Nitrogen Cycle

disclaimer: this lesson has not yet been tested on school children

the quality of your lesson can go down as well as up

So there are some topics which just bring a cold chill to the heart when you contemplate planning the relevant lesson. A classic example of this is the Nitrogen Cycle. I’ve never taught it well, and I’ve seen several other people teach it to no useful effect. I’m bored, the students are bored – and we’re both slightly cross that any exam board would decide to include it in a specification. Covering important ideas is one thing, but we’re trying to get young people excited by science!

So is it just something you write off as a bad lot, hold your nose, teach the lesson as quickly as possible, and race on to something with more obvious appeal?

In a spirit of confession and openness, here is my Nitrogen Cycle lesson of recent years.

Nitrogen Cycle Exercise plus The Nitrogen Cycle

The idea is that they try to figure it out using the pictures as clues. Please note that I am at least trying to provoke active learning. I don’t expect them to get all of the blanks, but they should surely be able to figure out the middle bit with wee and poo and death and food. Shouldn’t they?

But no – they look blank, they look helpless, they look pathetic. No two ways about it, the lesson doesn’t work.

Back to the drawing board. To come up with something more successful, we need to determine the problem. I think a large part of it is that The Nitrogen Cycle comes from nowhere. It’s just this random topic that we insert into some convenient gap in the time table. There’s no reference point, no indication as to why it matters, and it’s just not interesting when all you’re expected to do is learn the various pathways and the unpronounceable and virtually unspellable micro-organisms.

But how to make it interesting? I wonder if we need to start with the atom itself….

So here are some ideas I’ll be trying next time the Nitrogen Cycle has to be taught. I’m thinking of A-level students. And I think I’ll cover it at the end of Photosynthesis in Year 13….

Opening question:

Name 5 biological molecules that contain a nitrogen atom…

With a bit of discussion between them I’d expect at least amino acids/proteins, nucleic acids, ATP, chlorophyll, NAD…

What does nitrogen bring to the party?

At this point I want them to think about why the properties of nitrogen make it so important to the biological molecules they’ve named. They already know about carbon and oxygen, so why does life also require nitrogen?

I’d expect this to take quite a lot of thought, discussion and prompting. I would want to remind them of carbon’s 4 bonds and the ability to form long chains. We would revise oxygen’s electro-negativity and the central importance of hydrogen bonds. Eventually, I’d hope to arrive at a point where they see that nitrogen is a bit like carbon and a bit like oxygen. It can form multiple bonds, but it doesn’t share its electrons nicely.

Where exactly are these properties important? Give specific examples.

This is great thinking fodder. Remember, the top universities are looking for students who both understand ideas and can apply them. Remember, the GCSE and A-level assessment is changing – factual recall is down (represents a max. 15% at iGCSE), using your brain is up. Will a question come up on the properties of nitrogen? Who knows! But it’s not a relevant query. This is training them in thinking, in not being afraid of the unfamiliar but tackling it head on.

Come on, describe some specific examples that you’ve met as part of the A-level course.

That generally puts the cat among the pigeons. An accusation that they’ve done this and should know it.

Tell me about proteins. What’s the role of nitrogen in building a protein?

Or maybe I’ll put the questions into an exercise and get them to work together in groups. Perhaps with some helpful diagrams that they can work with.

For DNA, proteins and chlorophyll, explain the importance of nitrogen in their structure and function.

So I would expect them to track down the nitrogen in the organic bases – maybe look at their own DNA model

and realise that the electronegativity of nitrogen is vital for the hydrogen bonds that connect the two stands.

And for protein, again referring to their models….

….they can trace it back to the peptide bond and the hydrogen bonds that stabilise the secondary structure.

As for chlorophyll, it needs that porphyrin ring to hold the magnesium ion. That ring is made possible by a combination of carbon and nitrogen…

So it’s key! We need to know more about it. The scene is set….

Question: where is most of the nitrogen on earth?

