Question 1

Which of the following statements best explains why Pasteur's swan-neck flask experiment was considered definitive in disproving spontaneous generation?

Accepted Answer

The swan-neck flask allowed air to enter but prevented dust and microbes from reaching the broth, so no growth occurred unless the neck was broken.

Question 2

A scientist isolates a microorganism from a hot spring with a cell wall lacking peptidoglycan. The organism is most likely classified as:

Accepted Answer

An archaeon

Question 3

Which of the following best describes the difference between a molecule and a compound?

Accepted Answer

A molecule consists of two or more atoms bonded together, while a compound is a molecule containing atoms of more than one element.

Question 4

A patient is diagnosed with tuberculosis. Which staining technique would be most appropriate to confirm the presence of Mycobacterium tuberculosis in a sputum sample?

Accepted Answer

Acid-fast stain

Question 5

Which of the following is a correct application of Koch's postulates in identifying the causative agent of a new infectious disease?

Accepted Answer

The suspected microbe must be isolated from a diseased host, grown in pure culture, and cause the same disease when introduced into a healthy host.

Question 6

A bacterial cell is placed in a hypertonic solution. Predict what will happen to the cell and explain why, using the concept of osmosis.

Accepted Answer

Water will leave the cell, causing it to shrink due to osmosis moving water from low to high solute concentration.

Question 7

Which of the following best explains why phospholipids are essential for the structure of cell membranes?

Accepted Answer

They form a bilayer with hydrophilic heads facing outward and hydrophobic tails inward, creating a selectively permeable barrier.

Question 8

A Gram-negative bacterium is treated with an antibiotic that disrupts its outer membrane. Which of the following is a likely consequence?

Accepted Answer

Release of endotoxin (Lipid A), potentially causing a strong immune response in the host.

Question 9

Which of the following best describes the function of ribosomes in both prokaryotic and eukaryotic cells?

Accepted Answer

They synthesize polypeptides by translating messenger RNA.

Question 10

A researcher is using a phase-contrast microscope to observe live, unstained cells. What advantage does this technique provide over bright-field microscopy?

Accepted Answer

It enhances contrast of internal structures without staining, allowing observation of living cells.

Question 11

Which of the following is a property of water that is essential for life and directly contributes to the ability of cells to maintain temperature homeostasis?

Accepted Answer

High heat capacity, allowing water to absorb significant heat without a large temperature change.

Question 12

Which of the following best explains why ATP is considered the main short-term energy supply for cells?

Accepted Answer

ATP contains high-energy phosphate bonds that, when broken, release energy quickly for cellular processes.

Question 13

A scientist discovers a new microorganism that is single-celled, photosynthetic, and has a cell wall. It is most likely classified as:

Accepted Answer

An alga

Question 14

Which of the following best describes the process of group translocation in bacterial cells?

Accepted Answer

A substance is chemically modified during transport across the membrane, preventing it from diffusing back out.

Question 15

Which of the following is a correct pairing of a macromolecule with its monomer?

Accepted Answer

Protein — amino acid

Question 16

A bacterial cell with a thick peptidoglycan layer and teichoic acids is most likely to appear what color after a Gram stain, and why?

Accepted Answer

Purple, because the thick peptidoglycan retains the crystal violet stain.

Question 17

Which of the following best explains the evidence supporting the endosymbiotic theory for the origin of mitochondria and chloroplasts?

Accepted Answer

They contain their own circular DNA and 70S ribosomes, similar to prokaryotes.

Question 18

A sample contains a mixture of cocci in clusters, bacilli in chains, and spirochetes. Which staining and microscopy combination would best allow you to distinguish all three morphologies?

Accepted Answer

Simple stain with bright-field microscopy

Question 19

Which of the following best describes the role of buffers in microbial growth media?

Accepted Answer

They prevent drastic changes in pH, maintaining an environment suitable for microbial metabolism.

MCB2010 Exam 1 Study Guide: Foundations of Microbiology (Chapters 1–4)

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