[patfada]

I have read that photosynthesis does not break the carbon oxygen bond in carbon doxide but incorporates the CO2 into carbohydrates, and that it takes a lot of energy to split CO2 into its constituent elements. Fossil fuels are composed of hydrocarbons in which the carbon is bonded to hydrogen not oxygen, so somewhere along the line something has done the work to break the carbon oxygen bond. Does this happen as part of the process of fossilisation - e.g as a result of high pressure and temperature? Or is it the result of a biological process?


Thanks

Pat

[AWK]

I have read that photosynthesis does not break the carbon oxygen bond in carbon doxide but incorporates the CO2 into carbohydrates

not true
Assimilation of carbon dioxide is possible by breaking one bond in this molecule.

Fossil fuels

This is a big problem of organic geochemistry - there are many monographs on this subject. A good start can be encyclopedic entries regarding The Carboniferous Era (the period in earth history)

[Borek]

Does this happen as part of the process of fossilisation

Generally speaking - yes, dehydration of carbohydrates is part of the fossilization (this is not entirely equivalent to just the breaking of the C-O bond). As AWK signalled, details can be quite complicated.

[wsohcontest1]

I guess this article may help you with it:


https://www.sciencedirect.com/topics/earth-and-planetary-sciences/organic-carbon

[Enthalpy]

Triglycerides (fats) contain mainly C-H bonds and little oxygen. Without fossilisation, plants (palm, maize, peacock, sunflower... and many more) produce them, and animals too (we build up grease for storage from nearly any excess food). Bees make wax, which comprises mainly monoesters, diesters, hydrocarbons, fatty acids.

More generally, life can and does make molecules that are very energetic. That's not a limit.

[Babcock_Hall]

The first reaction in the Calvin cycle fixes carbon dioxide using a derivative of a carbohydrate (the oxygen atoms of carbon dioxide are still present at this point).  The product of the first reaction are more oxidized than carbohydrates are (the average oxidation number of the carbon atoms in a carbohydrate is zero).  Therefore, the text steps of photosynthesis reduce the product of the first reaction back to the same oxidation state as carbohydrates.