Monthly Archives: March 2015

Co-operative pregnancy

The briefest of burbles this week as we’re setting up the Year 12 Practical Skills Assessments – 38 students – and it’s all a bit manic.

So, pregnancy testing kits. Even I would not ask for a student volunteer to donate urine to show how they work – finding out that you’re pregnant, whether it’s a moment of life-affirming joy, or an unmitigated disaster, is not something that should happen in a Biology lesson. Mind you, I would have no problem asking a volunteer to use a fertility testing kit – and several brave girls over the years have done so.

I did test the urine of the class female hamster (Hettie)

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with a pregnancy testing kit, as she had recently mated with the male (Herbie)

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and we had high hopes of baby hamsters. The test came up negative but, which turned out to be correct, but we still don’t know if HCG (Hamster Chorionic Gonadrotrophin) is sufficiently similar to HCG (Human Chorionic Gonadotrophin) for the test to work if she was pregnant. Maybe in the summer term when Hettie and Herbie will meet again…

Anyway, pregnancy testing is on the OCR A2 spec. How to teach it? Specifically, how to teach it so that they learn how it works, rather than telling them how it works so that they then have to go away and learn it?

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I started by showing them the positive test for George, our youngest son. There he is, bless him, George’s first communication with the outside world, a little message saying, “I’m here! Look after me!” I still look on this as faintly miraculous. I give them a little bit of human detail – we had hoped for a girl, 3rd time round, but on the 20 week scan, along with the bones and kidneys and brain ventricles and beating heart, there was another structure visible that could only mean one thing, another bloody boy… A few tears in the carpark afterwards… but once George had actually manifested himself as George, we obviously wouldn’t change a thing.

But how does the actual test work?

I set it as a kind of Dragons Den/The Apprentice/Young Enterprise exercise. I asked them to imagine they were the development team at GSK and you’d come up with a brilliant idea to invent a pregnancy testing kit. Make millions from grateful women the world over! And then told them to invent it. From scratch. No research allowed.

It was joyous. They quickly decided that they needed to look at it from the consumer’s point of view as well as the biological point of view. What would the customer want? Has to be reliable and easy to use. So urine rather than blood. Something in the urine that is uniquely associated with being pregnant. That means it’s also got to be small enough to get through the basement membrane (i.e. molecular mass < 69,000 in the kidney.

At this point I provided a bit of scaffolding – the molecule you’re looking for is HCG. Released by the embryo very early on in pregnancy to prevent the yellow body breaking down and maintain the supply of progesterone. I love this – the idea that your baby is chemically manipulating you right from the start.

They quickly come up with the idea of some kind of receptors. They’ve picked up on my much repeated assertion that if you can do jigsaws, you can do Biology. But somehow they’ve got to colour code the receptor. And they’ve got to arrange things so that there’s a control line as well as the positive/negative line. Someone finally hits on antibodies, and I scaffold some more, telling them that specific antibodies can be manufactured in sheep, and that antibodies can be tagged at the end of the constant region with the colour of their choice. Much amusement when someone imagines centrifuging a sheep (rather than the sheep’s plasma).

They keep going. They hit on the principle of capillary action. Perhaps the antibodies could move along a fabric or something? But then they need to be stopped. But only if they’re bound to HCG. Er, this is getting complicated. But they sketch it out, and I provide a bit more help, and they’re there. Pretty much. So when we finally draw out the diagram and sketch a positive/negative test, and answer some interpretive questions, they already know and understand it. pregnancy tests

It was a fabulous example of co-operative learning – it wasn’t a particularly bright group, but they trusted my implicit assertion that, yes, you can do this, and they worked together, every student making suggestions and thinking aloud. None of them could have done it on their own. As a group, they did.

They were thrilled at their own cleverness, and fascinated by the cleverness of the testing kit. And to add to my own happiness at a lesson that had worked so well, SLT had popped in to observe it as part of one of their Learning Walks.

Back to the PSAs! Have a good week.

It’s alright, ma, I’m only bleeding

The Biotutors discussion forum was getting hot and bothered last week over blood. Someone had wondered whether it would be OK to allow a student to test for blood glucose levels. The advice offered was almost unanimous – NO! Absolutely not! Do not touch with a barge pole! Too dangerous! So many ethical issues! No, no, no, no, NO.

