Monthly Archives: January 2015

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!


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!

Strawberry and Coconut genetics

I forget who gave me the idea (I’m afraid I can’t claim it as my own), but if you’re currently extracting DNA from onions with fairy liquid (as my poor, weeping Year 12s used to do), then I’d recommend switching to strawberries and coconut shampoo as I did this year. Smells delicious, looks spectacular DSC_8169 (a little like you’ve liquidised a hamster), and produces prodigious quantities of what they’re happy to accept is DNA (though, truth to tell, most of the white goop is almost certainly pectin).

But onions (cheaper), strawberries (make sure you use coffee filter papers – the goop is too thick to go through standard lab filter paper) or frozen peas (frozen peas, along with onions, are the recommended vegetable of choice for the NCBE), there are ways of telling this story. I saw a teacher recently end the Year 12 Nucleic Acids topic with the DNA extraction exercise, reflecting their belief that practical work is a “just a bit of fun”, tagged on at the end if you’ve got time after the serious business of delivering immaculate notes and diagrams. By then, however, the end product comes as something of an anti-climax because they already know all about it. So what’s the point?DSC_8172

I prefer to do it like this…

Start with the DNA extraction. It’s fun, it’s messy, you can throw in some interesting questions on why you need to use detergent, 60’C water baths, protease and ice cold ethanol, and they end up with great goopy snot-like dribbles of “DNA” – several 1000km of the stuff if you reckon on 1m per cell.

Again, I should stress that if you want a higher percentage of real DNA, then onions or frozen peas are better, but given that we’re not going to sequence/amplify/carry out X-ray crystallography with the extracted material, I’m happy with my strawberries. The key learning point, apart from interpreting the extraction design, is that cells contains loads of this stuff, so it must have some really important function.


OK, so there it is, DNA. What next? Well, there’s obviously loads of it, so it presumably has some importance to cells, but what exactly does it do and how exactly does it do it? They’re motivated to find out more so I send them off to think through some of the classic experiments that identified DNA as the molecule of inheritance.DNA experiments exercise

Next lesson, it’s time to explore the structure. You could just tell them, of course, but why not get them to work out the structure for themselves? I do no more than tell them that nucleic acids are polymers of nucleotides, and sketch the structure of a simplified nucleotide for them. They then do exactly what Watson and Crick did – cut out card models and try to fit them together.DNA model instructions DNA model parts (tip: make sure your sugar/phosphates are on a different colour card to your organic bases). Again, I must cite my sources – this is another of Bill’s typically brilliant creations.


What makes this wonderful to watch is that even if they can remember A-T and C-G from (i)GCSE, they can now see why it has to be that pairing – A to T to 2, C to G to 3 (say it out loud), is my tip for remembering the number of hydrogen bonds.


We then bring all the nucleotides together in a large class molecule…

DSC_8202…and I play them the clip from DNAi where Jim Watson recalls the moment when they saw it  – the morning of February 28th, 1953. I tell them he got a Nobel prize for doing what they’ve just done – if you make your students feel brilliant, then they will do brilliant things.

We go back to the model and discuss it. What can they see? They can see that, to put it together, the two strands have to run anti-parallel. They can see the symmetry that the purine/pyrimidine pairing gives. It’s easy to point out the 3’ 5’ direction. I mention the footnote to the original Nature paper – “It has not escaped our notice that the specific pairing we have postulated immediately suggests a possible copying mechanism for the genetic material”

Can they see it as well? Yes they can! That base pairing means each half is a template for the other may be half remembered from (i)GCSE, though not with the clarity provided here. The hydrogen bonds which provide such a ready means of unzipping the molecule are also starkly obvious. Their next homework will be interpreting the design and results of Meselson and Stahls’ beautiful experiment. DNA Replication Meselson Stahl prep Meselson Stahl experiments

And so on. We hang our model from the ceiling and attempt to make it 3D and helical. It comes in very useful when explaining PCR to the Year 13s.

In the next lesson, when I finally give them a simplified diagram to label, DNA basic structure the detail they recall and include is fantastic. Because they figured it all out for themselves while I made a coffee and fed the hamsters.

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.

Escaping the Bell Curve

Happy New Year!

I hope you’re all feeling fully rested and recovered and ready for the rigours of the Spring Term. I’m getting back into the swing of things, following an unusually useful and productive training day on Monday, learning about the wonderful Firefly VLE.  No, honest, no irony intended, Firefly is really amazingly brilliant. You’ll wonder how you ever managed without.

Anyway, this week’s burble was inspired by a book that Santa left in my stocking – Better by Atul Gawande. If you’ve not read anything by this chap, you really should. He’s a North American surgeon by trade, but he is also an eloquent and profound writer on medical matters and gave a superb set of Reith lectures this year on The Future of Medicine which are well worth a listen.

