AP BIOLOGY

Detailed explanation-1: -During electron transport, energy is used to pump hydrogen ions across the mitochondrial inner membrane, from the matrix into the intermembrane space. A chemiosmotic gradient causes hy drogen ions to flow back across the mitochondrial membrane into the matrix, through ATP synthase, producing ATP.

Detailed explanation-2: -The electrons flow through the electron transport chain, causing protons to be pumped from the matrix to the intermembrane space.

Detailed explanation-3: -Complex I can pump four hydrogen ions across the membrane from the matrix into the intermembrane space, and it is in this way that the hydrogen ion gradient is established and maintained between the two compartments separated by the inner mitochondrial membrane.

Detailed explanation-4: -During the reduction of oxygen, two H+ ions are extracted from the matrix and transferred to the reduced oxygen atom, thus forming water (H2O). Simultaneously, the complex pumps 4 H+ ions into the intermembrane space.

Detailed explanation-5: -When hydrogen ions are pumped from the mitochondrial matrix across the inner membrane and into the intermembrane space, the result is the creation of proton-motive force (d is correct). The proton-motive force describes the force created by the tendency of hydrogen ions to move down their concentration gradient.