What is the characteristic of animals that are born alive?

Viviparity is the characteristic of animals that are born alive. Viviparous animals give birth to live young that have developed inside the mother's body. The developing young receive nourishment from the mother through a placenta or other specialized structure. Viviparity is found in a wide variety of animals, including mammals, some fish, some reptiles, and some amphibians.

In mammals, the developing young are nourished by the placenta, which is a specialized organ that connects the mother's circulatory system to the fetus's circulatory system. The placenta allows oxygen and nutrients to pass from the mother to the fetus, and it also removes waste products from the fetus.

In some fish, such as the guppy and the platy, the developing young are nourished by a yolk sac. The yolk sac is a sac that is attached to the embryo and contains nutrients that the embryo needs to grow.

In some reptiles, such as the rattlesnake and the copperhead, the developing young are nourished by the mother's oviducts. The oviducts are the tubes that carry eggs from the ovaries to the outside of the body. In viviparous reptiles, the oviducts are modified to allow the developing young to receive nutrients from the mother.

In some amphibians, such as the salamander and the frog, the developing young are nourished by the mother's skin. The mother's skin is modified to allow the developing young to absorb nutrients from the water.

Viviparity is an important adaptation for animals that live in environments where the conditions are not always favorable for reproduction. Viviparity allows animals to protect their young from predators and from the elements. It also allows animals to reproduce even when there is a shortage of food.