Protons (H+) accumulate in the thylakoid space during electron transport between photosystems I and II.?

Question

The excess of protons in the thylakoid space

A enters the photorespiration pathway

B converts NADP to NADPH and generates ATP in the process

C The cyclic sysstem is used when there is insufficient NADP+ present to absorb electrons in plant cells

D More carbohydrate is produced during cyclic photophosphorylation then during noncyclie photophosphorylation

Answer 1

i think its a....

Answer 2

Not B The conversion NADP to NADPH is not caused by a proton gradient, it is simply caused by NADP+ reductase. The electron transport chain that follows photosystem I creates a proton gradient, but it isn't used to catalyze the reaction: 2NADP+ + 2H+ + 4e- --> 2NADPH According to the textbooks I'm looking at NADP+ reductase doesn't need a proton gradient to catalyze the reaction.  

The protons are used when NADP+ is converted to NADPH but the protons don't cause the converstion of NADP+ to NADPH. Also not that much ATP is produced in the process, because when NADP+ is reduced the electrons are given away still high in energy; so not the large of a proton gradient is established.

Not C The cyclic system is used when there is insufficient ATP for sugar production.

Not D No carbohydrates are produced during cyclic photophosphorylation because no NADPH is produced.

Lets look at A. The excess protons are used to create a chemical gradient. ATP synthase uses the proton gradient to phosphorylate ADP into ATP. Since the ATP uses electrons that are excited by light its called photorespiration.

In my opinion the answer is A.

Answer 3

It's B.  Plants get electrons from water (H2O).  Light (photon energy) excites electrons making it move around.  The electrons get passed down along the e- carriers like cytochrome b6f all the way to Photosystem I.  The electron combines with H+ to form a hydrogen atom once again, which combines with NADP+ altogether to form NADPH.  This happens in the cholorplast stroma.  On the other side, the thylakoid lumen has excess H+ from the breakdown of water (H2O) to molecular oxygen (O2).  H+ from plastoquinone is also pumped across the membrane (against concentration gradient ) from the stroma side to the thylokoid lumen side.  All the excess H+ accumulating in the thylokoid lumen naturally go back down its concentration gradient to power the ATP synthase and catalyze the reaction of ADP+ Pi ---> ATP

So, the end products of the light reaction component of photosynthesis are NADPH and ATP (O2 is a waste product released into the atmosphere).  NADPH and ATP are used in the dark reaction (light independent) of photosynthesis to make glucose from CO2 and ribulose 1,5 bisphosphate.

I hope that helps you understand the big picture of photosynthesis.