No major theme or single lesson this week, just a few random ideas that I’ve used in lessons this week, either as introductions or illustrations, part of the essential punctuation of any lesson plan to prompt thinking, help clarify or just provide some variation.
Year 13 and Hox Genes…
This follows their investigation into the Lac Operon (which worked beautifully this year – just fabulous results – see 25th Sptember 2014). With no introduction, I start the lesson with this Mitchell and Webb sketch. After the initial shock and hilarity, ask the question – what is the serious underlying point here? Why don’t people grow buttocks on their heads? (or 19 penises for that matter, if you decide to show the next clip in the sequence). The genes for buttock formation are all there in the cells of your head. Why is it a head at all, and not, say, an arm? Sounds silly? Show some pictures of fruit flies growing legs out of their faces and eyes at the end of their legs. Hox genes for blog I’ve also included a little animation to illustrate the point that these genes are exactly the same in all animals. So a hox gene taken from a fruit fly will perform exactly the same job in a mouse. Or a shark. Or a chicken. Or you…
Year 12 and Potato Osmosis….
…and trying to push them beyond the simple explanation of mass gain vs mass loss as a result of water potential gradients (which they should have been able to do in Year 9). I want them to explain the whole shape of the graph. They look confused. What does this mean? It can take them a while to see what I’m getting at as I push for a more rigorous description, but the question is, why does it lose more and more mass as the sugar concentration increases? And why does it start to level out at the highest sugar concentrations?
Going from the abstraction of the graph to the specifics of potato tissue is not easy, and one class was clearly struggling, so I turned to a trusty balloon to help them visualise it and make the link.
Sketch the graph on the board. Inflate a balloon. Balloon = potato cell. Air = water. All clear?
Move it along the line – sugar concentration has gone up – water potential difference is greater – what happens? Let a little air out of the balloon.
Move it further along. What happens? Let a little more air out.
By the time you get to the plateau, there’s no air left to come out – the mass of the balloon/cells won’t change much.
They liked this. Hope you do too.