In order for energy to be able to be created, ATP(adenosine triphosphate) needs to form in either photosynthesis or krebs cycle from ADP + P(from NADPH). When ATP is available, huge amounts of energy are released when needed by slicing one P atom from ATP So that it can again become ADP and undergo lots of processes to become ATP again. So energy is added from tearing of Phosphate Atom due to tearing of phosphoanhydride bonds. This is possible because of process known as hydrolysis, when ATP is in equilibrium with water and some electrons. And the process of ADP becoming ATP is recharging and occurs in mitochondria.
The processes are hydrolysis and rechargeation, but most important process is Krebs Cycle, where all of this happens.
The products of one process are the reactants of the other. Notice that the equation for cellular respiration is the direct opposite of photosynthesis: Cellular Respiration: C6H12O6 + 6O2 → 6CO2 + 6H2O. Photosynthesis: 6CO2 + 6H2O → C6H12O6+ 6O.
