Respiration is defined as the burning of food molecules to release energy in the form of ATP or ADP. There are two types of respiration - aerobic respiration, which uses oxygen and produces more energy, and anaerobic respiration, which does not use oxygen and produces less energy. Respiration occurs in plants through their roots, stems, and leaves, and in animals through specialized respiratory systems like lungs. The respiratory system in humans includes the nostrils, nasal cavity, pharynx, larynx, trachea, bronchi, and lungs.