Which of the following organs is NOT part of the digestive system?

• A. Liver
• B. Stomach
• C. Small intestine
• D. Kidney

Answer: (D)

The main idea is understanding which organ is not involved in breaking down or absorbing food. The digestive system includes the mouth, esophagus, stomach, small and large intestines, and accessory organs like the liver, pancreas, and gallbladder that contribute enzymes and bile to aid digestion. The liver, stomach, and small intestine all participate directly in digestion—stomach acid and enzymes break down food, the small intestine absorbs most nutrients, and the liver makes bile to help digest fats. The kidney, on the other hand, is part of the urinary system and its primary roles are filtering the blood, balancing fluids and electrolytes, and forming urine, not digesting food or absorbing nutrients. So the kidney is not part of the digestive system.