Meselson and stahl cultured
e. coli for several generations in a medium with a heavy isotope of nitrogen, 15n. they transferred the bacteria to a medium with a light isotope of nitrogen, 14 n. after two rounds of dna replication, half the dna molecules were light (both strands had 14n and half were hybrids (15n-14n. what did the researchers conclude from these results?

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.