External Fertilization occurs when an organism fertilizes outside the body. The process of external fertilization usually requires a water body. Here both the eggs and sperms are released into the water. The majority of external fertilization occurs during spawning. In the priceless spawning, several eggs are released by the females at a time when the males also release several sperms. This fertilization or reproduction process is influenced by sunlight and temperature. The benefits of performing external fertilization in an aquatic body are that the eggs do not dry up. The spawning of eggs and sperms in external fertilization leads to greater biodiversity along with higher chances of genetic survival.
What is External Fertilisation?
External fertilization is a type of reproduction in which the sperm of a male creature fertilizes the egg of a female organism outside of the female’s body. Internal fertilization, on the other hand, is when sperm is delivered via insemination and subsequently mix with an egg inside the female organism’s body. External fertilization is most common in aquatic habitats when both eggs and sperm are discharged. Fertilization occurs when the sperm reaches the egg. The majority of external fertilization occurs during the spawning phase when one or more females release their eggs and one or more males discharge sperm in the same location at the same time. The temperature of the water or the length of daylight may cause the reproductive material to be released. Almost all fish, as well as crustaceans (like crabs and shrimp), mollusks (like oysters), squid, and echinoderms, spawn (such as sea urchins and sea cucumbers).
Mention Some External Fertilization Examples
Aquatic animals generally release their gametes directly into the environment. It mostly takes place in fish and amphibians. Descriptive external fertilization examples are that of salmon, trout fish, and codfish. Both the female and male release their eggs and sperms respectively into the water where they diffuse and fertilize. In the list of external fertilization examples, aquatic animals such as mammals and sharks are exceptions.
Features of External Fertilisation:-
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Fertilization has an extremely low success rate.
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Unlike internal fertilization, the male and female must produce a significant quantity of gametes to assure reproductive success.
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To start external fertilization, you’ll need a body of water. On land, the sperm would perish.
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The majority of gametes perish without being fertilized, putting most animals at a reproductive disadvantage.
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External fertilization, on the other hand, is a straightforward reproductive method that does not necessitate the use of hormones or mating rituals.
Solved Examples
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Explain The Process of External Fertilization In Frogs in Brief.
Ans: It is known that frogs lay eggs that hatch into tadpoles. The reproduction occurs by the process of external fertilization. The females release their eggs into the water which are then fertilized by the male sperm. Although the majority of the species of frogs undergo external fertilization, there are some frog species that reproduce through internal fertilization too. Scientists have discovered recently that certain frog species instead of laying eggs, carry tadpoles inside them. This finding was a very unusual one as external fertilization is a common reproduction method for amphibians.
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Mention a Few Disadvantages of External Fertilization.
Ans: A few common disadvantages of external fertilization are mentioned as follows:
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A very major disadvantage of external fertilization is that a large number of gametes remain unused.
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The aquatic environment is often very harsh. It is. It is not always suitable for reproduction or fertilization.
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The offspring are subjected to danger from predators.
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There is no guarantee that the sperm will come in direct contact with the egg.
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The zygote often desiccates.
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Mention the External Fertilization Advantages Along with Examples.
Ans: A simple major external fertilization advantage and benefit is that the chances of union between the gametes are high as a vast number of sperms and eggs are released into the water. External fertilization has greater synchronization and is a much simpler process as compared to internal reproduction. The majority of algae reproduction are external fertilization examples.
Fun Facts About External Fertilization In Animals
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Coral animals send their eggs and sleep separately. The water currents eventually carry the gamete so that they can fertilize.
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The male counterparts have more gametes compared to that females.
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Birds have their eggs fertilized even before they are laid.
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In external fertilization, an unfertilized egg can never be laid.
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A large number of offspring are produced in external fertilization.
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External fertilization results in genetic variation.
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Most of the species of fish fertilize externally.
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Algae also show external fertilization. The reproduction in algae is basically of three types: isogamy, anisogamy and oogamy.
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Algae have no embryo formation and asexual reproduction takes place through spores such as zoospores.
External Fertilisation in Humans
Humans use external fertilization as well, but it is not natural. Ovarian ducts have been obstructed in a few females. The sperms are unable to reach the eggs, and the woman is unable to conceive. Doctors gather newly released eggs and sperms and keep them together for several hours for in-vitro fertilization in this case. After fertilization, the zygote is delivered to the female’s uterus and the development process begins within her body, which takes about a week.
External fertilization is used by all fish and amphibians. However, it is not as effective as internal fertilization, and the chances of survival are lower.