CBSE Class 9 Answered

Stem cells are undifferentiated cells that have not yet fully specialized. Stem cells can self-renew or develop into specialized tissues and organs. The stem cells may be embryonic stem cells or adult stem cells.

Stem cells can also be found in small numbers in various tissues in the fetal and adult body. For example, blood stem cells are found in the bone marrow that give rise to all specialized blood cell types. Such tissue-specific stem cells have not yet been identified in all vital organs. Hematopoietic stem cells form blood, endothelial stem cells form the vascular system (arteries and veins), and mesenchymal stem cells form bone, cartilage, muscle, fat, and fibroblasts. Stem cells can also be obtained from other sources, for example, the umbilical cord of a newborn baby. In addition, scientists have also discovered the existence of stem cells in baby teeth and in amniotic fluid.