Cellular respiration is the chemical process that generates energy by breaking down food molecules when oxygen is present (Prentice Hall). The chemical equation of cellular respiration is 6O2 + C6H12O6 6CO2 + 6H2O + Energy, which means that the reactants of cellular respiration are oxygen and glucose while the products are carbon dioxide, water and energy (Gregory). Cellular respiration is fundamental to life because it provides all cellular processes with the energy needed to function. This process involves glycolysis, the Krebs cycle and the electron transport chain (Dr. Fankhauser). Glycolysis, which occurs in the cytosol of the cell, is the anaerobic catabolism of glucose that leads to the release of energy and the production of two molecules of pyruvic acid (Gregory). In this phase of cellular respiration, the cell contributes two molecules of adenosine triphosphate (ATP) as activation energy, but ends up with four molecules of ATP after glycolysis has taken place (Dr. Fankhauser). A glycolysis reaction extracts four high-energy electrons and transfers them to nicotinamide adenine dinucleotide (NAD+, an electron acceptor). After accepting a pair of high-energy electrons, NAD+ becomes NADH, an electron carrier, and holds the electrons until they can be transferred to different molecules. In this way, NAD+ can transfer energy from glucose to different points in the cell (Prentice Hall). The Krebs cycle, which occurs in the mitochondrial matrix of the cell, is the aerobic process in which pyruvic acid from glycolysis is used to produce carbon dioxide (CO2), NADH, ATP and flavin adenine dinucleotide (FADH2) (Gregory). In this cycle, pyruvic acid is broken down into CO2 into a series of energy-stealing residues... middle of paper... in both plants and animals, however, photosynthesis is only performed by plants. This is because animals are unable to produce their own food and must ingest it. The two processes occur in different parts of the cell; photosynthesis occurs in chloroplasts while cellular respiration occurs in mitochondria (Prentice Hall). Cellular respiration allows organisms to convert food into usable energy through glycolysis, the Krebs cycle, and the electron transport chain. The net production of ATP from a single glucose molecule through cellular respiration is 36 ATP molecules, with two ATP molecules from glycolysis, two ATP molecules from the Krebs cycle, and 32 ATP molecules from the electron transport chain. Since cellular respiration plays an important role in helping an organism function properly, an organism would die without this process (Dr. Fankhauser).