Deck 3: Observing Microbes

Question 1

In the figure below,line "C" points to the microscope's

A) ocular lens.
B) objective.
C) condenser.
D) light source.

Answer 1

C

Question 2

What is the purpose of fixation in a staining procedure?

A) to preserve the organisms
B) to adhere bacterial cells to the slide
C) to impart color to the sample
D) to heat the sample

Answer 2

B

Question 3

You are performing a Gram stain on Gram-positive bacteria and you stop after the addition of the counterstain.What is the appearance of the bacteria at this point?

A) purple
B) colorless
C) pink
D) blue

Answer 3

A

Question 4

What is the total magnification of a specimen viewed with a 10x ocular lens and a 35x objective lens?

A) 10x
B) 3.5x
C) 350x
D) 3,500x

Question 5

The cell wall of Gram-positive bacteria contain(s)

A) only a single layer of peptidoglycan.
B) a thick layer of lipopolysaccharides.
C) a thinner and more porous cell wall than Gram-negative species.
D) a thick layer of peptidoglycan.

Question 6

You are performing a Gram stain on Gram-positive bacteria and you stop after the addition of the mordant.What is the appearance of the bacteria at this point?

A) purple
B) colorless
C) pink
D) blue

Question 7

In a compound microscope,which is the accurate pathway of light?

A) light source, condenser, objective, specimen, eyepiece
B) condenser, light source, eyepiece, specimen, objective
C) eyepiece, objective, specimen, condenser, light source
D) light source, condenser, specimen, objective, eyepiece

Question 8

In the figure below,line "B" points to the microscope's

A) ocular lens.
B) objective.
C) condenser.
D) light source.

Question 9

Which of the following is the correct order of the Gram-stain regents?

A) iodine, crystal violet, safranin, ethanol
B) ethanol, crystal violet, safranin, iodine
C) crystal violet, ethanol, iodine, safranin
D) crystal violet, iodine, ethanol, safranin

Question 10

Resolution is

A) the ability to detect individual cells.
B) using a microscope to be seen.
C) increasing the size of an image.
D) the smallest distance two objects can be separated and still be distinguished.

Question 11

In the figure below,line "D" points to the microscope's

A) ocular lens.
B) objective.
C) condenser.
D) light source.

Question 12

You complete a Gram stain on Gram-positive bacteria;however,you over-decolorize your sample.What color will your bacteria be at this point?

A) purple
B) colorless
C) pink
D) blue

Question 13

Assume you stain Bacillus with malachite green with heat and then counterstain with safranin.What type of stain would you be performing?

A) a differential and endospore stain
B) a differential and Gram stain
C) a simple and endospore stain
D) a simple and Gram stain

Question 14

Which of the following is FALSE about a properly completed Gram stain?

A) It is a key tool used in the identification of bacterial species.
B) It is reliable only for fresh cultures.
C) It differentiates bacteria based on their cell wall components.
D) At the completion of the stain, Gram-negative cells stain purple.

Question 15

Which of the following equals one millimeter?

A) 10-3 m
B) 10-6 m
C) 10-9 m
D) 10-12 m

Question 16

Assume you stain Bacillus with malachite green with heat and then counterstain with safranin.Through the microscope,the green structures are

A) cell walls.
B) capsules.
C) endospores.
D) bacteria.

Question 17

In Gram-negative cells,which layer is disrupted by the decolorizer in the Gram-staining procedure?

A) techoic acids
B) outer membrane
C) peptidoglycan
D) mycolic acid

Question 18

Which of the following statements is INCORRECT?

A) In fluorescence microscopy, fluorescent-labeled cellular structures are identified.
B) In light microscopy, the object appears light against a dark background.
C) In phase-contrast microscopy, organelles appear as light/dark patterns by variation in refractive indexes.
D) Electron microscopy uses electrons to visualize the specimen.

Question 19

You are performing a Gram stain to differentiate between Gram-positive and Gram-negative bacteria.At the end of the procedure,a Gram-positive cell will appear

A) purple.
B) colorless.
C) pink.
D) blue.

Question 20

Which microscope is used to observe specific fluorescent-labeled structures?

A) a compound light microscope
B) a phase-contrast microscope
C) a fluorescence microscope
D) an electron microscope

Question 21

Which of the following is INCORRECT?

A) Congo red is a negative stain.
B) Malachite green is an acid-fast stain.
C) Methylene blue is a simple stain.
D) Fluorophore is in an antibody stain.

Question 22

Which of the following statements is correct?

A) Safranin is a primary stain.
B) Iodine is a counterstain.
C) Ethanol is a decolorizer.
D) Crystal violet is a mordant.

