Which of the following best explains why red blood cells (RBCs) depend exclusively on glucose for ATP production?

• A. RBCs contain large stores of glycogen that are used for fatty acid synthesis, so they primarily convert glucose to lipids.
• B. RBCs can only use ketone bodies, but dietary glucose is needed to produce enzymes that allow ketone utilization.
• C. RBCs preferentially use proteins because their membranes block carbohydrate entry, requiring conversion of amino acids into ATP in specialized organelles.
• D. RBCs lack mitochondria, so they rely on anaerobic glycolysis which uses glucose as substrate and cannot oxidize fatty acids or ketones.

Answer: (D)