Problem 75 - Objective Biology for NEET

Question

Internal fertilization is seen in (a) Pleurobrachia (b) Fasciola (c) Ctenoplana (d) All of these

Step-by-Step Solution

Answer

The organism among the given options that experiences internal fertilization is Fasciola (option b).

Step 1: Understanding the Terms

Firstly, it is important to understand the terminology. Internal fertilization is the union of an egg and sperm cell during sexual reproduction inside the female organism's body.

Step 2: Identify the Organisms

Next, identify and learn about the three organisms mentioned in the exercise. Pleurobrachia and Ctenoplana fall under the category of Ctenophores or comb jellies. Fasciola is a genus of parasitic flatworms.

Step 3: Organism Reproduction Research

Research how these organisms reproduce. Pleurobrachia and Ctenoplana present a type of fertilization known as external fertilization, where the eggs are fertilized outside the female body. On the other hand, Fasciola, such as Fasciola hepatica, reproduce through internal fertilization.

Key Concepts

Internal Fertilization

Internal fertilization is a reproductive strategy where the sperm fertilizes the egg inside the female's body. This method offers several advantages, particularly in providing a stable environment for the developing embryo. The moisture and consistent temperature inside the body protect the gametes and the resulting zygote. This form of fertilization is common among land animals, including mammals, birds, and some reptiles. Internal fertilization also allows for greater parental investment, as the embryo can be more closely monitored and cared for during its development inside the body.

External Fertilization

External fertilization occurs outside the female's body, usually in aquatic environments where water can facilitate the movement of sperm to the egg. This type of fertilization is typical in many fish, amphibians, and some invertebrates, such as Ctenophores. Despite exposing the gametes to environmental factors, this method allows organisms to produce a large number of offspring at once. The sheer volume of eggs fertilized increases the chances of survival for at least some of the offspring, offsetting the risks associated with external environmental challenges.

Ctenophores

Ctenophores, also known as comb jellies, are marine invertebrates recognized for their distinctive features like rows of cilia, which they use for locomotion. These creatures often reproduce through external fertilization. Ctenophores release their eggs and sperm into the water, where fertilization occurs outside their bodies. This method is suited to their aquatic environment, where currents and tides aid in mixing the gametes. Ctenophores are fascinating because their reproduction results in a high number of offspring, although only a few survive to adulthood due to predation and environmental factors.

Parasitic Flatworms

Parasitic flatworms, such as those in the Fasciola genus, exhibit internal fertilization. These organisms have adapted to live within a host organism, and their reproductive strategies reflect this lifestyle. Internal fertilization in parasitic flatworms is advantageous as it ensures reproduction within the stable environment provided by the host. Parasitic flatworms often have complex life cycles, sometimes involving multiple hosts, which facilitates the dissemination and continuation of the species throughout various environments. These adaptations, including internal fertilization, help them efficiently exploit their ecological niches.