Question

what are the two principal functions of erythrocytes?
multiple choice
to pick up nitrogen from the tissues and unload it in the lungs
to pick up oxygen from the lungs and deliver it to tissues
to pick up carbon dioxide from the tissues and unload it in the lungs
to pick up nitrogen from the tissues and unload it in the lungs and to pick up oxygen from the lungs and deliver it to tissues
to pick up oxygen from the lungs and deliver it to tissues and to pick up carbon dioxide from the tissues and unload it in the lungs

Explanation:

Erythrocytes (red blood cells) contain hemoglobin. Hemoglobin binds to oxygen in the lungs (where oxygen concentration is high) and releases oxygen in the tissues (where oxygen concentration is relatively low). Also, hemoglobin can bind to carbon dioxide in the tissues (where carbon dioxide is produced as a metabolic waste) and release it in the lungs (where carbon dioxide is exhaled). Nitrogen is not a gas that erythrocytes are primarily involved in transporting in this context.

Answer:

To pick up oxygen from the lungs and deliver it to tissues and to pick up carbon dioxide from the tissues and unload it in the lungs.