The monomers of starch and glycogen food molecules first enter aerobic respiration at which step?

• A. Oxidative phosphorylation
• B. Electron transport chain
• C. Citric acid cycle (Krebs cycle)
• D. Glycolysis

Answer: (D)

Verified step by step guidance

1. Understand that starch and glycogen are polysaccharides made up of glucose monomers. These glucose molecules are released during digestion and enter cellular respiration.
2. Recall the process of aerobic respiration, which consists of several steps: glycolysis, the citric acid cycle (Krebs cycle), and oxidative phosphorylation (including the electron transport chain).
3. Recognize that glycolysis is the first step in aerobic respiration, where glucose is broken down into two molecules of pyruvate. This occurs in the cytoplasm and does not require oxygen.
4. Note that after glycolysis, the pyruvate molecules produced can enter the mitochondria for further processing in the citric acid cycle, followed by oxidative phosphorylation.
5. Conclude that the monomers of starch and glycogen (glucose) first enter aerobic respiration at the glycolysis step, where glucose is metabolized to produce energy intermediates like ATP and NADH.