Right, now it’s time to consider diatomic nitrogen and why it’s so difficult to insert nitrogen atoms into large molecules. Let’s check out some enthalpy data.

N to N = 945.4 kJ/mol-1

Compare water (464 x 2) or carbon dioxide (805 x 2) kJ/mol-1

Basically, this is a molecule that’s less reactive than water! Demo trying to burn water for comedy value.

At this point I’d get them to research, in outline, the Haber process. What do we have to do when we want to rip nitrogen out of the atmosphere and combine it with other atoms?

450’C at 200atm with an iron catalyst. Yikes!

What is the challenge for any living organism wanting to go it alone and DIY its own nitrogen containing molecules?

Time for them to do some more research. What organisms can do this, what conditions do they need in order to do it, and where are these conditions found?

So, finally, after all this preamble, we’re dipping our toes tentatively into the nitrogen cycle. But this is seriously amazing and worth lingering over a bit. I like the contrast with our clumsy, clunky human chemistry, using sheer brute force to break the triple bond, and the beautiful elegance of biology, able to achieve the same ends at atmospheric pressure and the temperature of the soil. Primo Levi says this about photosynthesis:

“if the elaboration of carbon were not a common daily occurrence, on the scale of billions of tons a week, wherever the green of a leaf appears, it would by full right deserve to be called a miracle.”

I think the same sense of wonder is appropriate here.

There are some great images of the Rhizobium inside the legume nodules. What a cool relationship!

Rhizobium and nodules

This feels like the end of the lesson to me, so homework would be writing the diary of a nitrogen atom, detailing its adventures as it passes through every point of the nitrogen cycle…

As I say, I’ve not taught this, so caveat emptor. What do you think?

 

 

on the CREST of a wave

After two years of our new, practical based KS3 SoW, someone (not me!) had the brilliant idea of letting the Year 8s finish the summer term with a Bronze CREST Award.

If you’re not familiar with the CREST scheme, this website gives all the details. Note that the awards can count towards Duke of Edinburgh! But basically students choose a question, their own question, and then set about answering it through experimental investigation.

Lots of reasons for liking this – first and foremost being that I didn’t have to try and plan a new set of lessons on Electromagnetism (as was on the old SoW). Or, indeed, any new lessons at all. I liked the concept of individual projects and complete ownership of what they would be doing. And, hey, it’s what the course was all about. Had to be a winner! I had happy visions of loads of brilliant and original projects run by brilliant and motivated students. Loads of kudos for the dept. and the school and so on.

How would it go?

I started with a review of the last two years. What do the following have in common?

• hamster mazes
• apple juice
• burning wood
• lemon juice, vinegar and sulphuric acid
• fertiliser
• reaction time
• brine shrimp hatching
• weed competition
• rockets
• maggot behaviour

They quickly realised that these were the investigation where they been asked to design and carry out their own experiments. so if nothing else, it had been memorable!

Right, I say, enthusiastically, now it’s your turn! And I tell them about CREST, and give them some links, and set them thinking. Only trouble is, I’m on a 1st Aid training refresher course, so have to leave them, and don’t find out their thoughts until the following lesson…

It’s certainly interesting talking to the students 3 days later. They have ideas, some more developed than others, but it’s hard to gauge the extent of interest or engagement.

At one extreme, two students have mapped out their project to look at the effect of soft drinks on plant growth. They’ve designed the experiment, identified the controls, ordered the relevant apparatus, and are starting to research the theory. I don’t need to do much here – a few questions, pointers, clarifications, but they’re good to go.

And at the other end, some just want to drop a Mentos into a bottle of Coke because they can remember that from primary school and have wanted to do it again ever since. This requires a bit more help. I don’t want to crush their dream entirely, but they need to work this into a question where they can look at variables, controls, measurements….

