Tag Archives: lac operon

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 http://www.theotherbranch.co.uk/item.php?pro=SPUZD. 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!

Paul

TECHNICAL NOTES for lac operon

Intro to Lac Operon

Lac Operon