How Does Internal Fertilization Ensure Reproductive Success?
The process in which there is a fusion of sperm with the egg also known as the Ovum to produce a Zygote is called Fertilization. It is the vital and primary stage of sexual reproduction. Fertilization can be external or internal.
What is Internal Fertilization?
For sexual reproduction, male penis insertion into the vagina of a woman is important. A male inserts his penis into the vagina of a woman, after which the penis secretes sperm into the female reproductive tract to fuse with the egg. If the fusion takes place within the female parent, that is known as Internal Fertilization. In both humans and animals, the fusion of gametes takes place internally. In internal fertilization, a zygote is formed within the mother and gets its nourishment from her.
Three Ways in Which Internal Fertilization Produces Offsprings
There are three ways in which internal fertilization produces offsprings
Oviparity
Ovoviviparity
Viviparity
Oviparity
The fertilized eggs are laid outside the body of the mother. The egg receives nourishment from the yolk. Some examples of oviparous are fish, amphibians, reptiles, etc.
Ovoviviparity
The fertilized eggs are retained in the female, and the embryo receives nourishment from the yolk. When they hatch, the young ones are fully developed. This is seen in some bony fish, sharks, lizards, snakes, etc.
Viviparity
In this, the young one develops inside the mother and receives nourishment through the placenta. Most of the mammals, a few reptiles, and cartilaginous fish are viviparous.
Advantages of Internal Fertilization
The advantages of internal fertilization are:
Chances of fusion of gametes are more.
The probability of successful fertilization is increased.
The mates are selective.
The chances of dehydration of gametes decreases.
The young one is protected against predators and the outside environment and hence chances of survival are increased.
Internal Fertilization in Humans
Disadvantages of Internal Fertilization
It becomes quite difficult to bring both the male and the female into intimate contact.
At any given point of time, there’s only a limited amount of offspring that is produced.
There is a relatively higher chance of sexually transmitted diseases getting passed on.
Example of Internal Fertilization
Fertilization in humans is internal. The male introduces the sperms into the female reproductive tract. The sperm fuses with the egg in the ampulla of the fallopian tube. This results in the formation of a zygote that undergoes mitosis to form an embryo. The embryo is then implanted into the uterus. The entire process of development of the child takes place inside the uterus. Once the child is completely developed, it is delivered. However, with Internal fertilization, there is a high risk of sexually transmitted diseases in individuals. But, at the same time, it is also considered to be one of the most favorable methods of fertilization.
What is External Fertilization?
The mode of reproduction wherein the male organism’s sperm fertilizes the female organism’s egg, but outside of her body, is referred to as external fertilization. Unlike internal fertilization, where insemination takes place, this mode of reproduction tends to work differently as in this method, the sperm and the egg are released in an external environment.
External fertilization generally tends to occur in water or moist areas so as to facilitate the movement of the sperm to the egg; spawning is the term used for the process of release of the sperm as well as the eggs into the water.
Characteristics of External Fertilization
Unlike internal fertilization, this procedure requires the production of quite a large number of gametes by the male and the female organisms so as to ensure reproductive success.
It is not possible for external fertilization to take place on land as the sperm would end up dying on land. Thus, a water body is necessary for the process.
It is considered to be quite a simple reproductive strategy. This is mainly because this mode of reproduction does not require the presence of any hormones and neither does it involve any sort of mating rituals.
Advantages of External Fertilization
It is known to produce a much larger number of offspring as compared to internal fertilization.
Results in increased genetic variations.
It becomes easier to find mates as the gametes that are released tend to drift away.
Disadvantages of External Fertilization
Most of the gametes end up dying without ever being fertilized.
A very low rate of success of fertilization.
Chances of the zygote or gamete getting desiccated.
Various environmental hazards, predators, etc., tend to decrease the chances of fertilization.
Quite a large quantity of gametes are left unfertilized and are thereby wasted.
