Tag Archives: Year 9

Malteser and sardine salad


I must say that I’m not overly impressed with WordPress. For one thing, you’ve probably noticed an annoying box at the top of my home page. No idea how it got there, no idea how to get rid of it. Grrrr. And then, when I tried to form a Word Cloud to help people find certain topics or resources, it took me hours to achieve absolutely nothing. Double grrrr.

Anyway, it’s achieving its main function of hosting my burbles and linking them to specific resources. And it’s free, so I really shouldn’t grumble.

I’m going to stick with Year 9s this week. Bill’s flipped diffusion worked brilliantly, as did the follow up, and they can now describe and explain diffusion based largely on what they have observed and deduced. My one modification for next year is to include a classic “cheat” that I’m sure we’re all guilty of – the warm/cold diffusion rate was different, but not as much as you might expect. So next year I’ll be providing 0.1M cold acid to compare with the 1M warm acid (though, of course, they will be told that the concentrations are equal). I’d love to hear other examples of this kind of educational economy with the truth – it would make a good post!

Next up, we’re going to review why diffusion is important. I like to use this Powerpoint sardine simpler version – another Bill creation – for them to observe and interpret. What’s going on here? It’s very neat. Notice, incidentally, how creative you can be with this much maligned software, once you’ve learned some of the basic animation features. Notice, too, the complete lack of notes! There’s a few questions to go with this, linking back to the microscope work they’ve done on Protoctists a few weeks back meet Mr Paramecium .

I then ask for a volunteer. They might be hesitant as they’re not sure what to expect, but I reassure them. I tell them they’re an amoeba. I remind them that they need a constant supply of oxygen. I produce a box of maltesers. Each malteser represents oxygen. We imagine that they need one oxygen every 3 seconds to survive. I then shovel maltesers into them at the rate of around 1 every 3 seconds. All good fun. The idea is that a single celled organism can rely on simple diffusion from the environment for its oxygen demands.

I then ask for 10 volunteers. No hesitancy now! I line them up in a row, with the original amoeba at the far end. Now they’re cells in a multi-cellular organism. Same rules apply. They each need a malteser every 3 seconds. Can they still rely on diffusion from the outside world? It’s great – the maltesers never get past the 2nd or 3rd “cell” – so they immediately see the problem – it’s too slow, and the oxygen all gets used up anyway.

Back to the powerpoint! Look at the sardine and the idea of an oxygen transport system. And then they all dissect a sardine (or mackerel, or herring, or whatever comes off the slab!). The excitement over this activity is astonishing! I like to set little challenges, so as well as getting them to cut out the gills and dip them in water/observe under the binocular microscope, I encourage them to try and find the swim bladder without bursting it, to find the heart, to not reduce the fish itself to a pile of mangled sushi… Labelling and annotating this diagram Why a Sardine cannot rely on Diffusion alone for its oxygen supply can always come later…

Right, I’ve got a train to catch. More next week!

Year 9 diffusion

Good morning!

My Year 9s have finished their animal/plant cell introduction to iGCSE with an exercise where they pretend to be Martian scientists who have taken two samples of life from Earth – a geranium and a student – and are trying to figure out whether they’re just slightly different versions of the same thing, or whether they are fundamentally different. It’s a fun way of getting them to work out the key classification points, without actually telling them.

They’re now into diffusion as a logical extension of this – what do cells need? And how do they get these things? Always keen to try something new, I started this year with Bill’s exercise (attached). Like all great ideas, it’s deceptively simple. But look at it in a bit more detail, you start to see not only why is it fun, engaging and challenging, but also why it works so well as a learning activity. Note the lack of preamble, no “today we’re going to study diffusion…” introduction, just straight into a “do this and figure it out” approach.

It’s fun – they love the little cubes (though they were disappointed to learn about their lack of edibility) and are genuinely intrigued by the colour change. They can explain this at one level – the challenge is to push them beyond the “acid is moving into the cube” description, to something more rigorous about particles. But they quickly see the effect of concentration and by the end of the activity they’ve basically worked out the definition of diffusion for themselves, and seen/measured that it happens more quickly if the difference in concentration is greater.

I’m following this up with an adaptation of my olde introduction to diffusion (attached). As well as making lots of different sized cells, they’re also going to compare diffusion rates at two different temperatures. Again, they work it all out for themselves. The questions are for homework.

Next week I’ll tell you how I move this on to multi-cellular organisms and maltesers…

Have a great week/weekend!


1LT1 – Flipped diffusion in jelly blocks 1

Acid bath and agar blobs with temperature NOV 2014

Cheeky Year 9 microscopy

Do you look at cheek cells with Year 9? It never works, right? Oh, alright, I know there’s some disagreement on this. Bill swears it works every single time. I, on the other hand, have never, ever, ever found even a single cheek cell from the usual SwabYourInnerUpperCheekWithACottonBud technique. Seriously, not one. Even when rigorously following the Burnett Protocol. I had pretty much given up on it. After all, there are so many more interesting, findable cells out there – all the protoctists, sperm cells (no, not what you think – we get them from a cattle breeding centre), and so on. On the other hand, apart from red blood cells, it’s about the only cell of theirs they get to see, and there’s something quite soulful about watching a cluster of you slowly dying on a slide… and reflecting that that tiny dark blue smudge contains all the information needed to make another you.

So, what to do? Well, we carry out PCR with our Year 13s and after mixed results with eyebrow hair root cells, we got spectacular improvement with cheek cells obtained with a saline rinse. And it struck me, hey, look at that cell pellet in the centrifuge tube! It must be full of….. 5 minutes later, I was looking at ridiculous numbers of cheek cells under the microscope. 70 in a single HP view. Over 1000 in a single MP view. Lovely great plump juicy obvious unmissable clumped cheek cells. No more fruitless hunting around a slide!

And it was great. The Year 9s were slightly put off by the saline rinse, but gamely went for it. I encouraged really vigorous rinsing for one minute, accompanied by scraping the inside cheeks with their teeth. Three 60 second twirls in the mini-centrifuge gave a huge cell pellet. Extract it with the end of a split spill (makes a nice little paddle for scooping it up), on to slide, stain, and there are actually so many cells that you have to gently squish them flat with the cover slip. Highly recommended.

And relentlessly pursuing my objective of making my students do all the work, I came up with this idea for covering Krebs cycle. This can be rather dry, even with the wonderful John Kyrk website animations, so what can you do? Well, how about getting them to interpret the results, just as we do for Calvin’s results on Light Independent reactions? I’ve attached the exercise – let me know what you think!

That’s it for now. Have a great week!


Unravelling metabolic pathways a la Hans Krebs

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!


TECHNICAL NOTES for lac operon

Intro to Lac Operon

Lac Operon