Step 1: Read the diagram:
A is a solid ball of cells. It transforms into B, a hollow ball with an inner clump (C) and an outer single layer (D).
This is the change from morula to blastocyst.
Step 2: Part (i)(1): identify the parts:
A is the morula, a solid ball of 8 to 16 cells.
B is the blastocyst, the stage that implants in the endometrium.
C is the inner cell mass (embryoblast).
D is the trophoblast, the outer layer of cells.
Step 3: Part (i)(2): fate of C:
Right after implantation, the inner cell mass differentiates into the embryo.
It forms the three primary germ layers: ectoderm, mesoderm and endoderm. All organs of the body arise from them.
Step 4: Part (i)(3): special cells in C:
The inner cell mass contains stem cells.
These cells are pluripotent. They have the potential to give rise to all tissues and organs of the body.
Step 5: Part (ii): role and source of oxytocin:
Oxytocin acts on the uterine muscle (myometrium). It causes strong contractions that push the baby out during parturition.
It is released from the posterior pituitary (neurohypophysis). It is made by hypothalamic neurons and stored in the posterior pituitary.
Final Answer:
A = morula, B = blastocyst, C = inner cell mass, D = trophoblast. C forms the embryo and holds stem cells that can form all tissues. Oxytocin from the posterior pituitary stimulates uterine contractions at birth.
