Question

why plants don,t need specialized respirtory system?

Answer 1

They do need - but they don't have lungs, they have stomata.
Plants need carbon dioxide to get the energy out of the food they make. Obviously, plants don't have lungs or gills, so how do they breathe? They breathe through special little holes on the underside of their leaves called stomata.
The stomata allow fresh air to enter the leaf, where the plant's cells can take out the carbon dioxide. When the gas exchange is completed, the plant emits oxygen back outside through the stomata again.