Question

Please explain this "For every four electrons (from 2 H2O) transferred in the light reactions, twelve protons are added to the H+ reservoir in the thylakoid lumen, resulting in the production of three molecules of ATP.

Answer 1

OK.

As high energy electrons are passed along the electron transport chains, their energy is used to pump protons across the thylakoid membrane into the lumen. That creates a concentration gradient. Essentially, it converts the energy in the electrons to potential energy in the concentration gradient.

As those protons - the H+ molecules - diffuse back down that concentration gradient, they pass through protein complexes which are kind of like water wheels: as protons pass through them, they add a phosphate to ADP to make ATP.

That way the potential energy stored in the concentration gradient is restored as chemical energy in the high energy bond in ATP.

Clear, blue?

Answer 2

Yes, i get this part
but i dont get the math part
1H2O = 2 electrons + 2H+ + 1/2 O2
so 2 H2O should only have 4H+ , why does the book says 12 protons?

Answer 3

Because the protons which are pumped across the membrane do not come from the electron donating water molecules.

Answer 4

ohh, so some are from the stroma going to the lumen, and some are from the water molecule?
and each 4 H+ will generate 1 ATP through the ATP synthase?

Answer 5

Yes, exactly!

Answer 6

thanks blues, sorry but i have one more question
do you know how many ATP and NADPH are generated in 1 non cyclic flow?

Answer 7

You're welcome, but not off the top of my head, I don't actually.

Answer 8

oh ok then :)