Teacher Script for Discussion Introduction for "Is It Alive?"
Imagine yourself as a butterfly. You flit around for only two weeks in which time you eat a little nectar, catch a breeze (or it catches you) and mate. One day you land on a mighty saguaro. Now, you're a very thoughtful butterfly and you ask yourself, "Is this thing I'm sitting on alive?" Can you answer your own question?
Take two minutes to think about this and discuss this with the others in your group.
I'm going to walk around and try to help you. Why do you think that is so? Can you give more evidence for your idea? Is that similar to something else?
Let's collect all the original ideas from each of the groups. Group number one, give me one of your ideas please........
Sometimes there might be a problem with the time frame that we have to observe things. A butterfly could even think that humans were non-living if it saw us when we were asleep.
Some of you may know that biology text books have a section on "What is Life?". Usually they say there are five conditions that a thing must meet in order to be considered alive. They are 1) reproduction, 2) growth, 3) nutrient acquisition, 4) irritability (or the ability to respond to the environment) and 5) they must be packaged in cells.
Which of the text book's concepts did you come up with? Which of the text book's concepts did you not come up with? Which of your ideas do you think the text book should adopt?
In your groups, answer the question, "What could be dead for awhile, yet still come back to life?"
Are seeds alive? Are spores alive? Are bears alive when they hibernate? (There is an on going debate whether bears go into a deep enough sleep to be considered hibernating- but that is biology!) Are spade-foot toads alive most of the year? Are lichens alive when they are desiccated?
When an organism can completely dry out and still re-animate itself when rehydrated it is called poikilohydric. Most plants require a constant water content and they are called homiohydric.
In your groups, answer the question, "What would the advantage of 'dying' for awhile be in the desert?"
[Escaping the heat and extended droughts.]
In your groups, answer the question, "What would the advantage of staying alive in the desert all year be?"
Colonize areas, use resources not being used by other organisms, "Make hay while the sun shines!" as John Clyde Murray used to say.
I'm going to place a small petri dish on the ground before you with little scraps of stuff on top of the dirt. Don't bend over or anything, but just observe it as if you were just walking in the desert and just happened to look down. Write any observations that you can of it, and keep asking if you can prove it is alive or dead. Please make a sketch of what you see in the petri dish from your lofty perspective.
Now, we are going to get a little closer and observe just a little better. Please pick up the dish, being very careful not to disrupt the dirt inside. With the dish on the table in front of you, please draw the contents of each of the divisions of the dish. Remember that drawing is more detailed than sketching.
Now, using any magnification you have, observe closely and draw with great detail. Make sure that you write down at least four observations of each of the samples in your petri dish.
Tomorrow we will be learning to identify the differences between these organisms, but for today, I'd like you to just write down your observations and drawings. I am now going to walk around and help each of your groups out.
Keep all of your work. We will be learning more about them tomorrow.
{Give plenty of time for this section) I could foresee 1/2 of an hour or more if the interest is there.}
Lichen are very slow growing organisms. They have the ability to stop growing when there isn't enough water. Again, this is known as poikilohydric. (Vascular plants that keep a constant water pressure are homiohydric.) Around Tucson, the amount of water present in the soil is of utmost importance. Typically there are less than three weeks of growing days (days where it has rained or rained the day before and hasn't evaporated.) This makes for very little growth in a year. The rest of the time all metabolic activity ceases. Is this death?
Questions that you should be asking your students is about their observations. Can you be more specific? Can you show evidence of your idea? Why do you think that?
This activity allows you to also gauge their level of thinking and participation ability.