Body Structure
A tadpole starts out as a body mass with an elongated tail. As metamorphosis takes effect, it begins sprouting legs and arms and grows small teeth that allow it to eat algae and small bugs. The body elongates, and the tail shrinks. The main difference, however, in the body structure of a tadpole is that it has gills. Gills allow the tadpole to breathe underwater. This is important because it does not have legs and arms yet, or the muscular structure to support itself on land.
Frogs have a strong muscular structure that allows them to be mobile both on land and in the water. Their hind legs are long and powerful, and their feet are webbed for greater swimming efficiency. Most importantly, mature frogs breathe through lungs instead of gills. Mature frogs can no longer breathe under water.
Movement
Tadpoles have one way of moving: swimming. Tadpoles will stay in the water until they evolve into frogs. Young tadpoles are not very proficient swimmers and attach themselves to foliage until they are more developed. As they mature, the tadpoles begin to learn to swim by moving their tails back and forth.
Frogs, on the other hand, can both swim and hop. The difference between a frog swimming and a tadpole swimming is the means of propulsion. Tadpoles use their tails, but frogs have no tails. Frogs use their hind legs and propel themselves forward in a kicking motion. On land, frogs can move by hopping around, something that tadpoles are not capable of.
