Which of the following statements about lymphoid organs are correct?
A. The thymus is quite large at the time of birth but keeps reducing in size with age.
B. Both bone marrow and thymus provide micro-environments for the development and maturation of T-lymphocytes.
C. The spleen is the main lymphoid organ where all blood cells including lymphocytes are produced.
D. In the primary lymphoid organs, immature lymphocytes differentiate into antigen-sensitive lymphocytes.
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → A, B and D only
Lymphoid organs are the organs where lymphocytes arise and/or mature and multiply. The primary lymphoid organs are the bone marrow and the thymus, where immature lymphocytes become antigen-sensitive. The spleen, lymph nodes, tonsils and similar organs are secondary lymphoid organs.
A. The thymus is quite large at the time of birth but keeps reducing in size with age. — True. The thymus is a lobed organ near the heart. It is large at birth and becomes very small by the time puberty is reached.
B. Both bone marrow and thymus provide micro-environments for the development and maturation of T-lymphocytes. — True. This is the role the book gives to both primary lymphoid organs.
C. The spleen is the main lymphoid organ where all blood cells including lymphocytes are produced. — False. All blood cells, including lymphocytes, are produced in the bone marrow. The spleen is a secondary lymphoid organ that filters the blood and stores erythrocytes.
D. In the primary lymphoid organs, immature lymphocytes differentiate into antigen-sensitive lymphocytes. — True. Bone marrow and thymus are where this differentiation takes place; the mature lymphocytes then move to the secondary lymphoid organs.
NCERT Extract:
Immune System in the Body – “… The primary lymphoid organs are bone marrow and thymus where immature lymphocytes differentiate into antigen-sensitive lymphocytes. … The bone marrow is the main lymphoid organ where all blood cells including lymphocytes are produced. The thymus is a lobed organ located near the heart and beneath the breastbone. 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.”