Middle and High School … from a Montessori Point of View
This year we have a lot of food in the curriculum. My objective is to make sure everything is edible and add as much more as I can.
Sprinkling salt on slices of squash creates the concentration gradient necessary for osmosis to suck the liquid out of the squash cells, creating little water droplets.
Now we batter them and fry them up to make tempura.
For comparison, the image adjacent shows what happens to the cells of a plant when the water leaves (osmosis under the microscope).
One way to represent the process of mitosis is through dance. One of my students suggested they do an interpretive dance for their natural world personal project. I think they were mostly kidding, but with a fair bit of encouragement they did end up doing it.
The dance is much more literal than it probably needs to be since I helped a bit with the final product. I still think it’s pretty useful though because it’s abstract enough that you have to know the mitosis process to figure out what’s going on. So much so, I had them perform it twice at the end of our synthesis discussion. The second time through I narrated it so the steps would be clear to everyone.
I think it might make for a good “spark the imagination” lesson if one was needed.
Right now the dance needs four people, two for the chromosomes and two for the centrioles, but it would be really neat if the entire class participated by representing the cell membrane.
The diagram with the steps is: mitosis.svg. The instructions are below.
What are the fundamental needs of life (as we know it)? Energy, water, living space and stable internal conditions. These are physical needs of all organisms from bacteria to plants to mammals. Humans share these needs too, and this was one of the things we talked about in natural world this cycle. However, in social world studies we also discussed how people have psychological needs that, as far as we can tell, are different from those of single celled organisms: celebration, community, entertainment, and, among other things, what my students call understanding, which includes religion and spirituality.
My technophilic students also interjected that we, humans, have a need for electronics.
Electronics? My first thought was that they were being facetious, and they may have well been. But as we talked about all the other needs during our synthesis discussion last Friday I began to realize just how fundamental electronics have become to life as we know it.
Electronics are tied into the way we meet those fundamental physical needs. Organizing shipping and distribution of food requires complex scheduling software and databases. The operation of the pumps that extract our groundwater and deliver it to our houses are controlled by microcontroller. With MRI’s and computerized records our health and well-being (maintaining those stable internal conditions) are increasingly influenced by electronic technology. And in our homes, the elegant knobs and dials of thermostats on furnaces and ovens are giving way to smooth if inelegant digital displays.
Even our understanding of the world we live in, of the effects of global climate change for example, is based predominantly on sophisticated computer models and confirmed by computerized satellite systems (see NCAR for example).
So have we reached the point where electronics are a fundamental need of society, and how long will it be before we as individuals become inseparable from our electronics devices? Are we all cyborgs now? And the ultimate question: Should we be teaching more electronics in middle school?
While we were working on the needs of living things a couple weeks ago, we acquired two fish; goldfish, fifteen cents apiece.
It was supposed to only be a mental exercise. If you put a water plant, Egeria densa in this case, in an enclosed jar and left it in the sunlight, the plant should use the carbon dioxide in the water to produce oxygen during photosynthesis. A similar jar kept in the dark would produce carbon dioxide and use oxygen as the plant respired.
That was the practical part. Students measure the pH of the water before and after a day in the light and dark. The pH of the jar in the dark should go down as the added carbon dioxide makes the water slightly more acidic. Bromthymol blue solution in the water changes color very nicely within the pH range of this experiment, but, in a pinch, you can also use the pH color strips that are sold for testing aquarium water.
My students did the experiment, made their observations and came to conclusions. Then the lab activity asked them to think about what would happen if you put a fish into each of the jars, to see if students are able to extrapolate based on a well rounded knowledge of respiration and photosynthesis.
My students did the mental experiment, but the next day our two fish turned up, uninvited at least by me.
I’d anticipated something like this so I’d picked up a small fish tank at a yard sale over the summer. I’m not opposed to keeping animals in the classroom, as long as I don’t have to take care of them. Fortunately, since we’re studying life, keeping organisms and attending their needs is something the kids are learning and there is no better way to learn that via practice.
Our fish are surviving. The students have added some gravel and structures to provide habitat. The waterplants, still in there to provide oxygen, seem to be thriving despite some browsing by the goldfish.
One of the few rules is that anything added to the tank should have some purpose to help support the needs of the fish. I’m also encouraging the students to think of ways of maintaining conditions in the tank which would minimize their work. Hopefully some filter feeders, maybe small clams, and similar organisms will turn up and we can talk about ecology. I may have to nudge them in that direction though.
