Year 13 and Respiration – as I’ve blogged before, this is a story best told backwards, but I feel I’ve become so engrossed in teaching the extraordinary theory, that the investigative practical work has been a bit neglected. I feel a bit embarrassed, however, that I didn’t spot this opportunity years ago. Flippin’ obvious? See what you think…
So, we’ve powered through ATP, Chemiosmosis and how the ETC maintains the necessary proton gradient. They’ve built a molymod glucose and then oxidised it without using oxygen, to highlight how it’s the hydrogen atoms derived from glucose that are the source of the vital electrons. They know about dehydrogenase enzymes and NAD, but we’ve yet to touch either glycolysis or Krebs – the details of how glucose is stripped bare can wait.
It’s compelling stuff, but lots to take in, so as a pleasingly colorful break from the hardcore theory, I have always used a variation of an old OCR practical exam…
… and my emphasis has always been on a) making the connection between TTC reduction and dehydrogenases, and b) thinking carefully about the experimental design.
But it’s never really worked as a classroom activity, other than a fun challenge in how many ways they can describe variations of the color pink. It’s not challenging, it’s not engaging, and, to be frank, it’s not a whole lot more exciting than watching paint dry. This is the problem with any exercise where they just have to follow a recipe; the students carry it out dutifully enough, but they inevitably end up gossiping about other things and don’t learn anything during the course of the lesson.
This year, I just presented them with the reagents and apparatus, introduced them to TTC as a Redox indicator, and then asked them to use the stuff provided to test the hypothesis that respiration:
- involves reduction
- of glucose
- by living cells
- requiring enzymes
- and anything else that they can think of…
- with close attention to their CONTROLS….
The difference to the lesson was, just, wow. The students were now forced to think about what they were doing and why they were doing it. Working in pairs, they spent 30 minutes planning and rationalising their strategy, before finally trying it out. They puzzled about how to record the rate of TTC reduction, they had to think very hard about why the different sugars showed different rates and why yeast could reduce TTC with no glucose added. They got things wrong and they missed things out, but they remained interested and engaged throughout, and learned far more in the process.
The final proof was half way through, with all their boiling tubes set up and slowly pinkening, when the fire alarm went off. They did not want to leave the lab – they were happy to risk a firey doom rather than miss out on the experimental results that they were personally invested in, that they had full ownership of. Reluctantly realising that this wasn’t an option, they tried to smuggle the tubes out of the lab during the evacuation, until I pointed out that this would play havoc with their careful control of temperature…
So out we went, with lots of anguished glances back at their tubes of pink yeastiness.
(Happily, there was plenty of time for them to get back into the lab and finish off their investigation).
So a resounding success – he says modestly – but note how easy it is. I changed nothing about the practical, nothing to the technician’s order form – I just saved a few pence on photocopying the recipe. Flipping at its purest and best. Give it a go!