Question 23

Which images display organelles?

A) 1 and 2
B) 2 and 4
C) 1 and 3
D) 3 and 4

Question 24

What is an advantage of fluorescence microscopy?

A) It allows for the preservation of the specimen.
B) It provides the greatest resolution.
C) It has the ability to stain live specimens.
D) It has the ability to detect specific microbes.

Question 25

Which image shows Giardia lamblia visualized with a scanning electron microscope?

A) 1
B) 2
C) 3
D) 4

Question 26

Which of the following is mismatched?

A) darkfield microscopy-uses visible light
B) fluorescence microscopy-uses a fluorescent light
C) scanning electron microscopy-produces a three-dimensional image
D) compound light microscopy-produces a light image against a dark background

Question 27

Which of the following is powerful enough to visualize ribosomes?

A) a compound light microscope
B) an electron microscope
C) a fluorescence microscope
D) a darkfield microscope

Question 28

A(n)________ microscopy microscope produces halos of bright lights against a dark field.

A) compound light
B) electron
C) fluorescence
D) darkfield

Question 29

Which of the following depicts the steps of the Gram stain in the correct order?

A) crystal violet, ethanol, iodine, safranin
B) safranin, iodine, ethanol, crystal violet
C) crystal violet, iodine, ethanol, safranin
D) safranin, ethanol, iodine, crystal violet

Question 30

Which type of stain would be the most useful in helping clinicians decide which class of antibiotics to prescribe?

A) negative stain
B) simple stain
C) endospore stain
D) Gram stain

Question 31

Which microscope technique is best used for visualizing the surface structures of cells and viruses?

A) phase-contrast
B) bright-field
C) scanning electron
D) darkfield

Question 32

Which microscope best allows the observation of internal cell structures in a natural state?

A) compound light microscope
B) phase-contrast microscope
C) darkfield microscope
D) electron microscope

Question 33

Which of the following is FALSE concerning darkfield microscopy?

A) Contamination in the medium can scatter light.
B) It can be used to identify spirochetes.
C) Images are dark against a light background.
D) High resolution cannot be achieved.

Question 34

Which microscope uses variations in refractive indexes to display specimens?

A) bright-field
B) fluorescence
C) phase-contrast
D) transmission electron

Question 35

Why is the presence of a capsule clinically significant?

A) It protects the bacterial cell from lack of nutrients.
B) It protects the bacterial cell from engulfment by white blood cells.
C) It protects the bacterial cell from heat.
D) It protects the bacterial cell from the staining regents.

Question 36

In the figure below,which depicts cocci in chains?

A) 1
B) 2
C) 3
D) none of the labeled areas

Question 37

The purpose of the condenser is to

A) focus light rays onto the slide.
B) magnify the image from the objective lens.
C) decrease the refractive index.
D) improve resolution.

Question 38

You are observing a bacterial specimen on the 100x objective but have forgotten to put the immersion oil on the slide.The specimen will appear

A) smaller with better resolution.
B) larger with poor resolution.
C) somewhat fuzzy with poor resolution.
D) the same.

Question 39

If a microbiologist forgot to heat-fix a bacterial smear before staining,what would probably happen?

A) Bacteria might wash off the slide.
B) The stain would not stick to the bacteria.
C) The bacteria might decolorize too quickly.
D) The color of the stain would be too dark to see the bacteria.

Question 40

In the Gram stain,which step is critical in differentiating Gram-positive from Gram-negative cells?

A) crystal violet
B) safranin
C) mordant
D) ethanol

Question 41

The bending of light as it enters a substance that slows its speed is known as

A) reflection.
B) refraction.
C) absorption.
D) scattering.

Question 42

The size at which objects become visible depends on the resolution of the observer's eye.Typically eagles can resolve objects much smaller or farther away than humans can.Please explain why.

Question 43

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

A) Crystal violet differentially stains Gram-positive cells.
B) Gram's iodine differentially stains Gram-positive cells.
C) Ethanol differentially destains Gram-negative cells.
D) Safranin differentially stains Gram-negative cells.

Question 44

Immersion oil is used with the ________ objective.

Question 45

Magnification without increase in resolution is called ________.

Question 46

A ________ is the only way to observe live specimens.

Question 47

Using a compound microscope,the image is magnified at the ________ and the ________.

Question 48

Bacteria that grow as rods are commonly referred to as ________,whereas bacteria that grow as spheres are known as ________.

Question 49

What is the purpose of the mordant in the Gram-stain procedure?

Question 50

Electron microscopy uses beams of ________ to generate high-resolution images.

