An antibody molecule is represented as:

What is immunity based on?

In which lymphoid organ are all blood cells,including lymphocytes,produced?

Primary lymphoid organs $- P$
Secondary lymphoid organs $- Q$
$I -$ Appendix, $II -$ Peyer's patches of small intestine,
$III -$ Thymus, $IV -$ Spleen, $V -$ Lymph node, $VI -$ Bone marrow, $VII -$ Tonsils
Select the correct option for $P$ and $Q$.
$\quad P \quad \quad Q$

How many peptide chains are present in an antibody molecule?

Transplantation of tissues/organs often fails due to non-acceptance by the patient's body. Which type of immune response is responsible for such rejections?