Q: A researcher is using a light microscope with a blue filter and a 100x oil immersion objective lens (numerical aperture = 1.25) and a 10x ocular lens. What is the theoretical limit of resolution for this setup? Use the formula $$d = \frac{0.5 \times \text{wavelength}}{\text{numerical aperture}}$$ and assume blue light has a wavelength of 450 nm.

$$d = \frac{0.5 \times 450\ \text{nm}}{1.25} = 180\ \text{nm}$$

Question 1

Which of the following statements best explains why smaller microbial cells tend to have faster metabolic rates than larger cells?

Accepted Answer

Smaller cells have a higher surface area-to-volume ratio, allowing for more efficient nutrient uptake and waste expulsion.

Question 2

A scientist isolates a microorganism from a boiling hot spring in Yellowstone. Which of the following characteristics is most likely to be found in this organism's membrane?

Accepted Answer

Ether bonds between glycerol and isoprene side chains in the membrane lipids.

Question 3

Which of the following best describes the function of the S-layer in Archaea?

Accepted Answer

It provides structural strength, protects against osmotic lysis, and confers cell shape.

Question 4

A patient is infected with a Gram-negative bacterium. Which component of the bacterial cell envelope is most likely responsible for the toxic symptoms such as diarrhea and vomiting?

Accepted Answer

Lipid A component of lipopolysaccharide (LPS)

Question 5

Which of the following best explains why lysozyme is ineffective against the cell walls of Archaea?

Accepted Answer

Archaeal cell walls lack peptidoglycan and may contain pseudomurein with $$\beta(1,3)$$ linkages, which are lysozyme-insensitive.

Question 6

During Gram staining, why do Gram-positive cells retain the crystal violet-iodine complex after the alcohol decolorization step?

Accepted Answer

Their thick peptidoglycan layer traps the dye complex, preventing it from being washed out.

Question 7

Which of the following transport systems in prokaryotes uses the energy from phosphoenolpyruvate (PEP) to chemically modify and transport sugars across the membrane?

Accepted Answer

Group translocation

Question 8

A bacterium is observed to move toward a light source. Which term best describes this behavior?

Accepted Answer

Positive phototaxis

Question 9

Which of the following statements about bacterial endospores is FALSE?

Accepted Answer

Endospores can survive for millions of years in a dormant state.

Question 10

A researcher is using a light microscope with a blue filter and a 100x oil immersion objective lens (numerical aperture = 1.25) and a 10x ocular lens. What is the theoretical limit of resolution for this setup? Use the formula $$d = \frac{0.5 	imes 	ext{wavelength}}{	ext{numerical aperture}}$$ and assume blue light has a wavelength of 450 nm.

Accepted Answer

$$d = \frac{0.5 	imes 450\ 	ext{nm}}{1.25} = 180\ 	ext{nm}$$

Question 11

Which of the following is a function of bacterial capsules?

Accepted Answer

They aid in attachment to surfaces and can protect against dehydration.

Question 12

Which of the following best describes the role of porins in Gram-negative bacteria?

Accepted Answer

They function as channels in the outer membrane for the entrance and exit of solutes.

Question 13

A bacterium is found to have a single flagellum at each end of the cell. What is the correct term for this flagellar arrangement?

Accepted Answer

Amphitrichous

Question 14

Which of the following is a key difference between the cell walls of Gram-positive and Gram-negative bacteria?

Accepted Answer

Gram-positive bacteria have a thick peptidoglycan layer with teichoic acids, while Gram-negative bacteria have a thin peptidoglycan layer and an outer membrane containing LPS.

Question 15

Which of the following best explains why Mycoplasmas are resistant to antibiotics like penicillin?

Accepted Answer

They lack a cell wall, so there is no peptidoglycan for penicillin to target.

Question 16

Which of the following is NOT a characteristic of living cellular systems?

Accepted Answer

Ability to reproduce only sexually

Question 17

A bacterium stores excess carbon as poly-$$\beta-$$hydroxybutyrate (PHB). What is the main advantage of storing carbon in this form?

Accepted Answer

PHB is insoluble, reducing osmotic stress on the cell.

Question 18

Which of the following best describes the mechanism by which flagella rotate in bacteria?

Accepted Answer

Proton motive force drives motor proteins that spin the flagellum.

Question 19

Which of the following is a correct statement about the function of fimbriae and pili?

Accepted Answer

They are involved in attachment to surfaces and in genetic exchange between cells.

Question 20

Which of the following historical experiments provided the strongest evidence against the theory of spontaneous generation?

Accepted Answer

Louis Pasteur's swan-neck flask experiment showing that sterilized broth remained free of microbial growth unless exposed to air.

Microbiology Study Guide: Chapters 1 & 2 – The Microbial World and Microbial Cell Structure & Function

Study Guide - Practice Questions

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