Monthly Archives: February 2016

A total Mockery

Back after half term and the 6th form, Year 12s and 13s alike, are neck deep in Mock exams. What joy. I quite like all the extra free time when, for about the only time in the entire year, I almost feel I’m in control. Doesn’t last long – suddenly the actual papers arrive and it’s my turn to be neck deep in the damn things, marking, and then writing reports. You all know the routine.

So, not a lot of teaching this week either. A fun session with my Year 8s today, analysing various ores (I really like teaching Chemistry!), some sex education with my Year 7s yesterday, using Herbie the hamster as a sort of approachably neutral route into male reproductive anatomy.

So, this hamster, is it a boy or a girl? And how can you tell?

A hamster’s testes are about the size of its head, so they’re hard to miss.

So, what does he need those for?

We revise sperm, eggs, fertilisation, and then look at some testis slides under the microscope – they do lovely drawings of the tubules and most of them actually see the sperm in the central tubes.

But if Herbie wants children, where do all those sperm (forming at 1,500 per second!) need to get to?

And so on.

Alas, my plan to illustrate the topic with breeding hamsters has failed, due to Hettie’s Xmas mishap, followed by Emily’s mysterious demise. The best laid plans of hamsters and men….

Right, back to the Mock marking. Normal service will be resumed at some point!

For Ruth

Some time towards the end of last year I received a lovely message from someone who had been on the same science PGCE course as me. This was at Homerton, way back in (gulp) 1999. She wondered how I had managed to stay so enthusiastic about teaching over the last 15 years. I promised to provide a burbicular reply and, as it’s currently half term with no lesson ideas to describe, here goes…

I think it’s important to admit that I’ve been very lucky. Lucky with the students I’ve taught, the schools I’ve taught at and the departments I’ve worked in. I’ve had some absolutely wonderful and inspiring colleagues who have shared the sense of fun and creative adventure that come with the job. My line managers have also been very generous and supportive in giving me the freedom to do pretty much whatever I like – a sense of autonomy is key to job satisfaction.

Self-confidence is important. I’ve never been too bothered by public exam results – I strongly believe that students who are interested and excited by your subject will want to do well, will work very hard in order to do well, and end up, surprise surprise, doing well. Endless past paper questions supported by endless past mark schemes seems to me the surest way to kill enthusiasm, both for student and teacher. I don’t have many rules in my lessons, but absolutely no-one gets to ask, “do I need to know this for the exam?” “What?!?!? You’re asking whether you NEED to know about how motor proteins literally walk their transport vesicles along your cells’ cytoskeleton super-highways? Sorry, why are you studying Biology?” In truth, the situation hardly ever arises.

But there are two absolutely vital ingredients. First, I love, absolutely love, Biology. Having done a first degree in English Literature, I’ve had to teach myself Biology as I go along. That made for a hairy first year, where I was seldom more than half a page ahead of the class, and where the precocious Year 9 student who asked my about the precise function of ribosomes had me almost in despair (I hadn’t got to ribosomes in the textbook at that point). So I’ve had all the exhilaration of learning a subject for the very first time (lordy lordy, how Biology has changed since I did it for A-level!) a process that continues to this day (what an unfair advantage Biology has, with new discoveries and innovations appearing every day in the news – right now, I’m goggling with amazement at the extraordinary T-cell trials on cancer patients). My enthusiasm for Biology, my amazement that a)this stuff actually happens and b)we’ve figured it out, is entirely genuine. It’s something I tell my students as they emerge, blinking with wonder at the intricacies of Chemisosmosis, breast milk antibody production, or DNA replication – think how wonderfully lucky we are to be alive at a time and place in history where we actually understand How It Works.

But enthusiasm alone butters no parsnips in the classroom. The second reason that I continue to love teaching is the creative bit, the process whereby you convert your own love of a subject into a format that makes it interesting, accessible, enjoyable, stimulating, memorable for the students. I continually ask myself – would I enjoy this lesson? Do I find this interesting? Would I tell my parents about this? Last week, I managed to get my Year 8s to work out the speed of light based on the eclipses of the moons of Jupiter. Relax – it’s not on any specification – but I was fascinated by this. First, the historical context, how Ole Romer first realised that light must have a speed in the first place. And then the ingenious, pain staking observations and measurements that produced an answer astonishingly close to the actual figure. I wanted my students to know about this, but I also wanted them to do it for themselves. How do you do that? How do you structure a lesson in such a way that enables students to replicate the work of a 17th century genius? I thought about role play – students revolving round each other and eclipsing each other – but eventually I came up with a model involving a candle, a tennis ball, a nitrogen molymod and a hydrogen molymod. They had to set this up as a mini-solar system and to imagine themselves on the blue ball, looking out into space. What would they see? What could they measure? What would change as the Earth circled the Sun? Could they put it all together?

