One Variety of Sea Slugs Cuts Out the Energy Middleman 232
dragonturtle69 writes with this story, short on details but interesting: "These sea slugs, Elysia chlorotica, have evolved the ability to gain energy via photosynthesis. Forget about genetic modifications for sports enhancements. I want to be able to never need to eat again — or do I?"
Re:eating (Score:5, Informative)
whoosh.
The sun rises on the eastern horizon just as you are going to bed after sitting at your computer all night.
Re:eating (Score:1, Informative)
They didn't say the sun was setting, just where it was located when one was going to bed, hence implying that the target of the comment is thought to stay awake until sunrise.
Re:eating (Score:1, Informative)
Yup, and it rises in the east... at the wee hours of the morning when most of us geeky types are finally heading to bed. :P
Re:Nitpick (Score:5, Informative)
No, the statement is essentially correct. The slugs harvest (i.e. gain) energy via trapping photons with chlorophyll. They store that energy as chemical bonds in sugar molecules. They then release the energy as needed by metabolizing the sugar. Photosynthesis is the coupled capturing and storing of energy so saying that it "gains" energy via photosynthesis is a reasonable simplification.
Re:Nitpick (Score:2, Informative)
Photosynthesis is not like solar power generation that converts sunlight into a different form of energy (electricity).
Instead it uses the energy to produce an energy source (similar to coal as you point out). This energy source is then metabolized into energy. The sun's energy is used indirectly.
Still it is very cool to see an organism that isn't a plant being able to use the sun for more than just heat.
Re:Nitpick (Score:3, Informative)
To summarize the article:
Slugs have somehow included algae DNA with its own, and are now capable of actual photosynthesis. The DNA that was copied didn't code for the creation of chloroplasts, so the slugs have to consume a sufficient amount of algae before they can begin the process.
As long as they are exposed to light for 12 hours per day, they can live without the need for food.
Re:eating (Score:5, Informative)
I just did a few quick calculations. Assuming humans have 2 square meters of skin, and stood naked in direct sunlight in the best conditions for 8 hours per day, and assuming 5% efficiency for photosynthesis, we would only get enough energy to provide for 11 hours of sleep (250 BTU/hr), 7 hours of sitting still (400 BTU), 4 hours of light work (650 BTU) or 1 hour of heavy work (2400 BTU). We'd still probably need to consume 2/3 or so of our normal caloric intake from food.
Sources:
http://www.solarexpert.com/Heat-theory.html [solarexpert.com]
http://hypertextbook.com/facts/2001/IgorFridman.shtml [hypertextbook.com]
http://www.answerbag.com/q_view/514275 [answerbag.com]
http://www.ccmr.cornell.edu/education/ask/index.html?quid=1021 [cornell.edu]
Re:been a while since bio class (Score:5, Informative)
Chlorophyll itself is made in the cytoplasm, and actually requires relatively few new genes for an animal to be able to produce it, since the complicated steps of its biosynthesis are identical to the heme structures it is already able to make. The real difficulty, and one that this sea slug seems to have been able to surmount according to the Wikipedia page, is the production of the "oxygen-evolving complex," a metalloenzyme with a manganese-calcium core which transfers absorbed energy to a bound water molecule to break it into electrons, protons, and molecular oxygen. Heterotrophic organisms don't produce anything like it.
Re:eating (Score:3, Informative)
Yeah. I know it's not perfect, and that all 2 m^2 of skin wouldn't actually be receiving full sunlight. I was just trying to emphasize that even with unrealistically optimal conditions, we wouldn't get nearly enough energy from the sun to live on photosynthesis alone.
Yes, Sea Anemones for one (Score:3, Informative)
Re:Nitpick (Score:3, Informative)
If you think about the laws of thermodynamics, you will realize that "uses the energy to produce an energy source" is just a confusing way to say "cnoverts the energy to another form and stores it".
Re:Nitpick (Score:3, Informative)
Here's the thing. Animal cells have the ability to do a lot of biochemistry, but they have very limited ability to do some exotic chemistry that is essential to animal life. The major example of this is a molecule called adenosine triphosphate, aka ATP. All life uses ATP as an energy source.... lemme back up. Chemical reactions are reversible. To get from the reactants to the products requires that you put in a certain amount of energy to get to an intermediate state, and then you get out a certain amount of energy as it goes to the final state. We generally regard the reactant state as higher-energy than the product state (although that's not necessarily true: if you're consistently pulling out one of the reactants, you'll consistently push the products to become reactants.) Enzymes serve to lower the energy that it takes to go from reactants to products.
There are certain classes of chemical reactions that the body *really* wants to force in one direction, so what happens is we have enyzmes that take reactants and ATP, and by splitting the ATP into adenosine diphosphate and a phosphate group, which releases a *lot* of energy, the reactant - product reaction is driven in the direction the body wants. The thing is: animal cells don't have the ability to make ATP. It's a difficult thing to make, and takes a lot of energy (of course, since it releases a lot of energy when it breaks down, it takes more to make the molecule.) So what animal cells have done is ingest bacteria, which we now call mitochondria: they were captured (maybe a billion years ago) and are now used to do the weird chemistry our cells can't do alone. The bit where eukaryotic (animal and plant) cells captured bacteria is where we developed the ability to be large multicellular creatures, rather than just a few cells sort of cooperating. Plants have done the same thing, twice: both mitochondria and chloroplasts are captured bacteria. Chloroplasts contain the structures that convert the energy of captured photons into high-energy molecules that plants use to drive their complicated reactions.
So, these sea slugs have done two interesting things: they've developed the ability to make their own chlorophyll, which is pretty amazing, the equivalent of finding a plant that can make hemoglobin, and they've managed to accomplish the same sort of symbiotic relationship with cyanobacteria that plants and animals did roughly a billion years ago when they formed mitochondria and chloroplasts. The sea slugs are engaging in convergent evolution and ending up with both plant and (primarily) animal characteristics.
Re:There are other ways to do this (Score:2, Informative)
Couldn't you just form an symbiotic relationship with algae or photoplankton, allowing them to live inside you for protection in return for using them for energy? Aren't there already animals that do this?
There are. That process is well understood, and thus, not all that interesting to scientists. What this slug does in addition to that is novel and thus interesting.
Re:Actual evolution? (Score:2, Informative)
Is this actual, observed evolution? Is this the proof creationists are always demanding?
Yes and no. It is one of thousands of examples of observed evolution, and the process is already well proved. This will not stop the demands, however, since the demands are not made in good faith...
Re:eating (Score:3, Informative)
and assuming 5% efficiency for photosynthesis
Interestingly, this estimate is right around the theoretical maximal efficiency of photosynthesis. As outlined in Current Opinion in Biotechnology 2008, vol. 19, pp. 153-159 (sorry, subscription only), the maximum theoretical efficiency of C3 photosynthesis is a mere 4.6%. C4 photosynthesis has a bit higher potential at 6.0%.
We can't even reach these efficiencies in plants (best for crops in a growing season is 2.4% for C3 or 3.7% for C4; see above reference), so sarahbau is right in saying that the amount of energy we could hope to get from this is quite low.
Re:eating (Score:3, Informative)
If the joke wasn't that we stay up through all hours of the night
It was.
“that big, bright, yellowish thing on the eastern horizon when you go to bed” – funny.
“Where I live the sun sets on the western horizon” – not so funny.