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It is possible that the problem is simply one of resource authors using familiar but outdated language.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.