According to the Hardy—Weinberg principle, microevolution occurs when ____
a. a population experiences a shift in allele frequencies
b. no mutations are occurring in a population
c. a population is closed to migration from other populations
d. a feature of an individual animal changes through use or disuse
e. when a population has different forms of the same gene
ANSWER: a
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Geosmins are
A. a strain of Bacillus. B. nitrogen-fixing bacteria. C. metabolites that give soil its odor. D. produced by Rhizobium. E. metabolites that give soil its odor AND produced by Rhizobium.
Which statement summarizes the distinction between nonpolar and polar covalent bonds?
A. The difference in electronegativity of the atoms in a nonpolar covalent bond is very large. B. The electrons are more evenly and symmetrically distributed in orbit among atoms in a nonpolar covalent bond. C. The electrons are more evenly and symmetrically distributed in orbit among atoms in a polar covalent bond. D. Polar covalent bonds are formed when the atoms gain or lose electrons to bond and become oppositely charged ions.
Which of these hormones causes cell elongation, promotes apical dominance, and stimulates root branching?
A) Gibberellin B) Cytokinin C) Abscisic acid D) Ethylene E) Auxin
Explain why a scientist would need to increase the dilution rate in a chemostat from 0.20 hr-1 to 0.50 hr-1.
A. When the dilution rate is low, the availability of an essential nutrient is limited, creating an environment where the organism synthesizes nutrients rapidly to overcome the deficit in the media thus producing toxic waste products. Increasing the dilution rate provides a greater quantity of the nutrient effectively slowing growth and minimizing the level of waste. B. When the dilution rate is low, the total available energy provided by the media exceeds the maintenance energy required by the culture. Increasing the dilution rate flushes out some of the organisms to strike a balance between available energy and maintenance energy. C. When the dilution rate is low, the availability of an essential nutrient is limited, creating an environment where the organism can expend energy on survival only, not growth and reproduction. Increasing the dilution rate enables an increase in cell density. D. When the dilution rate is low, cell reproduction is high, creating a space limitation for the rapidly-dividing organisms. Increasing the dilution rate slows growth to free up available space.