A. Define stem cells and differentiation, and describe the different types and the extent to which they are present during the life of an individual (include the fertilized egg as well as the adult that eventually results).

Question

What will be an ideal response?

Answer 1

A. Stem cells are cells that are mitotic and not fully differentiated. Differentiation is the process cells undergo as
they become more and more specialized in structure and function as is typical of the specific tissues they compose.
The fertilized egg and the cells resulting from the first few cleavage divisions after fertilization are totipotent, which
means they can ultimately produce all the types of cells in an adult. Within the first week after conception, the cells
begin differentiation and become capable of producing many types of cells but not all. These cells are pluripotent.
By adulthood, stem cells can be described as multipotent, which are stem cells that can produce many of the cell
types in a specific tissue, and committed stem cells, which can only become one specific cell type within that tissue.
B. Epithelial and connective tissues have active populations of multipotent stems cells, which replace cells lost to
damage or normal turnover. Muscle and nervous tissues contain stem cells but appear to be unable to replace lost
cells. They were once thought to lack stem cells altogether.
C. Once cells are fully differentiated, they can no longer divide to produce more cells. Disease conditions or injuries
that result in cell loss may be remedied by treatment with appropriate stem cells. Examples are neurological injuries
and diseases marked by irreversible damage to cells that cannot (yet) be replaced by new cells.