Question

which statement best describes the matter and energy conversions that take place in the electron transport chain?
a. energy from atp is used to convert hydrogen to hydrogen ions and electrons.
b. *energy from electrons is used to release hydrogen ions and cause them to flow.
c. energy from nadh is used to add electrons and hydrogen ions to fad molecules.
d. energy from water molecules is released as water is broken down into oxygen and hydrogen.

Explanation:

In the electron - transport chain, electrons are passed through a series of electron carriers. As electrons move, energy is released which is used to pump hydrogen ions across a membrane, creating a proton gradient. This gradient drives the flow of hydrogen ions. Option A is incorrect as it is the opposite of what happens (ATP is produced, not used to split hydrogen). Option C is incorrect as the main process is not about adding electrons and hydrogen ions to FAD from NADH in terms of the overall energy - conversion driving force. Option D describes a process related to photosynthesis (water - splitting) rather than the electron - transport chain in cellular respiration.

Answer:

B. Energy from electrons is used to release hydrogen ions and cause them to flow.