Скачать или смотреть Fertilization |Internal and External Fertilization| Chap # 14 | Biology Class 10 | Lec # 11 (PTB)

External fertilization and internal fertilization are two different methods by which organisms reproduce and fertilize their eggs. These terms refer to how the sperm and egg meet and fuse to form a zygote, which eventually develops into a new individual.

External Fertilization:
External fertilization occurs when the sperm and egg combine outside the body of the organism, typically in an aquatic environment such as water. This method is common among many aquatic species, including fish, amphibians, and certain invertebrates. Here's how external fertilization generally works:
Release of Gametes: Both male and female organisms release their gametes (sperm and eggs) into the water.

Fertilization in the Environment: The sperm and egg meet and fuse in the surrounding water. This usually requires a specific timing and location to increase the chances of successful fertilization.

Zygote Development: Once fertilization occurs, the zygote forms and starts developing. In aquatic environments, the zygote might be carried away by currents or adhere to a substrate.

Vulnerability: External fertilization often leads to a high number of gametes being released to increase the odds of fertilization. However, this method is also less controlled and more susceptible to predation and environmental factors that could hinder successful reproduction.

Internal Fertilization:
Internal fertilization involves the fusion of sperm and egg inside the body of the female organism. This method is characteristic of many terrestrial animals, as well as some aquatic species where external fertilization isn't feasible. Here's how internal fertilization generally works:
Copulation: Mating partners engage in copulation, during which the male transfers sperm into the female's reproductive tract. This can involve specialized organs, such as a penis or an intromittent organ, to deliver the sperm.

Fertilization Inside the Body: The sperm meet the egg within the female's reproductive tract, where the conditions are often more controlled and protected compared to external environments.

Zygote Development: After fertilization, the zygote starts developing within the female's body. In some cases, the embryo might receive nourishment from the mother through structures like placenta or yolk sac.

Protection: Internal fertilization provides a higher degree of protection for the developing zygote and embryo from external threats, as well as better control over fertilization timing.

Mammals, including humans, birds, reptiles, and certain insects, are examples of organisms that predominantly use internal fertilization. The choice between external and internal fertilization is often influenced by the organism's habitat, behavior, reproductive strategies, and the challenges presented by their environment



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