Types

• Unlimited stem cells, otherwise known as embryonic stem cells, are created from discarded embryos, typically obtained from fertility clinics. Unlimited stem cells are able to grow into any kind of cell.
  Limited stem cells, otherwise known as adult stem cells, can be found in developed human tissue, but are quite hard to utilize. Unlike unlimited stem cells, limited stem cells can only grow into cells of the same tissue from which they came, and, once obtained, must either be transplanted or put in cold storage.
  
  

Function

• Stem cells can continuously divide once they are removed from their embryos, after which they can be conditioned by experimentation to grow into specialized cells for the part of the body they are meant to be transplanted into. Otherwise, they are unspecialized and are capable, in laboratory situations, of dividing for long periods of time (up to and beyond a year) without developing into a specific, specialized cell.
  
  

Obtaining a Stem Cell

• Typically, the acquiring of embryonic or unlimited stem cells from fertility clinics requires the approval of the patient. Unlimited stem cells are made from embryos, specifically in the blastocyst stage, that are three days old and have been discarded in the process of vitro fertilization, as doctors do not implant every single embryo into the patient.
  There is also a potential alternative to the common form of obtaining unlimited stem cells, known as somatic cell nuclear transfer, or therapeutic cloning, where a patient's genetic material is inserted into an unfertilized egg. The result is stem cells carrying the same DNA as the patient, preventing the patient from rejecting the transplant. Unlike reproductive cloning, therapeutic cloning does not involve insertion into a uterus.
  
  

Uses

• Because unlimited cells can grow into any type of cell, they carry the potential to heal a variety of diseases, injuries and ailments, either by being placed in the body or by helping the development of healing drugs. According to the website Tell Me About Stem Cells, stem cells have the potential to treat cancer, Alzheimer's, Parkinson's, diabetes, hepatitis and even burns, among other ailments, given proper research. Particularly of note is a stem cell's continuous division, which can help scientists understand the similar continuous replication of cancer cells.
  As for limited stem cells, they have been used in hair, skin and bone marrow transplants.
  
  

Controversy

• Because the current method of obtaining stem cells requires using discarded embryos, there has been much controversy regarding this line of research. This is a moral issue because many people liken the embryo to being a human being despite it never growing into a fetus or even entering a human body. This is due to the belief that an individual's life begins at fertilization and that embryos are therefore vulnerable and are being exploited.