40. The cells of inner cell mass of a blastocyst stage mammalian embryo are
(1) totipotent                                       (2) pluripotent
(3) multipotent                                     (4) unipotent

In mammalian embryogenesis, the blastocyst stage is a critical milestone where cells start to specialize and organize into distinct lineages to form the embryo proper and supporting structures. The inner cell mass (ICM) within the blastocyst is a cluster of cells with a unique and vital role in development.

The ICM cells are not totipotent; instead, they are pluripotent. This means they can give rise to all three germ layers — ectoderm, mesoderm, and endoderm — which collectively form every tissue type in the fetus. However, unlike totipotent cells (such as the zygote and early blastomeres), ICM cells cannot differentiate into extraembryonic tissues like the placenta.

This pluripotency makes ICM cells the source of embryonic stem cells, widely studied for their ability to contribute to diverse tissues and regenerative medicine. The outer layer of the blastocyst, the trophectoderm, forms extraembryonic structures instead.

In summary, the correct statement about the cells of the inner cell mass of a blastocyst stage mammalian embryo is:

(2) pluripotent

This fundamental concept informs both developmental biology and therapeutic strategies leveraging stem cell pluripotency.

Answer: (2) pluripotent