CERTAIN CHEMICALS ARE FOUND IN BOTH PROCESSES
Look at the first molecules formed when glycolysis splits glucose in two. Compare them to the final direct products of photosynthesis (in the Calvin cycle). They are identical! That is, two molecules of glyceraldehyde-3-phosphate (G3P) are the initial products formed when glucose is split in glycolysis, and they also are the molecules that react to form glucose at the end of photosynthesis.

Note that glycolysis is catabolic (simpler substances are the result of the breakdown of complex molecules) and the Calvin cycle is anabolic (complex molecules are synthesized from simpler substances).

Other chemicals also are found in both aerobic respiration and photosynthesis. In fact, the reactants of aerobic respiration (glucose and O₂) are the products of photosynthesis! Similarly, the products of aerobic respiration (CO₂ and H₂O) are the reactants of photosynthesis!