In human physiology, what is the primary function of erythrocytes (red blood cells)?

• A. Produce antibodies to neutralize pathogens in the bloodstream
• B. Transport oxygen from the lungs to body tissues and help carry carbon dioxide back to the lungs
• C. Initiate blood clotting by forming a platelet plug at sites of vessel injury
• D. Provide immune defense by phagocytosing bacteria and presenting antigens

Answer: (B)

Verified step by step guidance

1. Step 1: Understand the role of erythrocytes by recalling their main structural features, such as the presence of hemoglobin, which is a protein specialized in binding gases.
2. Step 2: Recognize that erythrocytes lack nuclei and organelles, which limits their functions primarily to gas transport rather than immune responses or clotting.
3. Step 3: Identify that hemoglobin within erythrocytes binds oxygen in the lungs and releases it in body tissues, facilitating oxygen delivery throughout the body.
4. Step 4: Note that erythrocytes also assist in transporting carbon dioxide, a waste product of metabolism, from tissues back to the lungs for exhalation.
5. Step 5: Differentiate erythrocytes from other blood cells such as leukocytes (immune defense) and platelets (blood clotting), confirming that their primary function is gas transport.