Monthly Archives: September 2018

Flippin’ obvious…

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…

Fuschia Fizz

or maybe

Pink Fizz with different substrates

… 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.

No more!

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!

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Long time, no burble…

Yes, still here, still teaching Biology, still trying new things…

Here’s an idea that worked quite well, with both my Year 10 classes this year.

Each desk (of two students) has a little tray with four small beakers and two teaspoons. The four small beakers contain, respectively, water, sugar, salt, and a solution of red colored food dye.

Arranged around the outside of the lab are 20 large beakers, completely empty.

The game is this – each of the large beakers must receive a small amount (say, the amount you could get on the very end of a teaspoon) from each desk every 20 seconds. All clear? Good.

Go!

Pandemonium ensues, as students race back and forth across the lab, transporting small amounts of sugar/salt/water/red liquid from the small beakers on their desk to the large beakers around the lab.

It’s hilarious to watch, as they get increasingly frantic, especially as I’m shouting out the 20 second intervals, and pointing out large beakers that are conspicuously empty. But after 4 or 5 minutes, it’s time to yell…

“Stop!!!”

And gently admonish them for being so wastefully inefficient. There is, I assure them, a much much easier way of achieving the same thing. Can anyone suggest an improvement?

And in both classes, one bright spark said, “Why not just put the sugar and salt and water and red liquid together?”

Go on then, I say, do it.

The bright spark demonstrates by pouring everything into one small beaker, producing a vivid red liquid which is mainly water with the various solutes dissolved in it. They then walk slowly around the edge of the lab, putting a tiny drop from their beaker into each of the large beakers.

What, I ask, has this person just made? And what do the large beakers represent?

The colour provides a handy clue. Yes, it’s blood…. which means the beakers are…? Exactly – the cells/tissues.

…there follows a discussion on why water is such a great transport medium – dissolve stuff in it, and wherever the water goes, the dissolved stuff goes too – and then we can introduce the structure of plasma and the functions of blood.

More next week, on practical Genomics….