Question 1

Which scientist's experiment with swan-neck flasks provided strong evidence against spontaneous generation by showing that broth remained sterile unless exposed to dust and microbes?

Accepted Answer

Louis Pasteur

Question 2

A patient is diagnosed with tuberculosis. Which staining technique would be most appropriate to identify the causative organism in a sputum sample, and what unique cell wall component does this technique detect?

Accepted Answer

Acid-fast stain; waxy mycolic acids

Question 3

Which of the following best explains why Gram-negative bacteria are more resistant to certain antibiotics than Gram-positive bacteria?

Accepted Answer

They possess an outer membrane containing lipopolysaccharide (LPS)

Question 4

A microbiologist observes a flexible, spiral-shaped bacterium that moves using internal axial filaments. Which term best describes this organism?

Accepted Answer

Spirochete

Question 5

A bacterial culture is grown in a tube of thioglycolate broth. After incubation, growth is observed only at the very bottom of the tube. What is the most likely oxygen requirement of this organism?

Accepted Answer

Obligate anaerobe

Question 6

A medium contains bile salts and crystal violet to inhibit Gram-positive bacteria, and lactose with a pH indicator to distinguish lactose fermenters. Which type of medium is this, and what is its name?

Accepted Answer

Both selective and differential; MacConkey agar

Question 7

A bacterium has a generation time of 30 minutes. If you start with 2 cells, how many cells will there be after 2 hours, assuming no cell death? Use the formula $$N = N_0$ 	imes 2^n$$, where $$N_0 is $$the initial number of cells and $$n is $$the number of generations.

Accepted Answer

$$N = 2 	imes 2^4$ = 32$$

Question 8

Which of the following statements about prions is correct?

Accepted Answer

They are infectious proteins that contain no nucleic acid

Question 9

During DNA replication, which property ensures that each daughter DNA molecule contains one original and one newly synthesized strand?

Accepted Answer

Semiconservative replication

Question 10

A scientist wants to cut a plasmid at a specific DNA sequence to insert a gene of interest. Which enzyme should be used, and what is the general function of this enzyme?

Accepted Answer

Restriction nuclease; cuts DNA at specific recognition sites

Question 11

Which of the following best describes the main function of a bacterial capsule?

Accepted Answer

Protecting the cell from phagocytosis and aiding attachment to surfaces

Question 12

A patient presents with flaccid (limp) paralysis after eating improperly canned food. Which organism is most likely responsible, and what is the mechanism of its toxin?

Accepted Answer

Clostridium botulinum; blocks acetylcholine release at neuromuscular junctions

Question 13

Which of the following is found in eukaryotic cells but NOT in prokaryotic cells?

Accepted Answer

Membrane-bound organelles such as mitochondria

Question 14

A microbiologist wants to obtain a pure culture from a mixed broth containing two bacterial species. Which method and medium should be used, and what is the main purpose of this method?

Accepted Answer

Streak plate on TSA; to obtain isolated colonies

Question 15

Which of the following best describes the process of transformation in bacteria?

Accepted Answer

Uptake of free (naked) DNA from the environment

Question 16

A food product is preserved by adding large amounts of salt. Which principle explains why this inhibits microbial growth?

Accepted Answer

Salt reduces water activity, causing water to leave microbial cells

Question 17

Which of the following is a correct match between a medically important bacterium and the disease it causes?

Accepted Answer

Yersinia pestis – Plague

Question 18

Which phase of the bacterial growth curve is characterized by the fastest, constant rate of cell division?

Accepted Answer

Log (exponential) phase

Question 19

A scientist is studying a microorganism that grows best at a pH of 3.5. What is the best term for this organism, and what is the typical pH range for most human pathogens?

Accepted Answer

Acidophile; pH 6.5–7.5

Question 20

Which of the following best describes the role of tRNA during translation?

Accepted Answer

Carries amino acids to the ribosome

BIO 220: General Microbiology Midterm Study Guide

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