Amphibia are vertebrates, represented in the UK by frogs, toads and newts. In other countries there are also salamanders. Amphibia can survive both on land and in water. In water they obtain oxygen by absorbing it through their skin. On land they can breathe through their skin but they also use their lungs. Although, in the UK, amphibia can spend a great deal of time on land, they have to return to water to reproduce.
Frogs swim by using their powerful hind legs. The webbed feet increase the surface area that pushes against the water. At the surface, their eyes and nostrils are above the water line. They can remain under water for prolonged periods, taking in dissolved oxygen through their skin which is richly supplied by a network of blood capillaries.
Feeding. A frog has an extensible tongue with a sticky surface. It can flick the tongue out to catch an insect resting on a leaf or even in flight. The food is mainly worms, slugs, beetles and other insects.
Breathing air. The frog draws air in through its nostrils and pumps it into the lungs by movements
of its mouth floor.
Body temperature. Amphibia are often described as ‘cold-blooded’ but, in fact, their temperature varies with that of their surroundings.