SAT Subject Biology Practice Question 458: Answer and Explanation

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Question: 458

8. 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.

The bacterial culture is constantly infused with oxygen to ensure a high rate of reproduction among the bacteria and a healt

A. obligate aerobes
B. obligate anaerobes
C. tolerant anaerobes
D. facultative anaerobes
E. simple anaerobes

Correct Answer: D


D Organisms that use oxygen when it is available and survive by fermenting when oxygen is not available are classified as facultative anaerobes. You should have at least been able to eliminate choices A and B; the word obligate implies that they MUST be a certain way (e.g., always aerobic or always anaerobic), and these bacteria are able to switch.

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