Question

how does a sinlge celled fertilised egg grows into an adult in human beings

Answer 1

The male and female reproductive organs of human beings become functional only after attaining sexual maturity. Then various changes take place in human body. During puberty sexual hormones and gametes begin to be produced. The male gamete- sperm- is introduced inside the female vagina by copulation. Sperms are active and mobile and reach ovary and then pass into fallopian tube to fertilize the ovum.

• Fertilization occurs in the fallopian tube if copulation takes place during ovulatory period.
• Embryo’s development starts immediately and menstruation stops.
• Embryo moves down to the uterus and implantation occurs.
• To enable implantation, the uterus goes through changes in order to be able to receive the embryo. The endometrium of the uterus called, "implantation window" is characterized by changes to the endometrium cells. The cells grow over the embryo enclosing it into the endometrium and surround the embryo. These changes bring the blastocyst nearer to the endometrium and immobilize it. And the embryo attached in the uterus firmly.
• The time period of foetus development till birth is called gestation. Foetal development inside the mother’s body takes approximately 9 months.
• By the end of gestation the act of giving birth is called as parturition.