The body of living beings is based on two types of cells i.e. Germs cells and Stem cells. Germ cells are associated with the meiotic division of cells and help to make new organism. While stem cells are the cells which have the ability to renew themselves and grow through mitotic division. The mitiotic division enables these cells to differentiate into different range of specialized cells. Stem cells are present in all kinds of multi cellular cells. For stem cells to divide in other undifferentiated cells, it is necessary that either the stem cells be totipotent or pluripotent. It means they should be able to give rise to any mature cells. But sometimes multipotent or unipotent cells are also referred as stem cells.

The stem cells which have the tendency to differentiate into embryonic cell types are called as totipotent. These types of cells can make a complete organism. First few divisions of fertilized egg also give rise to totipotent cells. While pluripotent cells are actually taken out from the totipotent cells and they have the ability to differentiate into all types of cells. On the other hand multipotent stem cells have the ability to differentiate into a number of cells but they produce cells which are closely related to each other. Unipotent cells are able to produce only one type of stem cells that is their own type. But they distinguish themselves from other cells in the sense that they have the ability of self-renewal.

Properties of stem cells are best explained when they are observed in vitro. In in vitro observation, a method called colonogenic assays is used. In these assays characterization of single cells is observed by their ability to differentiate and self-renew. Stem cells can be isolated based on their properties. It is a common debate that the stem cells which are observed in vitro, their behavior changes when they are observed in vivo. It is uncertain that the stem cells will behave in the same manner in in vivo environment as they behaved in in vitro environment.

Embryonic stem cells are a type of stem cells. They are derived from the inner surface of the blastocyst which is an early stage embryo. They have the property of renew themselves. Embryonic stem cells are actually pluripotent. It means that they have the ability to differentiate themselves into three primary germ layers i.e. ectoderm, endoderm and mesoderm. The property of pluripotency distinguishes the embryonic stem cells from adult stem cells which are found in adults. Adult stem cells have the ability to produce only a limited number of cells but embryonic stem cells can generate all cell types in the body.

Opponents of the embryonic stem cell research disagree that embryonic stem cell technologies are good for human life. They think that these technologies devalue the human life that is why these technologies should not be practiced. But the scientists who favour this research, they say that embryonic stem cell technologies are beneficent for medical field. It is also noted that creation of embryonic stem cells in excess for in vitro fertilization can be donated and also can be used for the research.

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