All of which fills me with despair. After all, what could be more interesting, what could be more motivating or exciting, than looking at your own blood? Allowing and enabling students to do this should probably be a requirement of the A-level course. It’s very easy, it’s completely safe and it is utterly fascinating. Risk assessment? Yes, it needs to be sterile (easy). It’s advisable to get parental permission in advance (try this letter template blood typing letter for blog). It obviously has to be an “opt in” activity (in 15 years, I’ve never had a student opt out). Sometimes a student faints (be aware of this, watch out for it, ask them to alert you if they start feeling faint, and deal with appropriately if it happens). But there is absolutely no reason why you shouldn’t do it. Still not sure? Well, the ASE and CLEAPPS are both perfectly happy with it and have published procedures for taking blood samples safely. You can do it!

Now, if you’ve never done this, I can see why it might seem a bit intimidating, so it obviously makes sense to trial it on yourself/other teachers before rolling it out for a class. You also need to think about the class. I’m happy to do it with my Year 10s – you might prefer to keep it for the 6th form.

I also demo it on myself in the lesson, partly to show that I’m not asking them to do something I can’t or won’t do myself, but also to run through the protocol for them all to see. You can make this reasonably dramatic and play it for laughs (if you’re like me).

So I tell them about the bad old days when you literally had to summon up the nerve to jab yourself with a lancet. It wasn’t easy! Pushing the button on a plastic spring-loaded pre-set single use disposable captive lancet (http://www.expresschemist.co.uk/Accu-Check-Safe-T-Pro-Plus-x200.html) is a doddle by comparison.

I say they need to choose a “sacrificial” finger. I reassure them that sensation will return in a year or two. Probably. The disposable lancets have 3 depth settings, so you can determine the length of the steel blade that will plunge into your flesh – …. I ask my class to select the appropriate length for their teacher. They take great delight in always choosing the longest one.

Use the side of your finger. The pad of the finger has far too many nerve endings and will be quite sore afterwards. The top of the finger, just behind the nail, just seems too close to the bone! The side of the finger, about half way along the last phalange, is nice and fleshy, has lots of capillaries, but is relatively un-sensitive.

It’s good to shake your arm thoroughly before stabbing yourself, to encourage blood flow. Sterilise the side of your finger with the sterile cleansing wipe (https://www.eurekadirect.co.uk/Hygiene-Infection-Control/Wipes/Alcohol-Free-Wipes/Sterile-Alcohol-Free-Cleansing-Wipes). Place the lancet firmly against the stab site on the sacrificial finger…

… and then….

… press the button. It’s instantaneous. You might feel a little jab, you might feel nothing at all, but it’s actually a huge anti-climax after all that build up. But! You should have blood. If it seems a tad slow emerging, then squeezing, or “milking” your finger can encourage the flow; after all, you’re not going to need very much. Or you might be a bleeder – take what you need and then stop the flow (pressure followed by a plaster).

So, you’ve got blood. What are you going to do with it?

The obvious thing is to look at it. I do this in year 10, when they just look at the red blood cells. All they need, apart from their blood, is a slide, a drop of saline, a coverslip and a microscope. And simply watching the little biconcave discs spinning in the plasma (you actually see the cells in 3D, which you don’t get from a prepared slide) is pretty compelling, even soulful. It also gives an immediate impression of the tiny-ness and numerous-ness of cells – there are at least 4 million cells per micro-litre, but even at x400, they are very, very small.

I do this again in Year 12, when they learn to stain with Leishmans’ to show up the white blood cells. What are the relative numbers, red vs white? How many different types of white blood cell can they identify? Using haemocytometers is a good option here, too. The motivation levels are sky high.

So looking at blood is very cool. But there’s more.

Why not measure blood glucose? It couldn’t be easier – after all, it’s something diabetics routinely do several times a day. When I’ve had a diabetic student in the class, they’re usually only too delighted to talk about their condition, demonstrate what they do and explain how it affects their lives. A simple electronic blood-glucose monitor, which you can pick up in Boots, does the job admirably (though you need to check every year that the disposable test strips haven’t expired).

This is what I do.

