Observed evolution (antibiotic resistance, pesticide resistance) Knowledge-Based Practice

Questions

1. 1.

   When the use of a specific antibiotic is discontinued in a clinical setting, the frequency of resistant bacterial strains often decreases over subsequent generations. Which statement best explains this observed evolutionary shift?

   • A) Bacteria actively identify the absence of the drug and eliminate resistance genes to avoid genetic overload.
   • B) The absence of the chemical agent causes targeted reverse mutations that restore the original drug susceptibility.
   • C) Discontinuing the treatment triggers rapid genetic drift that systematically eliminates all specialized alleles.
   • D) In the absence of the antibiotic, maintaining resistance mechanisms often imposes a metabolic fitness cost, allowing susceptible bacteria to outcompete resistant strains.
2. 2.

   Why are the rapid development of antibiotic resistance in bacteria and pesticide resistance in insects widely cited as direct empirical evidence for evolutionary theory?

   • A) They demonstrate that exposure to lethal chemicals directs organisms to intentionally mutate their genes to ensure survival.
   • B) They show that major macroevolutionary transitions between distinct taxonomic classes occur within several generations.
   • C) They illustrate that individual organisms physiologically acclimate to toxic agents and transmit acquired somatic traits to their offspring.
   • D) They provide measurable, directly observable examples of natural selection altering allele frequencies in populations over short timescales.
3. 3.

   Which observation provides the most direct evidence that antibiotic resistance evolves through natural selection acting on pre-existing genetic variation rather than drug-induced mutations?

   • A) Bacteria exposed to gradually increasing concentrations of an antibiotic produce thicker peptidoglycan cell walls to prevent drug entry.
   • B) Resistant bacterial colonies grow only when cultured in an environment with high nutrient concentrations and continuous drug presence.
   • C) Pathogenic bacteria acquire resistant phenotypes exclusively after entering a host organism that is currently undergoing antibiotic treatment.
   • D) Resistant bacterial clones can be identified on replica plates in identical spatial positions before any contact with the antibiotic occurs.
4. 4.

   A farmer repeatedly sprays a crop field with the same chemical insecticide over multiple growing seasons, but over time, the chemical becomes increasingly ineffective at controlling the pest population. Which statement best accounts for this observed evolutionary change?

   • A) Individual insects gradually built up a physiological tolerance to the chemical during their lifespans.
   • B) The chemical directly induced targeted mutations in somatic cells to help the pests survive.
   • C) Survivors developed an immune response to the toxin and passed this acquired immunity to their offspring.
   • D) Insects possessing pre-existing genetic variations that conferred tolerance survived and reproduced, increasing the frequency of resistance alleles in the population.
5. 5.

   Which of the following best explains how bacterial populations develop resistance to an antibiotic over time?

   • A) Pre-existing genetic variations confer survival advantages to certain individuals, leading to differential reproduction in the presence of the antibiotic.
   • B) Exposure to the antibiotic induces targeted mutations that allow non-resistant bacteria to actively develop defense mechanisms.
   • C) Individual bacteria gradually acquire physiological immunity during their lifespan through repeated non-lethal exposure to the drug.
   • D) The chemical potency of the antibiotic degrades systematically as the overall density of the bacterial colony increases.

Answers and step-by-step solutions appear after you finish the test.