Question

Implantation, Parturition, Ovulation, Gestation, Fertilization (Stages leading to the formation of foetus and birth).

Answer 1

A new organism is formed when the male and female gametes fuse with each other and lead to fertilization of the female gamete which implants itself into the female reproductive organs and grows and after some time takes birth and then grows into a well-developed organism.

Complete answer:
Both male and female organisms are born with reproductive organs which become functional only after puberty. When the organism hits puberty gametogenesis occurs during the process of formation of gametes. Males produce sperms by the process of spermatogenesis and females produce eggs by the process of oogenesis. After the oogenesis the egg is released from the ovary by the process of ovulation. After ovulation the uterus prepares itself for fertilization which if doesn’t occur then the menstrual cycle happens. If the male and female encounter a sexual intercourse and get the male gametes deposited inside the female body (Insemination) then those male gametes reach the female gamete and fertilize it. This is the process of fertilization. After the female gamete/egg is fertilized it starts to divide rapidly forming a mass of 2, 4, 8, 16 cells known as blastomere. Embryo having 8-16 cells is known as a morula. Morula divides and forms blastocyst and the blastomeres form the trophoblast layer which attaches to the endometrium of the uterus. After this attachment the uterine layer divides rapidly and covers the blastocyst. As a result of this the blastocyst gets embedded into the endometrium of the uterus and this process is known as Implantation. The period starting with the implantation to the birth of the new organism is known as Gestation period. In human beings this period lasts for 9 months during which the embryo develops into an organism with fully functional organs. Gestation is also referred to as pregnancy. When the gestation period is about to complete, the uterus starts to have vigorous contraction which leads to the delivery/expulsion of the foetus. This is known as parturition. The signals for uterus contraction are generated by the fully grown foetus and placenta and are known as foetal ejection reflex.

Note: During the start of gestation period the mammary glands of a female undergo differentiation and start to produce milk after parturition. This process is known as lactation and is very important as it is the first food for the newborn and is rich in colostrum which provides it lifelong innate immunity.