[Biology Class Notes] on Internal Fertilization Pdf for EXAM

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