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.
This electron transport chain in cellular respiration will take the energy stored in NADH and FADH2 during the Krebs cycle and convert it to chemical bond energy in the form of ATP. In eukaryotes, this reaction takes place on the inner mitochondrial membrane, as is shown in Figure 4.26.