What organ is responsible for filtering blood and acting as a reservoir?

The spleen is responsible for filtering blood and acting as a reservoir, which makes it the correct choice. It plays a crucial role in the immune system by filtering out old or damaged red blood cells and platelets from circulation. Additionally, the spleen acts as a blood reservoir, holding a supply of blood that can be released into circulation in times of need, such as during intense physical activity or blood loss.

The other options serve different functions: the liver is primarily involved in metabolic processes, detoxification, and the production of bile; the kidneys filter waste products from the blood to form urine but do not act as a reservoir; the gallbladder stores bile produced by the liver but is not directly involved in filtering blood. Understanding the distinct roles of these organs helps clarify why the spleen is recognized as the organ with both filtering and reservoir capabilities.