Stem cell research raises many questions. What are they? Why are they important? Where do you get them? How can they be used? What ethical questions have they raised among us? Stem cell research is a very controversial, but promising study. “Stem cells are like little children who, as they grow up, can access various professions. A child can become a firefighter, a doctor or a plumber, depending on the influences in their life or environment. In the same way, these stem cells can become many tissues by making certain changes to their environment” (Parks 8). A stem cell is an undifferentiated cell capable of regenerating into another type of cell. Stem cell research began with the discovery of cells in 1665, when Robert Hooke recognized cells as the basic unit of life. In 1827, Karl Ernst von Baer stated that the life of mammals begins with the insemination of an egg. Later, in 1838, Matthias Jakob Schleiden stated that the basic structure of all plants is the cell. The following year, in 1839, Theodor Schwann declared that cells were also the basic structural unit of all animals, constituting, with Schleiden's discovery, the beginning of cellular theories. In 1855, Rudolf Virchow stated an essential law of cellular behavior: “all cells arise from existing cells”. Years later, SL Schenk attempted to fertilize a human egg outside the human body in 1878. His attempt failed, but became the first recorded work to achieve ex utero fertilization. In 1902, Gottlieb Haberlandt suggested the idea of ​​totipotency for plant cells (each cell of a mature plant has the capacity to revert to an embryonic form that can grow and differentiate into each cell of which the plant is made). In 1909, Alexander A. Maximow predicted the ex...... middle of paper ......ss called engagement. Stem cells located midway in one of these branches are called adult stem cells because they are destined to become specific types of tissue in adults and are thought to have lost the full potential of embryonic stem cells (Parks 10). Works Cited Haerens, Margaret. Embryonic and adult stem cells. Detroit: Greenhaven, 2009. Herold, Eve. Stem cell wars: inside stories from the front lines. New York: Palgrave Macmillan, 2006. Newton, David E. Stem Cell Research. New York, NY: Facts on File, 2007. Print. Panno, Joseph. Stem cell research: medical applications and ethical controversy. New York, NY: Facts on File, 2005. Print.Parks, Peggy J. Stem Cells. San Diego, CA: Reference Point, 2009. Print. Parks, Scott, Christopher Thomas. Stem cells now: from the experiment that shook the world to the new politics of life. New York: Pi, 2006.