Which of the following steps in cellular respiration is associated with release of maximum number of ATP molecules? A Glycolysis B Kreb’s cycle C Oxidative phosphorylation D Reduction of NADP

The correct answer is:

C. Oxidative phosphorylation

Explanation:

• Oxidative phosphorylation is the step in cellular respiration that produces the largest number of ATP molecules. This process occurs in the inner mitochondrial membrane and involves the electron transport chain (ETC) and ATP synthase. The proton gradient generated by the ETC drives the production of ATP, yielding approximately 28–34 ATP molecules per glucose molecule.
• Glycolysis produces a net gain of 2 ATP molecules.
• Krebs cycle (citric acid cycle) directly produces 2 ATP molecules per glucose molecule. However, it also generates NADH and FADH2_22​, which contribute electrons to the ETC for ATP synthesis.
• Reduction of NADP occurs in photosynthesis, not cellular respiration.