Photosynthesis and Energy Stores

Getting a group of British physics teachers to agree to a new consensus is like herding cats: much easier in principle than in practice.

Herding cats is much easier with CGI… (Screenshot taken from

However, it seems to me that, generally speaking, the IoP (Institute of Physics) has persuaded a critical mass of physics teachers that their ‘Energy Stores and Pathways’ model is indeed a Good Thing.

It very much helps, of course, that all the examination boards have committed to using the language of the Energy Stores and Pathways model. This means that the vast majority of physics education resources (textbooks and revision guides and so on) now use it as well — or at least, the physics sections do.

Energy Stores and Pathways: a very brief overview

There’s a bit more to the new model than adding the word ‘store’ to energy labels so that ‘kinetic energy’ becomes ‘kinetic energy store’; although, truth be told, that’s not a bad start.

I have banged on about this model many times before (see the link here) so I won’t go into detail now. For now, I suggest that we stick with the First Rule of the IoP Energy Club….

With apologies to Brad Pitt and Chuck Palahniuk, Image from ‘Fight Club’ (1999)

You can also read the IoP’s own introduction to the Energy Stores and Pathways model (see link here).

The Problem with Photosynthesis

The problem with photosynthesis is that it is often described in terms of ‘light energy’. The IoP Energy Stores and Pathways model does not recognise ‘light’ as an energy store because it does not persist over a significant period of time in a single well-defined location. Rather, light is classified as an ‘energy carrier’ or pathway (see also this link)

A ‘bad’ description of photosynthesis which doesn’t use the Energy Stores and Pathways language

It is possible that the problem is simply one of resource authors using familiar but outdated language. It would seem that exam board specifications are punctilious in avoiding the term ‘light energy’; for example, see below.

From the AQA Combined Science (Trilogy) specification, page 39

How to describe Photosynthesis using the Energy Stores and Pathways model

It’s very simple: just say ‘plants absorb the energy carried by light’ rather than ‘plants absorb light energy’.

In diagram form, the difference can represented as follows:


Over time, I think that the vast majority of physics teachers (in at least in the UK) have come to see the value of the ESP (Energy Stores and Pathways) approach.

I think that I speak for most physics teachers when we hope that biology and chemistry teachers will come to the same conclusion.

H’mmm…if navigating physics teachers towards a consensus is like herding cats, then to what can we liken doing the same for a combined group of physics, biology and chemistry teachers? Perhaps herding a conglomeration of cats, dogs and gerbils across the boundless, storm-wracked prairies of Tornado Alley. In the dark. With both hands tied behind your back.

Wish us luck.

2 thoughts on “Photosynthesis and Energy Stores

  1. paulmartin42 January 4, 2021 / 5:31 am

    Your catchphrase: “Do not talk about Energy unless you are gonna do a calculation” did not resonate with me, so I went and reviewed my own history and was surprised how little energy was mentioned. At school I used the worthy Nelkon texts, and been inspired by the Nuffield little red Physics books. Since neither are in my possesion I checked my inherited CJ Smith Intermediate Physics and found really only one page devoted to kinetic & potential energy which reminded me of (boring ?) electrical energy formulae manipulation too.

    At University, twice can I recall energy being mentioned (excluding quantum): first, was a farewell chat from the retiring Head of Department where he said he hoped that we had gained a Physics appreciation to be able to appreciate the effect of handful of joules dropped in a cup of coffee. Some maybe had not, despite the small novelty final year exam paper which consisted of such questions as: “Calculate the maximum output power of a mouse”.

    Only when I was in the Lighting business was Energy important: for Lighting Design and energy saving. Lately, in my education career and most recently teaching Science at Primary there was little about energy. Thus despite my misgivings, that it’s not all about the calculations, I now more than appreciate where you are coming from. 

    However, I am concerned about your approach to fellow scientists. I am not sure I agree with all the “compliance” points you make in your comparison table - lack of copy and paste option and space reduce my ability to comment point by point. But with regard to your final one: practical investigation of Light intensit on photosynthesis rate I note that there are many suggestions on Google eg varying lamp wattage and/or distance on some seaweed. I imagine that the planning conversation will revolve about the “Light Energy” not necessarily its transfer. Furthermore, it makes me think that you should augment your catchphrase with the word ” experiment”

    • e=mc2andallthat January 29, 2021 / 5:39 pm

      Sorry for the delay in replying(!) Thanks once again for the comprehensive comment — I really appreciate the time taken to reply. I must confess that I do sometimes exaggerate or over-state my case for polemical effect: but this only to encourage other teachers (especially specialist teachers of biology in this case) to adopt the “IoP model”. Although I was initially a sceptic I’ve gradually become convinced it is helpful from a teaching standpoint. I would admit to sometimes the positive points of the model are sometimes a matter of nuance or emphasis, particularily when it comes to the photosynthesis investigation, but I think that in this context, “watts” is a more useful concept than “joules” in terms of planning the investigation. Since the IoP Energy model does not recognise “light” as an “energy store” (in joules) but rather as an “energy pathway” (in watts), I thought it would be helpful if all science teachers used the same terminology. I still think that may take a little while, but I still think it’s an effort worth making.

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