Cell respiration
Cellular respiration is the process by which cells release energy from glucose (food) and convert it into usable energy called ATP. It mainly happens in the cytoplasm and mitochondria. First, glycolysis takes place in the cytoplasm, where one glucose molecule is split into two pyruvate molecules and a small amount of ATP is produced. The pyruvate then enters the mitochondria and goes through the Krebs cycle, where it is broken down further, releasing carbon dioxide and producing energy-carrying molecules. These molecules then move to the electron transport chain, where their energy is used to produce a large amount of ATP. Oxygen acts as the final electron acceptor and helps form water. Therefore, the overall process can be remembered as glucose + oxygen → ATP + carbon dioxide + water. Cellular respiration provides the energy cells need for activities such as growth, movement, repair, transport, and other life processes.