Assuming, for the moment, that we could create dermal cells with chloroplasts in them, which seems eminently possible considering the genetic engineering we have been doing lately.
I did the math, and according to chlorophyll’s efficiency versus how much light would hit you in a well-lit place, having photosynthetic skin could gain you several hundred calories per day: not enough to live on but perhaps prolonging life or avoiding starvation in marginal caloric situations.
So:
Did I do the math wrong (I assumed around %30 chlorophyll efficiency and absorbing light from a prone position)?
What other obstacles would lie ahead, such as:
– Need to regulate the chloroplasts (I don’t know how much structure there is in eukaryotes to regulate their chloroplasts and mitochondria, versus how independent they are.)
– Need to use the rest of plants’ coping strategy vis a vis free radicals (for instance, would we have to megadose on carotenes in order to avoid cancer, since the process of photosynthesis involves massive free radicals?)
– Problems in getting the sugar from the skin into the body (I assume that if Vitamin D can do it, sugar would do it also?)
Well I tried this
1500 Cals = 6000kJ
Over 24 hrs that mean you radiate about 70W
So we need to receive a significant portion of our power from light
Incident Light is 900W/m[sup]2[/sup] roughly
Area of a head is about .2m[sup]2[/sup] Lets make it 0.4 m[sup]2[/sup]. Let’s also say that 10% conversion is what you get.
900*.4*.1 = 35W Not bad really.
Now you’ll likely sleep or be indoors where the light levels are significantly lower than 900 w/m[sup]2[/sup] the advantage likely drops to 15 W or so. Over the course of a day that’s about 300 Cals.
I hope. I hate converting units, but I like doing it more than the stuff currently composting on my desk.
Since it would mainly be useful in emergency situations maybe a lot of these problems could be solved by making just a sort of temporary bandage you can put on. A spray of some mild acid on the location to open up a little blood supply then slap it on.
Of course then the main problems then would be rejection and storage but those are problems we have a better handle on so far.
Just slapping chloroplasts into skin cells wouldn’t do you a lot of good. The enzyme that actually fixes carbon, ribulose-1,5-biphosphate carboxylase/oxygenase (RUBISCO) is composed of 8 large and 8 small subunits. The large subunits are coded for by chloroplast DNA, but the small subunits are coded by nuclear DNA. There are similar issues with Chloroplastic ATP Synthetase subunits.
To get things to work, you’d have to figure out how to coordinate nuclear and chloroplastic protein synthesis. That’ll likely take a few years work.
