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What is an Amniotic Egg? - Definition & Examples

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  • 0:00 Amniotic Eggs: The Basics
  • 1:49 Examples of Amniotic Eggs
  • 3:32 Lesson Summary
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Lesson Transcript
Instructor: Adrianne Baron

Adrianne has taught high school and college biology and has a master's degree in cancer biology.

This lesson is going to introduce you to amniotic eggs by defining and explaining the various parts of an amniotic egg. We will also cover some examples of amniotic eggs and look at how they differ in mammals.

Amniotic Eggs: The Basics

Doors with locks. Access gates. Alarm systems. What do these things have in common? They're all methods which we use to protect ourselves. Protection is a natural need for all living organisms. Birds have nests high up in trees, and some animals burrow holes into the ground as a means of protection. We function better when we feel that we are in a safe environment.

Before we're even born, we need to be protected. The need is first addressed when embryos are developing within the egg. Embryos are surrounded by a set of fluid filled membranes called the amnion. The fluid inside the amnion, called amniotic fluid, acts as a cushion to help protect the developing embryo from physical danger. Eggs that contain an amnion to protect the embryo are referred to as amniotic eggs.

There are other parts to the amniotic egg as well, which makes sense since the embryo needs more than to just be protected. There is a yolk sac inside of the egg that provides the nutrients to feed the developing embryo. We of course know that any living organism that eats will also need to excrete waste. This is one of the functions of the allantois. This sac-like structure also helps with gas exchange so the embryo is able to breathe.

There are two more structures that further help to protect the embryo. The chorion is a membrane that encloses all of the structures that we mentioned above. The chorion is then surrounded by the albumin, which is a fluid filled with protein. The last structure of the amniotic egg is the egg shell, which allows gases to pass through, but keeps fluids from passing into or out of the egg.

Examples of Amniotic Eggs

Now that you know what an amniotic egg is, you may question which animals use amniotic eggs. The answer to this question is any reptile, bird or mammal. Animals that use amniotic eggs are called amniotes. Let's look at a few examples now.

Reptiles are believed to be the first animals that were able to live and reproduce on land. The amniotic egg allowed this to happen because the water needed for reproduction is enclosed in the egg. Their egg includes all of the above-mentioned structures. Reptiles fertilize the eggs internally and then lay them in their nests.

Birds also use amniotic eggs for reproduction. They make use of internal fertilization and lay their eggs in their nests. Many birds sit on their eggs as the embryo is developing inside. The structures are the same as we discussed, and the egg shells are hard but still porous to air. As a matter of fact, you can see some of these structures any time you eat eggs. The egg yolk is the same yolk as described above, and the albumin is what we often refer to as the 'egg white.'

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