The attachment of the developing embryo to the uterine wall.
Explanation
Human reproduction follows a specific chronological sequence of events: gametogenesis, insemination, fertilization, implantation, gestation, and parturition. Implantation is the pivotal event that establishes a pregnancy within the uterus.Option-wise Analysis:
- The fusion of sperm and egg nuclei. is incorrect: The fusion of the haploid sperm nucleus with the haploid egg nucleus is termed fertilization. This process occurs in the ampullary region of the fallopian tube and results in the formation of a diploid zygote.
- The attachment of the developing embryo to the uterine wall. is correct: Implantation refers to the attachment of the developing embryo (specifically at the blastocyst stage) to the endometrium (the inner lining) of the uterine wall. This event typically occurs approximately 7 days after fertilization and leads to pregnancy.
- The release of the mature egg from the ovary. is incorrect: The process of releasing a mature ovum (egg) from the Graafian follicle of the ovary is known as ovulation.
- The expulsion of the foetus during birth. is incorrect: The expulsion or delivery of the fully developed foetus from the uterus at the end of the gestation period is called parturition (childbirth).
Key Takeaway: Implantation is the embedding of the blastocyst into the uterine endometrium, which is essential for the establishment of pregnancy and the subsequent formation of the placenta.