Read the following passage carefully and answer the given questions.
Cancerous cells just continue to divide giving rise to masses of cells called tumors. Benign tumors normally remain confined to their original location and do not spread to other parts of the body and cause little damage. The malignant tumors, on the other hand are a mass of proliferating cells called neoplastic or tumor cells. Transformation of normal cells into cancerous neoplastic cells may be induced by physical, chemical or biological agents. Ionising radiations like X-rays and gamma rays and non-ionizing radiations like UV cause cancer. Cancer-causing viruses are called oncogenic viruses which have viral oncogenes. The substances to which an immune response is produced are called allergens. The antibodies produced to these are of IgE type. Common examples of allergens are mites in dust, pollens, animal dander, etc. The primary lymphoid organs are bone marrow and thymus. The secondary lymphoid organs provide the sites for interaction of lymphocytes with the antigen, which then proliferate to become effector cells.
The primary lymphoid organs are:
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → Thymus and bone marrow
Lymphoid organs are the organs where lymphocytes arise, mature and multiply. In the primary lymphoid organs, immature lymphocytes become antigen-sensitive lymphocytes. The mature lymphocytes then move to the secondary lymphoid organs, where they meet antigens.
Option (1) Appendix and spleen — Incorrect. Both are secondary lymphoid organs. The spleen is a large bean-shaped organ that filters the blood and catches the microbes carried in it. Mature lymphocytes come to these organs; they do not mature here.
Option (2) Tonsils and Peyer’s patches of small intestine — Incorrect. These are lymphoid tissues in the lining of the throat and of the small intestine. They are secondary lymphoid tissues that guard the body against microbes entering by the mouth.
Option (3) Bone marrow and lymph nodes — Incorrect. The bone marrow is a primary lymphoid organ, but lymph nodes are secondary. They catch the microbes and antigens carried in the lymph, and the lymphocytes present there are activated. So only half of this pair is right.
Option (4) Thymus and bone marrow — Correct. The bone marrow produces all blood cells, lymphocytes included. The thymus provides the place where T-lymphocytes develop and mature. These two are the primary lymphoid 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.