Read the passage and answer the following question:
The blastomeres in the blastocyst are arranged into an outer layer called trophoblast and an inner group of cells attached to trophoblast called the inner cell mass. The trophoblast layer then gets attached to the endometrium and the inner cell mass gets differentiated as the embryo. After attachment, the uterine cells divide rapidly and covers the blastocyst. As a result, the blastocyst becomes embedded in the endometrium of the uterus . This is called implantation and it leads to pregnancy. After implantation, finger-like projections appear on the trophoblast called chorionic villi which are surrounded by the uterine tissue and maternal blood. The chorionic villi and uterine tissue become interdigitated with each other and jointly form a structural and functional unit between developing embryo (foetus) and maternal body called placenta. The placenta facilitate the supply of oxygen and nutrients to the embryo and also removal of carbon dioxide and excretory/waste materials produced by the embryo. The placenta is connected to the embryo through an umbilical cord which helps in the transport of substances to and from the embryo. Placenta also acts as an endocrine tissue and produces several hormones like human chorionic gonadotropin (hCG), human placental lactogen (hPL), estrogens, progestogens, etc.
What is the process called when the blastocyst becomes embedded in the endometrium?
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → Implantation
The passage states that “the blastocyst becomes embedded in the endometrium of the uterus. This is called implantation and it leads to pregnancy.”
The blastocyst reaches the uterus and its trophoblast layer attaches to the endometrium, the inner lining of the uterus. The uterine cells then divide fast and cover the blastocyst, so it becomes buried in the endometrium. This embedding is implantation, and pregnancy begins with it.
The other terms name different steps. Fertilisation is the fusion of sperm and ovum, which happens earlier in the fallopian tube. Cleavage is the series of mitotic divisions of the zygote that form the morula and then the blastocyst. Differentiation is the later change of cells into the layers and tissues of the embryo.