The inner cell mass of the embryo contains some cells which can give rise to all the tissues and organs. They are known as:
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → Stem cells
The inner cell mass of the blastocyst becomes the embryo. It forms three germ layers, ectoderm, mesoderm and endoderm, which build all the organs. Some of its cells can still become any tissue or organ.
Option (1) Ectoderm — Incorrect. The ectoderm is only one of the three germ layers, so it gives rise to only some tissues.
Option (2) Blastomeres — Incorrect. Blastomeres are the cells formed by cleavage of the zygote, before the inner cell mass is formed.
Option (3) Trophoblast — Incorrect. The trophoblast is the outer layer of the blastocyst; it attaches to the endometrium and helps form the placenta.
Option (4) Stem cells — Correct. Only stem cells can still become any tissue or organ; the ectoderm forms only some tissues, and the trophoblast is not part of the embryo proper.
NCERT Extract:
Pregnancy and Embryonic Development – “… Immediately after implantation, the inner cell mass (embryo) differentiates into an outer layer called ectoderm and an inner layer called endoderm. A mesoderm soon appears between the ectoderm and the endoderm. These three layers give rise to all tissues (organs) in adults. It needs to be mentioned here that the inner cell mass contains certain cells called stem cells which have the potency to give rise to all the tissues and organs.”