I’m not sure what the fish’s names are as there seems to be some controversy among the students. With a little luck they’ll survive until we start comparing religions. Two years ago we had a frog who passed away at just the right time for us to have to figure out what religion he/she was so we could perform last rites.
And no, I did not kill the frog.
We spent the afternoon period on science. I’d given some individual microscopy lessons during the last immersion, where we looked at exciting protozoans moving around in pond water. This time they tried their hands at onion cells and staining with iodine, using a very nice and clear YouTube video posted below (kyliefansunited, 2008) as a reference.
The immersion oil had arrived in the mail earlier in the week so we got to try out the 100x oil lenses. We can now see structures inside the nucleus quite nicely.
Other things did not go so well. I’d written up, using the excellent recommendation of Anna Clarke, what I though was a neat exercise to look at the effect of osmosis on the cells of a waterplant, Egeria densa. The small group struggled with it, I think in large part because they were not quite prepared (had not done the background reading), and weren’t working very well together today. I’ll keep it on the schedule, but next time I’ll have to think hard on if it will be necessary to tweak the exercise.
In a bit of a hurry, I swung by the pet store and picked up the aquatic water plant with the thinnest leaves I could find. It turned out to be Egeria densa, and while not the Elodea recommended by my expert contact Anna Clarke as a good subject for some microscope work, it seemed quite similar.
I needed the plant for an osmosis experiment. Dropping a little salt water on leaf cells of a freshwater plant should suck all the water out of the vacuoles and through the cell walls, potentially collapsing the cells (wouldn’t that be cool). I’d never done this before so I was quite curious to see what would actually happen.
The leaves have multiple layers of cells, so it’s hard to distinguish much at the center of a freshly clipped leaf, especially at high magnification. But if you look at the cells at the edges of the leaves, you can see some really neat looking, spiky cells, for which, I’m willing to bet, biologists have some really cool, multisyllabic name.
With a little bit of immersion oil and a 1000x objective, the spiky cells are good subjects for magnification: they’re a bit larger than their neighbors so they’re easier to see; their chloroplasts are distinct; and you can even make out the nucleus without staining.
Then I added the salt solution, and while the cell walls stayed strong, the cytoplasm collapsed into a little droplet at the center of the cell. The chloroplasts and the nucleus were all bundled together in this central blob (see the image at the top of the post). It’s quite the neat effect, though not exactly what I thought to see.
An interesting side note is that the cell nuclei show up very nicely with iodine stain, but the stain also discolors the chloroplasts.
Catastrophic failure of one of our ovens! Last year when we started up the bread business, we bought two counter-top ovens within a couple of weeks of each other. They needed to be extra-large to fit two loaves of bread each, which made them a little hard to find. We got a EuroPro oven first, and when we found that it worked pretty well, we went back to try to get another. But just a week later, the store was out of stock and that type of oven could not be found in the city of Memphis or its environs.
Instead we got a GE model. The price was about the same, as was the capacity. We quickly realized that the GE was quite the inferior product. The temperature in the oven was never the same as what was set on the dial. Our bread supervisor at the time ran a calibration experiment, the results of which you can see above, so we still managed to use the oven. Only this year, three weeks into the term, it conked out.
We sold at least one underdone loaf before we realized what had happened, and received a detailed letter in response (which our current bread supervisor handled wonderfully in his own well worded letter). Fortunately, we have found a newer version of our EuroPro oven, which seems to work quite well.
I like the oven calibration exercise. It was a nice application of the scientific process to solve an actual problem we had with the business. Though I know it’s not quite the same, I like the idea of doing annual oven calibrations just to check the health of our equipment and help students realize that the scientific process is a powerful way of looking at the world, not just something you do in science.
Our assignments for natural world usually combine some reading and some type of activity, but all the short video clips available online are a great resource, so I’ve been adding them to the studyguides as I find them.
The above two-minute, cell division video is a great example. Mitosis is a process, so it makes a lot of sense showing it as an animation, rather than discrete pictures in a figure. The video makes deciphering what’s going on in the diagram in the textbook a whole lot easier to understand, while the textbook diagram fills in the detail so the whole thing makes more sense.
There are also a number of useful interactive animations online. John Kyrk’s is quite nice. I like how the CellsAlive animal cell mitosis page lets you step through each frame in the animation.
Wikipedia, as is so often the case, also has some nice images.
