an octahedron: basically two square based pyramids with their bases stuck together.
Most eukaryotic cells have mitochondria, which produce ATP from products of the citric acid cycle, fatty acid oxidation, and amino acid oxidation. At the mitochondrial inner membrane, electrons from NADH and succinate pass through the electron transport chain to oxygen, which is reduced to water.
Article Summary: The electron transport chain is the most complex and productive pathway of cellular respiration. Here's a straightforward, simplified explanation of how the ETC works. The Basics of the Electron Transport Chain.