Spinach chloroplasts are illuminated in the absence of ADP and Pᵢ,then the light is turned off and ADP and Pᵢ are added.ATP is then synthesized for a short time in the dark.Which of the following best explains this?
A)ATP is generated from the electron gradient accumulated in the light reactions.
B)ATP synthesis stops after the proton gradient dissipates.
C)ATP can be generated in the dark reactions if it becomes necessary for the plant to survive.
D)ATP synthesis can occur in the absence of light and electrons.

Question

Quizplus · Accepted Answer

The synthesis of ATP in chloroplasts is linked to the proton gradient generated during the light reactions. When the light is turned off, the proton gradient dissipates, and ATP synthesis stops. The addition of ADP and Pᵢ provides the necessary substrates for ATP synthesis to resume for a short time. Therefore, choice B is the correct explanation. Choice A is incorrect because while the electron gradient is necessary for generating the proton gradient, it is not directly involved in ATP synthesis. Choice C is incorrect because ATP synthesis in the dark reactions does not occur in plants. Choice D is incorrect because ATP synthesis requires energy and coupling with the proton gradient, which is generated by the light reactions.

Spinach Chloroplasts Are Illuminated in the Absence of ADP and Pᵢ,then