Vertebrates_Concept_5
Magnets
Magnets
Amphibians possess the ability to live in significantiy different habitats, assuming a different form at different stages of their life cycie. Amphibians begin life as inhabitants of an aquatic world that are abe to breathe in water; but as they mature and metamorphose into their adult form, they develop the ability to breathe air and move on land. This class of vertebrates was the first to conquer the land, and the fact that there are still many species around today shows how successful they have been.
Most amphibians return to water to lay their eggs. The eggs hatch into true aquatic animals, usually limbless and always with gills. This first stage of the life cyde may last for weeks or years, depending on the species. As most amphibians progress towards maturity, they will begin to develop limbs and lungs; some, like the frog, will even reabsorb their tails into their bodies. On reaching this mature stage, the amphibian will leave the confines of the water and move about on land. Some species of newt will live on land for a number of years, mainly keeping to damp areas, before returning to the water to breed.
Many of the more common frogs will progress through four stages of development: first the egg, which hatches into a free -swimming aquatic tadpole; then a froglet, which has the beginnings of the adult frog's legs but still retains the tadpole's tail; and finalIy the adult frog which is able to breathe. The fully aquatic stage of the development of an amphibian is also referred to as the larva.
Amphibians are the only group of 'higher' animals (apart from teenagers) that go through a fundamental change in their lifestyle, habitat and body shape as part of their natural development. Depending on availability and the ability of the school to provide an appropriate habitat, children can observe the changes in these animals as they happen. This demonstrates the idea of development (as opposed to growth) in a dramatic way.
Adult — the final stage of the life cycle in which reproduction is posslbie.
Froglet the stage of development of a frog which exhibits characteristics of both the tadpole and the mature frog.
Frogs have webbed feet for swimming — but the 'flying frogs' of Southeast Asia use their webbed feet to glide from tree to tree, or to parachute safely to the ground.
The Mexican axolotil is an amphibian with external, featherlike gills. It looks like a pale adult newt, but in fact, it is the larval stage of a salamander. It can lose its gills and metamorphose into an airbreathing adult, say 'can' because some axolotls do not metamorphose: some live their whole lives, including breeding in the water.
Amphibians are cold and clammy.
Well, as most of them live near or in water they do tend to be. But some, particularly toads, have a drier skin that gives them a warmer feel. Like all other ectotherms, they are the same temperature as their surroundings, so those that live in cold water will tend to be on the cool side, but in warm sunshine, they will be warmer,
Do all amphibians start life in water?
Not quite. Some frogs that live in particularly damp and humid parts of the tropics lay eggs on leaves, which hatch out directly into froglets,
This activity is only possible if you have access to a pond with frogspawn, so that tadpoles can be observed in their natural habitat, At regular periods during the spring and early summer, the children can observe the development of frogspawn into tadpoles and then froglets without disturbing them. They should not collect frogspawn for classroom observation. They can record and date the developments using drawings, photographs or a Video camera. These could be transferred to a computer for inclusion in a multimedia presentation.
The children can prepare drawings, pictures or download images from the internet to present displays on the life cycles of particular types of amphibian.