The cells of inner cell mass of a blastocyst stage mammalian embryo are
Rephrasing the Question:
What is the cell potency of the inner cell mass of a blastocyst?
The cells of the inner cell mass of a blastocyst are pluripotent (option 2).
This question refers to cell potency at different stages of an embryo – that is, what kind of cells a particular cell can turn into. A key thing to remember is that the more differentiated a cell becomes, the lower its cell potency gets.
The zygote has to create not only all the tissues of the individual, but also the tissues that help the embryo survive during gestation, like the placenta. The zygote gives rise to all these different cell types, so it called totipotent (toti = total = complete potency).
The second stage of the mammalian embryo, the morula, is an undifferentiated mass of sixteen cells, which are called blastomeres. Since the cells haven’t specialized yet, they too are totipotent.
Then the cells begin to differentiate, and the embryo undergoes cavitation. The resulting blastocyst has two distinct parts: the outer layer of cells (trophoblast) and the inner cell mass. The trophoblast will become the placenta, while the inner cell mass is what will become all the tissues of the individual. This means the cells of the inner cell mass can turn into any of the three germ layers (ectoderm, mesoderm, and endoderm) – this is called pluripotency (pluri = many).
Multipotent cells are those that are more limited in the types of cells they can become. The best way to understand them is through the example of the multipotent hematopoietic stem cells (HSCs), which can turn into neutrophils, macrophages, RBCs, etc., but can’t turn into epithelial cells.
A unipotent cell (uni = one) is one with the least cell potency and can only turn into one type of cell. For instance, a melanoblast can only become a melanocyte.
Singh VK, Saini A, Kalsan M, Kumar N, and Chandra R. (2016) Describing the Stem Cell Potency: The Various Methods of Functional Assessment and In silico Diagnostics. Front Cell Dev Biol Nov 22; 4:134.