Exchange of gases is a common life process in all living organisms, but it is not same in all.
1. Diffusion:
1. Single-celled organisms like amoeba or multicellular organisms like hydra and planarians obtain oxygen and expel carbon dioxide directly from the body by the process of diffusion.
2. In multicellular animals special organs are evolved.
3. Body size, availability of water and the type of circulatory system are some of the reasons for the animals to develop different types of respiratory organs.
2. Tracheal respiratory system :
In insects tracheal respiratory system is present in which small branches of trachea called trachioles carry air directly to the cells in the tissues.
3. Bronchial respiration : In fishes gills are utilised for the exchanges of gases. Blood is supplied to gills through capillaries which have thin walls for exchange of gases. This is called bronchial respiration.
4. Cutaneous respiration: 0 Respiration through skin is called cutaneous respiration. Eg: i) Earth worms and leeches. ii) Frog, an amphibian can respire through lungs and skin.
5. Pulmonary respiration : Most of the higher animals respire with the help of lungs. This type of respiration is known as pulmonary respiration. Eg: Mammals.
