Question

In human female the blastocyst -
A. Forms placenta even before implantation
B. Gets implanted to the uterus 3 days after ovulation
C. Gets nutrition from uterine endometrial secretions only after implantation
D. Gets implanted in the endometrium by the trophoblast cells.

Answer 1

Blastocyst is formed by the mitotic divisions in the diploid zygote which is the product of the fusion of male and female gamete. fusion of gametes produces zygote which undergoes multiple cleavages to reach the state of blastocyst. It is a hollow ball of cells approximately 18-32 in number.

Complete answer:
After the fusion of male and female gametes, there is rapid mitotic divisions which is also known as cleavage takes place. Cleavage is the process in which the cytoplasm of the zygote is divided equally. After 4 days a morula (a solid ball of 16-32 cells) is formed which then forms a blastula (hollow) stage. The blastula has blastomeres, the ones on the outer side called trophoblast and inner ones called inner cell mass. After 7 days, the blastula gets attached to the endometrium of the female uterus by trophoblasts. Before the attachment it gets nutrition from uterine secretions.
The placenta is formed after implantation.The placenta is the organ which develops in the uterus while a female is in her pregnancy. This organ is helpful in providing oxygen and other nutrients to the growing child and removes any unwanted products from the child's blood. It is of hemochorial type in human beings and helps to provide immunoglobulins to the baby to provide an innate immunity.
Blastocyst gets implanted after 7 days and that too with the help of trophoblast cells.
Gets nutrition from endometrial secretions before implantation

So, the correct answer is “Option D”.

Note:
The placenta is the structure that provides oxygen and nutrients to the baby and removes waste material from the child's blood. The placenta is attached to the wall of your uterus, and the umbilical cord arises from it.