The ATP synthase can be thought of as a type of molecule motor that is powered by the flow of through the subunits and their concentration gradient.

The ATP synthase can be thought of as a type of molecule motor that is powered by the flow of __H+_ through the subunits and __down_ their concentration gradient.

Explanation:

There are two steps for the synthesis of carbohydrates in plants; one is light reaction and other is dark reaction. In light reaction the ATP and NADPH are produced from sunlight and these molecules are utilized for combining the carbon molecules in dark reaction.

Before we discuss chemiosmosis (Mechanism of ATP production) we should know that light reaction takes place in the thylakoid membrane of chloroplast. During the light reaction electrons removed from water are excited by light in photosystem I and photosystem II. These excited electron release the energy while traveling down the electron transport chain which is utilized to pump the H+ ions to stroma from lumen. This build a concentration difference of H+ ions across the membrane.

So when these H+ ions flow from stroma to lumen i.e. higher potential to lower potential they passes through ATP synthase complex. ATP synthase produces the ATP by the phosphorylation of ADP that why mechanism is also referred as Photophosphorylation.

1.protons

2.Down

Explanation:

The ATP Synthase is an enzyme which catalyses the phosphorylation ADP to ATP, for synthesis of ATPs in the matrix of mitochondria and stroma of chloroplast.

                  ADP  + Pi     →     ATPs.

                                 ATPsynthase.

The  source of energy  to power the ATP synthase is from the electrochemical gradient  set up by diffusion of  protons from the intramembrane layer of mitochondria and thylakoid membrane,down   into the matrix or  stroma where the ATPase synthase is located.

The  force for the proton pump  into the intramembrane is   known as the Proton Motive Force.(PMF).it is set up by the electrical mechanisms of electron transport chain. It constantly pumps protons into the intramembrane layers, therefore setting up the electrochemical gradient.

The proton is obtained from the splitting of hydrogen atoms,  carried  by the co-factors NADH+ and FADH2,from the Krebs cycle into the matrix or stroma, into protons and electron.

             H2→→→ H+  + e-.

This explains the ATP synthase activities  for ATP synthesis.

your answer is "the 1950's"