Plant leaves and roots play a major role in the respiration process.
Leaves have small tiny pores called stomata which helps in the gaseous exchange.
Roots don't have stomata. They directly take up the air from the air spaces present in the soil.
Once the air is enters the cell, the oxygen from the air is utilised to produce energy from glucose. And as a result, the carbon dioxide and water are given out as the byproduct.