Overall, I’m encouraged, but not blown away. Patience, I remind myself, first time we’ve ever done this, it’s not going to be brilliant at the first attempt. Think about how to do it better next time…

By the third lesson, however, they’re flying. They’ve got past the most difficult bit – actually thinking of an idea – and are just throwing themselves into the work.  They’re finding something out about real science – it’s fun! They have complete ownership of their projects and are excited and motivated.

It’s not exactly work free for me – there’s no planning or delivery, but I do have to coordinate all their apparatus requests (top tip: make it absolutely clear that you will provide basic lab apparatus, but that if they want anything more elaborate, they provide it themselves!). Plus in the actual lessons, it’s quite intense, talking to all the groups – encouraging, advising, supporting – and scurrying back and forth as they think of new bits of apparatus they want or need. But the time flies by and suddenly it’s lunch.

This is going to work!

Have any of you tried CREST? I’d love to hear ideas or tips or any other experience of this.

Have a great week!

 

 

Spoon-fed markscheme regurgitation monkeys…

We were very disappointed this year to find that Blades have taken the traditional blood typing kits out of their catalogue. You can still get the Eldon card kits, but these are shockingly more expensive, much less fun, much more fiddly, and, we find, less reliable.

So we rang up Blades. Good news – they can still supply the original antibodies! Hurrah! Bad news – they took them from their catalogue because there was so little demand.

I was pretty depressed by this. As I’ve said before, it’s hard to think of a practical activity that is so immediately engaging, exciting and directly relevant to the students, whilst simultaneously covering so many interesting areas of A-level Biology.

Sure, blood typing itself isn’t on the syllabus. And sure, some people remain nervous about students taking their own blood – despite it being far safer than a blood injury in, say, rugby or hockey (or jabbing yourself with a needle in Textiles, for that matter).

A reminder that using student blood is absolutely OK.

Here’s how I use the blood typing protocol on our A-level taster day for Years 10/11 (though it would work equally well as an introduction to A-level at the start of the course).

Big SEM picture of red blood cells.

What are these then? What do you know about them?

Usual GCSE stuff on shape, function, flexibility, lack of nucleus and so on.

What do you know about blood types?

Quite a bit, it turns out, though generally a little confused. They’ve all heard of A and B and O and positive/negative, though they have no idea what this means. They have some vague idea that it’s important for blood transfusions.

Return to the picture of blood cells.

But how can blood be different? This is what your red blood cells look like. All of you.

Now for an Atomic Force Microscope image of a cell membrane.

 

Lots of suggestions as to what this looks like. Mountain ranges, craggy hills, and so on. But it’s a membrane.

That’s a bit more interesting that GCSE, isn’t it? What’s going on here? And, actually, if you’ve any curiosity at all, how could that GCSE fried egg drawing of a cell ever account for something as gloriously complicated as yourself?

I really like to stress the idea that at A-level, we start to find out what cells and their membranes are really like. It’s about trying to get that imaginative hook in place.

Very quick idea that craggy mountain tops are actually proteins. So you thought proteins were just something you needed to grow. And maybe, if you’re brain is on, for enzymes and digestion. But they’re FAR more interesting than that! There are zillions just in your cell membranes. Doing loads of jobs. And some of the proteins on the membranes of your red blood cells determine your blood group.

Cartoon of proteins of ABO group.

A and B proteins

Stress idea that A-level Biology is basically jigsaws. If they like jigsaws, if they understand jigsaws, they’re half way there.

So how could someone be AB? They immediately see it. Their red blood cells have both proteins.

How could someone be O? There isn’t an O protein. Slight pause, and, again, they get it. Their red blood cells have neither protein.

Quick mention of positive vs negative. Maybe show a clip from the Tony Hancock blood donor sketch. Just a different protein. Same idea.

OK, why do you have that particular blood group? Where did you get your blood group from?

No problems with identifying their parents as the culprits.

But your parents don’t give you proteins. They don’t give you red blood cells, for that matter. What do they give you?

Thankfully, they’ve all heard of genes.

