Monthly Archives: September 2014

Eating raw onion and turning on bacteria

Some people have been asking about the new A-levels and what we’re going to do. My preference, and the general feeling of the Curriculum Committee, is to abandon AS, free up the Year 12 summer for teaching (and having a year free of public exams!), and revel in all that extra time for practical work. But in the first year, when not all subjects have accredited specifications, we’ll still do AS for all subjects. I’m inclined to stay with OCR – better the devil you know – even if they can’t give me a clear answer on how my A2 students, who did their first set of PSAs on the field trip at the start of term, will not be disadvantaged with respect to all the students who do their PSAs after the 1st December when the mark schemes are released. C’est le dejeuner de le chien, if you ask me.

Anyway, back to the classroom. I’ve realised that I really really really really really like teaching Behaviour. We’re on to Insight Learning and after starting the lesson with the classic banana suspended from the ceiling and asking a student if they can get it down (disappointingly, in a girls school, they always get a sensible chair to stand on – back at SPS, you could always rely on the boy to give up after a desultory and ineffective leap, thereby enabling you to point out that he was definitively less intelligent than a chimpanzee), I then got the students to try and work out a number of wooden puzzles – this kind of thing I let them work in pairs and give them about 4 or 5 minutes on each one.

Discussion then focuses on how they set about solving them – mostly, it’s trial and error. But the Indian Rope Trick is almost impossible to solve with trial and error, you have to have the insight, the moment of lateral clarity that makes you realise how to do it. Most students don’t get it within the lesson (I’ll be honest – it took me 2 days!), but at least one always does – and you then get to describe and explain how you worked it out (and if don’t know how to do it, I’m not telling!). Can chimps/monkeys do the same? I then show them the Capuchin monkey BBC film (“Monkey Puzzle” – extraordinary film of extraordinary animals) and set a homework asking them to try and figure out what types of behaviour are on display.

Elsewhere, Year 9 have been comparing the cells of onions and bananas. Both plant cells, but utterly different (if you’ve not done banana, just smear a tiny amount on a slide and stain with iodine – they are jam-packed with starch grains, are blobby and irregular, and have really thin cell walls). The girls draw and annotate both, and then use their observations to explain the differences between onions and bananas. I usually eat a raw onion for comic (but also illustrative!) effect. Homework is to write a letter from an angry baby to its parents, explaining why they shouldn’t be weaning it on to raw onion and why can’t it have nice squishy banana insteady? This always generates splendidly indignant babies and really differentiates those who “get it” and those who don’t. The drawings usually tend to be magnificent too. Lovely lesson because, apart from eating the onion, I don’t do much.

And my other Year 13s have been turning on E.coli in the Lac Operon investigation. If you don’t do this, you really should (I can send protocol details if you’re interested). It’s brilliant! Two culture broths of bacteria, one cultured in lactose, one cultured in glucose – and measure how quickly they break down the indicator ONPG to a yellow compound (ONPG is broken down by lactase aka beta-galactosidase). Not surprisingly, the lactose culture, rapidly turns yellow. But what I still find amazing is that in the course of the lesson, the glucose culture, introduced to lactose only at the start of the lesson, does turn very faintly yellow within the hour – the repressor is off and the gene is being expressed! The students find it very challenging to explain the differences and, again, it’s a great differentiator. But mainly it’s just really cool.

That’s me done for this week. Happy teaching!


TECHNICAL NOTES for lac operon

Intro to Lac Operon

Lac Operon

Year 13 – behave!

Dear Everyone,

Happy New Academic Year! Not that new, come to think of it, given that we’re already 3 weeks in. I would have re-started these weekly burblings earlier, but I’ve been swamped with such joyous things as UCAS references, Departmental Review meetings and the Year 13 Field Trip (actually, this was pretty joyous, even if nothing but giant slugs turned up in the Live Mammal Traps ). It’s also meant I’ve not had time to plan lessons properly, which has resulted in some Year 7s and 9s being rather short-changed – ugh, the kind of lessons that keep you awake at night. Still, I’ve never taught Year 7s before, and they are very nice. And very small.

The practical highlight so far has been Behavioural stuff with the Year 13s. I do enjoy putting the students in my Skinner Box. You need to borrow a couple of power packs/switches/bulbs from Physics but otherwise it’s a doddle. Arrange some chairs/benches in a square, put a switch/bulb on opposite sides, allocate two students to the two switch/bulb set ups (with a set of instructions each – attached – and a tube of smarties each) and then put the other students in, one by one and see what they do. Highly entertaining.

And taxes/kineses with maggots always amazes me by how brilliantly it works. No background theory – just straight in. Choice Choobs (© Burnett 2005) are easy to make – just a cardboard tube with a hole in the middle for introducing the maggots, and a bung. Get them to design the experiment, collect the data, analyse with Chi2, research the behaviour etc. Why is this adaptive? And so on.

Kineses are even easier – A3 paper, food dye, A3 sized tray for putting over the top. Dip a maggot in the dye, pop it on the middle of the paper and let it go. Record distance travelled and number of turns for 30-60 seconds. It produces wonderful, Jackson Pollock-esque images, and it works. The maggots go twice as fast in the light, and turn much more in the dark. Again, design, collect, analyse, research. These are really nice ways of revising basic skills (what type of graph? Where are the error bars? How do you analyse? Standard deviation?) and brilliant at really nailing experimental design/controls (how do you know your maggots don’t just head north?).

It also throws up some good statistics stuff – If 8 maggots out of 10 head to the dark, it’s not actually a significant effect, even though it looks like a clear preference. So what do you need to do?

That’s it for this week!


Skinner box operator instructions 1

Skinner box operator instructions 2