Tag Archives: Year 12

Teddy’s bungee jump

Year 12. Carbohydrates. Sugars and polysaccharides. And a real shock to the non-chemists who despite lots of advice and warnings to the contrary, still manage to look aggrieved when biological molecules start appearing in the lab. I try to keep the pace brisk, so after an introductory lesson on glucose, where they build them with molymods and work out the formation and structure of a glycosidic bond for themselves, they cover all the other sugars with a homework on Sugar Cards (Top Trumps? Dating Agency introductions? Collectable Cards? Their choice!)



But if sugar biochemistry can be unpleasant, it’s nothing to the sense of horror when starch and cellulose appear. As if plants themselves weren’t bad enough, now we have to learn about their polysaccharides! Aarrghhh!!!!!

So I start with Teddy. Everyone over here! (a key part of all my lessons is to keep the students on the move). Meet Teddy!


He’s not had the easiest of lives, starting off as a handy board rubber (note black markings). But as you can see, he’s gamely decided to try a bungee jump. Only thing is, he can’t decide what to use for his rope – should he use a length of string (on the right)? Or should he use a length of spaghetti (on the left)? It’s a tricky one!

Students puzzled, intrigued, deeply amused.

So, what do you lot think? Spaghetti or string? String or spaghetti? Any thoughts? The piece of string? Why? Because it’s stronger.  Really? Well, it’s a good hypothesis, but how could we possibly find out?

So Teddy leaps from the chair safely secured to a piece of string. Tied to a piece of spaghetti, however (and good luck tying a realistic knot with spaghetti!), he plummets to the floor. Just in case they’re not convinced, I ask two students to have a quick tug of war with the string, and then the spaghetti. Yep, that was a good prediction – the string is much stronger.

But why on earth are we comparing string and spaghetti? Isn’t it like comparing warthogs with paint? What do they have in common? OK, they’re a similar shape, but surely that’s it. Anything else? No? OK, start with spaghetti – what is it? Yes, it’s food. What food group? What’s it largely made of? Starch. A carbohydrate. Excellent – great for carbo-blasting before a long race or a big match. Good. And where do we get starch from? Wheat.

All very straightforward. But what about string?

They usually get there pretty quickly. It’s cotton. Also a plant product. Made largely of plant cell walls. In other words, cellulose. Which is another? Carbohydrate.

We can now draw on what they learned from their sugar homework – they recall that starch is a polymer of alpha glucose, cellulose is a polymer of beta glucose – one makes fantastic food  but isn’t something you would make a T-shirt out of, the other makes everything from jeans to string, but isn’t remotely appetising, even with bolognaise sauce. But they’re both made of glucose! How is such a thing possible?

Now they need to build it, to actually see how and why the position of the OH group on carbon 1 can make such an enormous difference. These cut out card monomers building starch and cellulose template (orange for starch, green for cellulose) to enable them to do this. They cut them out and stick them together, carbon 1 to carbon 4, using the pattern shown on the instructions building starch and cellulose instructions and questions. The alphas are easy. But the betas? Some see it instantly, others take a while, but eventually they all figure out that you have to flip every other glucose to make the glycosidic bond work.

So now they can extend their oligo-saccharides by joining them to other people’s. I encourage liberal use of glitter/decoration to lend a festive touch (we’re closing in on Xmas at this time of term) and to lighten up the subject – heaven knows that plant polysaccharides need all the glitter they can get –


and now you have a model to illustrate all the other key learning points.  First the shape – the starch just spirals round and round, while the cellulose is a straight line. Now stack the cellulose molecules in parallel – why is this so strong? Lengthen the starch – why is this so great for storing energy? Oh, but there’s a problem with only having 2 available glucoses at any one time. What could we do? They suggest branches. Bingo! Add some 1’6 connections. Put it all up on a display board, cellulose flanking starch to represent a plant cell (-ish), and let them tackle the questions. Encourage them to take pictures of their molecules – good reference for revision.


Suddenly they’re excited. Are we going to build any more models? Oh yes. Just wait until we do proteins…

Miracle berries and my eureka moment

Sorry this is 24 hours late, but I’ve spent a very enjoyable day down at Streatham High School, taking a look round their new labs and discussing everything from iGCSE to KS3 science. It’s always so interested and useful to visit other science departments – we should do more of it.

Anyway, what shall I burble about this week? I was quite pleased with a new idea for introducing the Nervous System to Year 13. It was inspired by one of last year’s Year 13s who gave me some experience altering tablets as a thank you present. No, not what you’re thinking. It was pack of mberry miracle fruit tablets, available for £12.50 a pop at http://mymberry.co.uk/ and featured on the Graham Norton show https://www.youtube.com/watch?v=TJwuo2Y7KXs. The protein present, miraculin, causes a conformational change to your sweet receptors such that they bind to “sour” molecules. Result – a slice of lemon tastes like lemon sherbet. I got my Year 13s to suck on a slice of lemon, and then dissolve one tablet as per instructions on their tongue, and then try the lemon again. Sensational reaction! Then get them to explain it…  Along with all the revision of receptors and proteins, it’s a really neat way of showing that our perception of the world depends entirely on which part of our brain impulses get sent to…

What else? Well, I could tell you about the amazing fun I’m having with Year 7, or share the Year 12 practical investigation into osmotic inhibition of bacterial growth, or maybe the Year 9 Martian Biologist challenge – how can you tell the difference between Eleanor and a geranium? But I want to take a trip down memory lane and share my eureka teaching moment, when I suddenly realised what it was all about.

