Monthly Archives: February 2017

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.


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.


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…


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…


Protein Synthesis Race

And it’s back to my old favourite, Lego.

My Year 11s meet Lego as a way of understanding the link between DNA and proteins, and how the same amino acids can make different proteins depending on what instructions are being followed. See this Burble from a long time ago.

At A-level, of course, this is all covered in much more detail, but you still need some kind of fun activity to break up the theoretical background and help them visualise/conceptualise the different ideas.

I start by showing them a simple Lego model.


What might this represent?

DNA! announces someone, engaging mouth before brain.

OK, so right idea that it’s some kind of molecule, but why can’t it be DNA?

They see that it has more than 4 types of monomer.

Try again!

This time we arrive at protein. We revise amino acids, peptide bonds and so on.

OK, so it’s a protein, and you’ve just eaten it for lunch. What happens to it?

They rummage through their brains for some Year 9 digestion memories…. oh yes, it gets broken down…by proteases… so it can be absorbed… into the bloodstream…


We add some A-level detail – the peptide bonds are hydrolysed – but then, key question:

Where do they go?

This takes them a little longer. Go? What do you mean? But eventually they work out that the amino acids are being delivered, by the bloodstream, to cells all over the body.

Right! And what do the cells use them for?

Again, they can be pleasingly perplexed by this. It usually needs a prompt or two.

What can cells make out of amino acids?

Once they’ve worked out the answer, there’s a bit more A-level revision on the kind of proteins that might be made – channel proteins, protein pumps, ATP synthase, hair (for those lucky enough to possess hair making cells), ENZYMES!, hormones, mucus, collagen, haemoglobin – hurrah, they’re on a roll!

Right. And where does this happen? And how will all these proteins be different? So how does the ribosome know which order to put the amino acids in?

By now, they’re happy and confident and make the link to the genetic information in the nucleus. We quickly revise the basic principles of transcription and translation and why they’re necessary…

So! One half of the lab becomes the nucleus, with some chromosomes… (there’s a set for each team).


The other half of the lab becomes the cytoplasm, with some ribosomes… (again, a set for each team).


And a great pile of communal amino acids…


And in teams of two, they become RNA polymerase/mRNA, in a race to find the gene (they look for a Start codon on Chromosome 7), transcribe it (on a rough piece of paper) into mRNA until they hit a Stop codon, and then sprint to the ribosome to translate their copy into a colour-coded polypeptide…

It’s great. They have to think, they have to work together and communicate, they correct each other (if one forgets to turn T into U, for example), they have to apply their understanding, and it’s competitive!

One by one they bring me their completed polypeptides. Can you see which pair were given some mutated DNA….?


Lots of discussion points here. mRNA on a bit of scrap paper? That’s right – it’s short lived and disposable. Trade off for cell? Need to do it quickly, but need to do it accurately. Fast and you out compete other cells. But incorrect, and mutations can be disastrous…

And so on.

Half term tomorrow. Can’t wait. Have a good one!



A little bit of TLC…

I encourage my classes to bring their mobile phones to lessons. And I encourage them to make full use of the available technology – taking photos of demonstrations or practical results, looking up answers to esoteric questions, using the timer or the calculator. They know that if they start texting each other then the arrangement comes to a quick and brutal end, but I always feel that if my lessons become so dull that they’re forced to text each other for entertainment, then I kind of deserve it.

Anyway, I got my Year 13s to try something else today – using the time lapse video function to film Thin Layer Chromatography of mint photopigments. Doesn’t need to be phones – the link here was filmed with my i-pad – so if you have a class set of i-pads, you can always use them instead.

(nb WordPress won’t let me add videos without a paid subscription, hence the use of YouTube…)

As you can see, the carotene races beautifully up the strip, the phaeophytin does a great supporting act, but then the chlorophylls and xanthophyll, after a promising start, get a bit bogged down. Though look at that beautiful blue-green of the chlorophyll A!

If anyone has a better recipe for a running solvent I’d love to hear it!

And the relevant practical protocol and questions are here.


I like my last question: Why is butter yellow? It seems to random, after all the carefull rf value calculation and so on, but there are so many good biological synoptic ideas tied up in this.

Have a good weekend!