Question 1

Which of the following best explains how Louis Pasteur refuted the theory of spontaneous generation?

Accepted Answer

He used a swan-neck flask to show that sterilized broth remained free of microbial growth unless exposed to airborne particles.

Question 2

Which of the following is a correct pairing of a bacterial fermentation end product and the species that produces it?

Accepted Answer

Lactic acid – Streptococcus lactis

Question 3

Which of the following statements about the Gram stain is correct?

Accepted Answer

Gram-positive bacteria retain the crystal violet stain due to their thick peptidoglycan layer.

Question 4

Which of the following best describes the difference between fermentation and respiration in bacteria?

Accepted Answer

Fermentation produces ATP only by substrate-level phosphorylation and reduces pyruvate to regenerate NAD+, while respiration uses an electron transport chain and oxidizes pyruvate completely to CO$$_2.$$

Question 5

Which of the following is a correct distinction between the cytoplasmic membrane lipids of Bacteria, Eukarya, and Archaea?

Accepted Answer

Bacteria and Eukarya have ester-linked fatty acids, while Archaea have ether-linked isoprenoids.

Question 6

Which of the following scenarios would make it difficult to fulfill all of Koch’s postulates?

Accepted Answer

The suspected pathogen cannot be grown in pure culture outside the host.

Question 7

Which of the following best describes the composition of the lipopolysaccharide (LPS) layer in Gram-negative bacteria?

Accepted Answer

It consists of lipid A, a core polysaccharide, and an O-antigen side chain.

Question 8

Which of the following is a correct example of a positive, neutral, and negative effect of bacteria on humans or macroorganisms?

Accepted Answer

Positive: gut microbiota aiding digestion; Neutral: skin commensals with no effect; Negative: Streptococcus pyogenes causing strep throat.

Question 9

Which of the following best explains why there are more than 100 different types of peptidoglycan despite the invariance of its backbone?

Accepted Answer

Variations occur in the peptide cross-bridges and the types of amino acids used.

Question 10

Which of the following best describes the function of lysozyme, the antibacterial enzyme found in human tears?

Accepted Answer

It hydrolyzes the $$\beta-1$$,4 glycosidic bond between N-acetylglucosamine and N-acetylmuramic acid in peptidoglycan.

Question 11

Which of the following best describes the difference between substrate-level phosphorylation and oxidative phosphorylation?

Accepted Answer

Substrate-level phosphorylation directly transfers a phosphate group to ADP from a phosphorylated intermediate, while oxidative phosphorylation uses a proton gradient and ATP synthase.

Question 12

Which of the following is a correct statement about the stages of bacterial growth in batch culture?

Accepted Answer

The stages are lag, exponential (log), stationary, and death phases.

Question 13

Which of the following best describes a chemoorganoheterotroph?

Accepted Answer

An organism that obtains energy and electrons from organic compounds and uses organic carbon as a carbon source.

Question 14

Which of the following is NOT a correct method for counting bacteria, or is incorrectly described?

Accepted Answer

Counting colonies on a plate, which always gives an exact number of total cells present in the original sample.

Question 15

Which of the following best explains how magnesium (Mg$$^{2+}) is $$essential for bacterial cells?

Accepted Answer

Mg$$^{2+}$$ stabilizes ribosomes, membranes, and is a cofactor for many enzymes, including those involved in ATP utilization.

Question 16

Which of the following best describes the relationship between NADH and NAD$$^+ in $$redox reactions?

Accepted Answer

NAD$$^+ is $$reduced to NADH by accepting electrons during catabolic reactions, and NADH is oxidized back to NAD$$^+ by $$donating electrons to the electron transport chain.

Question 17

Which of the following would most likely increase the abundance of transport proteins in the cytoplasmic membrane of bacteria?

Accepted Answer

Low external concentrations of essential nutrients.

Question 18

Which of the following best describes the difference between macronutrients and micronutrients for bacteria?

Accepted Answer

Macronutrients are required in large amounts (e.g., C, N, O, H, S, P, K, Mg, Ca, Fe), while micronutrients are needed in trace amounts (e.g., Mn, Zn, Co, Mo, Ni, Cu).

Question 19

Which of the following best explains how bacteria can grow at temperatures above the boiling point of water?

Accepted Answer

They possess heat-stable enzymes and membranes with ether-linked lipids, and are found in environments such as hydrothermal vents.

Question 20

Which of the following is a correct definition of a halophile?

Accepted Answer

A microorganism that thrives in environments with high salt concentrations.

Microbiology Exam 1 Study Guide: Step-by-Step Guidance

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