The disadvantages of multicellularity are :
(1) Specialised cells often lose the power of division, so that injury is not repaired e.g., nerve cells.
(2) Regeneration ability of multicellular organisms decrease with specialization.
(3) Specialized cells may lose vital functions in order to carry out specific activity e.g. RBCs, sieve tube cells.
(4) Some unicellular organisms are immortal as their body gets distributed in their offsprings