Simplify the following text for a Grade 5 native English-speaking person.
Original: Stem cells are biological cells found in all multicellular organisms , that can divide through mitosis and differentiate into diverse specialized cell types and can self renew to produce more stem cells . In mammals , there are two broad types of stem cells : embryonic stem cells that are isolated from the inner cell mass of blastocysts , and adult stem cells that are found in various tissues .
Simplified: Stem cells are found in most , if not all , plants and animals .