Why fishes have two chambered heart and human four chambered?r=1218988584?

Question

Why fishes have two chambered heart and human four chambered?r=1218988584?

Answer 1

The reason why humans have a four-chambered heart is to maximize oxygen flow because of the presence of lungs. Two of the chambers in the human heart deal with non-oxygenated blood, which then sends the blood via the pulmonary artery to the lungs, which then oxygenates the lungs and sends the blood back to the heart to be redistributed throughout the body. This method of organization helps keep all the blood organized - no non-oxygenated blood will mix with oxygenated blood.

Fishes have a two-chambered heart because they do not have lungs - instead, they have gills. The way their respiration works is by counter-current exchange. The water flows one way over the gills, and because of the partial pressure of oxygen is lower in the blood, as the water passes over the gills, molecules of oxygen are basically "pulled" into the blood, oxygenating the blood. This blood then flows in a linear circuit and eventually returns to the heart, which then re-pumps the blood to the gills to be re-oxygenated. Because of this unique principle of counter-current exchange, the two-chambered heart is the optimal heart chamber configuration for a fish.