Yes, my little piranha fish?


That gets their attention. Slight pause, adjust voice for ultra shrillness, and…


To my surprise, many of my Year 9s spot the allusion – Fawlty Towers – though some think I’m referring to Basil Brush, and most look mystified.

We fondly recap on the health inspector episode -“it’s a rat, Manuel. Hamsters are small and cuddly. Cuddle that, you’ll never play the guitar again…”

…before I introduce a third Basil. Here he is:IMG_2038

Isn’t he lovely? All bright and green and perky? Well, what do you expect from M&S???

And, actually, there are four of them, but I start with one, placed on a balance.

We review possible changes to Basil, and they recall that he will probably lose mass because of water loss from his leaves. They can remember stomata and evaporation and gas exchange and so on. And then we record the starting mass: 374g.

Basil 2 weighs in at a similar 385g. But after putting him on the balance, I position a fan to blow air directly at him.

Basil 3 is a rather weedy 260g. He gets covered with a clear plastic bag.

And Basil 4 is a chunker, a bruising 451g. He also gets covered with a plastic bag, but this one is black.

So first important lesson of the day, M&S Basil plants all cost £1.50, so heft them carefully before you buy – the variation in mass is considerable!

Having carefully recorded all the starting masses, I ask them to write down predictions for how each Basils will have changed after 24 hours, when I see the class next. I also ask them to justify their predictions.

Moving round the lab, some need prompting to think about evaporation, some are wondering about growth, but I redirect them to transpiration – how will these treatments affect water loss from the leaves? I don’t mind if their predictions are right or not – I want them to think – so if, as some do, they argue that the black bag will absorb heat and thus increase evaporation, that’s fine by me.

And note that they don’t know what’s going to happen – this is not an experiment/demonstration to confirm something they’ve been taught, it’s a genuine investigation (though note the ease with which mass can be adjusted by a surrepstitious leaf removal or a sneaky out of lesson watering, if the results aren’t what you want…).

All of this takes 30 minutes, setting things up nicely for the hour long lesson the next day.

24 hours later, there is, happily, no need for such dishonesty. The Basils have behaved beautifully. We record the new mass for each plant and then I get them to answer the following questions.

  • Work out the mass change for each Basil.
  • Calculate the rate of mass change in g/hr.
  • Explain why this is not a fair comparison.
  • Now calculate the %age change in mass for each Basil and present this data in a suitable graph.
  • Do these results match your predictions? Try to explain the differences between the plants.
  • Which of the treatments is not properly controlled? What should we have done instead?

I was delighted with how well this worked. Firstly, the %age mass loss was exactly what you would expect – 25% for the windy Basil, 15% for the standard Basil, 8% for the Basil in the clear plastic bag, 5% for the Basil in the black plastic bag.

But the questions really got them thinking. They had to evaluate the experiment, process data, decide on the best way to present it, use SKU to explain the differences, and think carefully about controls. And it illustrated how even really bright students don’t immediately see what seems obvious to us. It took them a suprisingly long time to realise that the different starting masses made any simple comparison of mass loss invalid. Similarly, they needed a lot of prompting to realised that the black plastic bag altered both the humidity AND the light, though they were quick to suggest a better way of doing this when they did get there.

They all did super graphs – correctly choosing a bar chart – and they all talked intelligently about humidity and the effect of wind and, again with a little prompting, what might happen in the dark to reduce water loss still further.

We finish the lesson with my adaptation of the song from the musical Oliver, Fagin’s I am reviewing the situation… which I’ve turned into I am revising the transpiration.

Lyrics on request…

And next week, after further exposure to the fan, Basil 2 will look like this…


…and we can discuss wilting… and how to recover from it (wilted Basil responds brilliantly to watering).

And at the end of all this, 4 members of the department can go home with a Basil plant.


I had rather given up on Twitter. Mainly time constraints – who has time to do this? – partly a sense that it feeds into the ever shortening attention span, possibly a reaction to the use of Tweeting by certain political figures.

True, people I admire enormously thinks it’s fab (yes, you, sister), we’ve had training sessions from a fellow teacher who thinks it’s the best professional move they ever made (really?!?!), but I just haven’t got the bug.

And then today I checked into my Twitter account to see how my son was doing on his week long residential on the Isle of Wight (the school posts regular updates). To my astonishment, and delight, there were lots of people saying nice things about the Burbles, re-tweeting them (I think I have the terminology correct), posing questions, and generally being very positive. So thank you.

