Tag Archives: experimental design

Bupples and Benedicts

Back to burbles of a strictly biological nature this week, and a recent idea that passed quality control with Year 7.

So, what do you think of Benedict’s Test for reducing sugars?

To be honest, I’ve always regarded it a pretty boring part of any Biology course. Oh, it’s wonderfully colourful, and the students always enjoy the chance to get out the Bunsen burners, but given the intoxicating wealth of mind-boggling Biology available to anyone tasked with writing a specification, it’s odd that it repeatedly survives the cut, while Immunology (to take just one example) gets repeatedly hacked to the bone and beyond.

Now, one of my main projects this year is to completely re-write the Year 7 Scheme of Work. I want to move away from a course where factual material is delivered in vast, turgid chunks, to lessons that encourage curiosity about the natural world, asking interesting questions and answering them through experimental investigation – you know, something a bit like Science. As far as possible, as with all my teaching, I want them to find things out for themselves.

Being a general science course, I spent the autumn term working on Chemistry (Purification) and Physics (Energy) which has been a lot of fun, and I’ve learned loads as these are both well outside my area of expertise (particularly Physics, which I gave up when I was 14). But now we’re finally on to the first Biology topic and I’m feeling a lot more zonally comfortable. The theme is Cells and Human Reproduction and I’m basing it largely on apples and hamsters. Wonderful things, apples….

So, opening lesson, do they like apples? They nearly all do. Why? Because they’re crunchy! Well, lots of things are crunchy (bricks, gravel, celery, cockroaches) – there must be something else going on. Because they’re sweet! Aha, why are they sweet? Because they contain sugar! Good hypothesis! But how do you know? Ermmm….because sugar is sweet? Maybe, but lots of things might make something sweet, how do they know that it’s specifically sugar that makes apples sweet? Blank looks.

Right, working in pairs, they have 4 small beakers, one of sugar (glucose), one of distilled water, one of apple juice, and one with a mysterious blue liquid. Pausing only to demonstrate safe use of a simple water bath, I tell them to use the above to prove that apple juice contains sugar.

The blue liquid is, of course, Benedict’s reagent, but they don’t need to know that. And I deliberately don’t tell them that it’s a test for sugar, otherwise the whole learning outcome of the lesson is negated. What are they going to do?

I’ve praised curiosity and the value of testing ideas empirically since September, so they’re very happy to try lots of things. Again, it’s one of those lessons where you’ve got to be quite hands on, moving quickly between the pairs to hear their ideas and head the more ridiculous ones off at the pass. Some of them think they should separate the sugar from the apple juice by evaporation (echoes of the Purification topic) so I point out that I haven’t provided an evaporating dish – the water bath is for heating. Plus even if they did this, how would they know that the separated powder was sugar?

Many of them just shovel all the ingredients into a test tube and heat it. Oh the excitement! It goes brick red! Wow! Fantastic! Well done! What does that show? Ermmmm…. And at this point they really start to think.

So they heat the blue liquid with apple juice. It goes brick red! What does that show? Ermmmm….

So they heat the blue liquid on its own. Good. What explanation are you eliminating? Still doesn’t show its sugar, of course….

So they heat the blue liquid with sugar. And so on.

Nobody’s mentioned controls, fair tests, but they demonstrate that Ben Goldacre is absolutely right – children intuitively understand the principles of a scientific experiment.

By the end of the lesson, they’ve taught themselves Benedict’s test and, based on the follow up homework which I’ve just finished marking, the vast majority understand the importance of eliminating other possible explanations with controls. And they feel really pleased with themselves because they’ve done it all themselves. Better still, in the next lesson, they can all recall what they did and why they did it.

More on apples to follow – they are a fabulous biological teaching tool!

Have a good week.

Post Burble

Why bupples in the title…? It’s how my eldest son pronounced “apple” when he was 2 years old. I encourage my students to do the same.