So what’s the link? Hopefully, Year 11s/starter Year 12s should be able to recall the genes code for proteins. Year 10s need the idea introduced, but quickly absorb it. Follow this with an outline of the different alleles and the possible combinations to be A, B, AB or O.

alleles

At which point they’re nicely primed to find out their own blood group. Again, this blog post outlines how they take their blood.

Great excitement etc etc.

Lots of things you can do once the results are in. Collate the class data. Compare it to the distribution in the UK. The brighter ones are now starting to ask questions about why do we have different blood groups. Maybe compare the UK distribution with a more Mediterranean distribution. What’s going on here? The idea that allele frequency can vary from place to place. How could they explain that? One more thing that we return to later in the course…

It’s also quite fun to pair two students up and ask them to work out how many of the other students could conceivably be their children, based on blood group inheritance. Time to throw in the Charlie Chaplin paternity case.

Inheritance of blood groups with Charlie Chaplin

What do they make of that? General outrage at the scientific ignorance of juries.

But how does it work? Again, brighter students will have already asked this. How do the little circles (on the Eldon cards) “know” that blood contains A or B proteins?

OK, what can they see? What might those little red speckles actually be? Lots of suggestions, but eventually someone gets the idea that the red blood cells are clumping together. Right! Agglutination! Quick slide of anti-A/B antibodies.

agglutination

Why is this important?

And you’re right into the blood typing game. Ask for volunteers to do this. Encourage them to try and take blood from the nose. Make sure the volume is turned up high. They “get it” impressively quickly. And can see that while being O is great for donating, it’s not so great for receiving. And the other way around for AB.

And to wrap up?

I always finish with the Ann Boleyn hypothesis. Was she Rhesus negative? Does that explain her first healthy child, Elizabeth, born to a Rhesus positive Henry? And all the subsequent miscarriages, as her immune system, primed to make Rhesus antibodies, attacks the foreign blood cells? Maybe! I reassure the girls who are Rhesus negative that this will not be a problem when the start their own family.

OK, OK, blood groups themselves are not on the syllabus. But even if you’re not convinced by the possibilities described above, there were the new OCR Breadth and Depth in Biology AS papers to remind us that:

• A-levels are going to be more difficult and
• students will be expected to apply their understanding in unfamiliar contexts.

I recall a training day some time ago where a teacher/Chief Examiner urged us to provide notes that were basically bullet pointed summaries of the learning outcomes, and to teach by filling in past papers with the mark scheme. When I asked him how this helped his students deal with synoptic questions, he was rather evasive.

I know that lots of teachers and students like this kind of approach. Indeed, many teachers at the CPD sessions I run will say something along the lines of, “Well, yes, that was fun, but my students just want to be given notes on what will come up in the exam.”

Right.

Except that training students on past papers and markschemes will only ever succeed in:

a) boring them

and

b) making them very good at answering past papers.

You’re then hoping that the exam board will just lazily re-use those same questions. Hence the outcry on the student room discussion boards when OCR has the effrontery to set a question that requires them to think and to show that they actually understand the Biology they’ve been taught. Sign that Facebook petition! We don’t have notes on: a traditional English Folk song The Derby Ram/icefish/N-acetylglucosamine/Amanita citrina (INSERT favourite example here).

Come on, let’s get Blades to put those blood typing kits back in their catalogue. And let’s aim to inspire and excite our students, rather than turning them into spoon fed mark scheme regurgitation monkeys….

 

 

Bees and Barnacles and Bits and Bobs

Good morning! I hope you had a splendid half term break.