And Kathy, the time-lapse chlorophyll chromatography took about an hour to run.

Too late and too hot to continue now, but when the heat wave breaks, I have an idea I think people will like. It involves Basil…

Leaves and starch…

If, like me, you’re a fan of the SAPS website (Science and Plants in Schools), you’ll already be familiar with this variation on a theme. If not, read on, bated breath optional…

I think it’s a brilliant idea. Rather than testing an entire geranium leaf for the presence/absence of starch, the students cut leaf discs with a cork borer. This is an improvement for lots of reasons.

leaf discs boil

Firstly, as you can see from the picture,  the whole starch testing procedure is much easier if you’re working with small tissue samples, rather than a whopping great leaf. There’s no forcing the leaf into the testtube, no trying to delicately unfold it on the tile without ripping it. You can do repeats, it’s easier to see what’s going on, and so on.

It also means one geranium plant goes a lot further….

Better still, it opens the possibility for lots of different experimental treatments – because the cells in the cut discs remain alive for several days afterwards and will happily photosynthesize if given the right conditions.

Here’s what I got my students to do.

Destarch your geranium plant as per usual.

The pairs of students then cut 12 discs (per group) and floated them, top side up, in petri dishes containing either distilled water OR 5% glucose solution. Then one dish from each treatment (i.e. one water, one glucose) went under the light bank, and one dish from each treatment went into the dark.

Got that? OK, like the students, make some predictions. What would you expect?

It’s a great thinking exercise – testing their understanding of photosynthesis, the significance of the starch test, the structure of starch and the structure of a leaf.

24 hours later, they carry out their starch test on all 4 sets of discs.

leaf disc results

What’s really neat is that this is not an Either/Or result – you can clearly see different amounts of starch in each set of discs.

So, can you figure out which of A, B, C and D were…

  • in the dark on water
  • in the dark on glucose solution
  • in the light on water
  • in the light on glucose solution…?

Can anyone suggest other experiments you could carry out with these leaf discs?


When a tree loves a tree…

Plant sex with the Year 9s and a veritable plague of misconceptions to overcome.

I’m always fascinated by why students persistently get the wrong idea about something and enjoy the challenge of trying to find alternative approaches to these topics.

With plant sex, quite apart from the usual “It’s Plants So It Must Be Boring” reaction, there’s confusion about what’s actually going on – they don’t see any parallels with animal reproduction – and confusion over what all the different structures and processes actually are.

So I start by getting them to dissect and draw a seed – some kind of bean is ideal. A drop of iodine emphasizes the starchiness. They’re quite happy to do this, though slightly mystified.

Time for discussion.

What is a seed?

A baby plant!

OK, where’s the baby?

Back to their drawings/dissections. Look! Most of them haven’t seen it. When they finally do, they realise that the “baby” actually takes up a tiny proportion of the overall seed.

So what’s the rest of it for?

We discuss the parallels with the English aristocracy, packing your kids off to boarding school at the age of 2 – plants just take it one stage further, thought they do, at least, provide a little picnic to sustain their offspring before they can fend for themselves.

We set up some germination experiments with sweetcorn and our little propagator trays.


As you can see, these work beautifully (takes a week, for anyone hoping to cram this into a single lesson!), and we will have a busy lesson calculating class means (n=18 for each temperature!) and plotting graphs with range bars, and discussing what we didn’t control (the 4’C ones were in the fridge – and therefore in the dark – not controlling light with a plant??? tut tut…), and saying, hmmm, look, this is rather similar to your enzyme graphs….

Back to the story of seeds…

So, that thing inside the seed,  it’s not really a baby, is it? We need a different name. And, in fact, it’s an embryo.

So what needs to happen in order to make an embryo?

Pause. Giggles.

To much amusement, I stress that I’m not interested in the mechanics, I just want to know at the cellular level.

Yes, that’s right, a sperm needs to fertilise an egg.

At this point I say that I want them to look at an answer written under exam conditions. The test in question is on human reproduction, and the student is a Geranium. What, I ask, is biologically wrong with the following statements? (extracts from the following Powerpoint).

