You decide to repeat the Meselson-Stahl experiment, except this time you plan to grow the E. coli cells on light 14N medium for many generations and then transfer them to heavy 15N medium and allow them to grow for 2 additional generations (2 rounds of DNA replication). If the conservative model of DNA replication was correct, what is the expected distribution of DNA in the density gradient after two rounds of replication?
A. one band of light density and one band of intermediate density
B. one band of intermediate density
C. one band of heavy density
D. one band of light density
E. one band of light density and one band of heavy density
Answer: E
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A reagent that stains the stored food of a green alga black is
(a) India ink. (b) I2KI. (c) methylene blue. (d) both a and b.
Archaeopteris belongs to the now-extinct lineage of seedless vascular plants called ____, and is proposed to be the
possible ancestor of gymnosperms.
a. Charophyta b. Monilophyta c. Lycophyta d. proangiosperms e. progymnosperms
Which of the following represents the charged
environment inside a neuron and in the interstitial fluid that surrounds it?
a. negatively charged proteins inside; more sodium ions inside than outside; more potassium ions outside than inside b. positively charged proteins inside; more sodium ions inside than outside; more potassium ions outside than inside c. negatively charged proteins inside; more sodium ions outside than inside; more potassium ions inside than outside d. positively charged proteins inside; more sodium ions outside than inside; more potassium ions inside than outside e. negatively charged proteins inside; equal amounts of sodium and potassium ions inside and outside
Which of the following bodily fluids is commonly a source of infection by HIV?
A. breast milk B. semen C. vaginal secretions D. both semen and vaginal secretions E. breast milk, semen, and vaginal secretions