Tag: science

On Rabbit Digestion

Figure 1. Undigested fiber from rabbit fecal pellets.

One of my favorite things is when my students teach me something I didn’t know. One of those things is that rabbits eat their own poop.

Well not exactly. According to Dana Krempels, from the University of Miami, rabbit fecal pellets (poop) are different from the other type of droppings that lagomorphs actually eat, which are called cecotropes (Kempels, 2010; Rabbits: The Mystery of Poop). Cecotropes apparently have lots of helpful bacteria and nutrients. Rabbits that don’t get to eat them tend to suffer from malnutrition.

Figure 2. Rabbit fecal pellets, with one mostly dissected, in a standard petri dish.

Independent Research Project

For her Independent Research Project (IRP) this term, one of my students researched rabbits, and, as was required, tried to find them on our nature trail. She found indirect evidence. Small fecal pellets in the grassy area next to the trail’s exit, just where her research said they might be (which was quite nice). The pellets were brought inside, dissected, and examined under the microscope (see Figures 1 and 2).

The magnified image showed what appeared to be a partially masticated (chewed) piece of fiber, probably grass. This is where I was informed about the double eating called cecotrophy. My student hypothesized that this sample might be something that had not been fully digested and the rabbit would come back and eat it another time.

The Scientific Process

I really like the scientific process that went into this project, even though I’m not sure I agree with the final hypothesis. The project started with background research that yielded a plan for field observation. The field observation resulted in samples being collected and returned to the lab for analysis. The analysis produced some interesting, enigmatic results, which lead to a proposed hypothesis that integrated the observations based on the original background research.

The only things I would like to add to this type of IRP is to have students include a detailed scientific sketch, much like the sketches of the early botanists and naturalists. I really like how these drawings integrate acute observation and artistic interpretation.

Pumpkin Chuckin

Photo by <a href='http://en.wikipedia.org/wiki/File:Pumpkin_chucked_from_trebuchet_in_ohio.jpg'>Kevin D. Hartnell</a>.
Photo by Kevin D. Hartnell.

Mr. B’s put me on to the World Championship Punkin Chunkin Association, which has an annual competition. There’s a Discovery Channel program about it too.

Although my head-of-school is not partial to us throwing food around, a trebuchet would make a great project for physical sciences next year (Year B).

Microwave Science

Last year, for an IRP, one of my students did the experiment measuring the speed of light (and the wavelength of the waves) using marshmellows in a microwave. The video above (via Gizmodo) shows the pattern of the microwaves using some neon lights embedded in plastic. The video below, from MythBusters, shows superheated water in action; something I demo every time I make tea-water in the microwave.

Artistic satellite views of the Earth

The Tibetian Plateau. Image from the satellite Landsat 5 via the Eros Image Gallery.

For the geography nerds, but perhaps also for those with an appreciation of the natural beauty of the world. The US Geological Survey has a series of satellite pictures chosen just for their sheer beauty.

The Landsat satellites that take these pictures usually photograph in more than just the human-visible color spectrum. For many geologic and environmental purposes, different infra-red wavelengths are often better for seeing details on the Earth’s surface. The USGS has a nice primer on the Landsat program. Many of the color images posted here were reconstructed from different color bands.

Yukon delta. Image from Landsat 7: Earth as Art 3 collection.

The resulting images can be exceptionally beautiful and somewhat surreal. I like that there is an abstract surface beauty, divorced from the content, meaning and understanding that a closer analysis of the images yields to the eye of the trained observer: delicate swirls of algae might be signs of eutrophication to a biologist; dendritic deltas tell the geologist about sediment load, offshore currents and mass balance.

Phytoplankton bloom around the Swedish island of Gotland in the Baltic Sea is reminiscent of Van Gogh's Starry Night. Image from Landsat 7.

Humans, 90% bacteria + 10% us

90% of the cells in your body are bacteria and other provocative facts about the Domain Bacteria are the subject of a great but long article by Valarie Brown.

[R]esearchers have also discovered unique populations adapted to the inside of the elbow and the back of the knee. Even the left and right hands have their own distinct biota, and the microbiomes of men and women differ. The import of this distribution of microorganisms is unclear, but its existence reinforces the notion that humans should start thinking of themselves as ecosystems, rather than discrete individuals.
—Brown (2010), in Miller-McCune.

The article makes for great reading during this cycle’s work on classification systems and evolution. One choice paragraph summarizes the fundamental differences between the domains of life:

There’s such ferment afoot in microbiology today that even the classification of the primary domains of life and the relationships among those domains are subjects of disagreement. For the purposes of this article, we’ll focus on the fundamental difference between two major types of life-forms: those that have a cell wall but few or no internal subdivisions, and those that possess cells containing a nucleus, mitochondria, chloroplasts and other smaller substructures, or organelles. The former life-forms — often termed prokaryotes — include bacteria and the most ancient of Earth’s life-forms, the archaea. (Until the 1970s, archaea and bacteria were classed together, but the chemistry of archaean cell walls and other features are quite different from bacteria, enabling them to live in extreme environments such as Yellowstone’s mud pots and hyperacidic mine tailings.) Everything but archaea and bacteria, from plants and animals to fungi and malaria parasites, is classified as a eukaryote.
—Brown (2010).

