the bark are living. How do they get Oxygen and release Carbon Dioxide ?

The bark is a protective layer made of a variety of cells, some living cells inside and some dead on the outside. Gases, including oxygen, pass through the outer bark to and from the living cells of the inner layers of a tree. This is a form of respiration, or breathing. The gases move through stem pores called lenticels, whose function is equivalent to that of stomata, or breathing cells, found on leaves.