14. In the Meselson and Stahl experiment, the DNA in the parental generation was all N¹⁵N¹⁵, and after one round of replication, the DNA was all N¹⁵N¹⁴. What DNAs were seen after three rounds of replication, and in what ratio were they found?(A) one N¹⁵N¹⁴, one N¹⁴N¹⁴(B) one N¹⁵N¹⁴, two N¹⁴N¹⁴(C) one N¹⁵N¹⁴, three N¹⁴N¹⁴(D) one N¹⁵N¹⁴, four N¹⁴N¹⁴(E) one N¹⁵N¹⁴, seven N¹⁴N¹⁴

1. Which of the following events does NOT occur during light absorption in the vertebrate eye? (A) The retinal component of rhodopsin change from cis to trans form. (B) Rhodopsin, a G protein-coupled receptor, triggers a signal transduction pathway to close Na⁺ channels in the plasma membrane. (C) The light stimulus passes from rods and cones to bipolar cells and horizontal cells and then to ganglion cells, whose axons compose the optic nerve. (D) As light absorption increases, the rhodopsin response causes an increase in the release of neurotransmitter. (E) When integrating information across the retina, horizontal cells connect the rods and cones, and amacrine cells join with bipolar cells and ganglion cells

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