And it worked. Actually, one very useful thing about the model was that I could immediately see if a group was stuck, as they would start playing with the candle or throwing the tennis ball around. That was the cue for rapid intervention! But they did it, triumphantly demonstrating their deduction of 220,000 km/s and feeling justifiably pleased with themselves. When a lesson like that works, it can make your week.

Over the years, I’ve got better and better at this. I’ve grown to understand what works and what does not work in a classroom. And I’ve never wanted to stop trying new things. I dread the thought of getting into a rut. I dread the possibility that I might become dull or predictable or cynical. So I work very hard to try and stop this happening. I like the knowledge that I’m good at my job and I derive huge satisfaction from seeing the positive effect it can have on my students.

Ruth – has that answered your question?

 

Blindness, insanity and death

Tell them stories…

I love stories. They provide context. They make things memorable. They are ideal learning tools.

I also love a bit of theatre. Teaching is, at least in part, a performance art.

This lesson combines the two. The content isn’t terribly original, but even the weaker students remember every single detail… So listen up! I shall be testing you later…

So, I say, did any of you go on the Duke of Edinburgh expedition?

An excited babble of reminiscence follows.

Did you stay in a tent? Was it really cold and uncomfortable?

They compete for the most uncomfortable story.

Did you cook your own food? Yes? What did you have? Pasta? Most of them will have had pasta. What did you cook it on?

A pause to remember the name, and then, a Trangia!

Right, a Trangia. What’s the fuel for a Trangia? That purple stuff? Anyone remember the name? Methylated spirits. Did any of you spill it in the pasta? What did it taste like? Vile!!!!

Why does it make such a great fuel? We talk about energy content and flammability and I light a little evaporating basin full of meths.What’s the flammable component? Yes, that’s right. It’s methanol. An alcohol. A clear, colourless liquid that tastes like its close cousin, ethanol.

So why are methylated spirits bright purple and taste vile?

Do they add stuff to it? Indeed they do. It’s not a great idea to drink it.

I direct them back to the burning meths.

Note the flame, I say. Orange tips. Very useful.

Why?

Ah. So we talk about methanol and ethanol and I tell them of my time in Uganda where a jerrycan of the local hooch -waraji, or banana gin – would set you back about 50p (50p for 30 litres of neat spirits!). But before we started making our waraji and passion juice cocktails, we always poured a little on the floor and lit it. If it burned with a clean blue flame, all was well. But orange tips to the flames? We used it in the paraffin stoves (it was much cheaper than paraffin).

Why?

Well, a clear blue flame indicates that it’s ethanol, the stuff we call alcohol, and which our livers can break down to carbon dioxide and water.

But an orange flame indicates methanol. Our livers break down methanol too, but they break it down to something else.

I produce my next prop, a mouse pickled in a jar of formaldehyde.

Lots of good reactions to this, mainly sympathy for the mouse.

Look at this mouse, I say. It’s perfectly preserved! It will never rot! It will swim in its little bath of formaldehyde for all eternity. But how good is it at being a mouse? What do I mean? You know, mousey things. The squeaks and the scurrying and the nibbling cheese stuff that mice do. How mousey is it? Not at all. It’s bloody rubbish at being a mouse.

And this is the problem with drinking methanol. Your liver cheerfully metabolises it, but instead of producing water and carbon dioxide, which your body can deal with, it produces formaldehyde. And this travels round the body. And starts to pickle it. Starting with your retina. Your retina becomes perfectly preserved! It’ll last forever! It’s just not very good at being a retina any more. Then your brain. Blindness, insanity… it’s not a good way to go. If you’re ever in Uganda, I say, or, indeed, anywhere where people distil their own hooch (i.e. pretty  much everywhere), remember the orange flame test!

They like the story, they love the mouse, they enjoy the anecdotes, they are happy to remember character building DoE expeditions. But where’s this going…?

I often digress at this point to discuss the power of addiction. Who drinks methylated spirits? Er, no-one? But they’re wrong. And they shake their heads in astonishment at the thought of someone needing an alcohol high so badly that they’ll over come the repulsive taste and the gruesome side effects…. But then it’s time to get back to the plot…

So, I say, here’s the punchline. The enzyme that breaks down ethanol to water and carbon dioxide is called alcohol dehydrogenase – and this same enzyme is the one that breaks down methanol to formaldehyde. Which means, I say, increasing the volume and emphasis for dramatic (some might say melodramatic) effect, every DoE leader must guard against possible methanol poisoning, and carry in their medical kit a large bottle of…. what?

And they see it. They really do. They’re also delighted. Every DoE leader should include in their risk assessment and medical supplies, a large bottle of vodka! They think this is hilarious. Voddie! On DoE!!! But they also get the science. Swamp the alcohol dehydrogenase with ethanol and the active sites will be too busy to get round to metabolising the methanol (which can be safely excreted on the breath, or in sweat, or in urine….).

