amphibians exchange gases through their skin and lung surfaces the amphibian lung is a simple sac; the skin must remain moist for proper gas exchange; some lungless salamanders exchange gases only through skin frogs use positive pressure breathing air is pushed into lung frog opens nostrils and lowers floor of mouth air enters mouth through nostrils frog closes nostrils and raises floor of mouth air is pushed through pharynx and into lungs recoil of lungs. (passive) nostrils are opened to allow air release via elastic.