What is the pH of the mitochondrial intermembrane space during active electron transport?

During active electron transport, protons (H⁺ ions) are pumped from the mitochondrial matrix into the intermembrane space. This process occurs as electrons are transferred through the electron transport chain, which is located in the inner mitochondrial membrane. The movement of protons into the intermembrane space creates a concentration gradient, leading to an increase in the concentration of protons in that space.

As a result of this proton accumulation, the pH of the intermembrane space becomes more acidic compared to the matrix, where the proton concentration is lower. This difference in pH is critical for the functioning of ATP synthase, which utilizes the proton motive force generated by this gradient to produce ATP as protons flow back into the matrix.

Understanding that the electron transport chain actively transports protons helps clarify why the intermembrane space becomes more acidic. In contrast, other choices do not accurately reflect the biochemical processes occurring during this phase of cellular respiration.