Exam 1

Which of these answers correctly orders the series of microbes/cells from smallest to largest?

virus → bacterium → red blood cell → paramecium

A ball-shaped microbe is referred to as a

coccus

What happens if the wavelength of radiation is larger than the object being viewed?

no resolution

Fill in the blanks.

Psychrophiles favor the ______, since their membranes are more ______ as a result of the high proportion of ________ fatty acids present.

Cold environments, fluid, unsaturated

Which structure enables bacterial chemotaxis by rotating to produce runs and tumbles in response to chemical gradients?

Flagella

During PCR, the DNA polymerase must repeatedly synthesize DNA through many cycles of strand separation, primer binding, and extension. Most polymerases would lose activity under these conditions. Which property of Taq polymerase allows PCR to proceed efficiently?

It is thermostable due to its origin from a thermophilic bacterium.

Frederick Griffith’s experiment with Streptococcus pneumoniae provided evidence for the transfer of genetic traits between bacteria. Which statement best summarizes his experiment and its significance?

Griffith showed that a “transforming principle” from heat-killed virulent bacteria could transfer virulence to live non-virulent bacteria.

In the figure below, which fatty acid increases membrane fluidity, and what type of bond is responsible for this effect?

C; cis-unsaturated double bonds

The RPR assay tests for the presence of which lipid in the blood of patients suspected of infection with Treponema pallidum?

Cardiolipin

Which of the following best describes how a symporter transports molecules across a membrane?

It couples the movement of two substrates in the same direction, using the gradient of one to drive the other against its gradient.

Which of the following sequences correctly matches each scientific contribution with the scientist responsible for it, listed from top to bottom?

• Disproved spontaneous generation

• Developed vaccination

• First to visualize single-celled microorganisms

• Discovered antibiotics

• Discovered transformation in bacteria

Robert Koch, Louis Pasteur, Antonie van Leeuwenhoek, Alexander Fleming, Frederick Griffith

Which two components of the Gram stain form a complex that is retained by Gram-positive cells?

Crystal violet and iodine

Which of these experiments would NOT be a reason to fractionate bacterial cells?

To study the growth rate of E. coli in the presence of lactose

You study a bacterium that grows in very low-nutrient aqueous environments. Which type of transport mechanism is required to deliver nutrients from these environments, where nutrient concentrations are lower than inside the cell?

Active transport

The growth of most bacteria occurs through:

Binary fission

You are measuring growth in a bacterial culture. The number of viable cells remains constant, and when you check the medium, you find that the carbon source has been used up. In which phase of growth is the culture?

Stationary

Special channels that help water move across the membrane quickly are called:

Aquaporins

A microbiologist is investigating how different nutrients enter a bacterial cell. Based on the transport systems described in the lecture, which of the following statements is correct?

Symport and antiport are types of coupled transport where the energy from a driving ion moving down its gradient is used to move a solute up its gradient.

Which of the following best describes microaerophiles?

They require a small oxygen concentration to grow.

Match each micrograph with the microscopy technique used to produce it, from left to right:

Phase contrast, Bright field, SEM, Dark field, TEM

Which stain would be best to distinguish the smooth (S) and rough (R) strains of Streptococcus pneumoniae in Frederick Griffith’s experiment on bacterial transformation?

Negative stain

Microbes employ several mechanisms to maintain a stable internal pH despite changes in the external environment. According to known mechanisms of pH homeostasis, all of the following statements are correct EXCEPT:

Cells exposed to acidic environments increase proton influx to stabilize internal pH.

Identify the following components in the picture below, in the correct order from left to right: Inner membrane, outer membrane, peptidoglycan, LPS, periplasm

E, B, C, A, D

Which combination of numerical aperture and light wavelength provide the best resolution?

Numerical aperture = 1.0, wavelength = 400 nm

Suppose Pasteur’s swan-necked flasks containing boiled broth became cloudy 24 hours after boiling. Which explanation is most consistent with Pasteur’s experimental findings and does not support spontaneous generation?

Endospores in the broth survived boiling and germinated after cooling.

All the following statements about prokaryotic outer membranes are true EXCEPT:

They are lipid bilayers composed of identical phospholipids.

How can some cyanobacteria fix nitrogen while growing in the presence of oxygen?

They use special cells called heterocysts that protect the enzyme.

A bacterium that thrives in your stomach is probably a(n):

Acidophile

Filtration of samples to remove bacterial cells typically use micropore filters with pore sizes of:

0.2 μm

DAPI is a fluorophore that binds preferentially to AT-rich motifs in microbial DNA. Its specificity is determined by what?

Chemical affinity

Why are stains used in brightfield microscopy, and what is one major drawback of their use?

To increase contrast; specimens are killed

You isolate a microbe from a patient that does not grow on a MacConkey agar. Under the microscope, you observe endospores and a thick cell wall. Based on these observations, which is the most likely identification of the microbe?

Gram-positive bacterium

Which of the following solutions is most effective for lysing cells by causing them to burst?

Hypotonic solution

What is the best explanation for a Gram-negative bacterium appearing purple after performing a Gram stain?

The decolorizer was not applied.

The cell wall growth patterns of a various bacteria have been studied using fluorescently labeled D-amino acids. Why does this approach work?

The labeled amino acids are D-amino acids (not L-amino acids), so they are selectively incorporated into peptidoglycan.

A microbe grows only when a specific nutrient is supplied in the growth medium, but cannot synthesize this compound on its own. What is the most accurate term for this nutrient?

Essential nutrient

Which of the following prokaryotic transport mechanisms operates passively, without the need for direct energy input?

Facilitated diffusion

What is the smallest feature of microbes that can typically be observed using light microscopy?

Bacterial cell shapes

An organism that obtains energy from light and uses CO₂ as its primary carbon source for biomass production is classified as a

Photoautotroph

You are testing a new antiseptic for efficacy and determine that tis D-value is 5 minutes. You add the chemical to a test tube containing 1,000 CFUs of the test organism. How many cells remain viable after 15 minutes?

15 min / 5 min/cycle = 3 Cycles.

@ 5min: 1000 cells x 0.1 = 100 cells

@ 10min: 1000 cells x 0.1 = 10 cells

@ 15min: 10 cells x 0.1 = 1 cells

1 cell remains viable.

What is the most likely outcome if a barophilic microorganism is suddenly brought to sea level and exposed to atmospheric pressure?

The organism will experience membrane and protein destabilization, leading to death.

42. Why are obligate anaerobes unable to survive in the presence of molecular oxygen?

They lack enzymes such as superoxide dismutase (SOD) and catalase.

Which of the following specialized structures does NOT help microbes overcome environmental stress?

Lipopolysaccharide

Which of the following statements does NOT correctly describe the adaptations of the thermophilic microorganisms?

Increased unsaturated fatty acids to maintain fluidity at high temperatures

Which of the following agents can be used to disrupt or destroy the peptidoglycan cell wall found in bacteria?

All of these agents target peptidoglycan

What was the purpose of heating the liquid media in Pasteur’s swan-neck flask experiments?

Sterilization

What is the significance of cross-bridge structures in bacterial cell walls?

They are targeted by some antibiotics.

Which of the following bacterial surface structures is primarily involved in the horizontal transfer of genetic material between cells?

Sex Pili

Which modern biological insight most fundamentally challenges the assumption behind Koch’s requirement for a pure culture?

Many pathogens are obligate intracellular and cannot grow outside host cells.

The highest useful magnification for a light microscope is about

1000X