Final answer:
Embryonic stem cell research is controversial due to ethical concerns, while adult stem cells and induced pluripotent stem cells are potential sources of stem cells that are not controversial.
Step-by-step explanation:
Embryonic stem cell research is controversial due to ethical concerns surrounding the use of embryos. Embryonic stem cells are obtained from embryos that are typically created through in vitro fertilization but are not implanted in a woman's uterus. The controversy arises because some people consider embryos to have the status of human beings and believe that using them for research purposes is morally wrong.
A potential source of stem cells that is not controversial is adult stem cells. These stem cells are found in various tissues and organs in the body, such as bone marrow and skin. Adult stem cells have a limited range of differentiation but can still be used for certain therapeutic applications. Another potential source of stem cells that is not controversial is induced pluripotent stem cells. These cells are created by reprogramming adult cells to become pluripotent, similar to embryonic stem cells, but without the ethical concerns.