What are the different categories of stem cells based on their developmental flexibility, and how do they differ from one another?

Stem cells are categorized based on their developmental flexibility into four types: totipotent, pluripotent, multipotent, and unipotent. Totipotent stem cells can develop into any cell type, while pluripotent stem cells can develop into nearly all cell types. Multipotent stem cells can differentiate into several related cell types, and unipotent stem cells can only become one specific type of cell.

Totipotent stem cells, such as fertilized eggs, have the ability to develop into any cell type in the body. Pluripotent stem cells, found in early embryos, can differentiate into nearly every cell type. Multipotent stem cells, typically found in adults, can develop into a limited range of cell types related to their origin. Unipotent stem cells, also in adults, can only differentiate into one specific cell type. This hierarchy reflects the decreasing flexibility of stem cells as they become more specialized.