Life Science: Session 2
One of the best things about Life Science is how easy it is to bring the living world into the classroom. If your students are exploring the diversity of life on Earth through classification, you’ll have no difficulty providing an array of plants and animals for firsthand study. Terrariums and aquariums—such as those seen in the video in Stephanie Selznick’s first-grade classroom—are excellent small-scale study systems. The TerrAqua Column, which is described in Bottle Biology on this Web site, provides a similar opportunity.
As your students understandings of plants and animals grows, you may wish to introduce other groups of living things featured in the video—the fungi, protists, bacteria, and archaea. Some suggestions for bringing these life forms into your classroom are provided below.
Your students are likely to be familiar with typical examples of fungi—the mushrooms— and many will consider them to be plants. One way to help students distinguish between these two groups is to bring examples in and compare them side by side. The supermarket is a great source of these familiar fungi with most carrying a variety of types.
You might also start a field collection of fungi. During warmer and wetter months, a walk through the woods or a park can provide an astounding variety of specimens. Decaying plants and dead trees are great sources of fungi in the “wild”. Of course, no field specimen should ever be tasted!
Molds and yeasts are also examples of microscopic fungi that can be brought into the classroom. One way to collect molds is to use unpreserved bread to swipe different surfaces. The bread can be put into a plastic baggie and left for observation over time, with slightly moist bread being more likely to yield results more rapidly.
A more sophisticated way to culture both molds and yeasts is to purchase Petri plates with prepared media from a biological supply company. A type that contains “Sabouraud Dextrose Agar” selects for fungi, although “Trypticase Soy Agar” or “Nutrient Agar” will also work. These plates, which are sterilized when they are prepared, provide a food source for molds and yeasts. All you have to do is rub a cotton-tipped swab (which can also be purchased sterile if you wish) on a surface of interest and then apply it as a “streak” onto the plate, which is then incubated upside-down. The molds generally appear “fuzzy”, while the yeast colonies appear as “dots”.
There are few precautions in culturing fungi in this way—they grow in a closed container and are types that are already present in the environment. To dispose of the plates, spray with disinfectant solution, seal, and throw away. The only thing to be careful about is opening the plate—every time you do, you can introduce new microbes!
An example of culturing fungi in this manner can be seen in a Bottle Biology activity using the EcoColumn called “Basically, I’m a Fungi”.
The first time a student looks under a microscope at a drop of pond water is likely to hook them on the world of protists. This is what enthralled Anton Van Leuwenhoek, the inventor of the first microscope. There are few special “tricks” to observing these creatures—a compound light microscope, glass slides (depression slides are best), cover slips, and droppers are the basic supplies. You can also purchase solutions to slow them down, such as “ProtoSlo” or… if you don’t have a microscope, borrowing one from a middle or high school and sharing views of your samples with colleagues and administrators may even be a way of making a case for purchasing one. It’s even possible to distinguish between the plant-like forms, which are characteristically green, and the animal-like forms, which move in various ways.
Perhaps the most ubiquitous organisms on Earth are the bacteria. Your students are likely to be familiar with the word, and it is easy to bring meaning to it by culturing bacteria in your classroom—they’re on every surface. Like molds and yeasts, bacteria can be cultured on Petri plates with prepared media. “Trypticase Soy Agar” or “Nutrient Agar” will yield excellent results. Bacteria are cultured in the same way as fungi, by swabbing a surface of interest, applying it in a streak to the surface of the plate, and incubating it upside-down. Bacterial colonies will appear as tiny “dots” on the surface of the medium—each dot represents the offspring of one bacterium. To dispose of the plates, spray with disinfectant solution, seal with tape, and throw away.
An example of culturing bacteria in this manner can be seen in a Bottle Biology activity using the TerrAqua Column called “What is It?”
One reason that the archaea are fascinating is that they characteristically grow in extreme environments. For this reason, they are not good candidates for bringing into the classroom as live cultures—even microbiologists are challenged with getting them to grow out of their natural habitats. If you’re interested in introducing your students to this group, this Web site may be useful: http://www.ucmp.berkeley.edu/archaea/archaea.html.
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