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Difference Between Internal And External Fertilisation

Difference Between Internal And External Fertilisation

Fertilisation is a life process of forming a new organism of its kind by the fusion of male and female gamete. The male produces sperm, and the female produces an egg for the formation of a zygote. Zygote is the structure that carries the genetic information from both mother and father. This fertilisation takes place inside and outside the female body, called Internal And External Fertilisation.

Table of Contents:

  • What is Internal Fertilisation?
  • Advantages Of Internal Fertilisation
  • Disadvantages Of Internal Fertilisation
  • What is External Fertilisation?
  • Features Of External Fertilisation
  • Advantages Of External Fertilisation
  • Disadvantages Of External Fertilisation
  • External Fertilisation for Humans
  • Practice Problems
  • Frequently Asked Questions

What is Internal Fertilisation?

Internal fertilisation is the combination of sperm and egg after insemination for sexual reproduction. It takes place inside the female body. It is the syngamy of gametes that gives control to females over reproduction. As the name suggests, it takes place inside an individual’s body. The male sperm is introduced into the female reproductive tract for internal fertilisation. However, they are transferred in different ways by different animals.

There are three ways to create offspring by internal fertilisation: Oviparity, Ovoviviparity and Viviparity. 


In this method, the fertilised egg is kept outside of the mother’s body. The egg gets nutrition from the yolk. For example, amphibians, fish, birds and some species of reptiles are oviparous.


In this method, the fertilised egg is taken care of in the female and the embryo is fed by the yolk. The offspring is formed completely when the eggs hatch. For example, sharks, snakes, reptiles and some bony fishes are ovoviviparous. 


In this method, the offspring develops completely in the mother’s body. It gets nutrients from the placenta. For example, the majority of mammals and a few reptiles are viviparous.

Advantages Of Internal Fertilisation

  • The offspring has a high probability of survival, as it is fed by the parent.
  • High rate of successful fertilisation
  • High chance of surviving critical conditions.

Disadvantages Of Internal Fertilisation

  • There is a chance of generating many offspring.
  • Less competition among parents and kids.
  • Effort in finding a partner.

What is External Fertilisation?

External fertilisation refers to the reproduction in which the sperm fertilises the female egg outside the female body. It is the exact opposite of internal fertilisation. It is the syngamy of gametes that takes place outside the body. It notably takes place in water bodies. This type of fertilisation is observed in a few vertebrates, such as fish, sea urchins and all amphibians. The process of accumulation of sperm and eggs by males and females in an open environment is called spawning. When sperms swim away through water, broadcast fertilisation is used to unite them with eggs for fertilisation.

Features Of External Fertilisation 

  • The low success rate for external fertilisation.
  • Both males and females should produce maximum quantities of gametes to ensure successful reproduction.
  • External fertilisation must proceed in the water bodies because sperms may perish onshore.
  • Most gametes deteriorate without being fertilised, making reproductive disadvantages for most animals.
  • External fertilisation doesn’t require any kind of hormones for development, and it is a straight reproductive method. 

Advantages Of External Fertilisation

  • The female counterpart of reproduction contributes maximum time and effort.
  • Only a few offspring are generated.
  • The necessity of effort in finding a partner for fertilisation.

Disadvantages Of External Fertilisation

  • There is a low chance of survival, as they are readily preyed upon without parental care.
  • The majority of offspring die because they are unfertilised or die before reaching adulthood.
  • Offspring that rely on external fertilisation can survive only in a moist and humid temperature.

External Fertilisation for Humans

When a woman's reproductive system can not undergo natural internal fertilisation, they can opt for external fertilisation. Several female oviducts are not suitable for internal fertilisation, or the sperm can’t reach the eggs, which is why they are unable to reproduce. So physicians collect the newly released egg and sperm from the female, and the male preserves them for in-vitro fertilisation. Once it is fertilised, the zygote is transferred to the female uterus for the natural development process of the baby.

Practice Problems

Q1. In which of the following methods is the fertilised egg kept outside the mother’s body?

A. Oviparity
B. Viviparity
C. Ovoviviparity
D. None of the above

Answer: A. Oviparity

Explanation: In Oviparity, the fertilised egg is kept outside of the mother’s body. The egg gets nutrition from the yolk. For example, amphibians, fish, birds and some species of reptiles are oviparous.

Q2. Which of the following methods has less chance of survival?

A. Internal fertilisation
B. External fertilisation
C. Both a and b
D. None of the above

Answer: B. External fertilisation

Q3. Which of the following is viviparous?

A. Fish
B. Snakes
C. Birds
D. Mammals

Answer: D. Mammals

Explanation: Mammals are viviparous as the offspring develops completely in the mother’s body. It gets nutrients from the placenta. 

Frequently Asked Questions

Q1. What is a zygote?
Answer :
A zygote is a fertilised egg cell that is formed by the fusion of male and female gametes. This zygote attains further development into a new organism.

Q2. Can humans process external fertilisation?
Answer : Yes, when a human's reproductive system is unsuitable for internal fertilisation, they can opt for in-vitro fertilisation. In this case, the eggs and sperm are fused in a laboratory condition and then introduced into the female uterus for further development.

Q3. What organisms rely on internal fertilisation?
Answer : Organisms such as reptiles, birds, and plants like bryophytes and tracheophytes rely on internal fertilisation for reproduction.

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