Vibrio cholerae lives in water and gets toxin genes from a virus by phage conversion. The toxin kills the intestinal epithelial cells in the human host, resulting in massive diarrhea. Untreated cholera has about a 50% mortality rate. How do the bacteria benefit?
A. They don't -- humans are not the main host and their symptoms are maladaptive for the bacteria.
B. The bacteria reproduce faster in a dead human.
C. Diarrhea helps the bacteria to spread from person to person.
D. Killing humans provides nutrients for the bacteria.
Answer: C
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DNA transposable elements (DNA TEs) are:
A. a class of transposable elements that replicate and transpose via DNA replication and repair. B. a class of transposable elements that uses RNA as an intermediate. C. a class of transposable elements that uses DNA as an intermediate. D. a class of transposable elements that uses protein as an intermediate. E. a class of transposable elements that uses ribosomes as an intermediate.
How does the loop of Henle enable the mammalian kidney to produce hypertonic urine?
I-The ascending limb of the loop actively extrudes Na+. II-The descending limb interacts with the ascending limb to raise the osmolarity of the extracellular fluid in the renal medulla. III-The concentration is further enhanced by the presence of urea, which draws water out of the collecting ducts by osmosis. A. just I B. II and III C. just III D. I and II E. I, II, and III
__________ is a form of genetic exchange in bacteria that involves contact between two cells
a. Transformation b. Transduction c. Conjugation d. Binary fission e. Budding
Scientists studying a group of related bird species on an island archipelago discover that these species are always more closely related to each other within an island than they are between any two islands. The most likely explanation for this result is that
A. many ancestral bird species colonized each island. B. each bird species evolved different adaptations in allopatry and then colonized the other islands. C. one bird species colonized each island and then evolved into distinct species on that island through character displacement. D. each bird species became reproductively isolated by living on a different island, then later colonized the other islands and acquired new adaptations.