![]() Here, we discuss the adaptations that parasitic flatworms have developed to be able to transit from the different metabolic conditions to those they are exposed to during their life cycle.Ī crucial moment in the evolution of the planet was the change from an anoxic primordial atmosphere to one rich in oxygen (O 2). Thus, the architecture of the antioxidant systems is different, depending primarily on the superoxide dismutase, glutathione peroxidase, and peroxiredoxin enzymes represented mainly in the tegument. Catalase usually scavenges H 2O 2 in mammals however, this enzyme is absent in parasitic platyhelminths. Because of the aerobic metabolism, hydrogen peroxide (H 2O 2) is produced in abundance. ![]() ![]() Consequently, the flatworms developed several adaptations related to the oxygen gradient that is established between the aerobic tegument and the cellular parenchyma that is mostly anaerobic. As these organisms do not have a circulatory system, gas exchange occurs by the passive diffusion through their body wall. Platyhelminthes exhibit both aerobic and anaerobic metabolism depending on the availability of oxygen in their environment and/or due to differential oxygen tensions during certain stages of their life cycle. ![]() During the evolution of the Earth, the increase in the atmospheric concentration of oxygen gave rise to the development of organisms with aerobic metabolism, which utilized this molecule as the ultimate electron acceptor, whereas other organisms maintained an anaerobic metabolism. ![]()
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