The correct answer is 1 and 3 only. Key Points Stem cells are undifferentiated or partially differentiated cells in multicellular animals that can specialize in many types of cells and multiply endlessly to produce additional stem cells. In a cell lineage, they are the earliest form of cell. Tissue-specific stem cells (also referred to as somatic or adult stem cells) are more specialized than embryonic stem cells. Typically, these stem cells can generate different cell types for the specific tissue or organ in which they live. Hence, option 1 is correct. The only stem cells now used to treat disease are hematopoietic stem cells. These are the blood cell-forming adult stem cells found in the bone marrow. Every type of blood cell in the bone marrow starts as a stem cell. Stem cells are immature cells that are able to make other blood cells that mature and function as needed. Hence, option 2 is incorrect while option 3 is correct. Important Points Stem cells are divided into 2 main forms- Embryonic stem cells: The embryonic stem cells used in research today come from unused embryos. These result from an in vitro fertilization procedure. They are donated to science. These embryonic stem cells are pluripotent. This means that they can turn into more than one type of cell. Adult stem cells: There are 2 types of adult stem cells. One type comes from fully developed tissues such as the brain, skin, and bone marrow. They are more likely to generate only certain types of cells. For example, a stem cell that comes from the liver will only make more liver cells. The second type is induced pluripotent stem cells. These are adult stem cells that have been changed in a lab to be more like embryonic stem cells.