A mutation in the gene encoding the enzyme that cuts F factor DNA during conjugation would result in
A. an inability to draw the conjugated cells close enough to allow DNA transfer.
B. the inability of the recipient cell to replicate the F factor after transfer.
C. the transfer of single-stranded DNA instead of double-stranded DNA.
D. an inability to separate the recipient DNA from the donor DNA.
E. the inability of the donor DNA to move through the pilus.
Answer: D
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The most significant role played by pH buffers is to
A. prevent fluctuations in the acidity of solutions. B. increase the strength of acids and bases. C. prevent fluctuations in the salinity of solutions. D. limit major shifts in the amount of H+ and OH- in solution. E. keep pH low.
Membrane sterols, such as cholesterol, function in animal cell membranes to ____
a. increase the rate of diffusion b. store cellular energy c. facilitate ion transport d. maintain membrane fluidity e. receive chemical signals
Many songbirds breed in North America in the spring and summer and then migrate to Central and South America in the fall
They spend the winter in these warmer areas, where they feed and prepare for the spring migration north and another breeding season. Two hypothetical species of sparrow, A and B, overwinter together in mixed flocks in Costa Rica. In spring, species A goes to the east coast of North America, and species B goes to the west coast. What can you say about the isolating mechanisms of these two species? A) They must have strong postzygotic isolating mechanisms to spend winter in such close proximity. B) They must have strong prezygotic isolating mechanisms to spend winter in such close proximity. C) Their winter habitat has no bearing on their degree of reproductive isolation. D) Reinforcement must be occurring when they winter together.
Why are saturated fats considered a less healthy nutrient?
A) Saturated fats cannot be used for energy as the other fats can. B) Saturated fats raise HDL levels, which contributes to heart disease. C) Because saturated fats are from animal sources, they can produce allergic reactions. D) Saturated fats raise LDL levels, which contributes to heart disease.