During the electron transport chain of the light reactions in photosynthesis, which of the following occurs?

• A. Glucose is synthesized directly from carbon dioxide and water.
• B. Electrons move through protein complexes, leading to the formation of a proton gradient across the thylakoid membrane.
• C. Oxygen is consumed as the final electron acceptor.
• D. ATP is broken down to provide energy for the Calvin cycle.

Answer: (B)

Verified step by step guidance

1. Understand the context: The electron transport chain in photosynthesis occurs during the light reactions, which are part of the process plants use to convert light energy into chemical energy. This chain is located in the thylakoid membrane of chloroplasts.
2. Identify the key process: Electrons are excited by light energy in photosystem II and passed through a series of protein complexes, including the cytochrome b6f complex, photosystem I, and associated carriers. This movement of electrons is coupled with the pumping of protons (H⁺ ions) across the thylakoid membrane, creating a proton gradient.
3. Clarify the role of the proton gradient: The proton gradient is essential for ATP synthesis. Protons flow back into the stroma through ATP synthase, a protein complex that uses this flow to convert ADP and inorganic phosphate (Pi) into ATP via chemiosmosis.
4. Eliminate incorrect options: Glucose synthesis does not occur during the light reactions; it happens during the Calvin cycle. Oxygen is not consumed but rather produced as a byproduct when water is split to provide electrons. ATP is synthesized, not broken down, during the light reactions to provide energy for the Calvin cycle.
5. Conclude the correct answer: The correct process during the electron transport chain of the light reactions is the movement of electrons through protein complexes, leading to the formation of a proton gradient across the thylakoid membrane.