The _________ nervous system and __________ cells are dependent on carbohydrates for fuel.

The central nervous system and red blood cells are dependent on carbohydrates for fuel.

Explanation:

Carbohydrates are a primary source of energy for the body, especially for the central nervous system (CNS). The CNS, which includes the brain and spinal cord, requires glucose—a simple sugar derived from carbohydrates—to function optimally. Glucose is vital because the brain consumes roughly 20% of the body's total energy expenditure and relies almost exclusively on glucose for its energy needs under normal circumstances.

Similarly, red blood cells (RBCs) primarily utilize glucose as their energy source since they lack mitochondria, the organelles responsible for aerobic respiration. Instead, they metabolize glucose through glycolysis to produce ATP (adenosine triphosphate), which is essential for transporting oxygen throughout the body.

Thus, both the central nervous system and red blood cells have a significant reliance on carbohydrates for energy, making them crucial for metabolic functions and overall bodily health.