Common features between all the respiratory organs are:
(i) All the respiratory organs have large surface areas to get enough oxygen.
(ii) All the respiratory organs are thin-walled for easy diffusion of gases and substances.
(iii) All the respiratory organs (like skin, lungs. gills) have a rich supply of blood for transporting respiratory gases.
The mechanism of gaseous exchange between tissues and blood is as follows:
(i) The blood reaching the tissues has higher concentration of oxygen than in the cells so it gets diffused into the cells.
(ii) The carbon dioxide, which is formed in the cells, gets accumulated in higher concentration as compared in the blood, so it easily diffuses into the blood'
(iii) The blood with CO2, takes this gas to the lungs, from where it is expelled out during exhalation.
