Monthly Archives: July 2017

Loadsa dough…

First week of the summer holidays, and I’ve been spending my mornings in the village primary school, offering some sciencey type lessons. I must admit, I was a bit wary – I was told that as part of the end of term arrangements, the children were being divided into four teams of 25 of mixed age. Please could I do four mornings with each group.


I find mixed ability hard enough – I don’t believe that it’s possible to consistently and successfully differentiate in a class any bigger than, say, 2, – but mixed ability AND mixed age? From 6 to 11? From some fairly severe SEN to precoscious semi-genius? Deliver a hands-on practical science lesson?

Yeah right.

So, what would you do?

Tricky, isn’t it?

I wanted it to be fun, I wanted it to be messy, I wanted it to be different to what they would normally do, I wanted it to be science. It also had to be safe and it had to somehow involve all the children in some way.

In the end, I opted for the dough rising at different temperatures investigation. I raided the lab for water baths, measuring cylinders, spatulas, beakers, glass rods, timers and balances. My technician had the inspired idea of throwing in 25 junior lab coats. I added yeast, flour and glucose.

I asked their regular teacher to divide them into mixed age teams of 4, each at a table with the relevant apparatus. I reasoned that if nothing else, they would enjoy handling real science apparatus, learn to take some measurements, and make a lot of mess. If they learned anything else along the way, that would be a bonus.

Setting up, the water baths, set to 45′, 35′ and 20′, were around the edge of the room. Each table had the following:

  • 3 x 100ml measuring cylinders
  • 3 x empty plastic beakers
  • 1 plastic beaker containing strong white flour
  • a glass rod
  • a tea spoon
  • a small saucer of dried yeast
  • a small  beaker of glucose
  • a stop clock

One of the most useful aspects, from my perspective, was teaching the same lesson 4 days in a row. The first day was OK, but I made lots of mistakes and had to completely rethink the lesson plan – there were too many blank faced children who clearly either weren’t engaged or just couldn’t follow what was going on. In short, I tried to explain everything in one go, and then let them get on with it. As you’ll see, this was way too big an ask for primary school children! They managed, but needed lots of support…

Incidentally, I think this is a key skill to being a successful teacher. Teachers stress over lesson observation, thinking that their performance is being assessed, but actually a good observer is just looking at the students. Are they interested? Are they involved? Are they doing lots of different things? Are they asking good questions?  Are they actually learning something, or are they just writing stuff down? There are teachers who seem blissfully ignorant that their pupils are bored out of their skulls. You have to be aware of the success or otherwise of your lesson if you want to improve. That, of course, makes an assumption. Again, I am amazed by the number of teachers who show no interest whatsoever in becoming better at their job…

I digress..

So, on the second day, I started by getting each team to decide on an identifying picture/cartoon/initials that they can draw on the top of their 3 measuring cylinders so they can tell which ones are theirs.

And then I ask one child in each team to pick up the balance.

And turn it on.

They then passed it on to the child on their left. That child had to…

…find an empty plastic beaker and put it on the balance.

I ask each table to report the weight of the beaker. The beaker/balance combo is then passed to the next child who…

presses the on-button again.

This, of course, tares the balance. I check that all the balances now read 0.0g, before the two items are passed on again. The next child has to…

add exactly 20g of flour to the empty beaker.

This is more challenging, and if this has landed on one of the younger students, the older ones pitch in and help. I have told them that the best scientists work as part of a team. But I’m pleased with how this approach is guaranteeing that all the children get to do something. Plus it’s training them how to carry out a procedure they’ll have to do twice more.

The beaker with 20g of flour is then passed on to the next child (who in a team of 4 would be the first one again). This one has to…

add 3 spatulas of yeast to the 20g of flour.

It’s fascinating watching how so many of them struggle with this. It re-emphasizes the point that practical work requires and develops all kinds of skills, which we can’t take for granted.

The beaker of flour and yeast is passed on and….

… one level teaspoon of sugar is added.

I now ask them to choose one member of their team who can both walk in a straight line whilst at the same time carrying a beaker of water. This lucky student gets to

collect half a beaker of water from the 35′ water bath

and take it back to their table. Now it’s time to introduce the measuring cylinders. Taking nothing for granted, I demonstrate the lines, the numbers, the intervals. They seem quite happy with this, so I ask them to…

measure out exactly 25ml of water from their beaker into the measuring cylinder.