Understanding Plant Sex

“Human males produce millions of sperm to increase the chance of fertilisation. The babies have legs and arms that help them crawl to find the egg to fertilise it…”

They think this is hilarious. I push them for a precise explanation. What mistake has this student made? It’s the same mistake in the next answer:

“Male and female frogs mate in ponds. The female can lay up to 2000 embryos a week. The tadpoles have tails that help them swim to the egg to fertilise it…”

Isn’t that silly? This poor student has confused babies with sperm, and eggs with embryos, and then tadpoles with sperm. True, the student IS a Geranium – but even so…

But what about this? Here is a human student writing about plant reproduction.

“Dandelion seeds are wind dispersed. The seeds have little parachutes that are caught by the wind to carry them a long way to increase the chance of fertilisation.”

This stops them in their tracks. They have to stop, and think, and some will say, “there’s nothing wrong with this…” But after a bit of thought, they realise that the human has made the same mistake as the Geranium – conflating embryos with gametes.

We then walk through the rest of the Powerpoint, followed by some questions, to emphasize the parallels between human and plant reproduction, as well as some of the key differences.

Understanding Plant Sex

In the next lesson, they’ll have a think about why land animals have to mate, why that’s not an option for plants, and how they ingeniously get around the problem of dessication for the precious male sex cells…

Have a great Easter holiday.

Questions of bacteria

So what did my Year 9s decide to investigate with their new-found micro-biological skills?

In the end, the classes split about 50/50 into groups that had a very specific question – comparing the efficacy of different soaps, testing the 5 second rule, looking at the anti-bacterial properties of saliva (more on this later!) – and groups who just wanted to see what happened if they put stuff on the agar.

I wondered whether I should be frustrated by this lack of focus from the latter group, but in the end decided that they were simply displaying the genuinely curious approach of naieve scientists. They might not have formulated a hypothesis to test, but they were still exploring the natural world, poking it to see what happens, going “wow, that’s amazing!” when their plates disappeared under a luxuriant fungal foliage speckled with Staphylococci colonies…

But whatever shape their project took, the motivation and excitement of having complete ownership of their experiment was a joy to see. They could not wait to inspect their plates to see what had grown, to see what they had found out. Without exception, their write-ups reflected this, discussing their results thoughtfully and thoroughly.

So what did they find out?

Several discovered the importance of aseptic technique and the problems that can occur if you don’t employ it.

One very thorough and professional pair discovered that the fruit in the canteen did, indeed, accumulate more bacteria through the course of lunch time, as it was handled by more and more people.

I liked the project that sampled the locker handles from all the different year groups, suggesting that Year 7 are significantly less hygienic than any other.

There was a pretty graphic demonstration of the efficacy of Dettol – and several rather well planned projects that suggested the uselessness of washing hands at all.

Two groups showed very clearly that the 5 second rule has some validity – and I was amused by their comparison of apple, bread and jelly (!?!?). Splat.

And then there was dog saliva. A student managed to bring in a little vial of doggy drool from her canine pet. She and her friend set up plates seeded with E.coli and with paper discs soaked in the saliva. There were control discs, and comparison discs with human saliva and (wait for it) hamster saliva. Really? I asked, when they were preparing it. Yes, really. They were adamant they wanted salvia from the hamster.

So we awoke Herbie from his slumber and they persuaded him to chew on a cotton bud for a few minutes, and then rolled the cotton bud on the agar…

The hamster results were inconclusive, but there was no mistaking the huge halo of inhibition around the dog saliva. Awesome demonstration of lysozymic power!

Great fun, the whole thing, from beginning to end. And highly recommended.

Cell Cycle Snippets

I’m just starting the Cell Cycle/Cell Divison topic with Year 12.

I usually kick off with a question along the lines of what they were like when they first started life’s journey. Yes, that’s right, a zygote. A fertilised egg.

I draw a little cell on the board.

So what did that cell have to do in order to become you?

Again, correct; it had to divide.

I draw two little cells on the board.

And divide again.

I draw four little cells on the board.

What’s it become now?

No longer a zygote, but not yet a fetus, you’re an embryo. And so on. Until there’s roughly 50 trillion of them. Depending on the group, I might get them to calculate how many division this wold take.


OK, if that’s all that happened, what would you look like now?

A nice comedy moment this as they visualise the ever increasing 50 trillion cell blob that cell division alone would make them.

So what do cells need to know???

