Advanced Placement (AP) Biology Practice Exam

What process generates ATP using a proton gradient in mitochondria?

1. Glycolysis

2. Krebs cycle

3. Electron transport chain

4. Mitochondrial chemiosmosis

The correct answer is: Mitochondrial chemiosmosis

The correct choice for the process that generates ATP using a proton gradient in mitochondria is mitochondrial chemiosmosis. This process occurs during oxidative phosphorylation, a part of cellular respiration, and relies on the establishment of a proton gradient across the inner mitochondrial membrane. Here's how it works: during the electron transport chain, electrons are transferred through a series of protein complexes. As electrons move through these complexes, they promote the pumping of protons (H⁺ ions) from the mitochondrial matrix to the intermembrane space, creating a proton gradient. This difference in proton concentration across the membrane leads to a potential energy difference known as the proton motive force. Mitochondrial chemiosmosis harnesses this energy when protons flow back into the mitochondrial matrix through ATP synthase, a protein complex. The flow of protons through ATP synthase catalyzes the phosphorylation of ADP to form ATP, which is the primary energy currency of the cell. While glycolysis and the Krebs cycle contribute to cellular respiration and generate some ATP directly, they do not utilize a proton gradient to produce ATP. The electron transport chain is a crucial component in establishing the gradient but is not itself the process that directly generates ATP. Therefore, mitochondrial chemiosmosis is the specific