How did Meselson and Stahl rule out the conservative model of DNA replication using equilibrium density gradient centrifugation?
What will be an ideal response?
First, they grew E. coli cells in a medium containing only high-density nitrogen (15N). Then they allowed the cells to undergo successive rounds of replication in the presence of normal density nitrogen (14N). They used equilibrium density gradient centrifugation after each round of replication to separate the DNA produced by density. If the conservative model was correct, they would have found no intermediate-density DNA after a round of replication. However, after one round of replication, they found that the entire amount of DNA had a density exactly intermediate between 14N and 15N. Subsequent rounds of the experiment showed that semiconservative replication was the correct model.
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Liebig's Law of the Minimum states that:
A. there must be a minimum number of primary producers to support an ecosystem. B. primary production is usually determined by the abundance of just a single nutrient. C. primary production is limited by the nutrient that is least available for use by primary producers. D. primary production is limited by the nutrient that is in the greatest abundance for use by primary E. producers. F. primary production in all ecosystems is limited by the same nutrient.
Where are the largest reserves of carbon on the planet?
A. soils B. frozen lakes C. rocks and fossil fuels D. fossil fuels E. the oceans
Which event occurs last in the noncyclic pathway of
ATP formation? a. excitation of p700 b. transfer of energy to p700 c. formation of NADPH d. ATP synthesis e. transfer of electrons to p680
A(n) ____ includes the entire genome.
A. cDNA library B. transcribed library C. genomic library D. RNA library E. plasmid library