Question

In chloroplasts, ATP is synthesized from ADP plus inorganic phosphate (Pi) 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?

1) The ATP synthase molecules require a proton gradient to function.
2) The thylakoid membrane is impermeable to protons.
3) The reaction requires the presence of light.
4) The chloroplasts lack the necessary enzymes for ATP synthesis.

Answer 1

The evidence supporting the claim that no ATP will be synthesized without a proton gradient is that ATP synthase requires this gradient to function. ATP synthesis is driven by chemiosmosis, which relies on the energy from protons moving across the thylakoid membrane.

Step-by-step explanation:

The statement that provides evidence to support the claim that no ATP will be synthesized in the absence of a proton gradient across the thylakoid membrane is: The ATP synthase molecules require a proton gradient to function. This is because ATP synthase uses the energy from the exergonic movement of hydrogen ions (protons) moving from high to low concentration across the thylakoid membrane, a process known as chemiosmosis, to facilitate the attachment of a third phosphate group to ADP, forming ATP. Without the proton gradient, there is no potential energy to drive the synthesis of ATP. The other statements provided do not directly support the claim regarding the synthesis of ATP in relation to the proton gradient.