Monthly Archives: March 2019

A root through plants 2

Lessons 2 and 3…

Having tried to establish that plants are, indeed, living organisms, it’s time to launch into experimental investigation time.

I display a range of plant material – garlic, mint, ginger, chilli, basil, rosemary… what have they got in common?

All nice in the kitchen for adding flavour to food. OK, fine, but why do these plants have this ability? They’re not making these tasty compounds for us, but for themselves. Why?

We circle back to the idea of how plants defend themselves, not just against predators, but also against infection.

I then ask them to design an investigation to test the anti-bacterial properties of various plant extracts. I used to provide this method…

Investigating the Antibacterial properties of plants UPDATED December 2017

…but I now much prefer, where possible, to let them design the experiment for themselves. Learn by doing. Learn by making mistakes. So I demonstrate the technique – extracting the compounds, soaking the discs, being aseptic – but let them decide on the approach. Most of them will forget a control disc, many won’t do repeats, they won’t all think of all the necessary control variables – but my feedback will highlight these basic omissions and they’ll do better next time….

This is motivating and interesting and different and they clearly enjoy it….

… and it’s a practical that really works. Garlic – particularly if you put it through a garlic crusher – inhibits bacteria to a spectacular extent, as they’ll discover in the next lesson, creating vast halos of inhibition around the paper discs. Homework is to finish their experimental write up and then design an advert for a garlic flavoured toothpaste.

Collecting the results doesn’t take much time, so it’s time to move things on.

So I ask them if they remember their babies, the little brassica seeds that they planted a week ago. We take a look.┬áThese Rapid Cycling Brassicas are not misnamed – one week is quite enough to see dramatic results. Oh look, I say disingenuously, one lot of plants went under the light bank, but this lot got left at the back of the lab. Tut tut, careless me, hem hem….

The difference is dramatic and the impact immediate. There are – I kid you not – audible coos and gasps when I do my big reveal.

I get them to make careful observational drawings of the difference between this “inadvertent” experiment. This is always a good exercise in forcing them to look closely and carefully at something. I also get them to list the controls and to think about the measurable differences between the two treatments.

They produce beautiful drawings and we discuss the differences. Plants under light bank have….

  • larger leaves
  • more leaves
  • thicker stems
  • purple stems
  • much taller stems
  • hairier leaves

We’ve controlled temperature and air and number of seeds per module and type of soil and volume of soil and availability of water and type and volume of fertiliser and species of plant.

Yep, the only difference is the light. Simple conclusion: light = growth. More light = more growth.

I’ve yet to come across any other demonstration or practical that so quickly and effectively gets this vital learning outcome across. I would choose this over and above all my other photosynthetic teaching resources.

But where to go next….? Find out next week!

 

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A root through plants 1

Year 10 and plants is a graveyard slot tough gig at the Glasgow Empire at the best of times. Even bright, engaged, enthusiastic students will fail to engage with the topic and I have sometimes despaired at what can often seem like a pre-conceived rejection of everything to do with plants. Plants = Boring and there’s nothing you can do to change my mind!

As always, I keep refining, keep trying new ideas, keep looking for ways to excite their imagination and thence their interest. This might be an individual lesson, a new practical, a slightly different angle, and so on. But this year it has embraced the entire scheme of work, where I have gone back to what I consider to be the absolute basics.

  1. It has to tell a story
  2. It has to be an interesting story
  3. It has to be a story that makes sense, where the ideas and the concepts fall comfortably into the (hopefully!) receptive brains

Part of the problem, I suspect, is that too much of GCSE plant biology is abstract – the balanced equation, the various experiments which should be really fun and interesting but fail to find a a satisfactory context, all of which can leave students feeling confused, bored, disengaged.

So for the next 6 blogs or so, I’m going to take you through my new approach to teaching plants to Year 10. Lots of it is stuff I’ve done before – with a few new ideas thrown in, but it’s the over-arching theme that interests me and how it all flows from lesson to lesson.

Lesson 1

My usual introduction. I gather the class around me, pick a student who I know will be happy with what follows, and ask her to stand in a large cardboard box. It’s an unusual start to a lesson and amongst the giggles, there’s clearly curiosity. Where’s this leading?

I then ask the class if they’ve heard of the Mafia.

Yes, of course they have. We chat about Sicily, organised crime, gang loyalty, the rule of Omerta, and the punishments for anyone who breaks that rule. We agree that they are not nice people. For example, let us imagine that Izzi (in the cardboard box) has broken the rule of silence and an example needs to be set. We stand her in this box, fill the box with quick drying concrete, and then drop her off a remote bridge into very deep water.

This goes down very well and they are ghoulishly absorbed by the idea of a “cement shoe”. Except, I say, we’re feeling like a change, a more prolonged punishment. We’re not going to drop them into a lake. We are, instead, going to abandon them in the Serengeti. I let this sink in, and then ask, what sort of problems is Izzi going to face?

Predation is always the first suggestion. Yes, of course, all those lions and leopards and hyenas and vultures and so on. Why are they are a problem? Of course – she can’t run away and she has no protection.

OK, let’s give her a sub-machine gun to keep off all the things that want to eat her. What other problems will she face?

Food is generally next up. Yes, indeed, she can’t move around to find food. Still, never mind, let’s arrange for a sandwich delivery man to pass by once a day and give her a sandwich. And a bottle of water.

The point of the solutions is to a)keep the ideas flowing but also b)to show that she could survive with a few resources and a bit of ingenuity.

Once the immediate problems are suggested and overcome, I encourage them to┬ástart looking longer term. They realise, with much giggling, that if an attractive young man is deposited in the vicinity, also with a concrete block around his feet, friendship, romance, startingafamilyifitallgoeswellandtheydecideit’stherightthingtodohemhem is going to present another set of difficulties.

The brighter ones have already twigged where this may be heading, but I still ask the key question: what have I effectively turned this student into? They get it. A plant. The idea, of course, is that I’ve invited them to feel some empathy with a plant as a living organism faced with the same sort of problems any other organism faces.

Infuriatingly, despite the original and entertaining start, there is always some student who groans in despair and wails, “plants are so boring!!!” I control my temper and ask them sweetly to just give it a chance.

Anyway, boring or not, we’re off. We return to the problem of predation and discussing the kind of animals that predate plants – so not just cows and their ilk, but caterpillars, aphids, slugs, etc- and cover suitable defences – thorns, stings, spikes and chemicals. I show them these pictures of familiar plants up close and stress the biochemical ingenuity of plants, starting with the mechanism of sulphuric acid release from onion cells…

Trichomes and onion mechanism

I then put them into pairs and give them the name of a plant defence molecule. They have to find out the structure of the molecule, build it with molymods, and give a very brief presentation to the rest of the class about their molecule, which plant it comes from, and why it’s interesting. They really enjoy the challenge of building the molecules – some of which are fiendishly complicated – and the models give us a lovely lab display AND an important reference point for a future lesson. Stay tuned!

Plant secondary metabolite

I wrap up the lesson by getting them to plant lots of Rapid Cycling Brassica seeds, for reasons that will also unfold over the next few lessons….