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.
Anaphase: Lengthening microtubules push the two sets of chromosomes further apart. (from Wikipedia)
Wikipedia, as is so often the case, also has some nice images.
Microscope image of the undescribed species of Spinoloricus (Loricifera; stained with Rose Bengal) (image from Donavaro et al., 2010)
While there are quite a number of single-celled microbes that live in environments without oxygen (they’re anaerobic), multicellular organisms have now been discovered, living near the bottom of the Mediterranean Sea, that also do not need oxygen.
What’s really neat, and creates a great teaching point, is that these anaerobes don’t have mitochondria in their cells, so they can’t use oxygen for energy:
The creature’s cells apparently lack mitochondria, the organelles that use oxygen to power a cell. Instead they are rich in what seem to be hydrogenosomes, organelles that can do a similar job in anaerobic (or oxygen free) environments. – Vogel, 2010.
The conclusion paragraph of the journal article, would make a nice piece for students to mark up and process. It might even work better for use on a vocabulary test because you’ll need to understand the vocabulary to understand the text.
This is the first evidence of a metazoan life cycle that is spent entirely in permanently anoxic sediments. Our findings allow us also to conclude that these metazoans live under anoxic conditions through an obligate anaerobic metabolism that is similar to that demonstrated so far only for unicellular eukaryotes. The discovery of these life forms opens new perspectives for the study of metazoan life in habitats lacking molecular oxygen. – Donavaro et al., 2010)
Possible endosymbiotic prokaryote and hydrogenosome-like organelles. (from Donavaro et al., 2010)
The article, by Donavaro et al., (2010) also has an intriguing image of suspected “endosymbiotic prokaryotes”. Some organelles in cells are believed to have once been separate organisms that developed symbiotic relationships with their host cells. It’s nice to see an example of it in real life. Even if it’s a bit hard to interpret.
The ultimate implication of this discovery, is that there are probably a lot more anaerobic environments on other planets so the chances of finding extra-terrestrial multi-cellular life might not be as low as we’ve thought.
Another good interactive cell model, similar to the Teach.Genetics‘ Flash app I posted about earlier, can be found at CELLS alive. I first used the CELLS alive website two years ago and I like it because, while it has a much simpler picture than Teach.Genetics’, it has a nicely linked glossary of terms. The glossary is, however, a little technical, but it’s a nice exercise (and not terribly difficult) for students to decipher the basic information that they need.
Teach.Genetics has a bunch of “Print and Go” pdf lessons on their site, but also have a really neat interactive page where you can look inside an animal cell. What’s really neat about this flash app is that you can move around a little, round window as you scan through the cell membrane. You can also take the membrane away to see everything inside the cell at once, but that takes away the challenge.
When you use the little window you have to piece together what everything inside the cell looks like by memory. For a student new to the parts of a cell this might be a bit of cognitive overload, but once your somewhat familiar with the pieces, this makes for an interesting challenge.
The Teach.Genetics site and materials are free for educational use.
Although I’m pretty sure I’d explained this before, I had a student ask me today what makes the bread rise. He’d been combining the ingredients to make bread for the student run business with a rather thoughtful look on his face. So I told him that yeast is a fungus that “eats” the sugar in the honey and “releases” carbon dioxide bubbles, which get trapped in the dough causing the bread to rise.
I could see the look of disgust racing across his face at the mention of fungi, so I asked, “Would you like to look at it?” He did, and he was not the only one. So after lunch I broke out the microscope, which we have not used much this year since we’re doing the physical sciences this year. A slide, a cover slip, a drop of the residue from the glass jar we used to mix the liquids for the bread, a quick (so very quick) demonstration of how to use the microscope and whallah.
Under 10 times magnification you could see hundreds of cells moving across the field of view. The students were impressed by how many there were. Under 40 times magnification you begin to see cell structures.
Image from Wikimedia Commons, but yeast under the 40x microscope objective looks pretty similar.
We’ll look at yeast again next year when we’re focusing on the life sciences, but when I think of the Montessori axioms that the role of the teacher is to prepare the environment and to follow the child, I think of situations like this. At this time, in this place, after kneading dough for half a year, the student asked the question, and everything was ready for him to answer the that question and whet his appetite for more.
