Final answer:
The spleen stores red blood cells in its red pulp by removing damaged red blood cells and replacing them with new ones.
Step-by-step explanation:
The spleen is able to store red blood cells because it contains an area called the red pulp which consists of cavities that store blood. Within the red pulp, damaged red blood cells are removed and replaced by new ones. The spleen acts as a filtration system for the blood, removing damaged red blood cells and helping to maintain a healthy population of red blood cells in the body.