Explain the evolutionary changes in energy releasing system.

Explanation

(1)Exchange of gases is a common life process in all living organisms, but it is not same in all.
(2)Single celled organisms amoeba or multicellular organisms like hydra and planarians obtam oxygen and expel carbon dioxide directly from the body by the process of diffusion.
(3)In multicellular animals special organs are evolved.
(4)Animals either terrestrial or aquatic adopted different types of respiration and different types of respiratory organs mostly due to habitat in which they live.
(5)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.
(6)In insects tracheal respiratory system is present in which small branches of trachea called tracheoles carry air directly to the cells in the tissues.
(7)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.
(8)Respiration through skin is called cutaneous respiration.
(9) This type of respiration is seen in earthworm and leeches.
(10)Frog, an amphibian can respire through cutaneous pulmonary processes.
(11)Most of the higher animals respire with the help of lungs. This type of respiration is known as pulmonary respiration.