Final answer:
Stem cells are defined by their ability to indefinitely divide and specialize into different types of cells. This process, known as differentiation, is regulated by transcription factors that control gene expression. Multipotent stem cells are limited in differentiation to specific lineages.
Step-by-step explanation:
What defines stem cells? The defining characteristic of stem cells is their ability to specialize into other cells. This uniqueness comes from their capability to divide indefinitely and, under certain conditions, differentiate into various specialized cells. This specialization process is known as cellular differentiation, and it plays a crucial role in the development of a complex organism. The two main types of stem cells are embryonic stem cells, which are pluripotent and can become any cell type in the body, and adult stem cells, which are multipotent and can only become a limited range of cells. Differentiation involves significant changes in a cell's size, shape, metabolic activity, and function. All somatic cells share the same DNA, yet only a portion is expressed depending on the cell type, which dictates its individual characteristics. Transcription factors are proteins that regulate which genes are turned on or off in each cell, leading to the unique genetic expression necessary for a cell's specific function. Multipotent stem cells can differentiate within a particular lineage, such as blood cells.