Nice and easy, though never underestimate the ability of your students to devise ways of ballsing up a simple procedure. Because although they now have to…

pour the 25ml of warm water into the beaker with the 20g of flour, 3 spatulas of yeast and one teaspoon of sugar….

One cheerful group of boys pours it into the original stock beaker of flour. This only becomes apparent when they try to

use the glass rod to stir it all to a thick, runny paste

and merely succeed in creating a slightly damp floury lump.

And now, I announce, just in case they were finding this all a bit too easy, comes the really challenging bit! They have to…

pour their thick runny paste from the beaker into one of the measuring cylinders without any of it touching the sides….

Children of all ages love a challenge, and these are no different. The screwed up concentration on their faces is just a joy to behold. Of course, they all fail – though one girl was doing very well until her friend made her laugh and some dough smeared the side. But overall, it’s fine – they have enough paste in the bottom of the cylinder  for them to…

…measure the volume of dough in the measuring cylinder, write it down, and then transfer the cylinder to the 45′ water bath.

Phew! Now they just have to do it all again, twice, except that their second two cylinders will go into the 35′ and 20′ water baths respectively. And only then does the real fun start. Starting their stop clock, each team has to…

every 2 minutes, record the volume of dough in each measuring cylinder at the 3 different temperatures.

Initially, they are puzzled. What’s the point in this? But they quickly realise that the dough is rising! This has them scurrying back and forth in earnest. The primary school concept of a table is an interesting one, and we have to police the water baths as the measuring cylinders have an annoying habit of turning turtle, filling up with water, and losing all the crucial dough mix. But they take it very seriously, reading the volume carefully, and writing down the value with great aplomb, one girl writing “55ml EXACTLY”, just to emphasize the point. The excitement builds as dough in the 45’C measuring cylinders threatens to rise above the top and spill everywhere. Whose will rise the highest?

Eventually, it’s time to call a halt. I get them to all sit down with their measuring cylinders in front of them. So, they’ve done lots of measuring and used lots of different apparatus and developed all kinds of skills from team-work to spatula-work. But can they see the wood for the trees? What exactly have they shown?

This is really interesting. They don’t have the vocabulary or framework to make the link between the experimental design and what has happened in their measuring cylinders. But frame the question in a different way, and most of them seem to get the point:

What would be the worst place in your kitchen to leave dough to rise?

And this triggers some excellent questions from the older, brighter ones – but why? why do things happen faster at higher temperatures?

I’ve had positive feedback from parents, teachers and students, but I’ve got to be honest, though. I reckon that most of the students would say that the best thing about their science lesson was getting to wear the white lab coat…

That’s me done for the summer. Hope to be back in September.



Kill my babies, but let me eat meat!

Just a visual PS to the last post on energy flow through food chains.

Desk 1

Here’s the start of the game: there’s the pristine tropical island, with just a little corner of cultivation dedicated to growing enough plant food to sustain two people.

Desk 2

BUT…. they’ve decided they want to eat meat every day. Oh dear. The pristine wilderness is under threat!

Meanwhile, on vegetarian island…

Desk 3

…the population has doubled, but most of the island is still untouched.

Back on the isle of meat eaters, a doubling of the population has a more profound effect…

Desk 4

Animals at the top of the food chain are running out of space. The monkey eating eagles are endangered….

Veg-ville continues to cope reasonably well with population growth….

Desk 5

The population doubles again yet we’re still using less land than two people eating meat.

Compare this to the other island…

Desk 6

And here’s the really important question. Never mind the eagles, never mind the orang utans, never mind the vanished rainforest – what exactly are they going to do when the population increases again…?

As a sobering way to wrap up the topic, you could do worse than this…

Decisions, decisions…

Year 10 and Energy Flow Through Eco-systems. Not an obviously exciting lesson, I grant, but one with scope for some entertainingly confrontational role play. After all, it’s a tricky decision, give up eating meat, or kill your babies….

We spend a couple of lessons establishing the basics. The Leaf Litter practical – identifying, counting and weighing the crawly denizens of the detrivore community – after which I collect and collate all their data for them to draw accurate pyramids of numbers and biomass.

I also show them the Flamingo/Fish Eagle/Lake Bogoria clip from Life of Birds, to emphasize the spectacular fall in numbers as you move up the food chain, from algae (gazillions) to flamingoes (one million) to fish eagles ( a few hundred). David (Attenborough) provides the necessary descriptors.

