Read the following passage carefully and answer the given questions.
Immune System in the Body
The human immune system consists of lymphoid organs, tissues, cells and soluble molecules like antibodies. The primary lymphoid organs are bone marrow and thymus where immature lymphocytes differentiate into antigen-sensitive lymphocytes. After maturation the lymphocytes migrate to secondary lymphoid organs like spleen, lymph nodes, tonsils, Peyer's patches of small intestine and appendix. The secondary lymphoid organs provide the sites for interaction of lymphocytes with the antigen, which then proliferate to become effector cells. The bone marrow is the main lymphoid organ where all blood cells including lymphocytes are produced. Each antibody molecule has four peptide chains, two small called light chains and two longer called heavy chains. Hence, an antibody is represented as H2L2. Different types of antibodies are produced in our body. IgA, IgM, IgE, IgG are some of them. Techniques like radiography (use of X-rays), CT (computed tomography) and MRI (magnetic resonance imaging) are very useful to detect cancers of the internal organs.
Maturation of lymphocytes takes place in:
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → Bone marrow and thymus
Option (1) Secondary lymphoid organs — Incorrect. Lymphocytes reach the secondary lymphoid organs only after they have matured. There they meet antigens and multiply. So these organs are not the place of maturation.
Option (2) Bone marrow only — Incorrect. The bone marrow is the main lymphoid organ where all blood cells, lymphocytes included, are produced. But it is not the only place of maturation. T-lymphocytes mature in the thymus, so the word “only” makes this option wrong.
Option (3) Bone marrow and thymus — Correct. These two are the primary lymphoid organs. Here immature lymphocytes differentiate into antigen-sensitive lymphocytes, that is, they mature.
Option (4) Lymph nodes — Incorrect. Lymph nodes are small solid structures along the lymphatic system. They catch microbes and antigens carried in the lymph, and the lymphocytes there are activated. A lymph node is a secondary lymphoid organ, so it receives mature lymphocytes.
Note: The passage is taken from NCERT. NTA has put lines of the NCERT text together to make it. Most CUET (UG) questions come straight from NCERT, so study the book line by line, including figures and their titles.