This diagram illustrates the three suggested models of DNA replication. After describing the double-helix structure of DNA, Watson and Crick stated that this structure “... immediately suggests a possible copying mechanism for the genetic material.” Based on your knowledge of the structure of DNA, which of these three models were Watson and Crick most likely considering, and why?
a. the dispersive model, because it would take advantage of the mechanisms that create homologous recombination, a process with which Watson and Crick were familiar
b. the conservative model, because it is the only model that keeps DNA strands together, eliminating most potential sources of transcription errors during replication
c. the semi-conservative model, because each nucleotide can only bond to its complement, and each strand would rebuild a second strand from available nucleotides in the cell
d. the dispersive model, because it is the only model that would allow the DNA molecule to be reconstructed from end to end, copying a single nucleotide pair at a time.
c. the semi-conservative model, because each nucleotide can only bond to its complement, and each strand would rebuild a second strand from available nucleotides in the cell
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a. a water-soluble vitamin b. an iron ion c. glucose d. NAD+ e. a magnesium ion
Which of these is the best description of a virus?
A. chemical complexes of RNA or DNA protected by a protein shell B. a member of the kingdom Virusae C. the smallest bacteria known D. a noncellular living organism E. an invasive cell that cannot stop reproducing
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a. water holds less O2 than air b. O2 concentration in water is affected by solute concentration c. the density of water allows maximal ventilation over the respiratory surface d. O2 concentration in water increases at higher temperatures e. water keeps the respiratory surface wetted
Vessel elements differ from tracheids differ in that vessel elements contain pits
____________________ Indicate whether the statement is true or false.