Because this is a really interesting question – what’s going on here?

The following PowerPoint (@Burnett 2005) gives a simplified breakdown of how this all might be quantified as well as a beginner’s guide to why the energy stored in, say, grass, does not all get converted into rabbit.

Energy loss in food chains

In the past, I’ve tried to make this more rigorous using owl pellet dissection – can they use the contents of an owl pellet to calculate the area that a pair of barn owls would require?

Energy Flow from Voles to Barn Owls

But it’s over elaborate and I don’t think it worked very well – they miss the wood for the trees.

In any case, having provided the necessary background, ideas and theory, I’m more interested some of the broader implications of this inexorable law of energy transfers. In particular, how should it inform our choice of food and what we do with available land.

I’ve been playing around with ideas for how to explore this through role play for quite a few years. Again, none of my previous efforts have quite worked. So, for example, I came up with a kind of Monopoly version, where they had a laminated version of a map

island map for role play lesson

that they had to divide up into vegetable and meat cultivation, and then collect food calories (based on their allocation) from another student playing the part of Gaia.

Instructions for desert island survivor game

Having established this, I added more and more students to the island, playing the part of shipwreck survivors/African refugees/rivals from a local school, forcing them to reallocate land use if everyone was going to get sufficient calories per day. It was quite good fun (important note: even if a lesson fails, your students will forgive you if they can see that you were making an effort), but, again, it was over-elaborate and they spent so much time trying to do the calculations that they missed the key point of the exercise.

This year, however, I think I finally cracked it. See what you think.

I send all but six of the students out of the lab. These six form three pairs, each of which has a 70cm x 140cm desk. Each desk represents the island on which that pair have been ship-wrecked. There are no other survivors. The island is a lush, tropical paradise, awash with orang utans and parrots and butterflies and orchids. But they’ve got to eat, so they need to clear land for cultivation.

They have a collection of green and red bits of square card – 10cmx10cm, 20cmx20cm, and 40cm x 40cm.

The small green card represents the area of land that would provide enough plant based food for one person to survive. So with two of them on the island, they need a minimum of two small green cards. The rest of the island is left untouched. It’s an immediately visual impression of land use.

But they may not want to be entirely vegetarian. Most of them will want to include meat in their diet. Thing is, though, if they want to eat meat, one small red card represents the area of land that would support sufficient animals to eat meat only once every 10 days. So if they want to eat meat every day, they need to clear ten times as much land. Suddenly the island is looking rather different, the orang utans are feeling a bit constricted.

At this point I go and collect six more students and allocate two to each “island”. Look! Two more shipwreck survivors! And by an amazing coincidence, they’re old school friends! But what are they going to do about food?

The original students have to explain the game to the new students (peer to peer learning!) and then they all need to discuss and decide how they’re going to carve up the island. It’s an interesting contrast. One table is made up of vegetarians and their island is still largely pristine. Another is occupied by unapologetic carnivores and is covered in large red cards. But everyone is still able to enjoy their preferred diet, even if the orang utans are only just hanging on.

And then they have children. The remaining students are allocated, 3 per table, as the offspring of the original settlers. Obviously their babies are beautiful and adorable but, ahem, how are you going to feed them?

At this point, things get heated. Because based on the premise of the game, the island is not big enough to support seven people eating meat every day…. And so, with the brutal and decisive certainty of teenagers, faced with a choice of cutting back on their meat intake, or discarding their babies, the babies are thrown into the sea…

At this point, the interesting discussion can start. Why does it take so much more land to sustain a meat based diet? No, it’s not because the animals need space to move around – as one student suggests, it’s because you’re putting the energy in the vegetation through another organism before eating it. As 90% is going to be lost, you need 10x as much land.

This also explains why meat is so much more expensive than bread.

And it means how we decide to utilise farmland has profound ethical implications. Should we, for example, be clearing rainforest to grow cows/grow food for cows, just so rich people can eat beef every day?

And would any of them be willing to make any compromises to their diet (such as eating meat a few times a week, rather than every day) if it could contribute to conserving biodiversity, or using the same land to feed more people? Isn’t it immoral to eat meat in a world where so many people are starving?

If you like a feisty argument in your classroom, it works a treat!

Outline and questions here: Ship wrecked on a desert island energy flow June 2017 (1)