Which metabolic pathway converts glucose to pyruvate?

• A. Glycolysis
• B. Cellular respiration
• C. Fermentation
• D. Photosynthesis

Answer: (A)

Converting glucose to pyruvate is carried out by glycolysis, a sequence of enzymatic steps that occurs in the cytosol. In glycolysis, a glucose molecule is split and rearranged to form two molecules of pyruvate, yielding a modest ATP payoff and NADH. Specifically, there’s an upfront investment of energy followed by energy generation, giving a net gain of two ATP and two NADH per glucose. This pathway does not require oxygen, so it functions under both aerobic and anaerobic conditions and feeds the pyruvate produced for further energy extraction or fermentation, depending on oxygen availability. Cellular respiration refers to the entire energy-harvesting process from glucose, including glycolysis plus mitochondrial steps. Fermentation uses the pyruvate produced after glycolysis to regenerate NAD+ in the absence of oxygen, not to convert glucose directly to pyruvate. Photosynthesis builds glucose from CO2 and water using light, not converting glucose into pyruvate.