There are two processes by which cells secure the energy they need to conduct life processes. Plant cells undergo a process known as photosynthesis, which takes carbon dioxide from the atmosphere, water from the ground, uses energy, usually sunlight from the sun to produce glucose, which is used for the plant cells life processes. Oxygen is given off as a waste product in this process. Another process, used primarily by animal cells, is cellular respiration. In this process, the glucose mentioned as a product of photosynthesis, is taken by the animal cell and broken down by oxidizing it with oxygen. This releases energy, which is stored for use by the animal cell in the form of ATP. Carbon dioxide and water are two waste products produced by this process. Both these processes are described as "win-win" processes, because each one produces what the other one needs, in terms of reactants.