Final answer:
Red blood cells carry oxygen, white blood cells defend the body, and platelets assist in blood clotting.
Step-by-step explanation:
Red blood cells, or erythrocytes, are responsible for carrying oxygen throughout the body. They lack nuclei and contain hemoglobin, a protein that binds to oxygen and transports it to tissues. White blood cells, or leukocytes, are involved in the immune response and protect the body from pathogens and foreign substances. They have nuclei and lack hemoglobin. Platelets are cell fragments that play a role in blood clotting.