Transpiration is part of the water exchange system. The gas exchange system occurs through the stomata but is not part of transpiration. Transpiration occurs when plants absorb water through their roots and then give off water via the pores in their leaves. The process of transpiration cools plants down when they get too hot. Plants "sweat" in the same way that animals sweat to cool down. The water that is passed through the stomata evaporates and cools the plant down.
