Give reasons.
(a) The walls of capillaries are thin.
(b) It is necessary to match blood groups before giving a transfusion.
(a) The walls of the capillaries are thin so as to facilitate the exchange of gases and nutrients between the tissues and blood.
(b) It is necessary to match the blood groups before transfusion because the blood group of the donor must be compatible with the recipient's blood otherwise it may lead to serious consequences (clotting of the patient’s blood) that may be dangerous or even fatal.