Explanation of External Fertilization
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:-
Fertilization has an extremely low success rate.
Unlike internal fertilization, the male and female must produce a significant quantity of gametes to assure reproductive success.
To start external fertilization, you'll need a body of water. On land, the sperm would perish.
The majority of gametes perish without being fertilized, putting most animals at a reproductive disadvantage.
External fertilization, on the other hand, is a straightforward reproductive method that does not necessitate the use of hormones or mating rituals.
Solved Examples
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.
Mention a Few Disadvantages of External Fertilization.
Ans: A few common disadvantages of external fertilization are mentioned as follows:
A very major disadvantage of external fertilization is that a large number of gametes remain unused.
The aquatic environment is often very harsh. It is. It is not always suitable for reproduction or fertilization.
The offspring are subjected to danger from predators.
There is no guarantee that the sperm will come in direct contact with the egg.
The zygote often desiccates.
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
Coral animals send their eggs and sleep separately. The water currents eventually carry the gamete so that they can fertilize.
The male counterparts have more gametes compared to that females.
Birds have their eggs fertilized even before they are laid.
In external fertilization, an unfertilized egg can never be laid.
A large number of offspring are produced in external fertilization.
External fertilization results in genetic variation.
Most of the species of fish fertilize externally.
Algae also show external fertilization. The reproduction in algae is basically of three types: isogamy, anisogamy and oogamy.
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.
FAQs on External Fertilization
1. External fertilization occurs in which animals?
External fertilization occurs in a moist environment as it gives the sperm the ability to move about and reach near the egg. The process by which Sorensen and eggs are released into the water is known as spawning. A large number of eggs and sperms are produced at the same time. The offspring’s mature rapidly in this process. A major disadvantage of the spawning process is that the eggs have a very short life span. The rate of fertilization of gametes is also very low as there is no guarantee if the eggs meet the sperm. External fertilization commonly occurs in fishes and amphibians. Other aquatic animals also perform external fertilization.
2. Does external fertilization occur inland?
Water plays a very important role in the fertilization of eggs. The mobility of the gametes of both the male and female counterparts increases when it is in water. The water currents help the gametes to move towards each other. Although water is suitable for external fertilization to occur, there are some cases where the process takes place without the presence of water. For example, animals like earthworms perform fertilization in their cocoons. Scientist has tried to infuse external fertilization in the land but due to extreme lack of moisture, the process turns out to be a failure. Water is the best medium for external fertilization or spawning to occur.
3. Write the difference between external and internal fertilisation.
Internal fertilisation | External fertilisation |
It takes place inside the female body. With the help of the copulatory organ, male gametes are deposited in the female's body. Internal fertilization does not require the presence of water. Organisms that reproduce through external fertilization must either reside in the water or return to it to reproduce. Internally fertilized animals have successfully transferred to land life. | It takes place outside of the female's body. Fertilization occurs when a significant number of gametes are discharged into the surrounding medium (e.g., water). External fertilization needs the presence of water in order for the sperm and egg to join. Organisms that reproduce through external fertilization must either reside in the water or return to it to reproduce. A large quantity of eggs and sperm is required. |
4. Explain internal fertilization with examples.
Internal fertilization is the joining of an egg and sperm cell inside the female body during sexual reproduction. Internal fertilization, as opposed to external fertilization, gives the female more control over reproduction. [1] There must be a way for the male to deliver sperm into the female's reproductive system for internal fertilization to occur.
Examples: Live-bearers, such as platyfish and swordtails, reproduce by internal fertilization.
5. List examples of external fertilization.
Urchins from the sea
Chemotaxis is used to attract the sperm to the eggs. Their spawning is timed to avoid the eggs and sperms being diluted or floating away.
Frogs
The eggs are released into the water by the female. The male additionally fertilizes the sperm by releasing them into the water. The frogs' larval life is spent in water, while their adult life is spent on land.
Salmon
The gametes are discharged and then fertilized through an aperture just in front of their anal fin.
Coral Coy
During coral spawning, a vast number of gametes are released into the ocean. The coral larvae move up to the surface after fertilization to mature.
Starfish
They form groups and send out chemical signals to alert the other members of the group that they are about to spawn. The odds of fertilization success are increased because of the synchronized spawning.
