Which of the following statements regarding glucose is correct?

• A. Glucose is produced by the brain to fuel its activity.
• B. Glucose is not used during exercise.
• C. The brain uses only insulin to function.
• D. The brain requires glucose as much as it requires oxygen.

Answer: (D)

The brain runs on glucose and oxygen, and both are required continuously for its metabolism. It has a high energy demand, relies on glucose delivered by the bloodstream (the brain stores very little glucose itself), and uses transport mechanisms that do not depend on insulin to take up glucose. Because cellular respiration in brain cells needs oxygen to burn glucose, the brain’s need for glucose parallels its need for oxygen: without either, brain function declines rapidly. That’s why glucose is as essential to the brain as oxygen, making this statement the best choice.