Micro Chapter 3

A(n) __________ is equal to 0.000001 m.

micrometer

platform on which the slide is placed for viewing

stage

A paramecium is approximately 150 micrometers in length. What is this measurement expressed in millimeters (mm)?

0.15 mm

Most bacteria are in the __________ size range.

1-10 micrometer

Simple staining is often necessary to improve contrast in which microscope?

compound light microscope

The __________ of a compound light microscope focuses light from the light source on the specimen.

condenser

The __________ is the part of the microscope that controls the amount of light entering the condenser.

diaphragm

controls how much light from the illuminator reaches the specimen

diaphragm

Your lab partner tells you the bacteria are moving in his Gram-stained smear. You can conclude that __________.

he didn't properly fix the smear

Immersion oil is necessary when using the 100x objective on a compound light microscope

otherwise too much light is lost to refraction and the image will be fuzzy.

Which microscope is used to see detail of a 300-nm virus?

electron microscope

Which of the following is NOT a type of a compound microscope?

Electron microscope

can be viewed with the scanning electron microscope

- determining the three-dimensional shape and arrangement of bacterial cells - viewing the three-dimensional shape of a protozoan and the arrangement and distribution of cilia on its surface

can be viewed with the light microscope

- examining a clinical specimen, such as a sputum smear, for the presence of bacteria - examining a blood smear for the presence of malarial parasites

can be viewed by the transmission electron microscope

- viewing a cross section of poliovirus (30 nm) - viewing ribosomes (20 nm) within a bacterial cell - confirming the 9 + 2 microtubule arrangement in a eukaryotic flagellum - viewing the layers of the gram-negative cell wall in cross section

Which of the following is NOT visible through a compound light microscope?- - 1.5-mm tick - 5-µm nucleus - 0.02-µm ribosome - 15-µm white blood cell

0.02-µm ribosome

If you use a compound light microscope, a 2-µm bacterial cell is best seen at which magnification?

1000x

The acid-fast stain differs from the Gram stain procedure in the decolorizing agent used. What is the reagent used in an acid-fast stain, and why is it necessary?

Acid-alcohol is used to remove the primary stain from bacteria that do not have waxy cell walls.

Which type of light microscopy is used to visualize stained specimens?

Brightfield

__________ is important in medical microbiology because the results help physicians select appropriate antibiotics for treatment.

Gram staining

__________ acts to decrease refraction of light rays and thus increase resolution.

Immersion oil

What is the role of lenses in microscopy?

Lenses focus either light or electrons to create a magnified image of a specimen.

Acid-fast staining is used to detect members of which bacterial genus? Mycobacterium Streptococcus Staphylococcus Clostridium

Mycobacterium

Which waxy molecule, found in the cell wall of acid-fast bacteria, prevents these cells from being Gram stained? Mycolic acid Methylene blue Carbolfuchsin Acid-alcohol

Mycolic acid

Which of the following types of microscopy is most useful for viewing the internal structures of unstained specimens?

Phase-contrast

Which of the following types of microscopy is used to study the structure of the slimy accumulation of bacteria on an IV catheter tip?

Scanning acoustic

A microscopist is studying the surface pores on a bacterial specimen. Which microscope provides the best three-dimensional surface structure image?

Scanning electron microscope

In a typical brightfield microscope (seen in the animation), at which point does magnification begin?

The objective lens

Which of the following is a characteristic shared by both electron and light microscopes?

They both employ the use of objective lenses.

What is the fate of the electrons that interact with a specimen in an electron microscope?

They may be absorbed, reflected, or refracted by the specimen.

Which of the following statements is NOT true for both TEM and SEM?

The specimen must be sectioned before viewing.

What happens to the light rays when they hit the specimen?

They are reflected, refracted, or absorbed by the specimen.

In the Gram stain, what is the purpose of the counterstain?

