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.
The site of interaction of lymphocytes with antigen is -
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → Secondary lymphoid organs
Option (1) Pancreas — Incorrect. The pancreas is not a lymphoid organ. It is a gland that makes digestive enzymes and the hormones insulin and glucagon.
Option (2) Secondary lymphoid organs — Correct. The spleen, lymph nodes, tonsils, Peyer’s patches of the small intestine and the appendix are secondary lymphoid organs. Mature lymphocytes meet the antigen here. They then multiply and become effector cells that fight the infection.
Option (3) Bone marrow — Incorrect. The bone marrow is a primary lymphoid organ. Lymphocytes are produced and mature here before they meet any antigen.
Option (4) Thymus — Incorrect. The thymus is also a primary lymphoid organ. It provides the place where T-lymphocytes develop and mature. They meet antigens only after they move to the secondary organs.
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.