Which organ is involved in immune functions and filters old blood?

• A. Spleen
• B. Stomach and intestines
• C. Lungs
• D. Pancreas

Answer: (A)

Think about an organ that both supports immune defense and cleans up circulating blood. The spleen fits this role: its white pulp houses immune cells that respond to blood-borne threats, while the red pulp filters the bloodstream, trapping old or damaged red blood cells and recycling their components. The other options don’t combine these functions: the stomach and intestines digest food, the lungs handle gas exchange and air filtration, and the pancreas produces digestive enzymes and hormones. So, the organ involved in immune functions and filtering old blood is the spleen.