Why do plants not need a respiratory system

Plants intake carbon dioxide gas and use it with the suns energy (photosynthesis) to support growth and stay alive. They output the oxygen our respiratory systems need for life.

It's just as Rob says. In short, they do have a respiratory system. They just don't have lungs.

Same as written above and so that they don't need lungs.
but I add that each part of the plant - the roots, stem and leaves respire independently so they don't require a lung...