Final answer:
The process occurring about 10 days after conception where the developing organism attaches to the uterine lining for nourishment and protection is called implantation, and it marks the transition from the germinal stage to the embryonic stage of development.
Step-by-step explanation:
The process you are referring to, beginning about 10 days after conception, in which the developing organism burrows into the placenta that lines the uterus to be nourished and protected, is known as implantation. After fertilization, the zygote travels down the fallopian tube and begins cell division, creating a structure known as a blastocyst. This blastocyst then implants into the uterine lining around day 8 or 9 in a stage referred to as the germinal stage. Following implantation, the embryo enters the embryonic stage of development, which is characterized by significant growth, organ formation, and further differentiation.
During the pre-embryonic and embryonic stages, which occur before fetal development, the conceptus undergoes rapid cell division and differentiation, eventually forming all of the rudimentary organ systems necessary for further growth within the womb. The placenta, which forms shortly after implantation, plays a vital role in supplying nutrients and oxygen from the mother to the developing embryo via the umbilical cord.