All good things come to an end and my Year 13s and I were both very sad to finish the Behaviour topic last week. Still, we were able to launch straight into Bill’s brilliant Poke the Brain interactive powerpoint and next week they’ll be dissecting squid to locate stellar ganglia and giant axons, so motivation levels should stay high (even if the lab stinks of squid for days afterwards).
My other Year 13s are grappling with Respiration. This is a nice example of the importance of narrative and flow in teaching. As always, I’m looking for ways to get the students to do all the work while I make a coffee. I start with a quick round of Heads, Shoulders, Knees and Toes to warm things up. What did they need to do this? Lots of energy! Where do they get this energy from? Food! At this point, burn some sugar or scream a jelly baby. The jelly baby is more dramatic, but the burning sugar allows you to ask questions. What’s it doing? What’s the reaction? What are the waste products? What’s the equation? Remind you of anything? So why can’t we release energy like this in our cells? Compare the flaming sugar dish with a tube of yeast quietly bubbling away.
Then I show them the attached PP. Again, it’s designed to make them think. What’s this? (blank looks of panicked incomprehension!). Come on, you did this in Year 12. Oh, it’s glucose. No, it’s not, but right idea – look again. Oh, it’s a pentose sugar. Possibilities? Ribose or deoxyribose. Right. Next slide. What have I done to it? Added a phosphate. To which carbon? (wonderfully creative guesses at this point). Next slide. What’s this? If they’re switched on, they’ll identify an organic base. They might even be able to name it. What have we made? Eventually, they’ll stumble upon the right answer (stressed in the PP). What have I done now? Added a phosphate! And now?
ATP is a phosphorylated nucleotide.
I then use Guy Brown’s Energy of Life analogy of ATP as a gun. What does this look like? A handgun. What do guns do? Fire bullets. Click, and bang, the 3rd phosphate flies off with a big yellow flash. What happened? Release of energy. Right. If I want to fire the gun again, what do I need to do? Re-load it. But if I released energy when I fired it, what do I need to do to reload it? Put in energy. Where does that energy come from? Your food….
Show them the clip from Hidden Life of the Cell where the virus is moved along the cytoskeleton with motor proteins. It includes relevant and useful info on mitochondria.
Homework is then to find out about how ATP powers active transport, translation and kinesin (because they love the little motor proteins in The Hidden Life of the Cell).
Next lesson, they work out the basics of Chemiosmosis using the same experimental evidence as Mitchell (see attachment – and, by the way, how does anyone isolate a mitochondrial inner membrane, never mind do experiments with it?!?!?). Then we explore the concept in a bit more detail (see PP attached) and look at various animations. John Kyrk’s is probably the best. I also use a water turbine as a demo to give an analogy – deeply satisfying.
I keep challenging them with questions. After they’ve labelled up the Chemiosmosis sheet, what’s the obvious question? Blank looks. All these protons! Diffusing into the matrix! To power that little rotor! What’s going to happen? Ah, they get it. Things diffuse to equilibrium. So what have you got to do? Pump them back! What do we call that? Active transport. How do we normally power that? This is always a good moment as they try to make sense of a contradiction. Using ATP? But that’s what you’re trying to make… So, what’s powering this active transport? Where does the energy come from to pump the protons? Oh, glucose oxidation…
At this point I get them to do the TTC Fuschia Fizz experiment (attached) with no other background theory, and they draw some basic conclusions from that. I then get them to build a molymod glucose and ask them to oxidise it. But where’s the oxygen? Think redox. What else could you do? Oh, strip off the hydrogens. What are you left with? Carbon and oxygen. What happens to that? Excreted as CO2. Look at all that hydrogen! What could you do with it? Reduce something. Which then links to their TTC observations. I also like to explode lots of hydrogen balloons at this point.
Then it’s into the ETC, with NAD delivering the hydrogens stripped from glucose to power the proton pumps. Once you’ve done all that, you can finally look at how the glucose is broken down.
If you’re still with me (sorry, this is very long and rambling!) you’ll notice that it’s all in reverse. I think it works better than starting with glycolysis, because if you start at the beginning, there’s no sense of where you’re going and it’s hard to make sense of the point of all that reduced NAD.
Sometimes it’s better to tell a story backwards. Here’s a poster done by a student to bring it all together and show how all the separate stages connect.
That’s quite enough from me. Open Evening tomorrow, staff vs girls rounders at lunch, and Ultimate Frisbee club this afternoon. 4 weeks into the autumn term and I’ve never felt so tired!
Have a good weekend