What molecule is common to both c3 photosynthesis and the process of glycolysis?

The answer is G3P.(glyceraldehyde 3-phosphate). Photosynthesis is the process by which green plants utilize energy from the sun to make their own food. The process involves two stages; light dependent stage and light independent stage (Calvin cycle).The Calvin cycle uses 3PGA to produce a three carbon sugar G3P which is the converted to hexoses (6C), glucose. In glycolysis glucose from photosynthesis is converted to pyruvate. One glucose molecule yields 2 G3P in the first phase and in the second phase of glycolysis the G3P  yields 2 ATP molecules to form pyruvic acid. G3P acts as an intermediate between many biological pathways.