This is a really good discussion point as they figure out the necessary skill set of any cell. We eventually agree on the following:

  • it must know when to start dividing
  • it must know when to stop dividing
  • it must know where it is
  • it must know what’s it’s going to be

Right! Now we’ve got something to work with. Let’s start with the division process.

I’m sure you already have an impressive armoury of amazing replication factoids to impress your students with.

Here are some of my favourites.

  • The DNA in your cells could stretch from here to the sun and back 600 times. That’s 68,000,000 x 2 x 600 miles.
  • From zygote to fully formed, differentiated, multi-tissued, multi-organed functioning organism, takes a mouse 19 days. 19 days! That’s just incredible.
  • Copying takes place in a cell at 2000 base pairs per second.

So how long would it take to replicate the entire genome???

If they work their calculators correctly, they should figure that the 3,000,000,000 base pairs are copied in about 8 hours.

  • Polymerase has an error rate of between 1 in 1000 to 1 in 100,000.
  • Yet the overall mutation rate is 1 in 100,000,000 per cell cycle.

These mutations are the basis of ageing. But how to explain this discrepancy between error rate and mutation rate?

It’s a good way of introducing the idea of check points, controlled by an army of checking and correcting enzymes that oversee the process. You might even want to flirt with the concept of nucleotide excision repair.

But the key point is that these check points are REALLY important because you want your genome to look like this…


not like this…

karyogram 2.pngwhich is what the karyotype of a human breast cancer cell line, MDA 231, looks like.

There’s enough questions and disuccsion and intriuge here to last us another half hour or more. But when we’re done, we’ll launch into the cell cycle, followed by Mitosis, or possibly watch the FOP video by way of looking at the catastrophic consequences of cells not knowing what they’re meant to be…

An update on Year 9 microbiology projects to come soon!

the power of curiosity

Never underestimate the power of giving students autonomy.

As regular readers (both of you :-)) will know, I have no time for practical work where students already know the expected result.

The obvious and easiest improvement is to “flip” the practical, so that the students are puzzled/intrigued/surprised by the result and have to interpret the results for themselves, or at the very least are forced to ask the question “why?” so that the theory you then teach is in response to their curiosity.

But far better still is giving students the opportunity to ask their own questions, so that they have complete control, complete autonomy.

Take my Year 9s.

We had zoomed through Enzymes and Digestion so quickly that I was suddenly faced with the prospect of starting Plant Transport in February. I don’t know if you’ve ever tried to get potometers working in February, but it’s a pretty joyless and pointless exercise.

So I thought I’d use the time to introduce some Micro-biology and let them carry out some investigations. But it’s not on the spec.! bleat the bucket filling information shovellers.

Perhaps not. But leaving aside other considerations – such as motivation, excitement, interest – it’s a great way of putting their experimental design skills into another context.

So, lesson 1, a quick intro to aseptic technique and agar plates, followed by a little mini-project – how does bacterial load on finger tips vary with stage of washing? This takes a double lesson, as they need to be clear about various points, and I want them to do it properly, all ready to look at for the following lesson. I also want them to think about Controls and Measurements. Not only are there lots of good ideas and intelligent suggestions here, but they are also already wanting to introduce their own variations (can they use hand gel? can they compare air dried with towel dried? and so on). It’s a great illustration of what can happen when you encourage curiosity and independence.

Once all the plates are in the incubator, each one carefully divided up into Unwashed (Control), Wet, Soapy, Rinsed, Dried sections, I explain that they now have the necessary skills/techniques to ask their own question. What could they use these techniques to find out?

Next lesson, they get to look at their incubated plates, and, as generally happens, they see that washing your hands appears to have very little, if any, effect on the number of bacteria they transfer to the plate! The results actually weren’t all that spectacular, with very little bacterial variation, but they’re still fascinated by what they can see, and keen to plan their own projects.

Here’s some examples of what they went for:

  • testing the 5 second rule
  • comparing the hygiene of different year groups by sampling the surfaces of locker handles for bacterial load
  • investigating bacterial biodiversity in different habitats
  • investigating the efficacy of different anti-bacterial agents
  • investigating the bacterial load of different food preparation surfaces

and a few others that I can’t immediately recall.

Actually, the questions are irrelevant – what was so wonderful was how motivated and interested and excited they were at being allowed to do whatever they liked. They will have complete ownership, from beginning to end, and their results will be their results – a real taste of the thrill of doing original research.

A very happy end to the week. I’ll let you know how they get on…