External Fertilisation

Fertilisation is the union of eggs and sperms. Therefore, it is the process responsible for reproduction among animals and humans. This process is further classified into two subtypes, internal and external fertilisation.

What Is External Fertilisation?

External fertilisation is a method of reproduction in which a male organism’s sperms fertilise a female organism’s eggs, but outside the female body. This process is precisely opposite to internal fertilisation. In internal fertilisation, sperms combine with eggs via insemination within the female body.

Moreover, external fertilisation takes place in aquatic environments. Here, both sperms and eggs are released into the water, and once sperms reach the eggs fertilisation takes place. 

Additionally, most of the external fertilisation occurs during the spawning process. Here, one or more female organism releases eggs and similarly male organisms releases their sperms in the same region. This process takes place at the same time.

However, this release of the reproductive substance may be affected by the length of daylight or water temperature.

Animals Capable of External Fertilisation

Some of the prominent external fertilisation examples are –

  • Starfish

Starfishes use a more synchronized technique for their spawning. They gather at a place on a specific day and at a particular time. After that, they use chemical signal to indicate other members of their species to know that they are ready to spawn. Additionally, they use the daylight as an indicator. This synchronized process improves their chance of successful fertilisation.

  • Sea urchins

Since sea urchins live in places with a relatively fast flow of water, they run the risk of losing their sperms and eggs. Thus, they use the chemotaxis process to attract sperms towards eggs.

  • Corals

Even though corals can reproduce internally, they practice external fertilisation. They release a substantial number of gametes into the water while spawning. However, a tiny amount of those eggs fertilises via sperms.

  • Frogs

The external fertilisation in frogs occurs when female frogs release eggs into the water. At the same time, male frogs also release their sperms to fertilise those eggs. 

  • Fishes

Almost all kinds of fishes use external fertilisation for reproduction.

Advantages of External Fertilisation 

The external fertilisation advantages are –

  1. It creates more genetic variations.

  2. Produces a substantial number of offspring.

  3. Additionally, the gametes can easily drift, thus, the chances of finding a suitable mate is high.

Disadvantages of External Fertilisation

The problems of external fertilisation are –

  1. A large number of gametes stays un-fertilised, and are subsequently wasted.

  2. There is no guarantee that the sperms and eggs will come into contact.

  3. Moreover, the chance of desiccation of zygotes or gametes are superior.

  4. Various environmental hazards and predators reduce the life expectancy of new-born organisms.

External Fertilisation in Human Beings

The rate of external fertilisation in human beings is low, as it is not organic. In case any female has blocked oviducts, then her chance of conceiving is lower. The reason being, male sperms cannot reach the eggs.

In such a scenario she can opt for an inorganic process named IVF (In Vitro Fertilisation). In this process, freshly released eggs and sperms are collected and kept together for fertilisation to start. When it occurs, the zygote is then transferred into the uterus of the female. After that, further development of that zygote occurs within the female’s body. 

External fertilisation is not a common phenomenon among mammals; it occurs primarily among aquatic creatures. Apart from this topic, students can visit the website and the app of Vedantu to access other topics of biology. 

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FAQ (Frequently Asked Questions)

1. What is the Definition of External Fertilisation?

Ans. External fertilisation is a reproduction process which occurs outside the female organism’s body. Aquatic creatures primarily use this process. However, humans also use this process for reproduction, but not organically.

2. What are the Mediums Where External Fertilisation Primarily Occurs in?

Ans. External fertilisation primarily occurs in the water. The male organism release sperms and the female releases eggs, and when they reach each other, they fertilise. 

3. Which of the Following is a Disadvantage of External Fertilisation?

Ans. Two primary disadvantages of external fertilisation are a considerable number of gametes remains un-fertilised, and are subsequently wasted. Moreover, there are no certainties that the sperms and eggs will come into contact.