AP BIOLOGY

Detailed explanation-1: -These stem cells come from embryos that are 3 to 5 days old. At this stage, an embryo is called a blastocyst and has about 150 cells. These are pluripotent (ploo-RIP-uh-tunt) stem cells, meaning they can divide into more stem cells or can become any type of cell in the body.

Detailed explanation-2: -Sources of stem cells. Stem cells originate from two main sources: adult body tissues and embryos. Scientists are also working on ways to develop stem cells from other cells, using genetic “reprogramming” techniques.

Detailed explanation-3: -Summary: Researchers have analyzed all cell types in the human ovary and found that the hotly debated so-called egg stem cells do not exist. Researchers at Karolinska Institutet in Sweden have analysed all cell types in the human ovary and found that the hotly debated so-called egg stem cells do not exist.

Detailed explanation-4: -Totipotent stem cells. The zygote or fertilized egg is, of course, a totipotent stem cell. The known and well characterized totipotent stem cells are found only in early embryonic tissues and derive usually from the first few cell divisions after fertilization.

Detailed explanation-5: -The fertilized egg cell divides into two cells. Each cell then divides into two additional cells and so on until, after a few days of cell division, a tiny embryo develops. In the early stages, the microscopic embryo is made up of cells that have the potential to develop into all types of cells.