Category Archives: Year 10

Mapping Retinas

You can’t really go wrong with eyes. Oh, unless a student starts feeling queasy with the eyeball dissection. But it’s one of those Slam Dunk Open Goal Shoo In topics that you would have to work really hard at to make dull. So the following is just throwing some random ideas out there which you might consider (if you don’t already do them).

I start by making the entire class stare at a huge red heart projected on to the board for two minutes.

red-heart-vision-trick

Then immediately switch to a white screen. They love this – it’s weird, it’s unexpected, it’s slightly unsettling, and it stimulates the obvious question – what the…?

So then we map their retinas.

mapping-the-visual-field

This is a resource I found in an age old file 15 years ago or more, so it’s not original, but I love it. Keeps them usefully occupied for 45 minutes or so and all you need is some A3 paper, sellotape, meter rules and two pen lids, one red, one green. I’ve adapted it a bit and added a homework exercise with interpretive questions to help them understand the wonderful maps that they produce…

retina-map

Once they’ve figured that out, you can go back to the red heart trick and ask them to explain it.

And if you are dissecting eyeballs, do make sure you see how high the lenses will bounce…

 

Gob-smacked

A few burbles ago, I mentioned that I’d be reporting back on my Year 10 Biotechnology Club, and how they had fared in their attempts to work out Mendelian laws of inheritance from first principle. I hadn’t seen them for a couple of weeks because of various other commitments, but now I have. And, well, wow.

So, just to recap, this is what they did.

I got in some flies. Fruit flies. This is the place: http://blades-bio.co.uk/

We already use Drosophila in Year 13 to investigate sex linkage, but I thought it would be worth trying them on a talented and motivated bunch of Year 10s to look at basic autosomal inheritance. I was initially just going to get some vestigial winged flies and cross them with wild types, but looking at the catalogue I started to see the possibilities, and ended up ordering vestigial winged males and females, and ebony males and females. Then I got the girls to set up vestigial/ebony crosses.

You can’t really go wrong with this as an activity. It’s just brilliant fun – different, interesting, challenging, in every way.  Knocking out the flies, setting up the little breeding tubes, making sure the unconscious flies don’t get stuck in the blue food goo or get smeared across the sorting paper by heavy handed use of a paintbrush, checking the flies have come round, looking first for larvae and the little tunnels through the food, and then for pupae, and then finally for the alarming clouds of offspring…

But the excitement really starts when they knock them out again and look at the phenotypes.

Remember, these are students who haven’t done any genetics. So there’s no pre-conceived theory or received ideas to help them explain or predict. They just see for themselves, from their own crosses, that ebony bodies and vestigial wings have disappeared. Vanished. Every single one of those first generation flies are 100% wild-type.

It’s the kind of thrill that Mendel himself must have had when the pea dwarfiness disappeared. That’s funny…. what’s going on?

And so they cross the first generation flies. This raises the skill bar considerably, as they have to distinguish males from females based on a tiny little black bristle on their front legs.

Slightly stressful, too, as they don’t give them quite enough ether and are still trying to identify males under the binocular microscopes when the knocked out flies start their little break dances, and then start to escape…. It’s a race to set up the new tubes and fly mortality is high…

But a couple of tubes are successful, which was probably a good thing because there are LOTS of F2 generation offspring to count. The students are brilliant, sharing out the work, and dutifully tallying up the 4 different phenotypes. Because, lo and behold, ebony and vestigial is back. In the rather wonderfully perfect ratios of 95 normal wing, normal body, 34 normal winged ebony body, 24 vestigial winged normal body, and 5 of the fly they’ve not yet seen, those with vestigial wings and ebony bodies.

Go on, I say, work it out.

They’re good. Oh, golly, they’re good. By the end of the session, working together, with absolutely no input from me whatsoever, they report that the expected ratio should be 9:3:3:1

I’ll admit it, I’m shocked. I thought they might get the basic idea of dominant and recessive alleles and how a characteristic could disappear for a generation. I thought they might even figure out the ratio of a simple monohybrid cross. But they’ve only gone and worked out the predicted ratio of a dihybrid cross. And seen that their results closely matches their prediction.

Make your students feel brilliant and they will do brilliant things.

I’m now wondering whether we could roll this out as an investigation for the Year 11s when they actually do genetics in the SoW. Cost is a consideration – virgin females are not cheap – and you’d have to be very tight on health and safety – ether is nasty stuff – but it’s got to be more interesting than pea plants….

Go to run. OCR moderation sample request has just come in…

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!

Good Golly, Miss Molymod

Just a quick idea this week as I was working on the George learns to walk page.

Do your GCSE students struggle to remember the balanced formula equation for respiration?

Try this.

DSC_8241

Draw a molecule of glucose on the board and get them to build a molymod version (in pairs). They enjoy this. It’s a challenge and they’ve got to concentrate.

Get them to count the atoms. Link this to the formula for glucose.

 

Now give each pair 10 (it’s important that it’s 10!) oxygen molecules.

DSC_8243

Burning (i.e. oxidising) things in oxygen gives what waste products? Carbon dioxide and water.

So get them to completely oxidise their glucose molecule, using as many oxygens as they need, to give carbon dioxide and water.

 

DSC_8246

Look at the molecules they’ve built now. How many carbon dioxides? How many waters? And how many oxygens did you need? Can’t remember? Well, how many have you got left from the 10?

You could line the molecules up and get them to take a photo with their phone. Or get them to take photos as they go along.

DSC_8239

But, and here’s the thing, they remember the balanced formula.