Testosterone is an example of a chemical signal that affects the very cells that synthesize it, the neighboring cells in the testis, along with distant cells outside the gonads. thus, testosterone is an example ofa) an autocrine signal. b) a paracrine signal. c) an endocrine signal. d) both an autocrine signal and a paracrine signal. e) an autocrine signal, a paracrine signal, and an endocrine signal

Which of the following is an advantage of using embryonic stem cells in medical research? a. the use of embryonic stem cells is much less expensive than the use of adult stem cells. o b. no living tissue is damaged when scientists use embryonic stem cells. o c. embryonic stem cells are able to differentiate into a wider range of cells than adult stem cells. d. there is no controversy surrounding the use of embryonic stem cells.