To release the energy in glucose, plants and other organisms use a process called cellular respiration. Glucose molecules are first broken into pyruvic acid. This breakdown releases energy used to produce two types of molecules, called ATP and NADH. In the presence of oxygen, pyruvic acids can be further broken down to produce CO2, water, and energy to form more ATP. ATP is a carrier of energy, which can be used to do work in the cell. Carbon dioxide is the waste product of cellular respiration.