Question

In chloroplasts, ATP is synthesized from ADP plus inorganic phosphate (P) in a reaction catalyzed by ATP synthase molecules that are embedded in the thylakoid membrane. Which of the following statements provides evidence to support the claim that no ATP will be synthesized in the absence of a proton gradient across the thylakoid membrane?
A. Blocking electron flow from one carrier to the next in the electron transport chains blocks formation of a proton gradient in the thylakoid.
B. Increasing the proton concentration difference across the thylakoid membrane is not associated with a parallel increase in the rate of ATP synthesis.
C. No ATP is synthesized when channel proteins that allow the free passage of protons are inserted into the thylakoid membrane.
D. No ATP is synthesized while the Calvin cycle is synthesizing carbohydrates and using ATP and NADPH at a high rate.

Answer 1

Answer:A. Blocking electron flow from one carrier to the next in the electron transport chains blocks formation of a proton gradient in the thylakoid.

Explanation:

This is because the movement of electrons from higher energy protein carrier to lower energy protein carriers in the intramembrane of thylakoids produced energy. This is the quantity of energy needed to pump protons/ hydrogen ions from the stroma, through the intramembrane of the thylakoid membrane to the Cytosols.  

Continuous pumping of the protons across, produced proton chain.

Accumulation of hydrogen ions in the cytosols surrounding the outer double membrane of the chloroplast generated higher concentration gradient   of hydrogen ions compare to lower concentration in the stroma. This concentration gradients drives down  hydrogen ions/protons   along the proton channels through the ATPase synthase into the stroma. ATPase synthase is a protein that tap and transfer energy generated from moving hydrogen ions for  ATP synthesis .

Adenosine Diphosphate + Phosphate ions      ―ENERGY―>     ATP.

                                                             

If the flow of electron (electron transport chain) is stopped. The proton pump will cease because of lack of energy. Therefore, no concentration gradients to drive protons through the ion channels to generate energy for phosphorylation of ADP with inorganic phosphate (Pi)) to form ATP. Therefore the correct answer is A.

                                                                                                                                                           

Answer 2

Answer:

C. No ATP is synthesized when channel proteins that allow the free passage of protons are inserted into the thylakoid membrane.

Explanation:

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