While I am teaching the biology lab, I set this post to show up automatically at the same time. It describes what we do today, the same stuff we did back on April 02, 2006:
So, yesterday was the last, fourth meeting of the lab. We started out by going over their homework questions about the evolution of Vertebrates. I was quite happy that only one person in only one question confused development with evolution – something that I see, unfortunately, very often. The legs of the frog do not “evolve” out of the body once the tadpole starts losing its tail: the frog legs evolved out of meaty fins of its Crossopterygian ancestors. Also, knowing that one of the questions concerned Amphioxus, I made sure the previous week to say something about it. For most questions, the students were really ‘on the ball’ – it is nice to have a class without a single (at least openly) Creationist student.
The first excercise of the day was supposed to be electrophoresis – we were supposed to run a gel. However, Ward’s (second time this term) did not deliver the supplies on Friday (they will come on Monday and I can use them next time), so, without the chemicals, we could not do the excercise. Instead, we did a DNA fingerprinting excercise on paper, using paternity testing as an example. They were given two DNA sequences each from Mother, Child, Potential Father #1 and Potential Father #2. They were to use the restriction enzyme (scissors) to cut the sequences after T of each CAT sequence. Then, they figured out the sizes of the fragments and we drew the gel on the whiteboard representing what they would see if they actually had those sequences in real life.
It was easy then to figure out who the father was. We also mentioned some other reasons to use DNA fingerprinting, e.g., in forensic analysis (and yes, O.J.Simpson trial was mentioned). The technique has also shown that, contrary to millenia of misconception, the birds are not that loyal to their partners as we thought. Even in bluebirds, the poetic paragons of loyalty, some of the eggs are fertilized by the nest mate, and other eggs are fertilized by a fleshy neighbor. As a bonus, I gave them this to read and they loved it.
Next, I split the students into groups of four. We took some water-fleas (Daphnia) and placed them on microscope slides. In each group, one student did the ‘handling’ of the animals and chemicals, the second student called out the heart-beats seen under the microscope, the third student jotted down a dash for each heart beat and calculated the beats-per-minute value, while the fourth student kept time. For each treatment the students swapped roles. Each animal was first measured in fresh pond water, serving as its own control. Then, a drop of a treatment was added and the heart-rate counted again. The four treatments were caffeine, epinephrine (adrenaline), glucose and alcohol. Before the excercise started, the students stated their hypotheses and their expectations.
I was really happy to see how consistent the numbers were between groups, suggesting that they did the job correctly. Surprisingly, all four chemicals (in all replicates) induced slowing of the heart rate. We used the discussion time to talk about the biochemistry and physiology of the four chemicals, the effects of dose (the U-shaped curves), the compensation (e.g., the “crash” following a caffeine “high”), etc. It was taken as given that Daphnia and humans share much of their physiology: from utilization of glucose for energy (and formation of ATP), to existence of receptors for epinephrine and caffeine. No need to push evolution too hard – the common ancestry was an unspoken given.
After they finished their student evaluations, it was time for the last excercise of the course, the one they were all excited about – the dissection of the fetal pig. We worked all together, finding organs one at the time. For each organ, I asked questions about its function and often added some more interesting information (including the positive feedback loop I forgot to mention two weeks before, concerning the urinary bladder – thank you readers for the heads-up on that!). I think they had a blast!
And that was it for this session. I have a month free. Then, in May and June I will be teaching both the lecture and the lab. It is always good when the two courses are taught simultaneously by the same instructor. That way, I can make the too reinforce each other and work together well.