I like to use a volunteer who measures their blood glucose and then drinks a Coke/eats a Mars bar. We record the time and the mmol/litre reading on the board. Then it’s time to review digestion/absorption. What do they think the next reading will be and why?  When we’ve finished this discussion, about ten minutes later, we test the same student again. Whoosh! Look at that sugar spike! I always make this very dramatic. Oh no! If we exceed 11 mmol/litre then it’s hyperglycaemic coma and death!!! Aarrghhhh!!!! This prompts lots of good questions and discussion about why high glucose levels are dangerous. Hmmm, time to check again. Oh. It’s falling. Hurray! They’ll live!

But what’s going on?

Again, record the data, time and concentration and start talking about what is happening inside that student at that very moment. With 4 or 5 more measurements before the end of the lesson, all the students have the data plot a suitable graph for homework, adding annotations to explain/describe what’s actually going on in the volunteer’s body along the line. I also ask them to extrapolate the line to show how they think it will change over the next 6 hours. It’s a brilliant way of testing their understanding, forcing them to think about data gathered in real time. What’s not to love?

And then there’s blood groups. I use this as the taster lesson for Year 11s thinking about A-level Biology. The blood typing kits from Blades (http://www.blades-bio.co.uk/proddetail.asp?prod=CBK014) are very easy to use and interpret. And what a brilliantly synoptic topic! We’re talking about membranes and membrane-proteins and genetics and inheritance and multiple alleles and antibodies and resistance to cholera and Charlie Chaplin and allele frequency and selection pressures and Anne Boleyn and the utterly brilliant blood typing game… (http://www.nobelprize.org/educational/medicine/bloodtypinggame/game/index.html). Difficult, challenging, fascinating. Biology, in other words.

Next week, pregnancy!

Friends, Romans, countrymen, lend me urea

A few weeks ago I burbled on how I use Molymods to enable Year 10 students to work out the balanced equation of aerobic respiration. Today I did something similar with Year 13, as we start to explore the liver.

As with all such activities, I encourage them to take photographs with their phones as they go along, which they can use for reference/revision.

I started by asking each student to make an amino acid from basic Molymod atoms and bonds. Once the initial panic/hilarity subsided (“what? remember something from AS?!?!!?), they actually did OK, perhaps needing a reminder on what to use for the C=O bond. And although most, understandably, went for glycine, there was an alanine and a serine for variety.

So, a load of amino acids swirling around. They’ve been absorbed in the small intestine and taken to the liver via the hepatic portal vein for processing. They’re being plucked from the sinusoid by the hepatocytes – what could the liver cells do with them?

OK, so they’re the raw ingredients for proteins, perhaps they’ll get converted into enzymes or muscle or membrane proteins or electron carriers or whatever.

But what if there’s too many? The liver can’t store excess amino acids – and the amine group is toxic. What’s going to happen? We talk about deamination. I tell them it requires an oxygen atom and produces ammonia.

They then use their amino acid and an oxygen atom to build the products, and use that to write out the equation.

What have they made? Along with the ammonia molecule, I tell them they’ve made a keto acid. Keto acids can be respired, but if the body is forced to use protein for respiration (in diabetes, anorexia, Atkins diet…) then too much keto acid goes into the blood. Why is this a problem?

We talk about keto-acidosis, bad breath and other interesting distractions.

But what about the ammonia?

We pass round a dilute ammonia bottle and take a sniff. Even the dilute stuff is pretty eye-watering (the concentrated version takes the back of your head off!). And you’re making this in your liver! What do you do with it?

Yes, it’s got to be excreted. So I ask them to react two of their ammonia molecules with one carbon dioxide to form a water molecule and one other molecule…

They dutifully work through the reaction with the models and figure out the equation.

Hmmmm, what’s this? They’ve built a brand new molecule! What could it be?

The chemists gamely tried to name it – di-amine-carbonyl? But eventually a light bulb goes on in someone’s brain and they realise what they’ve made.

What I like about this is that they build a molecule of urea without knowing that that’s what they’re doing or what the structure of urea actually is. It transforms the dry ornithine cycle into something immediately interesting and relevant and hands on, and they can use their photos for reference when they eventually sit down to learn it.

Next week, blood!