SAT Subject Biology Practice Question 456: Answer and Explanation

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Question: 456

6. A population of ampicillin-resistant bacteria (Strain 1) is grown in a laboratory and is infected with a virus. The bacterial population begins to decline as the virus initially goes through the lytic cycle, then rebounds as the virus integrates into the bacterial chromosome to begin the lysogenic cycle.

The bacteria reproduce normally until they are heat-shocked. The rapid increase in temperature causes the virus to remove itself from the bacterial genome and enter the lytic cycle. Within several hours all bacteria are dead and a free virus is found in high concentration in the bacterial growth medium.

This free virus is used to infect a population of bacteria that is sensitive to ampicillin (Strain 2). After the expected decrease and rebound of this bacterial population (as above), the rebounded population was found to be ampicillin-resistant.

Evolution of a bacterial population occurs much more rapidly than evolution of a human population. This is because

A. the bacteria are smaller and thus more susceptible to change
B. the bacterial life cycle is short and many new generations can be produced quickly
C. humans do not evolve
D. humans can only reproduce during a portion of their life cycle, whereas bacteria can reproduce throughout their entire life cycle
E. bacteria do not require oxygen to survive

Correct Answer: B


B Evolution will always occur faster in an organism that has short generation times, simply because it is replicating its DNA more frequently and, thus, has a greater chance of mutations occuring.

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