Why do plants don't have respiratory organs ?

Explanation

Reasons :
(1) Each plant part takes care of its own gas -exchange needs.
(2) There is very little transport of gases from one plant part to another.
(3) Plant do not present great demands for gas exchange.
(4) Roots, stems and leaves respire at rates far lower than animals do .
(5) Only during photosynthesis are large volumes of gases exchanged and each leaf is well adapted to take car of its own needs during these periods. When cells photosynthesise availability of `O_(2)` is not a problem in these cells since `O_(2)` is released within the cells.
(6) The distance that gases must diffuse even in large, bulky plants is not great.