Give functions of the following :
(i) Blood platelets (ii) Sieve tubes (iii) Cardiac muscle.

Explanation

(i) They play a role in blood clotting .
(ii) Sieve tubes allow free diffusion of soluble organic substahce across the sieve plates.
(iii) It contracts and relaxes rapidly and continuously with a rhythm and is never fatigued to bring contractions and relaxation of heart chambers.