The correct answer is option 4, the spleen. The spleen plays a crucial role in filtering and removing old and worn-out red blood cells from the bloodstream. It acts as a recycling center for these cells. When red blood cells become old or damaged, they lose their flexibility and become less efficient at carrying oxygen. The spleen recognizes these cells and removes them from circulation. Once inside the spleen, these old red blood cells are broken down and their components, including iron, are recycled. The spleen also helps to remove any abnormal or damaged red blood cells that may be present. Therefore, the spleen is responsible for the destruction of red blood cells that are no longer functioning properly.