To make gram-negative cells visible

lens that is closest to the slide and provides initial magnification of a specimen

objective lens

lens that you look through

ocular lens

What does resolution mean?

the ability of a microscope to distinguish fine details and differentiate between two very close objects

In a negative staining procedure, the bacterial cells would appear __________ when viewed under a microscope.

unstained in a colored background

Resolution is very good when using an electron microscope because the __________ of the electron beam is much shorter than that of visible light.

wavelength

In the Gram stain, what is the purpose of the decolorizer?

To selectively remove stain from cells

In the capsule stain using India ink, capsules are distinguished as __________ surrounding cells.

clear halos

What is the correct order for the Gram stain process?

crystal violet → iodine → decolorizer → safranin

can be viewed with the unaided eye

examining your cat for the presence of fleas

What structure does light pass through after leaving the condenser in a compound light microscope?

specimen

__________ is an example of an acidic dye; __________ is an example of a basic dye.

nigrosin; crystal violet

3 true statements comparing electron microscopy and light microscopy

- Images produced by light microscopes can be in color, whereas electron microscope images are black and white unless they are artificially colored. - Electron microscopes can allow examination of viruses and internal cell structures, whereas light microscopes are limited to objects that are 0.5 micrometers and larger. - The electron microscope has greater resolution than the light microscope.

used after initial focusing to sharpen the image

fine focus knob

In the Gram stain, crystal violet is the __________.

primary stain

Which of the following is a lens found on electron microscopes but not on light microscopes?

projector lens

You are studying a cell structure that is approximately 100 nm in size. Which of the following provides the greatest magnification you can use to see this structure?

scanning electron microscope

Which microscope can be used to visualize DNA or botulinum toxin?

scanning tunneling microscope

Chlamydia trachomatis elementary bodies measure approximately 0.25 micrometers in diameter. What is this measurement expressed in nanometers (nm)?

250 nm

What is the total magnification of a specimen viewed with a 10x ocular lens and a 45x objective lens?

450x

Which type of microscope uses a metal and diamond probe that is gently forced down along the surface of a specimen?

Atomic force

Which of the following measurements is correctly matched with microorganisms of that size? - Yeast; 1 centimeter - Bacteria; 2 micrometers - Viruses; 10 micrometers - Bacteria; 10 nanometers

Bacteria; 2 micrometers

Which of the following statements comparing electron microscopy and light microscopy is FALSE?

Both the electron microscope and the light microscope use the same wavelengths for illumination.

Why do electron microscopes have higher resolving power than light microscopes?

Electrons have a smaller wavelength than visible light, leading to higher resolution.

(T/F)The greater resolution of the electron microscope compared to the compound microscope is due to the longer wavelengths of the electrons used to examine specimens.

False

__________ are too small to be seen with the light microscope without adding a mordant and carbolfuchsin.

Flagella

Which of the following types of microscopy can be used to specifically identify pathogens (such as Mycobacterium tuberculosis or rabies virus) in specimens?

Fluorescence

Which of the following is NOT true regarding the acid-fast stain? - Non-acid-fast microbes appear blue in a completed acid-fast stain. - If cells are acid-fast, they are gram-negative. - It is used to identify members of the genus Mycobacterium. - Acid-fast cells appear red in a completed acid-fast stain. - Acid-fast cells retain the primary dye after treatment with acid-alcohol.

If cells are acid-fast, they are gram-negative.

What is meant by light rays being divergent?

It is spreading out

A student is observing a Gram stain with the 100 × (oil immersion) lens. The image appears cloudy and dark. Which of the following actions will NOT increase the clarity of the image? - Using lens paper to clean any dirt or old oil off the lenses - Adjusting the condenser to better focus light through the specimen - Lowering the stage to increase the distance between the object and the objective lens - Increasing the light using the diaphragm

Lowering the stage to increase the distance between the object and the objective lens

Which of the following is the most convenient and appropriate unit for expressing the size of an average bacterial cell?

Micrometer

What metric unit would be most appropriate for expressing the size of most viruses?

Nanometer

A researcher is studying the number and arrangement of fimbriae covering the surface of a bacterial cell. Which type of microscopy would be most useful for this purpose?