It was my second term at St Paul’s. I was due to start the Immune System with Year 12 and I was planning my standard kind of lesson – project image of macrophage, tell them about macrophage, give out picture of macrophage, label on board, draw picture of phagocytosis, etc etc. In other words, not a lesson, but a lecture, with no active learning, just information delivery. Students all passive. Me hoping to enthuse them with the inherent brilliance of macrophages and the sheer ebullience of my teaching personality. Ahem.

And then, clearing out the filing cabinet in my lab, I found an old sheet left behind by the retiring biology teacher who I had replaced. Here it is.

The Immune System

Natural Immunity

In mammals, non-specific or natural immunity operates partly through PHAGOCYTIC white blood cells (leucocytes).

  1. Observe a prepared slide of a blood smear. Using an Atlas of Histology and Biology textbooks to help you, identify and draw labelled diagrams of a phagocyte and a lymphocyte.

Add to your diagrams the mean diameter for each type of white blood cell (in mm) and a concise description of the cell’s appearance.

2)        Draw annotated diagrams to illustrate the mode of action of a phagocyte.

From where are phagocytes derived?

What are the two main types of phagocyte? How may they be distinguished?

It doesn’t look like much. No fancy formatting or sexy SEM images or even a joke or two. But the lack of frippery probably helped me “get it”. And it was so simple! I just needed to step away from the white board, put down the marker pen, and stop talking. I needed to tell the students as little as possible. Quite the opposite. I needed to let them find out for themselves. Make them do all the work. Base it around practical observation or investigation. Make it a journey of discovery. Make it active learning. My job was to guide and enable, not just tell them stuff. It came as a revelation, though in fairness to my brilliant PGCE teachers, it was basically what they had tried to tell us during the teacher training course.

So why hadn’t I got it earlier? The fear, I think, is in letting go, relinquishing control of the class, because as long as they’re looking at me and copying stuff off the board, I’m doing my job and it’s all nice and safe. The only down side is that, underneath all the busy scratching of pens, the students are bored and not actually learning anything….

Anyway, I’ve modified this leucocyte activity a bit now – in fact, I use a simplified version with Year 11 to put some practical activity into what can become a very theory heavy topic. I basically just give them the blood smear and a microscope. I tell them to find the blood cells (a challenge, coz they’re so small, but they can do it!), and then to find the ones with purple inside them. Draw them. Draw them large (half a page each). Label as much as you can. What’s the purple stuff? How can you tell? And so on. They love the challenge, the variety, the element of the unknown, the discovery…

Ugh. 8 period day tomorrow, just to round the week off nicely. Good news, I end it with Year 7 fully indulging their pyromaniac tendencies!

Ta ra.

Year 12 and… what?

Half term is almost with us, hurrah, and I, for one, can’t wait. Lots of sleep lined up.

Whenever I’m planning a lesson, I always like to think of the opening, the lure, the hook. After all, the students are coming in from break, from lunch, from registration, with all kinds of distractions and probably the last thing they’re thinking of is Biology. I want to grab their attention as quickly as possible, get them on task and get them thinking. Projecting an SEM image of an embryo on a pin point – what’s this a picture of? The World War 1 shell casing – anyone know what this is? And so on.

See what you think of this introduction to a Year 12 lesson.

I start by asking if any of them like crosswords. Yes, no, not really. What about cryptic crosswords? Ugh, yuck, no. OK, try this. I project the clue “Beautiful girl in crimson rose(8)”. Huh? What? Don’t get it. So I talk them through how a cryptic clue work and ask leading questions so that they eventually see why the answer is, “rebelled” (8 letters, “belle” inside “red” meaning “rose”). Lovely, elegant clue, with classic misdirection in the defining part. But where’s it going?

Then I say that I’m going to show them my favourite ever cryptic crossword clue, and that they’re going to solve it, and feel really pleased with themselves. It’s HIJKLMNO (5). Bafflement. Consternation. What the…? But they also want to know the answer, they’re intrigued. Suggestions? It’s the alphabet. What, all of it? No, only the middle bit. Describe it. 8 letters in the middle of the alphabet. Which letters? HIJKLMNO. Describe it more succinctly. It’s the bit that starts with H and ends with O. More succinctly than that….

Everyone got it? You will. And that moment of transformation, from utter bewilderment and feeling stupid to understanding the answer is great.

I then switch to the cover of “Aliens Love Underpants”. If you’ve not come across this children’s book, I’d highly recommend it. It’s based on the premise that aliens are here, among us, and they are driven by the urge to steal our underwear. It’s why you can never find a matching pair of sock and why pants go mysteriously missing. When a giant asteroid is heading for earth, the aliens, distraught at the prospect of losing their pants supply, steal a zillion pants, stitch them together in a single gigantic pair of Y-fronts, and ping the asteroid back into space using the elastic power of all that underwear.

Then I show them a picture of Earth flanked by Mars and Venus. If you were an alien, exploring a new solar system in search of a new pants supply, which planet would you choose, and why? They get it. Pants means life. You head for the blue planet, you head for the water. And there’s the key question – why is water essential for life?

I’ve attached the pictures that go with this – I’ve also attached my Water Circus and associated homework assignment. My Water Speed Dating Party, where you constantly mingle and meet a new and rather attractive molecule that you feel a definite attraction to every nano-second, I’ll leave you to imagine…

Have a great half term. I’ll be back in a couple of weeks.


Aliens love underpants

Water Circus revised Sept 2013