Photosynthesis is the process by which photoautotrophs (organisms such as plants which are capable of making their own organic molecules) manufacture glucose. Photoautotrophs start out with water and carbon dioxide to produce glucose and oxygen. Photosynthesis occurs in two phases: 1) the light dependent stage, and 2) the light independent stage. During the light reactions, light energy splits water molecules into hydrogen atoms and oxygen atoms. The hydrogen atoms combines with a chemical called nicotinamide-adenine dinucleotide phosphate (NADP) to form NADPH2 (which the specification like to refer to as reduced NADP), this is used later in the light independent reactions. The oxygen atoms bind to each other and molecular oxygen (O2) is released into the atmosphere. Also, the light energy is used to produce the energy molecule called adenine triphosphate (ATP), which is also used in the light independent reactions. So, the main products of the light reaction are NADPH2, ATP, and O2. During the light independent reactions, enzymes use the energy from NADPH2 and ATP (formed in the light reaction) to convert carbon dioxide (CO2), obtained from the atmosphere, into glucose. The glucose can be stored for future use by the plant. The light independent reactions are also called the "Calvin Cycle," after the scientist who first described it. Cellular respiration is the process by which organisms break down glucose for energy. The big picture is that cells use glucose and oxygen to form carbon dioxide, water, and ATP (the energy molecule). There are two forms of cellular respiration: 1) aerobic (using oxygen) and 2) anaerobic (not using oxygen). In aerobic respiration, 1 molecule of glucose undergoes three processes called 1) glycolysis, 2)The conversion of Pyruvate to Acetly CoA, 3) the Krebs cycle, and 4) the electron transport chain. Oxygen is needed at the end of the processes to "pull" electrons through. The energy stored in the glucose is used to produce 36 molecules of ATP. ATP can then be used by cells for energy. Anaerobic respiration only involves glycolysis, which does not need oxygen. However, only 2 ATP are formed. This is only a very broad picture of photosynthesis and respiration. The things to remember are that photosynthesis uses carbon dioxide, water, and light to make glucose and oxygen, while respiration uses glucose and oxygen to make carbon dioxide, water, and ATP.