Question 51

CASE HISTORY
Jared,a 48-year-old,previously healthy man,was admitted to a hospital in Columbus,Ohio,after six days of increasing dyspnea (shortness of breath)and watery diarrhea.Jared also complained of a dry cough,myalgia (muscle pain),nausea,and vomiting.He appeared flushed and had dry mucous membranes.His temperature was 39°C (102.2°F),and his pulse rate was 103 beats per minute.Chest radiographs showed pneumonia with consolidation (formation of a firm mass)of the left lower lobe.His c-reactive protein (crP,a blood protein produced by the liver)was greater than 220 milligrams per liter (mg/l),a high level that indicates inflammation.
Before onset of symptoms,Jared recalled having cleaned the filter of an outdoor whirlpool spa.Culture from Jared's sputum and from the spa filter revealed Gram-negative bacilli consistent with Legionella pneumophila.The diagnosis was confirmed by fluorescence microscopy using direct fluorescent antibody (DFA)stain.The patient received intravenous amoxicillin and clarithromycin antibiotics for eight days before his condition returned to normal.
If the technician conducting the Gram stain in this case study had left ethanol on the prepared slide longer than necessary,what might be the effect on this slide and identification?

A) The bacteria on the slide may have been decolorized Gram-positive bacilli.
B) None. The timing of ethanol does not affect the outcome of a Gram stain.
C) None, since the bacteria appear Gram negative, they could not have been over-decolorized.
D) The bacteria on the slide may have been cocci rather than bacilli.

Question 52

Please label the figure below with different interactions of light with matter.Please describe what is happening with each interaction.

Question 53

Compare and contrast darkfield,phase-contrast,and fluorescence microscopy.

Question 54

Oil immersion is used in which type of microscopy and on which objective?

A) bright-field microscopy, 40X
B) bright-field microscopy, 100x
C) darkfield microscopy, 40x
D) darkfield microscopy, 100x

Question 55

In an acid-fast stain,carbolfuchsin specifically stains ________ of Mycobaterium tuberculosis.

Question 56

CASE HISTORY
Marianna and Julio,two children in Oklahoma aged 8 and 11,fell ill with food poisoning after consuming commercially canned hot dog chili sauce.The children complained of double vision and an inability to move their facial muscles.
Examination showed normal vital signs,symmetrical weakness (equal on right and left sides),and fixed pupils due to cranial nerve palsy (paralysis).Upper body paralysis gradually spread downward,and breathing became labored.
Botulinum toxin was identified in their blood by fluorescent monoclonal antibodies (antibodies produced by a genetically uniform cell culture).
The children were placed on mechanical ventilation (a machine that assists breathing)and treated with botulinum antitoxin.After several days,the children were removed from mechanical ventilation.They underwent physical rehabilitation for a full recovery.
The chili sauce was traced to a canning facility where six swollen cans tested positive for botulinum toxin A.From the cans,inspectors cultured a bacterium that grew only without oxygen,as in a closed can.A microscope showed that the bacterium had a distinctive club-shaped appearance.The bacterium was Clostridium botulinum,which produces botulinum toxin,the cause of botulism.One end of the club-shaped cell contains an endospore,an inert form of the cell that can germinate and grow in a closed container of food.Growing cells produce botulinum toxin,leading to botulism,a life-threatening form of paralysis.Microscopy of the pathogen's unique form confirms the identification.
Why was fluorescence microscopy used to help identify the causative agent of the children's disease,rather than bright field?

Question 57

Using the figure below,which of the following images depicts the absorption of light?

A) 1
B) 2
C) 3
D) 4

Question 58

What is the difference between a simple and a differential stain? Give one example of a simple stain and one example of a differential stain.

Question 59

Refraction occurs by the ________ of light and is the key property enabling a lens to magnify an image.

Question 60

Using the figure below,which of the following images depicts the refraction of light?

A) 1
B) 2
C) 3
D) 4

Question 61

CASE HISTORY
Purna,a six-year-old boy in India's state of Assam,fell ill with fever.At the time,prolonged rainfall had left vast pools of water,breeding mosquitoes.First the boy felt intense chills,and his temperature rose to 40° C (104° F).He experienced nausea and intense headaches and vomited repeatedly.The fever subsided,only to return three days later.After several weeks of cycling fevers,Purna was at last brought to a clinic for examination.He showed extreme anemia,with enlarged spleen and liver.A blood film slide revealed Plasmodium falciparum,a parasite that causes malaria.In the Assam outbreak of malaria,400,000 people were infected.Some travelers who returned to the United States experienced malarial symptoms months afterward.
Explain the role of fixation and staining in the use of microscopy to identify malaria infection.