In Meselson and Stahl’s experiments on E. coli, why was it necessary for the DNA produced in 15N- and 14N-rich media to be loaded into a gradient before being spun in a centrifuge?
a. The gradient provided a cushioning effect, preventing damage to the DNA.
b. The gradient prevented the DNA molecules from denaturing outside of the cell.
c. The gradient enhanced buoyant density, creating more discernible bands.
d. Centrifuges do not function unless the samples are more massive than just DNA.
c. The gradient enhanced buoyant density, creating more discernible bands.
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Answer the following statements true (T) or false (F)
1. A simple dot matrix is the best method to identify homologous sequences from a known sequence. 2. If a gene's sequence is compared among several different vertebrates and they are found to be 95% homologous, one can assume that the genes are derived from the same ancestral gene. 3. Sequences that are alike will produce a horizontal line in a dot matrix analysis. 4. The current genome databases are biased towards species that are important from a research, medical, or agricultural perspective.
Why is potassium deficiency in plants most common on light, sandy soils?
A. percolation of water through sandy soils leaches potassium from the soil. B. roots grown in sandy soil can't absorb potassium. C. potassium ions are too tightly bound to sand particles to be used by plants. D. plants grown in sandy soil don't require potassium.
Large polymers are formed from smaller subunits by which type of reaction?
a. oxidation b. reduction c. condensation d. hydrolysis e. decarboxylation
Which of the following is not a greenhouse gas?
A. hydrofluorocarbons B. nitrous oxide C. oxygen D. methane E. carbon dioxide