Difference Between Internal and External Fertilization
FAQs on Internal Fertilization Explained: Key Concepts & Advantages
1. What is meant by internal fertilization?
Internal fertilization is a mode of sexual reproduction where the fusion of male and female gametes (sperm and egg) occurs inside the body of the female parent. This process leads to the formation of a zygote within a protected environment, significantly increasing the chances of successful fertilization and offspring survival. It is characteristic of most terrestrial animals, including mammals, birds, reptiles, and insects.
2. What are the key differences between internal and external fertilization?
The primary difference lies in the location of gamete fusion. In internal fertilization, fusion happens inside the female's body, while in external fertilization, it occurs in an external environment, usually water. Other key differences include:
- Gamete Production: Internal fertilization requires fewer eggs, whereas external fertilization involves producing a large number of eggs and sperm to ensure success.
- Survival Rate: The survival rate of offspring is much higher in internal fertilization due to protection from predators and environmental hazards.
- Parental Care: Internal fertilization is often associated with a higher degree of parental care after birth or hatching.
3. How does internal fertilization occur in humans?
In humans, internal fertilization is a multi-step process. Following intercourse, millions of sperm are deposited into the female's reproductive tract. They travel towards the fallopian tubes, where a single sperm penetrates and fuses with a mature ovum (egg). This fusion, known as syngamy, results in the formation of a diploid zygote. The zygote then travels to the uterus, where it implants into the uterine wall and develops into an embryo.
4. What are some examples of animals that exhibit internal fertilization?
Internal fertilization is found across various animal groups. Common examples include:
- Mammals: Humans, dogs, cats, whales, and bats.
- Birds: All bird species, such as pigeons, eagles, and chickens.
- Reptiles: Snakes, lizards, turtles, and crocodiles.
- Insects: Ants, bees, butterflies, and beetles.
- Cartilaginous Fish: Sharks and rays.
5. Why is internal fertilization an evolutionary advantage for land animals?
Internal fertilization provides a significant evolutionary advantage for animals living on land. It solves the critical problem of gamete dehydration, as the moist internal environment of the female's body protects the sperm and egg from drying out. Furthermore, it ensures a higher probability of fertilization by bringing gametes into close proximity and shields the developing embryo from environmental threats and predators, leading to a much higher rate of offspring survival compared to external fertilization.
6. What are the different developmental strategies following internal fertilization?
After internal fertilization, animals exhibit three main strategies for embryonic development:
- Oviparity: The fertilized eggs are laid outside the female’s body and develop there, receiving nourishment from the yolk. This is seen in birds, most reptiles, and insects.
- Viviparity: The embryo develops inside the female's body, receiving nourishment directly from the mother, typically through a placenta. This results in the birth of live young, as seen in most mammals.
- Ovoviviparity: The fertilized eggs are retained within the female's body, but the embryo is nourished by the egg's yolk, not the mother's body directly. The young hatch inside the mother and are then born live. This is seen in some sharks, snakes, and fish.
7. Does internal fertilization also happen in plants?
Yes, internal fertilization is a key feature of seed-bearing plants (gymnosperms and angiosperms). After pollination, where pollen lands on the stigma, a pollen tube grows down into the ovary. The male gametes travel through this tube to reach the ovule. Here, fusion occurs inside the ovule, which is protected within the ovary. This process, especially the double fertilization in angiosperms, is a form of internal fertilization that is crucial for seed and fruit development.
8. What are the main advantages and disadvantages of internal fertilization?
Internal fertilization has distinct pros and cons.
Advantages:
- High Success Rate: Direct transfer of sperm increases the likelihood of fertilization.
- Offspring Protection: The developing embryo is safe inside the mother's body.
- Adaptation to Land: It allows reproduction to occur in dry, terrestrial environments.
Disadvantages:
- Fewer Offspring: Organisms typically produce far fewer offspring compared to those using external fertilization.
- Higher Energy Investment: The process requires more energy from the parents, especially the female, for mating and gestation.
- Risk of STDs: The physical contact required for fertilization increases the risk of transmitting sexually transmitted diseases.
