Dear Student
??????1. The exchange of gases on surface of stem and leaves occur due to stomata.
2. Process of gaseous exchange in stomata
i) Guard cells present swells up thus opening the stomata
ii) Exchange of gases takes place?
iii) Guard cells shrink thus closing the stomatal opening.
3. Gaseous exchange also occurs through lenticels present on the stem. These lenticels are tiny pores that helps the plant in exchange of gases.
Regards