Question

The addition of lungs and neural control of breathing has been viewed as an evolutionary advantage. However, examination of gas exchange membranes and circulation have suggested otherwise.

a. Give an example of a group of organisms that contradict this evolutionary advancement; hence, lacking lungs, but yet utilize a gas exchange mechanism of the highest efficiency as compensation.

b. In addition, discuss the limitations that hinder the above group when evolution intervened.

Answer 1

a) The best example for the organisms that lack lungs but has a better gas exchange mechanism is the fish. They doesn't have lungs. Gills become their respiratory organ. The dissolved oxygen in the water when pass through the gills gets diffused to the blood vessels present beneath the gills and the oxygen directly reaches the cells. Thus fish use oxygen in a better way without lungs.

b) The fishes can't breathe outside water. It is one of the main limitation that hindered this group when evolution intervened. The gills can't exchange atmospheric oxygen to the blood vessels. It has only one atria and one ventricle. When evolution became the organism with lungs and 3 and 4 chambered heart evolved. So the breathing is directly linked with circulatory system. The 2 chambered heart doesn't allow the fish to exchange the O2 and Carbon-dioxide with the atomphere.