Is it time to let MRS GREN die?

I’ll start out by saying that this is very much an opinion piece as opposed to something backed up by research (or even field testing). But it represents an issue I feel strongly about – that we justify a lot of content taught at KS3 on the basis that it is what we have always done. And yet it is still something we regularly debate as it doesn’t quite seem to work, as shown by the myriad of responses to Madeleine’s tweet the other day.

What is MRS GREN?

MRS GREN is an acronym for the processes performed by living organisms and is used as a set of criteria to determine whether something is living or non-living (not dead, that’s a whole other debate!).

  • Movement
  • Respiration
  • Sensitivity (in other words responds to its environment)
  • Growth
  • Reproduction
  • Excretion (in other words gets rid of waste)
  • Nutrition (in other words consumes / produces food)

It’s not directly stated in the KS1/2 or KS3 national curriculum but the use of it or something similar is alluded to in KS1 Year 2:

And in my 10+ years as a Biology teacher, it has been the staple start of the first Biology topic we teach in Year 7 as an introduction to the concept of cells.

The issues

I’ve grown to hate MRS GREN as it is (rather aptly) a massive can of worms. Just a cursory glance reveals that 5 of the 7 terms are tier 3, subject specific vocabulary, 2 of the terms (respiration and excretion) are at the centre of 2 of the most persistent misconceptions in Biology (respiration = breathing and excretion = egestion) and all of them are complex enough to demand a topic’s worth of curriculum time.

So what starts out at as a nice starter with links back to what they learned in Science at primary school rapidly descends into fielding questions like “what’s excretion?” and “isn’t respiration like breathing?” and the answers you need to give are based on knowledge that most of the students won’t have yet.

But diving a little deeper reveals a more fundamental issue. To the average 11 year old, MRS GREN does not work as a set of criteria to determine whether something is alive. Here are 2 examples that reveal this flaw:


Fire is non-living but judge it with MRS GREN with your 11 year old child hat on and it might not be so clear:

  • Movement – fire spreads
  • Respiration – fire consumes oxygen (not visible but might be prior knowledge)
  • Sensitivity – when you blow on fire it moves
  • Growth – fires get bigger
  • Reproduction – one fire can start another fire
  • Excretion – fire produces smoke
  • Nutrition – fire needs fuel


And what about a living organism that doesn’t fit the mould? To a child’s gaze, plants don’t conform to MRS GREN in the same way as their human reference point:

  • Movement – plant tropisms are rarely observable in a timescale children are used to
  • Respiration – plants don’t visibly respire (and there’s the “breathing” misconception…)
  • Sensitivity – see issue with “Movement”
  • Growth – this one is OK
  • Reproduction – as is this one
  • Excretion – plants don’t visibly excrete (and there’s the “egestion” misconception…)
  • Nutrition – plants photosynthesise, again this is not visible

So we have a non-living object that, to a novice learner, visibly appears to satisfy all of the MRS GREN criteria and a living organism that, depending on prior knowledge, potentially fails 5 of the 7.

The fix

Now I’m not going to bash one of the heavyweights of Biology education without providing an alternative.

I explicitly acknowledge that MRS GREN or something similar is likely to be familiar to the students but that it is flawed and is going to cause us trouble. I use the examples of fire and plants to highlight this but I deliberately simplify the language so that (near) all students can access.

And then I state that, from now on, we will have one simple rule to decide whether something is living or non-living:

“All living organisms are made of cells.”

I then bring in some hinterland on Hooke’s observation and description of cells in his Micrographia using an extract from Bill Bryson’s A Short History of Nearly Everything and finally make sure any lingering misconceptions are confronted using some refutation texts.

Later in Year 7 when we teach reproduction, this rule is expanded to become:

“All living organisms are made of cells and can reproduce.”

So why not try it with your classes this / next week? Check out my Year 7 Cells booklet on my resources page to see the full sequence.

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