Fishes to Frogs: Respiratory Adaptation

Respiration Evolution: Fishes to Frogs

The energy needed to sustain life depends on the reduction of oxygen during glycolysis, thereby producing ATP, water, and carbon dioxide. As multicellular organisms began to evolve and grow in size, the ability of the inner-most cells to receive enough oxygen to carry out cellular respiration was compromised. The absorption of oxygen through the outer cellular layers, called cutaneous respiration, evolved to become an important method for obtaining enough oxygen to sustain the evolution of larger organisms (Farmer, 1997).

Ancient fishes depended on cutaneous respiration to survive in oxygen-poor aquatic habitats, such as rivers, swamps, and tidal pools (reviewed by Farmer, 1997; Taylor, Leite, Mckenzie, and Wang, 2010). Cutaneous respiration was sufficient as long as these fish remained small in size, but the need to avoid predation would have increased the evolutionary pressure to grow larger. The combination of size...
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