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Principles of Biology

Four foundational truths of biology: cell theory, gene theory, homeostasis, and evolutionary theory.

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Is It Alive?
Teacher Contributed

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Is It Alive?

Life occurs in many incredible forms in many unexpected places. It isn't always obvious when something is alive so what do you need to look for to make that determination?

Student Exploration

You’re exploring a cave with a friend when you hear a drip…drip…drip… turning toward the sound you see...Snottites...


Look over the criteria given for a living organism in the Introduction to Biology concept collection. How would you test to see if the “snottite” matches the criteria? Whether you decide if it is alive or not, organize your ideas to persuade someone who disagrees with you that you are correct.

Extension Investigation

If you need help scratching a mental itch, use the resources below:

  1. What characteristics do you feel are essential to consider something alive?
  2. How does a “snottite” differ from organisms you are more familiar with?
  3. What do snottites use as an energy source? How is this connected to the environment they live in?

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