Answer to Question #118961 in Zoology for Shania kumar

Question

Why have amphibians never been able to break with their dependency with water or at least a moist environment and in most cases a fully aduatic stage

Answer 1

There are several reasons why this is not possible. Firstly, the fertilization of eggs takes place in the external environment, and not in the genital tract of amphibians, therefore, fertilization requires water. In addition, amphibians undergo indirect development through the stage of the tadpole because the yolk reserves are simply not enough to instantly form a young individual with completely corresponding anatomical structures as in adults. Another problem is the lungs, which are not very thorough and do not allow for a long time to be out of the water. Therefore, a huge part of the respiratory function relies on the skin, which is thickly expired by the blood vessels to improve gas exchange. That is, in this case, gas exchange is provided by diffusion through the skin into blood vessels and vice versa. Thus, amphibians can live in humid places and the moisture that they have there will be enough for the corresponding level of gas exchange, but the main barrier is reproduction.