Final answer:
The right atrium receives oxygen-poor blood from the body and pumps it to the right ventricle, while the left atrium receives oxygen-rich blood from the lungs and pumps it to the left ventricle.
Step-by-step explanation:
The right and left atrium are two of the four chambers of the heart. The right atrium receives oxygen-poor blood from the body and pumps it to the right ventricle, which then pumps it to the lungs to receive oxygen. On the other hand, the left atrium receives oxygen-rich blood from the lungs and pumps it to the left ventricle, which then pumps it out to the rest of the body.