A Complete Note On The Difference Between Internal and External Fertilisation


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NEET Preparation

The process that initiates the formation of new life is called fertilisation. During fertilisation, a single male gamete called sperm fuses with a mature female gamete called egg or ovum to create a zygote. After uniting, the sperm releases its genetic information by DNA in the middle of the ovum. 

This process enables this newly formed zygote to contain and combine important genetic data from both father and mother body individually. This single-celled formation is known as an embryo, the beginning of a completely new entity.

Depending on various species, fertilisation can be of two types- internal fertilisation and external fertilisation. The difference between these processes is prominent.

Following is a thorough discussion on the difference between internal and external fertilisation.

Internal Fertilisation

Internal fertilisation is a type of fertilisation when the merging of female and male gamete happens inside a female body. Usually, internal fertilisation is seen amongst terrestrial animals like birds, mammals, etc. and plants. However, some aquatic animals also follow this reproduction method.

Majorly, there are three ways by which males transfer their sperms inside the reproductive tract of females. Here they are-

  • Copulation

This method is commonly known as sexual intercourse where the male reproductive organ inserts into the female reproductive tract. Mammals, few birds, reptiles, etc. follow copulation for insemination.

  • Cloacal Kiss

This is the most common phenomenon in birds. In this process, two animals of different sex press and hold their cloacas and transfer sperms.

  • Spermatophore

Some land animals like insects and molluscs transfer spermatophores or a packet of sperms from males to females.

Types of Internal Fertilisation

Internal Fertilisation Can be Done in Three Ways.

  1. Oviparity

During this mode of internal fertilisation, females lay the fertilised eggs outside of their bodies. The eggs are covered with a hard shell, and yolks provide metabolic support to eggs. 

Example: Amphibians, Fish, Birds, and Reptiles.

  1. Viviparity

Viviparity is an internal fertilisation process in which the embryo develops inside the mother's body, and it receives nutrients via placenta. Females give birth to individual organisms.

Example: Humans, Cattle, etc.

  1. Ovoviviparity

In ovoviviparity, fertilised eggs remain in female bodies, and yolks act as the nutrient source for the eggs.

Example: Sharks, Snakes, Lizards, etc.

Advantages of Internal Fertilisation

  • In this method, the fertilised egg remains safe from outside attacks and adverse environmental conditions.

  • The chances of gamete desiccations are low and successful fertilisations are on a higher side.

  • In this process, offspring survival chances are high.

  • Numbers of sexual partners in internal fertilisation are selective.

Disadvantages of Internal Fertilisation

  • At a time, a smaller number of offspring can be produced.

  • Sometimes, syngamy becomes difficult for both sexes.

  • The production of male sperms has to be large in numbers for successful fertilisation.

  • Both males and females need behavioural and physiological coordination that are highly controlled by hormones.

External Fertilisation

In this mode of reproduction, male sperms fertilise female eggs outside the female body. Typically, external fertilisation happens either in moist areas or aquatic environments where sperms can easily move to eggs.

The release of both male and female gametes inside the water is termed as a spawning. However, both sexes need to release their gametes at the same time for successful fertilisation.

Example: Coral, Tube-dwelling polychaetes, Sea anemones, Fish, and Amphibians.

Advantages of External Fertilisation

  • By external fertilisation, the number of offspring can be huge.

  • As this mode of reproduction does not require contact, mates can be found easily. They release gametes and drift away.

  • A large number of genetic variations result from external fertilisation.

Disadvantages of External Fertilisation

  • The gamete desiccation rate is higher.

  • Outside attack and environmental disruption can reduce chances of fertilisation.

  • Also, a lot of unfertilised gametes is wasted.

  • Both males and females must release a large number of gametes for successful fertilisation.

As you can see from the above content, there are several differences between internal and external fertilisation. But for your facility, here is the difference between internal and external in a nutshell

Difference between Internal and External Fertilisation

Internal Fertilisation

External Fertilisation

Internal fertilisation implies the reproduction process, where the merging of gametes happens within the female body by sexual intimacy.

External fertilisation implies the reproduction method, where the combining of gametes occurs in external environments like water.

This mode of fertilisation can happen in three modes – oviparity, ovoviviparity, and viviparity.

This process of fertilisation can happen only in the outside environment.

After fertilisation, the further developmental process of the zygote happens in female bodies.

The entire reproduction process happens exteriorly. 

The survival rates of offspring are higher.

The survival rates of eggs and embryos are lower.

During internal fertilisation, a lesser number of gametes are involved.

During external fertilisation, a larger number of gametes are involved.

This reproductive mode may or may not create greater genetic mutations.

This way of reproduction surely creates greater genetic mutations.

Male gametes are deposited into female reproductive tracts.

Both gametes are deposited into outside surroundings.

Organisms that are involved in internal fertilisation can produce a lesser number of offspring.

Organisms that perform external fertilisation can produce a greater number of offspring.

Plants like bryophytes, gymnophytes, angiosperms, and pteridophytes perform this mode of fertilisation.

In plants, only most of the algae perform external fertilisation.

Examples: Reptiles, Mammals, Birds, etc.

Examples: Aquatic organisms.

Preparing for Your Exams

So, these two types of fertilisations- internal and external fertilisation are performed by different animals as their reproduction methods. Also, from the difference between internal and external fertilisation, you can easily understand the entire concept of this chapter. 

Now, all you need is to prepare yourself for the NEET examination by giving multiple mock-tests chapter wise. This way, you can assess your weakness and work on that. But above all, you should keep yourself positive and healthy.

You can practice yoga in the morning as that can increase your focus in study. You need to plan a routine and hope for the best.  

FAQ (Frequently Asked Questions)

1. What is the Most Important Disadvantage of External Fertilisation?

Ans. The major concern is, even after depositing hundreds of both gametes within proximity, the rate of wasted eggs and sperms is relatively higher. 

2. Which Fertilisation Process You Think Is Better?

Ans. After assessing the difference between internal and external fertilisation, it is understandable that depending on different habitations and other external and internal environmental conditions, both of these fertilisation processes are similarly necessary.

3. Which Reproduction Method Do Humans Perform?

Ans. Humans perform internal fertilisation to produce offspring.