Major changes take place in tadpole's digestive and circulatory systems during metamorphosis Why do you think these changes are necessary?   is for Amphibians section

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Tadpoles begin their life in water. Essentially, their diet is that of an herbivore and they consume algae in the pond. However, some may be carnivorous. This reduces competition between the juvenile tadpole and the adult frog. The adult's diet is that of a carnivore. Adaptations like their tongue which is an appendage used to capture food like insects, their maxillary teeth, which helps to hold and grind their prey, are all useful to fulfilling the niche of a carnivore. Therefore, the digestive systems are hydrolyzing different substrates with their enzymes and are different. The circulation in the adult frog needs to be able to supply blood to an active organism that can both swim, jump long distances, etc. Therefore, there has to be a more efficient method of circulation for the adult frog. Both can obtain respiratory gases through their moist skin, and there are blood vessels to help circulate oxygen below the skin. However, lungs are present in adult frogs which help breathe oxygen on land. A tadpole has a loop circulatory system and the adult frog has a more complex circulatory system with a three chambered heart. This helps keep oxygenated and deoxygenated blood somewhat separate, although there is a mix in the ventricle. But, it enables adult frogs to be much more active than the juveniles.

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