Photosynthesis and cellular respiration are said to form a continuous cycle because... the products of one process are the starting materials for the other. ... When water molecules are split to produce the electrons needed to replace those lost by photosystem II during photosynthesis, ... hydrogen is produced.
The process of photosynthesis is commonly written as: 6CO2 + 6H2O → C6H12O6 + 6O2. This means that the reactants, six carbon dioxide molecules and six water molecules, are converted by light energy captured by chlorophyll (implied by the arrow) into a sugar molecule and six oxygen molecules, the products.
