External Fertilization

What Is External Fertilization?

External Fertilization occurs when an organism fertilised outside the body. The process of external fertilization usually requires a water body. Here both the eggs and sperms are released into the water. 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 fertilisation or reproduction process is influenced by sunlight and temperature. The benefits of performing the external fertilization in an aquatic body are that the eggs do not dry up. The spawning of eggs and sperms in external fertilization lead to greater biodiversity along with higher chances of genetic survival. 


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Mention Some External Fertilization Examples 

Aquatic animals generally release their gametes directly into the environment. It mostly takes place in fishes and amphibians. Descriptive external fertilisation 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. 

What Are The Features of External Fertilization? 

  • The rate of succession of the process is very weak. 

  • The male and females need to produce a large number of gametes to ensure reproduction. Although most of the gametes are wasted as there is no guarantee of all the gametes fusing with each other. 

  • External fertilization is a much simpler process compared to internal fertilization. In external fertilization, there is no involvement of hormones, maturing concepts, ovulation or mating. 

  • It is a quick and less complex process. 

  • The maternal instincts of the animals undergoing external fertilization are less. Most of the gametes produced during the process of spawning are damaged by the surrounding predators. 

  • Genetic diversity is much higher when it comes to external fertilization.

Solved Examples 

  1. Explain The Process of External Fertilization In Frogs in Brief.

It is known that frog’s lay eggs which hatch into tadpoles. The reproduction occurs by the process of external fertilization. The females release their eggs into the water which are then fertilised by the male sperms. 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 a 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. 

  1. Mention a Few Disadvantages of External Fertilization. 

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 the predators. 

  • There is no guarantee that the sperm will come in direct contact with the egg. 

  • The zygote often desiccates. 

  1. Mention the External Fertilization Advantages Along with Examples. 

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 synchronisation and is a much simpler process as compared to that of internal reproduction. 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 fertilise. 

  • The male counterparts have more gametes compared to that of females. 

  • Birds have their eggs fertilized even before they are laid. 

  • In external fertilization, an unfertilised 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. 

FAQ (Frequently Asked Questions)

1. External fertilization occurs in which animals?

Ans: External fertilization occurs in a moist environment as it gives the sperm an 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. Rate of fertilization of gametes is also very low as there is no guarantee if the eggs meet the sperms. External fertilization commonly occurs in fishes and amphibians. Other aquatic animals also perform external fertilization. 


2. Does external fertilization occur inland?

Ans: Water plays a very important role in the fertilization of eggs. The mobility of the gametes of both the male and female counterparts increase 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. The 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.