  • Immune system
  • Excretory System
  • Reproductive System

On the origin of bodies:

"...A body is a very expensive thing to have. There are obvious advantages of becoming a creature with a large body: besides avoiding predators, animals with bodies can eat each other, smaller creatures, and move long distances. Both of these abilities allow the animal to have more control over its environment. But both consume a lot of oxygen. Bodies require even more energy as they get larger, particularily if they incorporate collagen. Collagen requires a relatively large amount of oxygen for its synthesis and would have greatly increased our ancestor's need for this important metabolic element.....It may have been the paleontological equivalent of a perfect storm to bring about bodies. For billions of years, microbes developed new ways of interacting with their enviroment and with one another. In doing so, they hit on a number of the molecular parts and tools to build bodies, through they used them for other purposes. A cause for the origin of bodies was also in place: by a billion years ago, microbes had learned to eat each other. There was a reason to build bodies, and the tools to do so were already there.

Something was missing. That something was enough oxygen in the atmosphere to support bodies. When the earth's oxygen increased, bodies appeared everywhere. Life would never be the same...."

- Neil Shubin, Your Inner Fish (2008)


BBC Interactive Body Systems Game

Neil Shubin, Evolution(PBS)-The Genetic Toolkit for Body Structure


Teachers' Domain- Resources

Revised May 2008 by Jonathan Dietz, dietzj@mail.weston.org