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Types of Fertilization

Fertilization is of two types:

1. External Fertilization

       It is the fusion of male gamete with the female gamete outside the bodies of parents. External fertilization takes place in those animals which live in water, such as fish and frogs. These animals produce a large number of eggs and sperms and release them into the water. The sperms swim towards the eggs and fertilize them.

2. Internal Fertilization

       It is the fusion of male gamete with female gamete inside the parent’s bodies. Internal fertilization takes place in most of land animals including humans, birds and reptiles. In internal fertilization the sperms are deposited inside the female’s body by males through copulation or mating. These sperms then fertilize the eggs of the female inside female’s body.

       Fertilization is internal in human beings i.e. million of sperms are introduced by males in the vagina of female by the process of copulation or mating. From the vagina, the sperms move to fallopian tubes with the help of their flagella. One of the fallopian tubes contains an ovum released during ovulation. Out of many sperms only one sperm fuses with the ovum to form zygote. Thus the process of fertilization of an ovum by a sperm takes place in the fallopian tube. When the ovum gets fertilized by sperm, the woman is said to be pregnant.

       The zygote divides rapidly by mitosis to form a hollow ball of hundreds of cells called embryo. The embryo moves down to uterus, and gets attached to its thick wall. The attachment of the embryo with the uterus is called implantation. After implantation a special tissue called placenta develops between uterus wall and the embryo (foetus). The function of placenta is to fulfill all the requirements of the foetus such as nutrition, respiration and excretion, which are necessary for its development.

       The development of the foetus inside the uterus takes place till the birth of the baby. The time period of the development of the foetus inside the uterus from the time of fertilization to the birth of the baby is called gestation period. The average gestation period or pregnancy period is about 40 weeks or 280 days. On the completion of the gestation period, the birth of fully developed baby takes place. This process of birth takes place by the contraction of the inner wall of uterus which pushes the baby out of the body of the mother through vagina and is called parturition or labour.

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