Death to Fast Plants

I quite like browsing the WordPress stats for Biological Burblings. At the time of writing, the blog has had visitors from 55 countries, with over 1000 different visitors in total making up the 2798 views.


It’s important to stay grounded, so only 8 likes (that’s a like every 372 views – thanks, guys….) and the fact that just 7 countries get into double figures for viewing is a striking contrast to, say, Zoe Sugg’s Zoella vlog that has had over 540 million visits since it started. I’m obviously in the wrong business.

I’m also deeply intrigued by the single figure visits from, say, Russia. Who was this person? What word/phrase did they put into their search engine? How disappointed were they when they ended up here?

Anyway, this is the last burble of 2015 as I’m now just 2 days from the 3 week Xmas holiday. I’m going to stick with my KS3 project, only this time I’m going to talk about something I tried with Year 8, as it absolutely captures what I think science teaching should be about.

The topic was Hydrogen, Metals and Acids. To be honest, I hadn’t changed much. The students really enjoy the Chemistry topics and apart from updating the resources and trying to make the lessons a bit pacier and a bit more investigative and a lot less note-takey, I had pretty much stuck to the script. But the final lesson was, I felt, a bit dry. They had to neutralise a base – ammonium hydroxide -with hydrochloric acid and then produce a purifed sample of the resulting salt, ammonium chloride.

All well and good. Lots of useful skills to develop here and they were conscientious and focussed and all ended up with small samples of a white powder in their evaporating basins. But the activity was titled “Making a Fertiliser”. This seems to be some GCSE legacy topic, an attempt to make neutralisation relevant and important. But it stopped there. The students were meant to look at their white solid and go, “aha! I’ve made a fertiliser!” And that was it.

But surely the obvious thing to do is actually try it out? It’s meant to be a fertiliser – so, what are fertilisers meant to do? Let’s see if it works!

I showed them the brilliant SAPS fast plant kits and asked them to design an experiment. They did this effortlessly, establishing the need for a control and then adding varying quantities of ammonium chloride to the 3 remaining cells. Two rapid cycling brassica seeds in each cell and they were tucked away under the home made lightbank….


home-made light bank – note brine shrimp tank, brine shrimp bottles, fly breeding bottles, fast plants, and general sense of complete untidiness….

There’s a reason they’re called Fast Plants. Planted on Friday, they had germinated by the following Wednesday and I was able to show the class their results. Their reaction was superb. At first, they assumed they had labelled their pots incorrectly. Because the pattern was exactly the opposite of what they had expected to happen.  In other words, the control, the cell with no ammonium chloride at all, had grown the most. The vast majority of cells with ammonium chloride hadn’t even germinated, and those that had showed significantly less growth. Check it out!


It was a glorious “that’s funny….” moment, where their assumptions and preconceptions were completely overturned. Perhaps it doesn’t sound much written down, but the look on their faces was priceless.

The result was consistent across all ten groups, so we could talk about the value of repeats, but the real learning came from the interpretation. Why did you think it would make them grow? Because you told us it would! Because the activity was “Making a fertiliser!” You lied to us! You killed our babies!

I reminded them that I, too, had no idea what would happen. They had tested an idea through experiment and discovered something completely new and unexpected. It’s called Science.

So we talked about why we might expect an Ammonium salt to work as a fertiliser – I showed them molymods of Ammonium and an amino acid, and got them to identify the atoms. Where can you get carbon, hydrogen and oxygen from? Yes, exactly, water and carbon dioxide. But what else is in amino acid? They see the common atom, the nitrogen.

So why didn’t it work? I encourage them to throw out testable ideas. Perhaps the chloride bit is toxic? Perhaps it fertilises in tiny amounts and poisons in higher concentrations?

This year it was a casual add on to the end of the topic that I thought might be quite fun. Next year, I’m going to build an investigation around it. Perhaps they could produce different ammonium salts with different acids and compare the effects? Perhaps they could look at this idea of really small concentrations? And so on.

Right, I’m done. Thanks for following the blog. I hope you all have a wonderful holiday. Next year, among other things, I plan to answer a questions posed by my old PGCE colleague Ruth in the comments section, on how I’ve managed to stay so enthusiastic. I must admit it’s worn a little thin in recent months, but I’ll see what I can do! And one of my SMART targets for next year is to get my “Likes” into double figures…. Go on, do your bit!

Back in 2016


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