How does the flow of oxygen take place within insects

"In the case of insects, the respiratory system is composed of a series of tubes called trachea within the body of the insect which opens to the outside atmosphere through small pores on the surface of the insect called spiracles. This system of tubes deliver oxygen directly to its tissues from the atmosphere."


       Even though insects require oxygen for its survival, the respiratory system of insects are completely different from that of humans. Unlike humans insects do not have lungs, instead they make use of a series of tubes called trachea for the process of respiration. Air enters trachea through a series of opening on the surface of the body of the insect called spiracles. Trachea branches repeatedly within the body of the insect to form a dense network of tubes.

       Each of these tube ends in a special cell called the tracheole, which provides a moist interface for exhange of oxygen between the atmosphere and the living cells. The liquid in the tracheole dissolves the oxygen within the trachea and then this oxygen is diffused with the cytoplasm of the adjacent cell. Simultaneously, carbon dioxide is duffused out of the cell as waste product to the atmosphere.

       The walls of the trachea are strengthened by rings made of chitin ( tough, protective, semitransparent substance), which helps prevent collapsing of the tube under pressure. In most of the large insects the movement of gases are effected by expanding and contracting its body volume using abdominal muscles along with closing some and opening some other spiracles.

       Scientists believe that the small size of insects are as a result of this limited and primitive respiratory system. During the Paleozoic Era when large sized insects existed, the insects were able to overcome this bottle neck due to the extra oxygen rich atmosphere. The oygen content in the atmosphere during Paleozoic Era is thought to be around 35 percent as opposed to the present day 20 percent. This limitation has ensured that the insects do not evolve into large insects.


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