Tuesday, May 23, 2006

Yet another teaching update: mid-term

On Saturday, I taught the Third Lab which went pretty much the same as the last time around, except that this group is so good! They know their animal phyla already!

The bacteria and fungi from the samples from their fingers did not grow (old agar on the plates, I bet), so we did it again with fresh agar and we'll look at the results next time.

The description of leaf stomata as "two Lima beans facing each other" is great for teaching middle school, but it is not exactly a good description. I finally, after many years, realized this and also realized that I am teaching adults, almost all of them parents! So, I told them exactly how it looks like under the microscope - like a vagina (actually vulva, to be anatomically correct). As soon as I told them that, all of them easily found the stomata on their slides.

Last night I taught the fourth lecture. According to the syllabus, I was supposed to drone on about classification of bacteria, and protista, and fungi, and plants, and animals. Bo-rr-ing! So, I did it...five to ten minutes each at the end of the lecture, only as a Coda, perhaps as a brief showcase of examples of diversity.

The lecture itself (and I will post the lecture notes as soon as I finish them) was about the way diversity arises. Thus I talked about the Origin of Life on Earth. I talked about our mental inability to fathom how long 4 billion years really are (and showed them this great animation to illustrate the idea).

Then I drew Gould's "left wall of complexity" graph on the board, and spent some time discussing the evolution of complexity and the blindness of evolution. I talked about the way evolution does not have complexity as a goal, and the way greater complexity can actually make an organism less fit, while a reduction of complexity can turn an organism into a lean, mean evolving machine (or an efficient parasite). This discussion was essential for the next part of the lecture...

....because I discussed the old and new ideas about the early evolution of life and the relationship between Archaea, Bacteria and Eukarya (and dismissed briefly, never to mention the terms again - the division into Prokaryotes and Eukaryotes, and the division into six Kingdoms). Of course, I had to mention endosymbiosis as a mechanism as well, but secondary simplification of Bacteria and Archea figures big in the most recent notions about the early evolution of unicellular organisms.

Then I spent the bulk of the lecture talking about the mechanisms by which diversity arises, thus repeating somewhat my evolution lecture of two weeks back, combining it with what I taught about development and the genotype-phenotype mapping, and using PZ's overview of Hox genes and bat development (given as handouts the previous week) to introduce the notion of a developmental toolkit and the greater importance of combinatorics of genes over the sequence of genes. I mentioned (and they love it when they hear about brand new findings in an introductory class) that Cnidarians do not have Hox genes and what that means. And I pounced on the similarities between genes/genomes in widely diverse organisms.

I explained how evolution of adaptation and evolution of diversity go hand in hand. I talked about six ways a genome can change and what it means for evolution of diversity: mutation, rearrangement, gene duplication, chromosome duplication, genome duplication and lateral transfer (both between unicellular organisms and, via viral carriers, between all organisms).

Then, I talked a little bit about the discipline of systematics and how cladistics works. I compared the old morphology-only methods of classification to modern genome-based methods and briefly discussed viruses.

Then, in the end, I spent a little bit of time on each of the major groups, starting with Bacteria, stressing that not all of them are pathogens and dicsussing at length the importance of the bacterial flora in our intestines, using the ecological concepts (e.g., succession) to explain how our intestine is an ecosystem.

For Archea, of course I had to explain what Deinococcus radiodurans is all about and I mentioned that it is only very recently that any Archaean has been implicated in any human pathology, and then only as an enabler, not really a pathogen itself.

I spent even less time on Protists, Fungi and Plants, summarizing only the basics of morphology, taxonomy and evolutionary trends (e.g., from gametophyte to sporophyte dominance in plants).

I spent more time on Animals, though, going into some detail into major transitions in the evolution of animals, e.g., evolution of tissues, evolution of movement, evolution of symmetry (first radial, later bilateral), evolution of psuedocoelom and coelom, the difference between Protostomes and Deuterostomes, and the evolution of segmentation.

When talking about Chordates, I talked about the most recent ideas about their origin, some cute details about lancelets, hagfish, lampreys and fish, about the invasion of land and Tiktaalik, about amphibian and reptilian adaptations to land, about Dinosaurs and the origin of birds, and about evolution of mammals. I told cute stories about the Platypus and the marsupials and the evolution of placenta and mammary glands.

I talked also about some specific cases of recent rearrangements in taxonomy, including the evolution of whales, the relationship between elephants and hyraxes, between Carnivores and Pinnipedieans (seals, etc.) and between rodents and rabbits.

Thanks to science blogs, I am up to date on the most current thinking in all areas of biology, not just in my specialty. It is so cool to talk about such stuff to students in intro classes - they feel privileged to be let in on the secrets of the scientists' kabal! And hopefully, they will click on the links I sent them and become readers of science blogs, get hooked and keep their interest in biology long after the class is over.

Next week is their first exam, followed by four lectures in Human Anatomy and Physiology, which I am going to turn into something more like "Comparative, Evolutionary and Ecological Physiology with the Human Example as a Starting Point". I'll keep you posted on how that goes over the next four weeks.

Previously on this topic:
Teaching Biology To Adults
Teaching Biology without Evolution...
On the Scientific Method in Biology
Teaching the bare bones of Biology
How I Taught Evolution Last Week
Teaching Update

Lecture Notes:
Biology and the Scientific Method
Cell Structure
Protein Synthesis: Transcription and Translation
Cell-Cell Interactions
From One Cell To Two: Cell Division and DNA Replication
From Two Cells To Many: Cell Differentiation and Embryonic Development
From Genes To Traits: How Genotype Affects Phenotype
From Genes To Species: A Primer on Evolution
What Creatures Do: Animal Behavior
Organisms In Time and Space: Ecology

Lab Notes:
Teaching Biology Lab - Week 1
Teaching Biology Lab - Week 2
Teaching Biology Lab - Week 3
Teaching Biology Lab - Week 4

Technorati Tag: teaching-carnival

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