What must occur for a message to be sent from the outside of the cell to
inside the cell?
a. a signaling molecule binds with a membrane protein.
b. transport proteins form a channel for a large molecule.
c. enzymes inside the cell catalyze a reaction.
d. a small, nonpolar molecule crosses the membrane.

Embryonic stem cells are cells derived from an embryo. these cells can be used to create new tissues for patients suffering from certain illnesses and disorders. which statement best summarizes why the use of embryonic stem cells could be seen as unethical? a. some people consider embryos to possess rights equal to those of fully developed human beings. b. extracting stem cells from embryos is a very energy-intensive process, which consumes resources that could be used elsewhere. c. embryos are difficult to obtain, so the monetary cost of using them for research outweighs their benefit. d. the process of extracting stem cells from embryos generates biohazardous waste that cannot be safely disposed of.