Do Frogs Have Amniotic Eggs

Learning Outcomes

Identify the classes of animals that are amniotes
Describe the main characteristics of amniotes

The reptiles (including dinosaurs and birds) are distinguished from amphibians by their terrestrially adapted egg, which is supported by ivextraembryonic membranes: the yolk sac, the amnion, the chorion, and the allantois (Figure one). The chorion and amnion develop from folds in the torso wall, and the yolk sac and allantois are extensions of the midgut and hindgut respectively. The amnion forms a fluid-filled crenel that provides the embryo with its own internal aquatic surround. The development of the extraembryonic membranes led to less dependence on water for development and thus allowed the amniotes to branch out into drier environments.

In add-on to these membranes, the eggs of birds, reptiles, and a few mammals accept shells. An amniote embryo was then enclosed in the amnion, which was in plough encased in an extra-embryonic coelom contained within the chorion. Betwixt the shell and the chorion was the albumin of the egg, which provided additional fluid and cushioning. This was a pregnant development that further distinguishes the amniotes from amphibians, which were and continue to be restricted to moist environments due their crush-less eggs. Although the shells of various reptilian amniotic species vary significantly, they all permit the retention of water and nutrients for the developing embryo. The egg shells of bird (avian reptiles) are hardened with calcium carbonate, making them rigid, but fragile. The shells of most nonavian reptile eggs, such every bit turtles, are leathery and crave a moist environment. Most mammals practice not lay eggs (except for monotremes such as the echindnas and platypuses). Instead, the embryo grows within the female parent'south body, with the placenta derived from two of the extraembryonic membranes.

Characteristics of Amniotes

The illustration shows an egg with the shell, embryo, yolk, yolk sac, and the extra-embryonic membranes

Figure 1. The key features of an amniotic egg are shown.

Theamniotic egg is the key feature of amniotes. In amniotes that lay eggs, the shell of the egg provides protection for the developing embryo while being permeable enough to let for the exchange of carbon dioxide and oxygen. Thealbumin, or egg white, exterior of the chorion provides the embryo with water and protein, whereas the fattier egg yolk contained in the yolk sac provides nutrients for the embryo, as is the instance with the eggs of many other animals, such as amphibians. Hither are the functions of the extraembryonic membranes:

Blood vessels in theyolk sac send yolk nutrients to the circulatory system of the embryo.
Thechorion facilitates exchange of oxygen and carbon dioxide betwixt the embryo and the egg's external surround.
Theallantois stores nitrogenous wastes produced past the embryo and also facilitates respiration.
Theamnion protects the embryo from mechanical shock and supports hydration.

In mammals, the yolk sac is very reduced, simply the embryo is still cushioned and enclosed within the amnion. Theplacenta, which transports nutrients and functions in gas exchange and waste direction, is derived from the chorion and allantois.

Boosted derived characteristics of amniotes include a waterproof skin, accessory keratinized structures, and costal (rib) ventilation of the lungs.

Practice Question

Which of the following statements virtually the parts of an egg are false?

The allantois stores nitrogenous waste and facilitates respiration.
The chorion facilitates gas commutation.
The yolk provides food for the growing embryo.
The amniotic cavity is filled with albumen.

Show Answer

Statement d is false.

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