Which organ is described by the following statements?
I. It is classified as a secondary lymphoid organ.
II. It primarily consists of lymphocytes and phagocytes.
III. It functions as a filter for blood, capturing microorganisms present in the bloodstream.
IV. It serves as a significant storage site for red blood cells.
V. This organ is shaped like a large bean.
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → Spleen
All five clues fit the spleen. It is a secondary lymphoid organ and a large bean-shaped organ. It mainly contains lymphocytes and phagocytes, it filters the blood by trapping blood-borne micro-organisms, and it holds a large reservoir of erythrocytes (red blood cells).
Option (1) Tonsils — Incorrect. Tonsils are secondary lymphoid organs, but they do not filter the blood or store red blood cells.
Option (2) Thymus — Incorrect. The thymus is a primary lymphoid organ, a lobed organ near the heart where T-lymphocytes mature. It is not bean-shaped and does not filter blood.
Option (3) Spleen — Correct. The spleen matches every statement: secondary lymphoid organ, lymphocytes and phagocytes, blood filter, reservoir of erythrocytes and bean shape.
Option (4) Bone marrow — Incorrect. Bone marrow is a primary lymphoid organ, where all blood cells including lymphocytes are produced.
NCERT Extract:
Immune System in the Body – “… After maturation the lymphocytes migrate to secondary lymphoid organs like spleen, lymph nodes, tonsils, Peyer’s patches of small intestine and appendix.”
Immune System in the Body – “… 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.”