Science Questions

Can we use chlorophyll as a source of energy?

Sat, 8th May 2010

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Question

Sahith asked:

Can chlorophyll can be introduced into our bodies, so that we can avoid hunger?

 

Answer

Chris -   Can chlorophyll actually be introduced into our bodies so that we could avoid hunger for example?  So when you get peckish, rather than have to eat something, you just go and bask in the sunshine (assuming you don't live in Britain where there is no sun!)

Dave -   I thought Iíd start off with a physics approach to this to see whether itís at all practical.  Youíve got about half a square metre of skin which you can point at the sun (youíve got about a square metre in total, but you can only point half of it at the sun at any one time).  The sun produces, at most if you're on the equator and on a really sunny day at midday,  about a kilowatt of sunlight per square meter.  Itís probably about half that on average during the day and it's only day time half the time Ė so on average over 24 hours about 250 Watts.  The maximum theoretical efficiency of photosynthesis is about 20%.  But thatís only compared to the half of the light it can absorb, so thatís only about 10% efficiency.  If you multiply those all up, you get about 12 Watts of power continuously throughout the day if your skin was completely saturated with chlorophyll, in practice the output would probably be far less than this.  Now it sounds like that might be quite useful but the problem is that when you're just sitting in a chair, vegging, you use about 60 watts of power.

So, it might help a little bit, but no it certainly won't solve all your problems.  I'm also guessing that the actual physiological issues would be quite serious.  I guess Chris youíre better to talk about those!

Chris -   Well some animals have done this to a great effect.  Thereís the Sacoglossan sea slug which famously in recent years has been discovered to actually have chloroplasts Ė chlorophyll containing bodies - in its skin.  This slug eats algae, marine microorganisms including sea weeds and things, and it has got this special system where it has tubes connecting the lining of its gut with its skin.  When it eats the algae, it gets the chloroplasts with the chlorophyll in from the algae and puts them under its skin.  Amazingly, the genome of the sea slug contains a number of additional genes from sea weed that can keep those chloroplasts alive.  So this sea slug really does augment its metabolism using sunlight.

Presumably, your worry would be if you start putting chlorophyll into the body, would the immune system have something to say about it?  The likelihood is, if you got it in there from birth, so you educated the immune system about it, I don't think thereíd be a problem.  Letís face it, if you're in a position to start turning people green, the likelihood is that you probably wouldíve surmounted the immune problem too, I would guess!

Dave -   I guess youíd need some quite serious genetic engineering to be able to add those genes into your body to be able to support the chloroplasts as well...

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Sahith asked the Naked Scientists: Can chlorophyll can be introduced into our bodies, so that we can avoid hunger? What do you think? Sahith, Mon, 26th Apr 2010



Only if you are a sea slug  ...


http://en.wikipedia.org/wiki/Kleptoplasty

Sloths have it on their bodies ...


http://www.britannica.com/facts/5/740908/blue-green-algae-as-discussed-in-cecropia-tropical-tree RD, Tue, 27th Apr 2010

I guess that it could be a conceivable possibility in a poor colour copy of Avatar....just kidding. It would be cool to be able to create energy in its "greenest form" ourselves efficiently. doppler1, Thu, 13th May 2010

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