CLAUS LUNAU / SCIENCE PHOTO LIBRARY CLAUS LUNAU / SCIENCE PHOTO LIBRARY
Culturing stem cells. Illustration of stem cells being cultured in a petri dish. Stem cells are undifferentiated cells that can produce other types of cell when they divide. There are three main stem cell types in mammals: embryonic stem cells, derived from blastocysts; adult stem cells, which are found in adult tissues; and cord blood stem cells, which are found in the umbilical cord. The cell types shown here include muscle cells, red blood cells (round), a nerve cell (yellow), and a ciliated cell (lower right).
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