Thursday, January 7, 2021

Ruminations on Eating Photons


Plants see photons.

People see photons.

Plants eat photons.

Do people eat photons? I suspect not. It would be too light a diet. 

The above was my first reaction to Carl Jennings’s latest column, “Eating Color: Color Perception in Plants” [ISCC News # 492 (2020), pp. 5-8]. Carl wrote from the viewpoint of an artist who embodied the title metaphor in his works. I, of course, tend to pursue more technical implications—starting with a joke. And, unlike all the trite photon jokes I had seen on the Internet, this one seemed to have a serious teaching point.

Let’s start with the seeing of photons. The chemistry of vision involves amplifying a rather weak photon signal (weak because it must be divided up in space, time, and spectrum), and the agent of the amplification is the discharge of a battery. When the battery is discharged, it must be recharged (using a lot of metabolic energy) before it can be used again. (Sometimes, as with retinal rods, the battery gets discarded and replaced, not recharged.) Seeing, either by plants or by animals, involves treating the photon as a signal and amplifying that signal chemically. Any vision system, plant or animal, uses energy by combining oxygen with other elements; hence respiration is a prerequisite for seeing.

Now let’s proceed to the eating of photons. Photosynthesis also has a battery that is similar to vision’s battery, but the energy goes the other way. Not only the photo-active material, but the whole organism increases in mass and energy as a result of the incident photon energy. Carbon adds to the mass of the organism and oxygen is released. 

I’ve just described the eating of photons by plants. Do animals eat photons in the same way? No, and I think the reason is that animals are not able to use the photons as a direct energy source. They have to eat in other ways, which are familiar to us. Photons are too light a diet to sustain animals directly. [One must note a small exception of this rule, the creation of Vitamin D via the Sun’s UV radiation on skin.]

I published a little about this subject in ISCC News # 427 (2007), p.7: “Power to the Pupil” (not a Hue Angles column). There my main focus was the creation of batteries using rather large amounts of visual pigment from animals, and also the design of solar cells using principles very similar to those used in certain cameras.

Some of you might complain at this point about my colloquialism of “seeing photons” in place of “information-processing an electromagnetic signal” and “eating photons” instead of “transmuting electromagnetic power into stored energy.” In anticipation of such a complaint, I can only say that less colloquial language might deny me immortality in the immense archives of photon jokes that persist ready for simple Internet search. Enjoy. 

Michael H. Brill