Ulcers are caused by the bacterium ____
a. Escherichia coli
b. Helicobacter pylori
c. Bacillus anthracis
d. Streptococcus mutans
e. Staphylococcus aureus
b
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Why should deepwater shrimp on different sides of the isthmus have diverged from each other earlier than shallow-water shrimp?
A) They have been geographically isolated from each other for a longer time. B) Cold temperatures, associated with deep water, have accelerated the mutation rate, resulting in faster divergence in deepwater shrimp. C) The rise of the land bridge was accompanied by much volcanic activity. Volcanic ash contains heavy metals, which are known mutagens. Ash fall caused high levels of heavy metals in the ocean sediments underlying the deep water, resulting in accelerated mutation rates and faster divergence in deepwater shrimp. D) Fresh water entering the ocean from the canal is both less dense and cloudier than seawater. The cloudy fresh water interferes with the ability of shallow-water shrimp to locate mating partners, which reduces the frequency of mating, thereby slowing the introduction of genetic variation.
Bidirectional synthesis was demonstrated by which of the following methods?
A. Bacteria were grown on 15NH4 until the entire DNA contained heavy nitrogen and then the cells were transferred to normal, light media for one round of replication. The resulting DNA molecules were separated in density gradients and compared to the expected results for each proposed model. B. Cells were labeled with low specific activity [3H] thymidine followed by a pulse of high specific activity [3H] thymidine. This experiment revealed that a new strand was growing away from the midpoint toward one fork. C. Cells infected with T4 bacteriophage were grown in the presence of radioactive nucleotides. When DNA was analyzed in alkaline CsCl gradients, the presence of short DNA fragments indicated that bidirectional synthesis had occurred. D. Cells were labeled with low specific activity [3H] thymidine followed by a pulse of high specific activity [3H] thymidine. This experiment revealed a gradient of radioactive density that is heaviest at both forked junctions. E. None of these answers is correct.
The large land mass that contained all the continents during the Triassic was called
a. Laurasia. b. Pangea. c. Gondwana. d. Atlantis. e. Africa.
Pawlowski and colleagues (2000 ) gathered data from over 3,000 Polish men, and investigated the hypothesis that sexual dimorphism in humans is the result of female choice
They found that there was a slight but significant level of sexual selection on ________. A) the body mass index (BMI) of men in their twenties, thirties, and forties for both marriage and producing offspring B) the weight of men in their twenties, thirties, and forties for both marriage and producing offspring C) the height of men in their twenties, thirties, and forties for both marriage and producing offspring D) the intelligence quotient (IQ) of men in their twenties, thirties, and forties for both marriage and producing offspring