Do you wonder if life exists on other planets? How would we know? How do we define life on Earth? What signs do we look for to decide if something is alive? Do we expect life on another planet to follow the same basic rules of life as they do on Earth?
These are some of the great questions that you can ask your class during the first introductory discussion of biology. It should give a hook to those students less interested in academic biology but who may have other interests such as science fiction.
I like to get my students excited about astrobiology. This is the field of science that considers not only the question of whether extraterrestrial life exists, but it also discusses whether life originated only on Earth, or if it is something that is spread throughout the universe. The actual field of astrobiology is quite interdisciplinary, touching on fields of such as astronomy, molecular biology, biochemistry, biophysics, geology and chemistry.
There is probably an infinite variety of scope and sequence arising from our initial question. At some point the students will no doubt bring up in the discussion ideas of cells and reproduction.
To challenge student thinking, I often set up a Traube cell observation. If you have not done this before, you will want to practice manipulating this set-up before using it in front of your class. I found it best to display this on screen using a projecting microscope or digital microscope camera. Basically you make up a weak solution of potassium ferrocyanide (K4
O) not more than 0.05 to 0.08 mol/L. A few millilitres of this solution will fill the well of a depression slide. When you place a tiny crystal of copper sulfate into the solution, life begins! Or, does it? Within minutes cells appear to grow around the crystal and they will continue growing. This will give ample opportunity for you to discuss what is in the solution and why it may or may not be living according to the definitions the students have developed.
You can use this Traube cell demonstration to segue into a discussion about how models are used in science to explain our world to ourselves.
In another aspect of the conversation you can ask students to think about how we protect other planets and moons from contamination by our visit or from bringing back exotic life contaminating our own planet Earth. This is an ongoing serious discussion among the space exploring scientists. Just as there is the Prime Directive in the Star Trek world, there is a 1967 Outer Space Treaty which provides the legal framework to protect the study of space from harmful contamination from Earth or adverse introduction of extraterrestrial material to Earth.
What if extraterrestrial life is never found? Well, we will continue to learn and benefit from the science of the search.
Note: Be sure to check out the WHMIS Material Safety Data Sheet on potassium ferrocyanide to ensure that your school district allows you to use this material. It may be harmful if swallowed and requires caution when handling as it can irritate the skin. I recommend that the teacher use this as a demonstration and not give younger students access to the chemicals.
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