The diagram given below shows a developmental stage of human embryo. Answer the following questions with reference to it :

(a) Identify and name the human embryonic stage shown.

(b) Mention its exact location in the normal pregnancy of a woman.

(c) Write one function of each of the two parts labelled 'X' and 'Y'.

The correct answer is:
(a) Blastocyst
(b) Uterine wall/endometrium/innermost layer of uterine wall.
(c) (Outer layer/trophoblast) ‘X’- helps in implantation in uterus/attachment to endometrium; (Inner cell mass) ‘Y’- gets differentiated into embryo.

Detailed Step-by-Step Explanation:

(a) Identification of the Embryonic Stage:
The diagram displays a hollow sphere of cells, which is characteristic of the mammalian blastula stage, specifically known as the blastocyst in humans. This stage is reached approximately 5–6 days after fertilization. It consists of an outer layer of cells called the trophoblast and an inner cluster of cells called the inner cell mass, surrounding a fluid-filled cavity (the blastocoel).

(b) Exact Location in Normal Pregnancy:
In a normal pregnancy, the blastocyst is located in the uterine wall (specifically embedded in the endometrium, which is the innermost glandular layer of the uterus). This placement occurs during the process of implantation, which secures the embryo for subsequent development.

(c) Functions of Labelled Parts 'X' and 'Y':

• Part 'X' (Trophoblast / Outer cell layer): The primary function of the trophoblast is to facilitate the attachment and invasion of the blastocyst into the endometrium of the uterus, a process called implantation. It also eventually contributes to the formation of the placenta.
• Part 'Y' (Inner Cell Mass / Embryoblast): The inner cell mass is a cluster of pluripotent stem cells located internally at one pole of the blastocyst. Its primary function is to differentiate and give rise to the tissues of the embryo itself (the fetus), as well as some associated extraembryonic membranes.