In his first book, Complications, he reflects on various aspects of medicine, exploring the practical and ethical issues thrown up by specific case studies. His compassion for his patients shines through, from the man who is morbidly obese and undergoing a stomach stapling operation, to the young girl facing amputation as a result of necrotising fasciitis I recommend it to all my prospective medical students. He’s wise, philosophical, reflective and humane – and he writes brilliantly.

Better is themed around the challenge of improving performance in medicine, in his own words, how “we must advance, we must refine, we must improve.” So, for example, there’s a fascinating chapter on hand washing to reduce risk of infection in hospitals. It’s not a controversial issue -everyone knows how, when and why they should wash their hands, but hardly anybody strictly follows the protocol. Why? There’s also an extraordinary and humbling chapter on what it’s like to work on the front-line of polio eradication in India, and yet another on the doctors who agree to assist at executions in the US. He also writes on the Bell Curve, the statistical reality that most doctors are average. He writes, “What is troubling is not just being average but settling for it. Everyone knows that average-ness is, for most of us, our fate. And in certain matters – looks, money, tennis – we would do well to accept this. But in your surgeon, your police department, your local high school? (my italics). When the stakes are our lives and the lives of our children, we want no one to settle for average.”

He draws on this with his final chapter based on a lecture he gives his medical students, suggesting 5  ways in which they might make a difference, how they could become a “positive deviant”, as they strive to push their performance to the right of the Bell Curve and escape “average-ness”. I think his suggestions also have purchase for the teaching profession which, you might argue, has much in common with medicine. See what you think – some of them I find very affirming, but I’ve made at least one New Year Resolution based on the following!

Ask an unscripted question

For Gawande, this is about engaging with patients on something other than their immediate concern, and with colleagues on something other than the immediate professional need. It helps him feel less like a cog in a machine.  For teachers, it might indicate the importance of going off piste with a class, to tell them a little bit about yourself, to show that you’re interested in them, that you’re not just an automaton designed to deliver a biology specification.

Don’t complain

“To be sure, a doctor has plenty to carp about: predawn pages, pointless paperwork, computer system crashes…. Wherever doctors gather, the natural pull of conversational gravity is towards the litany of woes all around us.”

Yep, guilty as charged. Substitute “teachers” for “doctors” in that paragraph, and “Michael Gove” for “predawn pages” and I don’t think anyone who has ever worked in a school would disagree. And it’s so easy to do. He goes on…

“But resist it. It’s boring, it doesn’t solve anything, and it will get you down.”

I think he’s right – especially about the not solving anything. And about it getting you down. And it being really, really boring. So, I am resolved! I will concentrate on the aspects of the job I find enjoyable and worthwhile and I will endeavour not to complain.

Write something

“I do not mean this to be an intimidating suggestion. It makes no difference whether you write five paragraphs for a blog, a paper for a professional journal, or a poem for a reading group. Just write.”

OK, so I’m ahead of the game on this one, as are many of you. But see how Gawande articulates why writing can have such a positive impact.

“by offering your reflections to an audience, even a small one, you make yourself part of  a larger world.  Put a few thoughts on a topic in just a newsletter, and you find yourself wondering nervously: will people notice it? What will they think? Did I say something dumb? An audience is a community. The published word is a declaration of membership in that community and also of a willingness to contribute something meaningful to it.”

Yes, exactly. I now realise that that’s why I started this blog – I just hadn’t fully thought through my motivation, never mind expressed it so eloquently. I like the sense that I’m contributing ideas that may get used in other schools, in other countries, with other students. I welcome the ideas and dialogue and feedback that follow. So I just write.

Measure something.

This might be more difficult for teachers – I personally think there’s far too much measuring in teaching, especially of children, and I loathe the corporate culture of target setting and key performance indicators that has infiltrated the profession. But perhaps it depends what you measure and what you’re interested in finding out. I like to look at how many A-level students subsequently choose to study Biology/Natural Sciences at university – that’s a real indicator of how inspired they are. Or you might want to rise to Ben Goldacre’s challenge and contribute to research on a national level.


“Look for the opportunity to change. I am not saying you should embrace every new trend that comes along. But be willing to recognise the inadequacies in what you do and to seek out solutions. So find something new to try, something to change.”

I think that this is a real risk for teachers, that we deliver the same lesson year after year – by doing so, we disengage from the subject and from our students. We stop reflecting on how well it’s working, if at all, and we become stale. There are lots of good reasons for this – time is in desperately short supply, inspiration is hard to come by when you’re stressed and exhausted, and you’re in a hurry to finish the specification before the exam.

But, deep down, we know when a lesson isn’t quite right, when we’re just painting by numbers. And I think we have a responsibility to our students to continually reflect on and assess what we do. So try something new! Re-plan one old lesson a week. Trial a new investigation. Take a different approach. Flip a practical. Your students will appreciate it, even if it doesn’t quite work. And you will learn something useful and insightful about your teaching. See also

Back to more specifically Biological Burblings next week.