All frogs begin their lives as tadpoles that breathe underwater using their skin and gills. As the frog grows, lungs begin to develop and the frog loses its gills at it begins to metamorphose.
A frog breathes with its mouth shut, as it is able to pull air in through its nostrils to its lungs using throat movements. This process is known as buccal pumping. There are many types of frogs that are able to absorb oxygen through their skin. Every couple of weeks, the skin of the frog is shed and eaten. The new skin is more permeable and better able to absorb oxygen and release carbon dioxide.