Tag: biology

More mitosis resources

Onion root tip cells, with chromosomes stained to show cells in different stages of mitosis. Image from uafcde.

One of our small group activities is to look at mitosis in onion cells. Anna Clarke, recommended the University of Arizona site which has an Online Onion Root Tips activity for those without access to the slides or microscope. It also provides a good review even if you do have those resources. Dr. Paul’s page on onion cell division is a good supplement to the Arizona site because of its great cell images.

If you’re feeling ambitious and want students to make their own slides, you can try the SAPS page on Mitosis in root tips.

Mitosis resources

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.

Spore: Lamarkian in the subtexts

Playing Spore.

During our last immersion, one of my students brought in the computer game, Spore. Although the game subtly indicates that it’s your progeny that gains evolutionary advances, the fact that you get to choose what you want (extra horns, poison sacks), and the fact that you can see yourself (or do I mean your creature) evolve on the screen, really smacks of Lamarckism. While it’s appealing to think, like Lamark, that you can pass on traits gained during your lifetime to your kids, despite some fascinating new research, that’s just not how evolution works.

Evolution is not directed by the organism but by their environment. In a population of organisms of any particular species there is going to be some variability due to simple, random genetic mutation. Some lucky members of the species might have a mutation that makes their muscles better at burning oxygen during sprints, making them able to run faster to get away from the lions. So they survive and pass their genes on, with their genetic mutation. Of course, if lions become extinct (disease maybe) then this trait may no longer be beneficial and something else, like maybe intelligence, would be selected for.

The game can capture your interest, however, so I’ve asked the student who brought in the game to come up with a presentation explaining why it would be useful to have the game in the classroom. I am, after all, not instinctively opposed to using computer games in class. I’m really curious to see what this game looks like from the student’s point of view.

Microscope photography!!!

Algae and amoebas at 400 times magnification.

Did you know that if you hold up a regular digital camera up to the eyepiece of a microscope you can take a great picture of a magnified slide! I didn’t. And I really didn’t think it would work when I tried it, but the results are remarkable. With a somewhat steady hand you can also make decent animations.

If you look carefully you can see the amoebas zipping around. I also have a really cool larger version too, which shows the entire slide..

I’ve never been very good at identifying things (I’m a lumper not a splitter) so all I think I can say for sure is that there are algae and protozoans in the picture. BiologyCorner has a nice identification guide for organisms usually found in ponds, which is part of one of their lessons, Biodiversity of Ponds.

Resurrecting the greenhouse

Two years ago, the middle school’s flagship project was to put up a fully functional greenhouse (using this design). It took all year but we did it. On the way, we got to practice geometry, mapping and construction, while learning and growing plants and studying soil profiles. It was so successful that, with our spring plant sale we broke even on the entire project.

Last year, however, the greenhouse was somewhat neglected. My plans to add an automatic window opener, which would have been a wonderful tie-in to our electronics and Newtonian physics studies, did not work out; we just did not have the time. We’d taken the plastic covering off, so only the bare, forlorn PVC frame was left standing around a plot of waist-high weeds.

Though I could not have predicted it, this year we have a strong core group of students who are highly enthusiastic about resurrecting the greenhouse and making it work. My suggestion was that we try to grow produce this fall that we could cook in December when we do our Dinner and a Show. Well, two weeks in, they’ve already put together a menu plan, weeding is well on its way and I’m being harassed to hurry up and arrange a trip to Home Depot. The excitement is so infectious that another student has volunteered to bring in his electric weed-whacker during the immersion. It’s amazing!

I’m having the hardest time not butting in. There is a beauty in seeing a well oiled machine executing a project or solving a difficult problem. But there is another even more wonderful aesthetic visible in a the birthing struggles of a nascent team. The forward motion of infectious enthusiasm is pulling puzzle pieces into its wake, and the pieces just seem to click into place when the time is right. I have to keep reminding myself that my job is to prepare the environment and let the kids do the rest.

Toilet Paper Timeline of Earth History

Image from Wikimedia Commons.

Jennifer Wenner has posted a beautiful demonstration of geologic time using toilet paper for the timeline at SERC. You’ll need a 1000 sheet roll and by the time you’re done there will be toilet paper everywhere.

This is a great demonstration because as you unroll the toilet paper you get a great feel for the long spans of time in the preCambrian when nothing much happens, and then, as you approach the present, events occur faster and faster. There’s 300 million years between the formation of the Moon and the formation of the Earth’s atmosphere. That’s 60 sheets! while modern man only turns up about 10,000 years ago, which is 0.002 sheets; about the width of the line drawn by a pen. Even the dinosaurs went extinct only 14 sheets from the end.

The SERC webpage has a spreadsheet with most of the important dates marked and translated into toilet paper units. The Worsley school in Canada has some nice pictures of the toilet paper being rolled out all the way down the hall.

History of life on Earth timeline (from NASA).

Living without oxygen

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.

(a) a hydrogenosome-like organelle. (image from Donavaro et al., 2010)

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.

DNAi: History of genetics and manipulating DNA

DNA. (from Wikipedia)

DNA interactive is another great resource for studying the history of genetics and how we manipulate and use it today (recommended by the indispensable Anna Clarke). They have lesson plans and nice pages on the modern techniques used to work with DNA.

Image from the DNAi webpage on gel electrophoresis. Electrophoresis is a bit like chromatography which might make for a good demonstration.

I have not done much with genetic sequencing myself and I found the website interesting and informative. I have, however, written programs to get and work with the GenBank database, which is not that hard since they have some easy tools to work with. I would love to figure out how to get a sample sequenced and then run it through GenBank to identify it. It would so nicely integrate the curriculum, using a practical exercise to solve a problem (like what species are on the nature trail), while using the same tools and resources that scientists use, and tie wonderfully into the short stories in Mirable.