Q4. Why is an antibody written H2L2?
Each basic antibody unit has four peptide chains: two longer heavy chains (H) and two small light chains (L) (NCERT page 135).
Q5. Which chemicals released from mast cells cause the symptoms of allergy, and which drugs reduce them?
NCERT names histamine and serotonin, released from the mast cells; drugs like anti-histamine, adrenalin and steroids quickly reduce the symptoms of allergy (NCERT page 137). Beyond the NCERT text: a serious allergic reaction, anaphylaxis, can begin very quickly and may be life-threatening, so it needs emergency help (MedlinePlus, “Anaphylaxis”, public domain).
Q6. How do interferons protect the body?
Virus-infected cells secrete these proteins, which induce antiviral defences in neighbouring cells and limit viral spread (NCERT page 135).
Q7. What happens to the thymus with age?
NCERT describes shrinkage to a very small size by puberty, but this is misleading anatomically. The thymus is prominent in children, generally grows through childhood and becomes increasingly replaced by fat after puberty; function declines with age.
Q8. Name the secondary lymphoid organs NCERT lists.
The spleen, lymph nodes, tonsils, Peyer’s patches of the small intestine and the appendix (NCERT page 138).
Q9. NCERT asks what ‘a suitable gene’ means for a DNA vaccine. What would it be?
A gene of the pathogen that codes for one of its antigenic proteins: a protein that makes the body produce protective antibodies and memory cells, without itself causing the disease (reasoned from NCERT page 136, where recombinant DNA technology makes a pathogen’s antigenic polypeptides in bacteria or yeast; NCERT Exercise 5, page 148).