Plants may synthesize energy-rich substrates but they certainly do not feed on nothing. They rely on an external carbon-source (carbon dioxide) just like every other organism be it plant, animal or fungi etc.. Meaning, they synthesize carbohydrates, but they are still in need of 'eating' the building blocks of which later becomes sugar. The difference between humans and organisms capable of photosynthesis is therefore not the notion of synthesizing macronutrients (humans do it as well: lipogenesis, glycogenesis ..), but the question of where the energy for synthesis derives from. In humans by oxidation of energy rich substrates, in plants by making use of light, a free source of energy.

Unfortunately in human lives, nothing comes for free.

Hi Shubhajit,

Yes we do. It's called chemosynthesis. Read all about it at:

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

In some deep ocean sites communities of living organisms (excluding bacteria) have been found which live entirely on chemosynthetic bacteria, with a complete food chain starting from these chemosynthetic bacteria, as primary producers in that type of deep ocean ecosystem.

Evidently at the depths where these communities have been found (4 km depth and deeper) photosynthesis is evidently excluded.

Cheers,

Frank

Hi Shubhajt,

As well said by Thomas and Frank, we humans can synthesis carbon sources like plants, but the energy source is the matter. Plants can obtain energy from sunlight, certain bacteria can obtain it from certain chemicals ( in organic chemicals). But we have to depend upon external food for energy.

As we believe in evolution, there might be a time where humans could obtain energy from some other sources and become auto tropes.

We can synthesize Vitamin-D in presence of sunlight. I was wondering if we can synthesize proteins and carbohydrates by some means from Vitamin D

actually you are not synthesising Vit D from sunlight, instead just converting its "pro" form into active form...

may be one day we might synthesise carbohydrates too as u said...

Dear Sjubhajit,

I have proposed in a theoretical series of papers a process named thermosynthesis, in which organisms made or make use of thermal cycling or a thermal gradient. In the papers I show that today's metabolism may have emerged from thermosynthesis during evolution. Thermosynthesis may very well still play a role in all kinds of biofouling, from the fridge in my kitchen, in cooling towers, upon the hull of ships, up to mold growth in spacecraft. Thermosynthesis can also explain that organisms survive for extremely long time underneath glaciers: they would lived on the thermal gradient between the ground and the ice above. Even the manna mentioned in the Bible may have grown on thermosynthesis upon rocks in the desert . . .

@Manu

Hi Manu,

Chemosythetic bacteria actually don't use organic chemicals but anorganic ones like H2S emitted in volcanically active zones in the deep ocean, lava upwelling zones where new land is formed. It is there that they are the primary producers in an ecosystem entirely dependent on the volcanic gasses emitted in these active zones. These zones are actually the drivers of the continental drift in the Atlantic between Europe-Africa and the America's. The Volcanic ridge somewhere in between the two continents has several zones where the chemosynthetic bacteria colonize the volcanic acitve zones, including higher organisms feeding on the chemobacterial strains. This zone for example surfaces in Iceland. The chemotrophic bacteria live on the energy released during oxydation of the anorganic gasses and chemicals released in these zones. So they are NOT heterotrophs, but genuine chemotrophs. There is a big difference there between those two ways of feeding. Actually these bacteria are called chemo-autotroph bacteria, which makes the difference with heterotroph bacteria (or other organisms) quite clear.

Cheers,

Frank

Fungal hyphae from a single individual can reach 10e4 m2 and live for centuries, but they feed on organic substrates and are sessile, they do not move but grow. The question is then how trophic can be a complex organism that walks? The range and fast energy requirement require at least for one day the carbon and nitrogen made by a rice plant with 5 culms in about 100 days. Going to fast speed and trucks ratios 1 year of current petrol world consume 1 million years of photosynthetic organic debris. Of course we can establish some biosynthetic ability for repairing deficiencies with gene therapy or even making blondies but for trophic mutations there are corals and few others. This fast energy could be a limit, anyway nice question.

Elysia chlorotica is one of the "solar-powered sea slugs", utilizing solar energy via chloroplasts from its algal food. I was fascinated to know about it: http://phenomena.nationalgeographic.com/2013/11/19/solar-powered-slugs-are-not-solar-powered/

Corals and mosses thrive on symbiosis with chloroplasts of photosynthetic hosts but the energy requirement, ER, for moving a man can be apportioned by the daily content of an adequate diet, and if we add a car and or a truck to him the ER goes up of 4-5 factors of scale. Even walking or writing he consumes in a day the equivalent of the photosynthetic production of a surface equal to his skin area that works for about 90 days. Probably we can decrease this gap by increasing efficiency but the autotrophic man should have big wings and slow motion

http://www.ecochem.com/resource_transpiration.html

http://www.bbc.co.uk/schools/gcsebitesize/science/add_ocr_gateway/green_world/photosynthesisrev1.shtml