Tag Archives: flipped practical

Enzymatic Virgins

After concluding Osmosis with the now traditional paper fight across a line of chairs, it’s time to launch the Year 9s into their next topic. As always, the method of launch is as critical as the actual launch itself.

This is the classic example of what Bill calls the “flipped practical”, one where the students have no idea what’s going on, but are forced into asking questions from their experimental observations. The subsequent explanations then slot neatly into the pre-formed holes in their neural networks (well, that’s how I like to imagine it). It’s all about the “That’s Funny…” reaction, the most exciting words in science according to Isaac Asimov (who he?). I like this because it really is how science works and it’s what makes science uniquely exciting.

  • those galaxies have a red shift, that’s funny….
  • none of the first generation are dwarf, that’s funny…
  • there’s no bacteria round that fungal contamination, that’s funny….

(insert your own favourites).

I also like it because, for me, it all snowballed from this example. We’ve found that just about everything in our lessons works, and works better, with the “flipped” approach. Students are more engaged, more excited, more curious when they don’t know the answer in advance. At this point, you may be in Basil Fawlty mode, “Can’t we get you on Mastermind? Next contestant, Dr Paul, special subject, the bleeding obvious…”

So maybe you already do stuff like this – but I know from the Training Days that I run that it’s a novel approach for many teachers, so if it is new to you, give it a go. After all, what’s the worst thing that could happen…? If nothing else, you can be sure that no student will say, “Oh, look, it’s doing what it’s supposed to do….”

Anyway, to my wonderful Year 9s. What am I saying? All Year 9s are wonderful. But wonderful or not, it’s time to start enzymes. Except that I don’t want to get bogged down in terminology and definitions and labelling active sites just yet. I want to open up some receptive gaps in their brains. So they do this. Catalase interpretation sheet

The lesson plan is pretty self-explanatory, but here are a few notes to help you negotiate around any pitfalls.

I introduce hydrogen peroxide. Do they know anything? Not a lot. It bleaches hair? offers someone. We chat a bit about its various uses,  but the key point I want to get over is the fact that it goes “flat”. After a year, it’s all turned into water and oxygen and you have to buy a fresh batch.

They take their protocols and collect the apparatus and then it’s all hands on deck getting round to the pairs to help them over the first hurdle. They’re not quite sure what to write. Rate of peroxide break down…? Yes, how quickly is it happening? Huh…? Well, what would you expect to see when it breaks down? Um…. what does it break down to? Water and oxygen. Right. And oxygen is a…? Oh, bubbles. Right! Have another look. How quickly is it breaking down? Very fast – it’s already finished! Think about it – how long did we say it took to go flat? Oh, very slowly? Right! Too slow to see, unless it’s a particularly perky batch in which case you might see a few bubbles around the edge of the boiling tube.

Then it gets exciting. Add potato – whoosh! Add yeast – fizz! Add liver – yee hah! Ideally, their tubes overflow. Get them to test it for oxygen, while they’re at it. What on earth has happened? What do these things have in common?

This invariably goes well, but, for me, it’s not the most effective part of the lesson. After all, they’ve seen similar stuff in Chemistry (at least, you hope they have!), and while it’s fun, it’s not completely novel. It’s when they heat it all up, boiling the yeast and cooking the potato and frying the liver. If they already know about active sites and denaturing this is simply confirming what you told them –but if they’re enzymatic virgins, the reaction is, “huh? That’s funny….”, because heat usually speeds things up. Here it has done quite the opposite. And they want to know why.

The pH foaming towers activity can also be squeezed into a double period with a competent and fast working group.

And so you end with a series of questions…

  • What is it about cells that speeds up this process?
  • Why does extreme heat stop them from doing it?
  • Why is it also affected by pH?

… which they will remember for the next lesson, when you can then introduce the word enzyme and, if you feel like it, use this Powerpoint animation. enzyme animation showing lock and key specificity and denaturing

Have a good week!

Paul

Health and Safety note

Make sure they’re heating the yeast/potato/liver safely – yeast in a test tube has a tendency to shoot violently out the end when boiled!