For each of the following questions, four choices have been provided. Select the correct alternatives. Which one of the following is not a feature of viviparous animals? (a) They give birth to young ones. (b) Embryo development takes place inside the female body. (c) Less embryonic care and protection. (d) Provides nutrition to the foetus through placenta.

Understanding the stages of embryo development in viviparous animals can be quite fascinating. Viviparous animals, including most mammals, are those in which the embryo develops inside the body of the mother. Unlike their oviparous counterparts, these animals do not lay eggs. The journey from conception to birth is intricate and varies widely among species.

It all starts when the egg is fertilized internally, usually via mating. From this point, the fertilized egg, now an embryo, begins to develop within a special structure called the uterus. Here, the embryo is nurtured and protected in a specialized environment, where it undergoes numerous developmental stages. These stages include cellular division, differentiation, and growth that transform a single cell into a complex organism ready for birth. A crucial aspect of this development is the connection to the mother's blood supply through the placenta, which provides the necessary nutrients for growth and allows for waste removal.

The process from conception to birth is closely regulated by various hormones, ensuring that the developing young reaches a state of maturity suitable for independent life outside the mother's body. The duration of this process, known as gestation period, is highly variable, from just a few weeks in rodents to up to 22 months in elephants. In essence, viviparous animals provide the embryo with a protective environment where it can develop safely until it is ready to survive on its own.

When studying animal reproduction, it is vital to differentiate between viviparous and oviparous animals. The distinction lies in how they bring new life into the world. Viviparous animals give birth to living young, while oviparous animals lay eggs that hatch outside the mother's body.

Embryo Development

In viviparous animals, development takes place within the mother's reproductive system, providing direct nourishment and protection. On the other hand, oviparous animals usually lay eggs in an environment where temperature and humidity levels are suitable for the offspring's development with little to no further parental care.

Nutritional Support

Viviparous species have evolved mechanisms like the placenta to nourish the developing embryo directly. In contrast, oviparous species rely on the yolk within the egg to supply all necessary nutrients until the young are capable of fending for themselves.

Embryonic Care

Oviparous species often have to engage in elaborate behaviors to protect their eggs from predators and environmental extremes, whereas viviparous species can often move about freely without worrying about the safety of static eggs. This difference can have profound implications on the survival strategies of the species.

The placenta is an organ unique to viviparous animals and plays an indispensable role in prenatal development. It forms a direct link between the mother and her developing embryo, serving multiple functions crucial for the young's growth and survival.

Exchange of Nutrients and Wastes

The placenta allows for the transfer of nutrients, such as glucose and amino acids, from the mother to the embryo. It also facilitates the removal of waste products from the embryo's blood to the mother's, where they can be excreted.

Oxygen and Carbon Dioxide Transfer

Besides nutrients, the placenta also enables the exchange of respiratory gases. The mother's blood supplies oxygen essential for cellular metabolism, whereas carbon dioxide produced by the embryo is transferred back to the mother's bloodstream for elimination.

Hormonal Support

The placenta also produces hormones that support pregnancy, such as progesterone and human chorionic gonadotropin (hCG). These hormones maintain the uterine environment, regulate the mother's immune response, and ensure proper development and growth of the embryo.

Interestingly, the placenta evolves to suit the needs of each species, with varying degrees of complexity and function. It is this incredible adaptability that has allowed viviparous animals to occupy diverse ecological niches and continue to thrive.