Towards the end of erythropoiesis in the bone marrow, a red blood cell loses its nucleus and becomes a

Correct Answer: D

Rationale: Reticulocytes (D) are immature RBCs post-nucleus loss, entering circulation. Proerythroblasts (A) are early, megakaryocytes (B) form platelets, progenitors (C) are stem cells.

Correct Answer: B

Rationale: Blood volume/kg decreases with higher body fat (B), as fat is less vascularized.

Correct Answer: A

Rationale: Thrombocytes (platelets, A) initiate clotting.

Correct Answer: C

Rationale: Hemoglobin yields amino acids (A), bilirubin (B), and iron (D); oxygen (C) is released, not a product.

Correct Answer: C

Rationale: Lymphocytes (C), especially B cells, produce antibodies.