Plants also get their free energy from respiration. There are no special organs or systems present for gaseous exchange in plants. Every cell of the plant carries out an exchange of gases according to its need.
The transport system of plants is composed of large conducting vessels i.e. xylem and phloem. This transport system is not involved in the transport of gases in plants.
Structures & Methods involved in the Gaseous Exchange in Plants:
1. Air Spaces between Mesophyll cells
The mesophyll cells of the leaves are specialized for photosynthesis. Large air spaces are present between these mesophyll cells. These spaces are directly involved in the exchange of gases. These air spaces are like honeycomb (six-sided). These air spaces are up to 40% of the total volume of the leaf.
Stomata are the main sources of the exchange of gases. These are present in the leaves and in the young stem. The land plants get their oxygen directly from the air. This air enters through the stomata into the plants.
A large number of stomata are present on the leaves. It is estimated that there are 12000 stomata per square centimeter of leaf surfaces in tobacco plants. These stomata lead into intracellular space between the mesophyll cells.
Cork tissues are present in the older stems. These cork tissues are formed of dead tissues. The cork tissues have special pores called lenticels. These lenticels are also involved in the exchange of gases.
Air is present in the spaces between the soil particles. The roots of the plants absorb this air.
5. Aquatic Plants
The water contains dissolved oxygen. The aquatic absorbs this oxygen.