Biological highlight of the last few weeks was probably a successful honey bee swarm collection. Our last surviving hive had starved to death in the really cold spell of mid-April – we felt very sad and rather guilty (we should have fed them!) on opening up the hive and finding the pathetic corpses of bees, buried deep in the cells in a desperate search for a drop of honey…

So when a swarm attached itself to the hazel tree in the garden, it was an obvious chance to renew our stock! And it was textbook. We shook the swarm into a box – they land with a satisfying thump. We put the box under the tree to allow the other bees to find them. Then, later in the day, we took the box up to our newly refurbished hive (lots of lovely wax comb and a sugary bait in the top). We had put a white sheet on the ground leading up to the entrance of the hive, and just dumped the swarm out of the box and onto the white sheet.

Well, I had seen videos and read accounts, but what happened next still blew me away. After a few minutes, the scout bees had found the hive, liked what they saw, and sent out the necessary signal to the rest of the swarm. Which promptly walked into the hive. I sat, transfixed, for an hour and a half as the 1000s of bees marched in orderly columns up the sheet and in through the entrance. Just incredible.

I’ve looked at the possibility of keeping bees in school and having an Apiary Club. I know that other schools do this successfully and I think our students would love it, but there are only so many hours in a day and I just couldn’t face going through the risk assessment process.

Anyway, back to the plot. Apologies for the slightly late burble-posting – I had a very enjoyable Tuesday in Taunton, contributing a session on Flipped Practicals to a group of Biology Heads. I picked up a brilliant idea for using barnacles in lessons, involving an invasive Australian species, Eliminius modestus, that attaches to small rocks and pebbles, making them easy to pick up. In a plastic bag in a cold box, they’ll last a month, “thinking” the tide is out. Collect some sea water at the same time and keep it chilled. For the lesson, students have a suitably barnacled pebble in a glass dish and cover it with cold sea water. The barnacles almost instantly spring into action and you can watch them “beating” their little food gathering legs in and out of the hole (technical term?) on top. This correlates beautifully with temperature, so as the sea water warms up, the beating activity increases. There’s a nice link to Darwin – E.modestus features in his monograph on the group – and I’m only sorry that being based in Oxford doesn’t make for convenient collection of the animals….

Other snippets from the day. I liked the equation: rtfg + atfq = exam success.

And I liked this picture:

Back in school today, I’ve started work on an A-level Nitrogen Cycle lesson. My existing lesson is awful and needs to be taken outside and shot. I’m quite pleased with the new version that is evolving but it’s not ready for sharing just yet. Watch this space. I’ve also been commissioned by the education branch of ASAB (Association of the Study of Animal Behaviour) to develop a lesson on cuckoo brood parasitism. Lots of role play with chocolate eggs and trying to think like a bird. It’ll eventually be free for access on the ASAB website and I’ll put the word out when this happens.

But for now, I’ll complete the story of our KS3 Summer Exam practical questions.

For Year 8,  I wanted to be a little more ambitious. We couldn’t do microscopes again – though they had enjoyed looking at osteocytes and imagining the lonely life in that little bone-clad prison – and they had already had some practical questions in progress tests on Forces – so no block sliding down slopes. What about Chemistry? The topic on Rocks won’t be in next year’s SoW (deathly deathly dull!) but they had really enjoyed the chemical analysis of malachite.

So I put in a question which required them to identify 3 unknown compounds provided in solution. Here it is.

Year 8 Summer Exam 2016 practical question

Can anyone spot the chemical error???

The outcome was interesting. They all (well, nearly all) successfully identified the metal. But they didn’t have enough chemistry to appreciate that a cation will only ever have one anion. And with the carbonate also giving precipitates with Barium chloride and Silver nitrate, most of them thought they had found Sodium Hydrogen Carbonate Chloride. So, that needs a bit of rewriting….

But they liked the process and took it very, very seriously. With most of the marks allocated to practical skills, the successful identification was less of a concern, and we had a tick list for what we wanted to see (wear goggles, label tubes, rinse tubes, etc). Certainly, the over-arching aim of emphasizing the singular importance of experimental investigation to Science was, I think, successful. I hope to see more evidence of this next week when I introduce them to their summer project – they’re all going to do a Bronze CREST award….

Have a good week.