Final answer:
The true statement about mitochondrial chemiosmosis is that a proton gradient is established across the inner membrane of the mitochondrion, which is essential for ATP synthesis through oxidative phosphorylation. So the correct answer is Option D.
Step-by-step explanation:
The statement that is true about mitochondrial chemiosmosis is 'D. A proton gradient is established across the inner membrane of the mitochondrion.' Chemiosmosis is the movement of hydrogen ions across a mitochondrial membrane, specifically from the intermembrane space into the matrix of the mitochondria. The process utilizes the electron transport chain to pump protons into the intermembrane space, establishing a concentration and electric gradient due to the hydrogen ions' positive charge and their aggregation on one side of the membrane. This electrochemical gradient then drives the protons back across the membrane through the ATP synthase, which generates ATP by adding inorganic phosphate to ADP, a process known as oxidative phosphorylation.
Therefore, it's not true that protons move up a concentration gradient (A), ADP is generated (B), or heat energy is required to establish the electron transport chain (C). These are misunderstandings of the process. The correct understanding is that the electron transport chain uses the energy from high-energy electrons to create a proton gradient that is later used to produce ATP.