Photosynthesis- a missing product

[NghiaFromVN]

As far as I am concerned, photosynthesis does produce h2o

But after studying both light and dark reaction, I didn't find out any water molecule produced

Can you help me point out which reaction does that

Edited September 15, 2016 by NghiaFromVN

[BabcockHall]

I may not be following you. Photosynthesis uses water as a reactant and produces molecular oxygen. I have not looked carefully at the carbon assimilation reactions with respect to whether they are water-producing or water-consuming.

[NghiaFromVN]

I edited my post. Each co2 fixed reqUIRE 2 NADPH so 6 need 12, which mean 12 pairs of electron or 12 water molecules. That is easy to understand, but where does that water product come from ?

[Strange]

Where does you final 6H₂O come from? From the extra 6H₂O you start with!

 

This page has the overall reaction as 6CO₂ + 6H₂O -> C₆H₁₂O₆ + 6O₂.

https://en.wikipedia.org/wiki/Photosynthesis

 

It then goes on to explain all the intermediate reactions.

[EdEarl]

Why not subtract the 6H₂O from both sides?

[Strange]

Why not subtract the 6H₂O from both sides?

 

 

Exactly.

[NghiaFromVN]

No, 6co2 will require 12 pairs of electron to enter the Calvin cycle, so you cannot subtract 6 h20, so where do those molecules come from ?

12 pairs of electron means 12 water molecules

[Strange]

You seem to be confusing the overall reaction (in which there are 6 H₂O on the left and none on the right) with the intermediate stages, where more water molecules may be involved.

 

For example, this shows that 6CO₂ will produce 6H₂O: https://en.wikipedia.org/wiki/Photosynthesis#Calvin_cycle

[BabcockHall]

I am going to suggest this bookkeeping as a simple way to make the electrons add up. Six carbon atoms gain a total of 24 electrons. The twelve oxygen atoms in six molecules of carbon dioxide can lose 24 electrons (each one changes from an oxidation number of -2 to 0). Six water molecules are needed to hydrate the six carbon atoms, in order to produce a carbohydrate. This way of thinking about photosynthesis is not intended to be mechanistically accurate; it is only intended to describe the stoichiometry.