Which one of the following has a large reservoir of erythrocytes?

The correct answer is Option (2) → Spleen

Option (1) Liver — Incorrect. The liver is a gland; it is not the store of red blood cells.

Option (2) Spleen — Correct. The spleen is a large bean-shaped secondary lymphoid organ. It contains mainly lymphocytes and phagocytes and acts as a filter of the blood; it also has a large reservoir of erythrocytes.

Option (3) Heart — Incorrect. The heart pumps blood; it does not store it.

Option (4) Bone marrow — Incorrect. Bone marrow makes blood cells; it is not their reservoir.

NCERT Extract:
Immune System in the Body – “… The thymus is quite large at the time of birth but keeps reducing in size with age and by the time puberty is attained it reduces to a very small size. Both bone-marrow and thymus provide micro-environments for the development and maturation of T-lymphocytes. The spleen is a large bean-shaped organ. It mainly contains lymphocytes and phagocytes. It acts as a filter of the blood by trapping blood-borne microorganisms. Spleen also has a large reservoir of erythrocytes.”