it is the skin
The skin.
The respiratory system and the circulatory system
Amphibians use their lungs, and use their thin skin when its moist.
cutaneous gas exchange
through gills
Stomata
The adaptive value of having the organ of gas exchange inside the body is increased effectiveness. It allows for more rapid movement of air across the lungs.
the mantle is filled rather than emptied.
Without getting into the gas exchange issue, amphibians start out life as eggs and larvae in the water. As they mature into adulthood they break free from the water and crawl onto dry land.
the organ that is involved in gas exchange is the lung. the specific lung structure that is the site for gas exchange is the alveolus which is part of the alveoli, which is found in the lung.
Because that is where the primary gas exchange happens.
We know that reptiles have lungs, just like many other animals do.
As young amphibians have external gills. As adults their skins are permeable to gas exchange. Reptiles breath only with their lungs.