Room 101: introducing enzymes to students as 'biological catalysts'

Spot the stick insect - something we were
allowed to do if we'd cleared away our
 practical kit quicker than everyone else

I can still picture myself sat in a Year 8 science lesson where I, like many others, was first introduced to enzymes in the context of the human digestive system. It was the quirkiest of the school's science labs, with a row of glass boxes lined up along the length of one of the walls, housing a plethora of biological specimens, although the only ones I remember were the family of stick insects.  One of the other unidentified creepy-crawlies did one day break free though,  and I arrived to class to find it sat on my desk - what turned out to be a lucky choice on its part as I was unperturbed. I expect that had it chosen another desk its adventure may have ended suddenly as a textbook crashed down on it from above, accompanied by shrieks of mild terror.

Students eventually getting to do what they always
 thought secondary school science was all about...

Anyway, back to introducing enzymes. The human digestive system seems to be a stalwart of Year 8 Biology; despite many renewals and reinventions of the curriculum it appears relatively unchanged. Starting with food groups and the classic but messy food tests (including the one day when students get the chance to use a bunsen burner how they hoped - to burn an eclectic array of stuff, crisps being ever-popular ). Once you can name the organs involved in digestion and describe what each part does on a macro-scale, students are still left with the confusing issue of just how lumps of food really get small enough to fit between the microscopic 'gaps' in the wall of the small intestine. Drum roll please....enter, enzymes!

So, in that science lesson, and many others I've heard talked about, the title 'Enzymes' is dutifully copied from the board and students ask just what on earth one of them is. 'A biological catalyst' comes the reply. Perfectly true, and a good definition it has to be said, so why am I so keen on hurling it into room 101? Well, here are my reasons:

1. Explaining a new term with a new term.

Many Year 8s haven't come across the word 'catalyst' before in the first place, and even those that have are unlikely to have encountered it in the chemistry sense  (as a substance that speeds up a chemical reaction). So we're (albeit often unwittingly) explaining to students what a new term means by using another new term we then need to explain. What's wrong with cutting out the middle man and describing enzymes as 'substances that speed up chemical reactions', or digestive enzymes as 'substances our body produces to help our food get broken down quicker'? There's nothing stopping us going back to this definition later and expanding or changing it. On the other hand, its also worth considering when the term itself can be defined, as we'll see next.

2. Can you really comprehend any definition of what an enzyme is before you know what it does?

I think this is a key, and interesting question to ask. Once students are shown what enzymes do in our digestive system they stand a much better chance of understanding any definition of them, plus their curiosity can be fostered. But perhaps more importantly, there is surely something incredibly frustrating for a student about starting a lesson (especially in science, which some students already feel they are no good at or not interested in) with a new word and a definition they don't necessarily yet understand. Are we really selling them the concept of enzymes? If we think about it for a second, enzymes are pretty neat, like a miniature army quietly beavering away in our gut without us giving them a second thought. Like a microscopic dating agency and divorce solictor for molecules all rolled into one. Giving students a chance to discover this for themselves should surely come first, then they stand a chance of being interested in, and able to comprehend (or even shape) a definition of what they are.

3. Which is more valuable - a precisely perfect definition borrowed from an expert, or a imperfect but evolving one that you write yourself?

Again, a vital question but one that requires some pondering. I've thought about this a lot, and as always there is no cut and dry answer, but I would always err towards the latter wherever possible as a teaching tool. Of course I'm not suggesting that students fill their exercise books with original definitions that are far from reality; this will inevitably hold their learning and motivation back (whilst also maybe losing some marks in tests or exams, though for me thinking in purely those terms is too narrow). But, seeings as language is the primary way students convey (to us teachers as well as examiners) what they have learnt, surely we are missing a prime opportunity for students to practice this when we give them a dictionary definition? In my experience, when students are asked to write down their own ideas about the science they've learnt, rich opportunities for reflection and refinement often ensue. Misconceptions make themselves known, an chance to give the whole class a challenge in dispelling them. Students come up with new analogies, bring in new real-life examples or make insightful links to other topics and subjects - often surprising us as teachers. Even if students write something slightly off the mark that isn't picked up in class, a glance at their books gives rich information about how much has been understood, giving a more informed starting point for future lessons, and perhaps even avoiding the oft-heard phrase 'but I taught them that last week, how don't they know it?' In essence, if students haven't put their learning into their own words, have they really learnt it?

So, there's my justification for throwing this into room 101 to never be seen again. Do you agree?