Internal fertilization is the process when the syngamy (union of male and female gamete) occurs inside the female body after insemination using copulation. In contrast, External fertilization is the syngamy outside the female body, that is in the outer environment especially in water bodies.
Internal fertilization is followed by mammals, birds, while external fertilization is supported by mostly aquatic animals and few amphibians.
We all are aware of the word fertilization, which defines the union of sperm (male gamete) and egg nucleus (female gamete) to produce diploid cell or zygote, which further develops or grow into the young ones of their generation. Internal and External fertilization are the two types of fertilization, which takes place among various groups of animals, and with this content, we will be discussing the diverse features of them.
Content: Internal Vs External Fertilization
Comparison Chart
| Basis for Comparison | Internal Fertilization | External Fertilization |
|---|---|---|
| Meaning | The process of fusion of male and female gamete (sperm and egg) taking place inside the body of the female, is called as internal fertilization. | The process of fusion of male and female gamete (sperm and egg) taking place in the external environment (in water bodies) and so-called as external fertilization. |
| Gametes released | Less number of gametes (sperms) are released, which gets deposited inside the female body. | Numerous gametes (sperms and egg) are released into the environment. These gametes are of male as well as of female. |
| Process involves | Only male gametes are released or discharged into the female genital tract. | Both male and female release or discharge their gametes in their external surrounding. |
| Further process of development (syngamy) occurs inside the body only. | Further process of development (syngamy) occurs outside the body. | |
| There are three types by which internal fertilization occurs: 1. Oviparity. 2. Viviparity. 3. Ovoviviparity. | It occurs only in an external environment. | |
| Examples | Mammals (including humans), Reptiles, Birds, Bryophytes and Tracheophytes. | Amphibians, Algae, Fish, etc. |
| Advantages | 1. There are more chances of survival of offspring, as they get parental care. 2. Even the rates of successful fertilization are much higher. 3. There are chances of success of survival of the offspring even in harsh condition. | 1. The offspring produced are higher in number. 2. Less amount of energy is required to find a mate. 3. Less competition between offspring and their parents. |
| Disadvantages | 1. Requires high energy to find a mate. 2. The offspring produced are few. 3. Larger contribution of the female parent only. | 1. Fewer chances of survival of the offspring, as there is no parental care and they (offspring) get preyed upon. 2. Due to unprotection, many offspring do not get fertilized or survive till their maturity. 3. Can survive in moistened or in the wet environment only. |
Definition of Internal Fertilization
Internal fertilization occurs in terrestrial (animal living on land) animals, plants, though it is followed by some of the aquatic animals also. This method is followed in three ways which are oviparity, viviparity, ovoviviparity.
Oviparity is followed by the animals that lay eggs outside, and the nourishment is provided to the offspring by the presence of the yolk in the egg. These animals are called oviparous, like birds, most amphibians, reptiles, bony fish, and some cartilaginous fish.
Viviparity is followed by mammals, few reptiles and cartilaginous fish. In this, the offspring develop within the body of a female and receive nourishment through the placenta from the mother’s blood. Later on, the developed offspring comes out from the mother,s body. These animals are called as viviparous.
Ovoviviparity, the eggs are retained in the female body, and the nourishment is provided from the yolk present in the egg only to the developing embryo. The egg hatched when the young ones are fully developed. Sharks, lizards, snakes follow this process.
Internal fertilization is also followed by almost all plants like bryophytes, pteridophytes except few aquatic non-vascular pants.
Definition of External Fertilization
Few vertebrates, fish, sea urchins, all aquatic invertebrates and most amphibians follow this process, where male and female gamete unite in the external environment. When sperms and egg are deposited in the open surrounding by male and female gamete, it is called spawning.
Another term ‘broadcast fertilization‘ is used when the sperms swim through the water to get unite with the eggs and get fertilized.
Key Differences Between Internal and External Fertilization
Given below are the essential points to distinguish the two types of fertilization processes:
- Internal Fertilization is defined as the process of fusion of sperm (male gamete) and egg nucleus (female gamete) taking place inside the body of the female by the insemination through copulation. On the other hand, external fertilization refers to the process of fusion of male and female gametes (sperms and eggs) taking place in the external environment (in water bodies). When sperms and eggs are discharged in the external surrounding, it is called as spawning.
- Less number of gametes (sperms) are released, which gets deposited inside the female body in the internal fertilization, while in external fertilization numerous gametes (sperms and eggs) are released into the environment. These gametes are of male as well as of female.
- The process of the internal fertilization takes place inside the female body, and the offspring develops there only, while in external fertilization this process happens outside the body that is in the external aquatic environment.
- Internal fertilization is of three types – Oviparity; Viviparity; Ovoviviparity. There are no such types of external fertilization.
- Internal fertilization is followed by Mammals (including humans), Reptiles, Birds, Bryophytes and Tracheophytes, while external fertilization is followed by Amphibians, Algae, Fish, etc.
- In internal fertilizations there are more chances of survival of offspring, as they get parental care, even the rates of successful fertilization are much higher, and there are chances of success of the survival of the offspring also in harsh condition. But there are certain limitations too of this process as it requires high energy to find a mate, the offspring produced are few and there, is the greater contribution of the female parent only.
- In external fertilization the offspring produced are higher in number, less amount of energy is required to find a mate and also there is less competition between offspring and their parents. But there are fewer chances of survival of the offspring, as there is no parental care and due to unprotection, many offspring do not get fertilized or survive until their maturity, mainly they can survive in moistened or in the wet environment only.
Conclusion
From the above content, we conclude that, both the process of fertilization though have some condition in common but varies other. But both are equally important for the one or the other organisms to increase their generation.
Ambuj Upadhyay says
brilliant and detailed explanation…found it useful.
Ayush Adhikari says
Thank you for your help