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Amphibian Life Cycle

Instructor: Ebony Potts

Ebony has taught middle and high school physical science, life science & biology. She's also been an assistant principal and has a doctorate in educational administration.

Have your ever looked at a frog and wondered how it came to be? How did it go from an egg, to the frog you may see hopping around a lake? In this lesson you will learn about the amphibian life cycle and the process that takes an amphibian from an egg to fully a developed organism using the frog as an example.

One day you and a bunch of friends decide to go down to the lake. While at the lake, you see what looks like a bunch of little fish, swimming around in the water. You, and your friends run home to get jars, and fill each jar with some of the little fish. You think to yourself, these will be great friends for the fish in my freshwater fish tank at home. When you get home, you pour the little fish into the tank, and don't give them another thought. After a while, you notice that your little fish are starting to sprout legs, and their tails seem to be shrinking. These are not fish at all they are tadpoles, baby frogs!

Amphibians

Amphibian
tadpole

Frogs belong to a group of organisms called amphibians. Amphibians have a backbone and are cold-blooded, their body temperature is dependent on the environment. Amphibians have some of the typical characteristics of fish and reptiles. They spend part of their lives on land and in water. They start their lives as eggs in water then develop into tadpoles who breathe through gills, like fish. They end their lives on land as adults who breathe air using their lungs and skin. Amphibians are a part of class Amphibia. This specialized class of organisms, includes over 3500 species. Amphibians, are broken down into three orders: Gymnophiona (worm-like organisms), Urodela (newts and salamanders), and Anura, (frogs and toads).

The life cycle of Amphibians

Eggs

Amphibians start their lives in water. The female amphibian will lay many, many eggs who all are fertilized outside of her body by the sperm of a male amphibian. Why so many eggs? The female lays so many eggs because most of them won't make it to adulthood. They will either dry out, be eaten by other organisms, or get damaged. The few eggs that get fertilized, and survive will hatch in 7-9 days.

Tadpoles

After the eggs of an Amphibian hatch they are called Tadpoles. Tadpoles breathe through gills like fish. They survive by eating the yolk that is still attached to them at first. As the tadpoles mature, the yolk will disappear, and they will begin to eat algae. After about four weeks the tadpoles will begin to grow teeth and skin over its gills. Between six and nine weeks into it's development, it will grow longer and develop what looks like a typical amphibian's head and legs. By the end of nine weeks, the tadpole will look more like a frog with a long tail and will start to eat insects.

Metamorphosis

From weeks nine on, a process called metamorphosis occurs. Metamorphosis is the final process that changes the amphibian from tadpole to adult. The amphibian now looks like a tiny frog with a tail. By the end of metamorphosis, the frog will lose its tail, grow a long tongue, and look like what we know of as a typical frog. The whole life cycle takes about a total of 16 weeks. In the end, the organism that started out as a egg, will find its way to water to begin the cycle again, with its own offspring.

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