Frogs are amphibians known for their ability to thrive in both aquatic and terrestrial environments. Their unique biological adaptations allow them to acquire oxygen from different sources, enabling them to breathe underwater.
How Frogs Breathe Underwater
Frogs primarily breathe underwater through a process called cutaneous respiration, which involves gas exchange directly across their skin. The skin of a frog is thin, moist, and highly permeable to gases, with a dense network of tiny blood vessels, known as capillaries, just beneath the surface. Oxygen dissolved in the surrounding water diffuses across the skin and enters these capillaries, moving into the frog’s bloodstream. Simultaneously, carbon dioxide, a waste product, diffuses from the blood through the skin and into the water. This method is efficient when a frog is submerged.
How Frogs Breathe on Land
When frogs are out of water, their primary method of breathing shifts to pulmonary respiration, using their lungs, alongside buccopharyngeal respiration, which involves the lining of their mouth and throat. Frog lungs are relatively simple, appearing as sac-like structures, well-supplied with blood vessels for gas exchange.
Frogs do not have a diaphragm or ribs like mammals. Instead, they use buccal pumping to inflate their lungs: lowering the mouth floor draws air in through the nostrils, which then close as the mouth floor rises, forcing air into the lungs. Skin respiration also continues on land, as long as the skin remains moist, but it plays a secondary role to lung breathing for air intake.
Amphibian Breathing Adaptations
Frogs possess these diverse breathing methods because they are amphibians, uniquely capable of living in both aquatic and terrestrial environments. This dual respiratory system provides a significant advantage, allowing them to exploit a wider range of habitats and adapt to varying oxygen availability. For instance, when submerged, their skin respiration is crucial, particularly during periods of inactivity or hibernation when metabolic rates are low. The ability to switch between cutaneous, pulmonary, and buccopharyngeal respiration enables frogs to maintain adequate oxygen levels regardless of their immediate surroundings or activity level. This adaptability allows them to seek refuge in water to escape predators or regulate body temperature, while still being able to forage and move on land.