College Biology Placement Practice Test 2026 - Free Biology Placement Practice Questions and Study Guide

The final stage of cellular respiration is the electron transport chain, which takes place in the inner mitochondrial membrane in eukaryotic cells. This stage is crucial because it is where the majority of ATP is generated during aerobic respiration.

During the electron transport chain, electrons derived from the NADH and FADH2 produced in earlier stages (glycolysis and the Krebs cycle) are passed through a series of protein complexes and electron carriers. As electrons move down the chain, they release energy, which is then used to pump protons (H+ ions) from the mitochondrial matrix into the intermembrane space, creating an electrochemical gradient.

This gradient is then utilized by ATP synthase, a protein complex, to facilitate the conversion of ADP and inorganic phosphate into ATP as protons flow back into the matrix. Additionally, at the end of the electron transport chain, electrons combine with molecular oxygen (the final electron acceptor) and protons to form water. This step is essential for maintaining the flow of electrons through the chain and for keeping the aerobic process running efficiently.

In summary, the electron transport chain is the final stage of cellular respiration, largely responsible for the production of ATP and the incorporation of oxygen, highlighting its pivotal role in energy