Time for a few notes and diagrams – as Feynmann used to say, once you’ve understood it, you can write it down.

To my delight, this year, a couple of Year 12s compared the formula of the two alcohols and wanted more rigour on the enzyme (what does the name tell you about its job?), and were able to work out that, yes, if you strip a couple of hydrogens off methanol, CH3OH, you do get formaldehyde, CH2O. It meant we had to explore the ethanol pathway in more detail, but that was fine too.

Stories…. tell them stories.

Virgil, UV and shake it up baby

I think you can tell a lot about a teacher from the way they approach certain topics. Take the Water Cycle. With a KS4 class. How would you go about it? I must admit that my first response to these kind of topics is either to set it for homework or give them some interpretive exercise to complete in class as quickly as possible so that we can get on to something more interesting. There may be something in the Water Cycle that appeals to the deep in certain pupils, but if there is, I can’t see it….

And then there’s my friend Bill. Bill doesn’t think a dull topic should result in a dull lesson. Rather than shying away from it, he sees it as a challenge. So he takes the students on an imaginative journey to ancient Rome. He tells them of Dido and Aeneas. He describes the Punic Wars and the massive boat building programme that resulted in the deforestation of Sicily. They research the effects of this environmental catastrophe and then have to write a poem on the Water Cycle in the style of Virgil, which they read to the class for some peer assessment activity.

He was rather pleased that this lesson was observed. I certainly wish I could have seen it!

More prosaically, I mentioned Year 13s extracting geranium leaf photo-pigments to analyse the absorption spectrum.

IMG_1077

We returned to it this week. Here it is. What colour is it? They agree, cautiously, that it’s green. Are they sure? They pause, worried about the trick question, but eventually decide that whatever’s coming next, it is definitely green.

But why is it green? In other words, why do we see it as green?

They’re a bit more confident about this. Because it reflects green light.

Right. So what is it doing with other wavelengths?

They feel it’s just a revision exercise from the homework so are quick to explain that other wavelengths are absorbed.

Very good.

Now, what about this?

We put the boiling tube of the pigment into in a box with a black cloth over it – students can peek in….) and shine a UV light on it.

IMG_1073

If you don’t think that is seriously cool, then you shouldn’t be doing Biology (indeed, I nearly lost my temper with a Year 12 student who stated confidently that “chloroplasts are irrelevant”).

Luckily (for them), my Year 13s are impressed (I don’t quite get gasps of wonder, but the spontaneous reaction is nonetheless gratifying).

Indeed, they are absolutely intrigued by this – it’s a lovely awe and wonder moment. So, remind me. What’s the green stuff? Chlorophyll. Why is it green? It reflects green light. Why isn’t it green in UV light?

This takes them a little longer, but they’re generally happy that an absence of green light means that it has nothing to reflect, so can therefore not appear green. But which end of the spectrum is UV? So why doesn’t it appear blue? Or violet? Why does it appear red?

So I show them a molecule of chlorophyll. Why the long hydrocarbon tail? Good AS revision of the membrane SKU they’ll need to tackling thylakoids. Yes, it needs a hydrophobic portion to sit happily in the thylakoid membrane. It’s the head bit that’s interesting, a porphyrin ring with a Magnesium ion in the middle, and pair of electrons whizzing around it…

So what do electrons do when they absorb light energy? They move up to a higher energy level. And then? If nothing else happens, they fall back down, to a lower energy level, emitting lower energy light (red light, with its longer wavelength) as it does so.

We can then see what chlorophyll actually does with these electrons when it’s part of the photosystem in the thylakoid membrane.

And the last thing this week is just plain silly. But it worked.

I had introduced enzymes to the Year 12s with the Sugar Shake app game I mentioned a few burbles ago. They loved the game, but really struggled with the observations. Perhaps I need to make it more structured? Half of them literally did not notice that the enzyme changed shape when the substrate entered the active site!

Anyway, there were the usual questions about how an enzyme can lower activation energy. I haven’t decided how good the following analogy is – it was spur of the moment improvisation – but it certainly works at one level.

Take two large lego blocks and put them in a bin/box. These are two molecules in solution that could join together. They’re in solution – so what will they be doing? I gently shake the bin to provide kinetic energy and, lo, you can hear the molecules colliding! But these are not successful collisions! I stop shaking and pick out the blocks to show that they have not joined together. How could we increase the likelihood of a successful collision? More heat! More kinetic energy! I frantically shake the bin and the molecules collide more frequently and energetically! But still nothing changes.

And then I take the blocks out and line them up in exactly the right orientation and then my hands apply a little induced fit. Look! They pop together with hardly any effort at all. Lining molecules up in exactly the right positions is clearly a key enzyme feature….

Happy bin shaking.