12. At 4:00 p.m. a closed flask of sterile broth is inoculated with 10,000 cells. The lag phase lasts 1 hour. At 9:00 p.m. the log phase culture has a population of approximately 41 million cells. The mean generation time is calculated as ______.
(A) 10 minutes
(B) 20 minutes
(C) 30 minutes
(D) 40 minutes
(E) 60 minutes

8. Small internal cell structures are best visualized with a ______. (A) light microscope (B) dark-field microscope (C) transmission electron microscope (D) scanning electron microscope (E) fluorescence microscope

9. Which of the following protects bacteria from lysis in dilute solutions and helps to determine their cellular morphology or shape? (A) Plasma membrane (B) Peptidoglycan (C) Capsule (D) Gas vacuoles (E) Flagella

10. Motile bacteria have been placed in an environment with a gradient of a chemical attractant. Which of the following behaviors would you predict? (A) The bacteria will randomly switch back and forth between runs and tumbles. (B) The bacteria will only exhibit runs away from the chemical. (C) The bacteria will reduce tumbling frequency. (D) The bacteria will reduce run duration in the direction of the chemical. (E) The bacteria will both reduce tumbling frequency and increase run duration in the direction of the chemical.

11. You are studying a newly discovered prokaryotic microorganism and are attempting to determine whether it will be classified in the domain Bacteria or in the domain Archaea. All of the following would be helpful in making that distinction except ______. (A) sequence of small subunit ribosomal RNA (B) type of membrane lipids (C) presence or absence of peptidoglycan in cell walls (D) presence or absence of double-stranded circular DNA genome (E) the assembly of flagella

13. A microbiologist is trying to isolate a pathogen expected to be present in very small numbers from a stool specimen in which there are abundant normal microbiota. Which strategy would most likely accomplish this purpose? (A) Culture on enriched media (B) Culture on differential media (C) Culture in an anaerobe jar (D) Culture on selective agar followed by enrichment culture (E) Enrichment culture followed by culture on selective agar

14. Which of the following does not inhibit protein synthesis? (A) Tetracycline (B) Streptomycin (C) Penicillin (D) Erythromycin (E) Chloramphenicol

15. Which of the following is not true of coronaviruses? (A) Coronaviruses contain envelope (B) Coronaviruses are negative-sense single-stranded RNA viruses. (C) Coronaviruses infect humans (D) Coronaviruses infect mammals (E) Coronaviruses infect avian species

16. Which of the following is not true of coronavirus disease 2019 (COVID-19)? (A) COVID-19 is not pandemic disease (B) COVID-19 entry into human cells is mediated by a cell surface receptor angiotensin-converting enzyme (C) Patients infected with COVID-19 may cause cytokine storm in patients (D) COVID-19 may block interferon-stimulated genes expression (E) All of the choices are correct

17. Which is not true of coronavirus disease (COVID-19)? (A) COVID-19 is an infectious disease caused by the SARS-CoV-2 virus (B) Older people and those with underlying medical conditions like cardiovascular disease or diabetes are more likely to develop serious illness (C) Older people and those with underlying medical conditions like chronic respiratory disease or cancer are more likely to develop serious illness (D) Get vaccinated when it's your turn and follow local guidance (E) All of the choices are correct

18. Which of the following is not true? (A) Viral envelopes are composed of lipids (B) Viral envelopes are composed of proteins (C) Viral envelopes are composed of carbohydrates (D) Viral envelopes are composed of nucleic acids (E) All of the choices are correct