Explain : The major surface of plant is in contact of air

Explanation

Each living cell in a plant is located quite close to the surface of the plant. .This is true for leaves .
In stems, the .living. cells are organised in thin lyers inside and beneath the bark. They also have openings celled lenticels.
The cells in the interior are dead and provide only mechanical support.
Thus most cells of a plant have at least a part of their surface in contact with ari. This is also facilitated by the loose packing of parenchyma cells in leaves. Which provide an interconnected network of air apaces.
`C_(6) H_(12) O_(6) + 6O_(2) to 6CO_(2) + 6H_(2) O + `Energy
The complete combustion of glucose, which produces `CO_(2) and H_(2)O` as end products yield energy most of which is given out as heat. If this energy is to be useful to the cell, it should be able to utilise it to synthesise other molecules that cell requires.
The key is to oxidise glucose not in one step but inseveral small steps enabling some steps to be just large enough such that the energy released can be coupled to ATP synthesis.