On Wednesday of the first week, I followed Mary, Allie, AJ, and Madonna as they worked with the "penguin climbing up a hill" scenario. Originally it was supposed to be a person, but I am so glad Rachel could only find a clip of penguins climbing a hill, because it brought up all sorts of interesting questions about homeostasis. (Of course humans do homeostasis too--but I think it's a little more obvious to people because penguins live in cold weather.)
My understanding is this: Organisms have a basal metabolism--a series of chemical reactions required to keep the organism alive. (Let's talk about animals because I am most familiar with them.) These chemical reactions require activation energy to be carried out (that's a type of energy we haven't discussed!) and are completed best at certain optimal temperatures, so thermal energy is required as well. But these reactions also generate thermal energy, some of which is lost to the environment, and some of which may be retained by the organism, especially an endotherm ("warm-blooded" organism. Thermoregulation (maintaining an optimal body temperature for chemical reactions) is a confusing part of basal metabolism for endotherms because it costs energy and generates energy and the animal stores energy and this is all to save energy...or something. It's confusing!
Organisms will also perform activities that take them beyond their basal metabolism--for example, climbing up a hill. Eventually this group will consider how you might figure out how much energy is required to get the animal up the hill, on top of whatever basal metabolism there is.
Segment 1: This is longest and probably the most boring to watch. A lot of the conversation sounds like "C turns to T, and T turns to K", which I can't follow very well especially without seeing the diagram. Nevertheless, I think there must be a lot of hints interesting about what their questions are and how they start to think about the problems. Here are two important exchanges:
Exchange 1 (at 1:13)
This is the first reference I saw to what the group will later discuss as respiration and metabolism.
AJ: Should C turn into T first?
Allie: No...I don't think so...because the ATP in your muscles gets broken up and used, and that's what makes your muscle move! So the chemical really does kinda go straight to the kinetic.
Exchange 2 (at 3:48)
Mary first addresses the idea of thermoregulation in the penguin. The group is discussing whether the penguin's thermal energy comes from the penguin's movement from "the previous step". (One confusing or interesting thing here is that the way the group uses "step" it could apply to the "acts" of Energy Theater, to the literal steps taken by the penguin, or to both simultaneously.)
Mary: And as we go higher, we'll be taking on more thermals too, right? I wouldn't think the thermal would be constant.
Madonna: So this thermal should be the first thermal to leave.
Allie: So you're saying you would not radiate on the first step.
AJ: It's pretty much already moving. So this T came from here, on the last step.
Allie: So what you're saying is he's already got his elevated temperature…
Mary: And he's gonna get warmer and warmer to a point.
Allie: But if we're saying he's already in motion, then maybe he's already reached his elevated temperature and he's radiating.
Segment 1
Segment 2: In this segment, Mary begins to discuss homeostasis. This is a little confusing, because the temperature of the penguin stays more or less constant, but the rate of generation of thermal energy (I think this is what she is thinking about) is not constant.
Mary: You know what? You know how he stays at a constant temperature, is he's probably kicking off more Ts...So it's not really a constant...thermal...
Allie: He gets hotter?
Mary: He gets hotter but his body regulates by kicking off more Ts.
Segment 2
Segment 3: This is the segment I shared with the I-RISE group last Friday. Here Allie is proposing that all C to K transformations (which they call "metabolism") are accompanied by some quantity of C to T transformations (which they call "respiration"). As a high school biology teacher, I would define metabolism as "all the chemical reactions that happen within an organism" and respiration as "the controlled release of energy from organic molecules". This is not the way these learners are using those words, and I will do my best to be clear about which definition is being used in a given context.
At 0:26, Allie says, "when you draw the circle of ATP, you do end up radiating energy at certain steps". In biological systems, "free energy becomes available for metabolism by the conversion of ATP→ADP, which is coupled to many steps in metabolic pathways" (College Board, AP Biology Curriculum Framework.) ADP can be combined with inorganic phosphate to regenerate ATP during cellular respiration. When Allie refers to "the circle of ATP", I believe she may be referring to a diagram like this.
At about the 1 minute mark, Stamatis tries to get the group to quantify the ratio of C to T transformation compared to C to K transformation; in other words, how efficiently is the penguin converting its chemical energy into the work of walking up hill. For this snippet, remember that to these learners, "metabolism" means C to K and "respiration" means C to T.
01:13.19]Allie: What's our bond energy on ATP?
[00:01:17.13]I don't know
[00:01:20.00]I should hope that this is more efficient
[00:01:23.03]I should hope there's more metabolism to respiration
[00:01:26.09]Stamatis: More C to K than C to T
[00:01:28.18]Allie: Otherwise we're pretty inefficient machines
[00:01:31.18]I mean we are pretty inefficient
Allie's comment really struck me because biological organisms are, I assume, EXTREMELY inefficient compared to mechanical systems. I believe in the process of cellular respiration there IS in fact more C to T than C to K. This comment made me consider biology as a kind of "engineering", where living things are evolution's various solutions to the "design problems" of life.
At 1:48, Stamatis asks, "How could a physicist think about this question?" Allie explains that they already HAVE looked into this question systematically and quantitatively.
[00:01:59.26]Allie: We looked at a research paper, and I think that's where we got the numbers
[00:02:08.25]ATP...they've got the circles for it and they'll tell you how much energy,
[00:02:14.16]how many Joules are released at each stage in the process, I think
[00:02:23.06]but I dont know...they don't usually tell you [00:02:28.04]how many, the energy that goes toward the muscle movement
[00:02:31.25]they just tell you how much energy is lost
A diagram like the one Allie is referring to might look like this:
Finally, Madonna brings up the concept that I would call basal metabolic rate--the amount of energy required to perform the chemical reactions that keep the organism alive.
[00:02:50.25]Madonna: Or you could have the penguin just stand there
[00:02:53.17]Allie: And see how hot he is?
[00:02:55.12]Madonna: And see how much energy it requires, just standing there
[00:03:00.21]Stamatis: And we know that about me, right?
[00:03:02.24] Madonna: And you could see how much more energy it requires for it to be moving
Segment 3
Segment 4: This clip is almost immediately following Segment 3. The group considers some of methods they might use to calculate how much energy would be needed to get Stamatis up Mount Everest. (I don't know why Stamatis changed the scenario from penguins to himself, other than that Stamatis must have a paralyzing phobia of penguins and doesn't like to talk about them.)
The discussion of basal metabolic rate continues:
Allie: C to T, this is just what we need to maintain our body temperature, right? So that would be our resting body temperature.
Madonna: It's energy lost to the environment
There is also an intriguing digression into body fat--I'm not so clear why it matters to their question, which is how much energy would be used--would it matter whether it comes from new food or from stored body fat? But it is a great example of how freakin complicated this system is!
Madonna: You probably also have to take into consideration body fat.
Stamatis: I'm assuming you would be getting thinner.
Allie: You might be burning off fat--the energy that they use is energy in their body.
Madonna: A substantial amount of the energy that they use is the energy in their body before they start. The calories that they’re eating while they're climbing aren’t necessarily all the calories...
Allie: We could try and eliminate that by finding someone who already is in good shape so if they hit hardships and they're in a snowstorm they're gonna be burning off their reserves. But I think if you find a person who is healthy and well-prepared for their trip, they're not gonna be losing a lot of weight.
Segment 4
I don't have a conclusion about all this yet. Maybe it needs to simmer.
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