Bacteria are prokaryotes. Image by Mariana Ruiz Villarreal.

Brown also gets into a discussion of if bacteria think:

[B]acteria that have antibiotic-resistance genes advertise the fact, attracting other bacteria shopping for those genes; the latter then emit pheromones to signal their willingness to close the deal. These phenomena, Herbert Levine’s group argues, reveal a capacity for language long considered unique to humans.
—Brown (2010).

Trimming this article down would probably make it a good source reading for a Socratic Dialogue.

Bacteria are the sine qua non for life, and the architects of the complexity humans claim for a throne. The grand story of human exceptionalism — the idea that humans are separate from and superior to everything else in the biosphere — has taken a terminal blow from the new knowledge about bacteria. Whether humanity decides to sanctify them in some way or merely admire them and learn what they’re really doing, there’s no going back.
—Brown (2010).

Tree of life

One of the easiest and most elegant ways of explaining the classification of organisms, the history of life on Earth, and the relationships between different organisms is to construct a phylogenetic tree. I have a great exercise I like that takes just some bits of colored paper, string, a poster board and some thumbtacks.

To start, each student writes the Latin domain, kingdom, phylum, class, order, family, genus and species names on separate pieces of colored paper. I hand out paper in stacks and give them strict instructions not to rearrange the order of the colors. Wikipedia is actually a great resource for this because they tend to be quite reliable on this if they have the specie you’re looking for (and they have quite a bit).

Students then tape the pieces of paper together on a string, species at the bottom, domain at the top, and, one by one, tack them to the poster board. As each student attaches their string to the board they say the common name of their organism and then recite the phylogeny.

When I did the exercise on Monday, I asked the students to use the organisms they’re working on for their independent research projects so everything started with the domain Eukaria. Interestingly enough, the Wikipedia pages don’t have the domain classification, probably because they think it’s too obvious, but I had a number of kids spend quite a bit of time trying to figure it out; they probably benefited from doing so I didn’t mind at all.

Constructing the phylogenetic tree.

Classifications that are the same are tacked one on top of the other, Eukaria on top of Eukaria, Mammalia on top of Mammalia and so on, so that, as students add their parts of the phylogeny, you begin to see the phylogenetic tree. We had insects, mammals, plants and reptiles, so there was quite a nice variety represented.

After about half a dozen lineages were on the board, the procedure began to get a bit repetitive, so I started to ask students to guess, based on the common name, where the next species to go on would diverge from the rest of the emerging tree. Students seemed to like this part of it. I had started with homo sapiens when I demonstrated the procedure so it was salutary for them to see how much the other organisms differed from humans.

When everything is tacked on, you end up with a cute picture of a the tree of life that makes a cute, but awfully real looking, phylogenetic tree. Students tack their pieces of paper on the string at different distances, some much closer together than others. As a result, the final tree is looks as though it shows the genetic divergence between the different groups. It a fake, but lends a sense of verisimilitude non the less.

What’s the difference between humans and animals?

In the field of cognition, the march towards continuity between human and animal has been inexorable — one misconduct case won’t make a difference. True, humanity never runs out of claims of what sets it apart, but it is a rare uniqueness claim that holds up for over a decade. This is why we don’t hear anymore that only humans make tools, imitate, think ahead, have culture, are self-aware, or adopt another’s point of view. – Frans De Waal (2010).

My students studied the question, what is life, last cycle, and through their readings and Socratic dialogue I’ve been trying to approach the question of what is sentience and what distinguishes humanity from other organisms (or robots for that matter).

We’ve found that the lines between us and them are very hard to draw.

Pushing the discussion into questions of morality, primatologist Frans De Waal has a wonderful post on where it comes from, and if there is any clear distinction between humans and other animals. He argues that morality is innate, a product of evolution, and there aren’t clear distinctions.

The full article is a worthy read, with good writing and well constructed arguments. It’s a bit too long for a Socratic Dialogue but might be of interest to the more advanced student, particularly those going through religious, coming-of-age, rites of passage, like preparations for confirmations and Bar Mitzvahs. While De Waal’s evolutionary reasoning has been used to argue against religion, he takes a much more subtle approach:

Our societies are steeped in it: everything we have accomplished over the centuries, even science, developed either hand in hand with or in opposition to religion, but never separately. It is impossible to know what morality would look like without religion. It would require a visit to a human culture that is not now and never was religious. That such cultures do not exist should give us pause. – Frans De Waal (2010).

Science of Cooking at the Exploratorium.

The Science of Cooking from the Exploratorium. (© The Exploratorium, www.exploratorium.edu)

The San Francisco Exploratorium has a wonderful website on the science of cooking.

They have a very nice bread science page that explains what happens with the yeast and gluten as you mix, kneed and bake bread. There is a set of recipes, including sourdough and Ethiopian Injera, that my students might want to try. They even have a great links page to pretty much everything you might want to know about the science of bread and how to manipulate it.

Checking eggs for cracks. (© The Exploratorium, www.exploratorium.edu)

I was also very interested in their pages on eggs, with the virtual tour of an organic egg farm, science of cooking, beating and mixing eggs, and a wonderful set of activities including removing the eggshell while keeping the membrane intact and demonstrating osmosis through the egg membrane.

And I haven’t even gotten into the pickles, meat and seasoning sections yet.