Problem 222 - Objective Biology for NEET

Question

Mammals are mostly (a) Viviparous (b) Oviparous (c) Ovoviviparous (d) All of these

Step-by-Step Solution

Answer

(a) Viviparous.

Step 1: Understand different modes of reproduction

Oviparous refers to animals that lay eggs, with little or no other embryonic development within the mother. This is common in birds, reptiles, and some mammals like monotremes. Viviparous is a term used to describe animals that give birth to live young rather than laying eggs. This is common in mammals, including humans. Ovoviviparous refers to species in which the embryo develops inside eggs remaining within the mother's body until they are ready to hatch. This is seen in some species of fish and reptiles, and rarely in mammals.

Step 2: Apply knowledge to the case of mammals

Most mammals are viviparous, meaning they give birth to live offspring. This includes humans, cats, dogs, and many other mammal species. There are some exceptions like the platypus and echidna, which are monotremes and lay eggs (oviparous). However, the majority of mammal species are viviparous.

Step 3: Choose the correct option

Considering the reproductive strategies of most mammals, it can be concluded that the correct answer is (a) Viviparous.

Key Concepts

Viviparous

Viviparous animals give birth to live young instead of laying eggs. This reproductive mode is typical in most mammals, such as humans, dogs, and whales. In viviparous reproduction, the embryo develops inside the mother, receiving nutrients directly from her. This process often involves a placenta, which is a specialized organ that facilitates the transfer of nutrients and oxygen from the mother to the developing offspring.

Here are some key characteristics of viviparous reproduction:

• Parental Care: Viviparous species often provide substantial care for their young during gestation and sometimes after birth.
• Development: The young are usually more developed at birth compared to those of oviparous species.
• Survival: The direct nutrient supply from the mother can lead to higher survival rates for the offspring in various environments.

The ability to give birth to live young allows viviparous animals to adapt to diverse habitats and conditions. These adaptations have helped viviparous mammals dominate many ecosystems worldwide.

Oviparous

Oviparous animals reproduce by laying eggs. This is a common mode of reproduction in birds, reptiles, and some amphibians. Among mammals, monotremes like the platypus and the echidna are oviparous and are unique exceptions among their peers. In oviparous reproduction, the embryo develops outside the mother's body inside an egg, which provides the necessary nutrients until hatching.

Key aspects of oviparous reproduction include:

• Egg-laying: The female lays fertilized eggs in a safe environment where they can develop independently.
• Nutrient Supply: The egg contains a yolk, which supplies the developing embryo with nutrients.
• Hatching: The offspring hatches from the egg once development is complete.

Oviparous reproduction allows animals to have multiple offspring simultaneously, increasing the likelihood of survival for at least some of the young. Despite being less common in mammals, it is the primary strategy in many other animal classes.

Ovoviviparous

Ovoviviparous species combine elements of both viviparous and oviparous reproduction. In these animals, the embryos develop within eggs retained inside the mother's body until they are ready to hatch. This method is seen in certain fish and reptiles, but it's rare in mammals.

Here are some important points about ovoviviparous reproduction:

• Internal Development: While the embryo gets its nutrients from the egg yolk, it remains inside the mother's body during development.
• Live Birth: Once development is complete, the young are born live as they hatch just before or during their emergence from the mother.
• Protection: Retaining the eggs internally can offer increased protection from environmental hazards and predators.

Ovoviviparous reproduction provides various survival advantages, particularly in environments where eggs laid externally may be at risk. It reflects a fascinating adaptation in the reproductive strategies of different species.