Scanning electron microscopy

Which of the following kinds of microscopy would be most appropriate for viewing the shape and arrangement of pili or fimbriae on the surface of a bacterial cell?

Scanning electron microscopy

A student completes a Gram stain on a bacterial smear that has a mix of gram-negative and gram-positive organisms. The student stops the procedure without adding safranin. What would be the outcome of the Gram stain?

The gram-positive organisms would appear purple, and the gram-negative organisms would be colorless.

What is the role of the ocular lens?

To recreate the image in the viewer's eye

Bacterial cells have an overall negative charge on their surface. If a bacterial smear is stained by a pink, acidic, water-soluble stain and then washed with water, which of the following describes the result that will be observed when viewing the stained slide under a microscope?

Unstained cells with no background

When stained, bacteria in the genus Mycobacterium are __________.

acid fast

Which of the following staining procedures is matched with the principal use for that stain? - endospore stain to visualize structures which enable bacteria to move and swim - acid-fast stain for microbes with waxy cell walls - flagella stain used to distinguish dormant structures formed during adverse environmental conditions - negative stain used to differentiate cell wall components

acid-fast stain for microbes with waxy cell walls

This microscope produces an image of a light cell against a dark background; internal structures are NOT visible.

darkfield microscope

Which of the following types of microscopy provides advantages for viewing live images?

darkfield microscopy

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

endospores

Which of the following pairs is mismatched? - scanning electron microscope - produces a three-dimensional image - scanning tunneling microscope - allows visualization of atoms - confocal microscope - produces a three-dimensional image - darkfield microscope - uses visible light - fluorescence microscope - uses a fluorescent light

fluorescence microscope - uses a fluorescent light

Which of the following describes the correct path of light in a compound light microscope, from the illumination source to the eye of the observer?

illuminator → condenser lenses → specimen → objective lenses → body tube → ocular lens → eye

In the Gram stain, crystal violet remains in gram-positive cells after treatment with alcohol because crystal violet--iodine (CV--I) complexes are trapped __________.

in thick layers of peptidoglycan

The __________ charge of a basic dye adheres to the __________ charge of bacterial cell surfaces.

positive; negative

The purpose of a mordant in the Gram stain is to

prevent the crystal violet from leaving the cells.

Immersion oil is used with the 100 × objective lens of the compound light microscope to __________.

prevent the loss of resolution due to refraction

In the Gram stain, if the decolorizing step is deleted, gram-negative cells will appear __________ at the completion of the staining procedure.

purple

__________ is the quality of the microscope that allows one to distinguish between two points that are very close together.

resolution

Which of the following pairs is mismatched? - alcohol-acetone - decolorizer - carbolfuchsin - basic dye - safranin - acid dye - crystal violet - basic dye - iodine - mordant

safranin - acid dye

In the Gram-stain procedure, a clear oval in the center of a cell could indicate __________.

the presence of an endospore

You are viewing a sputum smear that has been stained with an acid-fast stain. On this smear you see 5-micrometer-long red cells. You can conclude that __________.

there are acid-fast bacteria in the specimen

Acid-fast Mycobacteria differ from non-acid-fast bacteria by the presence of __________.

waxy material in their cell walls

Which of the following signs and symptoms is NOT associated with active pulmonary tuberculosis? - Fever - Chest pain - Weight gain - Cough with blood

weight gain

When an object is viewed through a light microscope with oculars that magnify 20 20× and a high-power objective lens that magnifies 100 ×, what is the total magnification of the object?

2000 ×

When using a 10× ocular lens and a 40× objective, the total magnification achieved is __________.

400

What does refraction mean?

A measure of the light-bending ability of a medium

Which type of microscope would allow the viewer to see ribosomes inside a cell?

A transmission electron microscope

Which of the following pairs of terms is properly matched? Methylene blue—decolorizing agent Steam heat—decolorizing agent Carbolfuchsin—decolorizing agent Acid-alcohol—decolorizing agent

Acid-alcohol—decolorizing agent

Why is a specimen smaller than 200 nm not visible with a light microscope?

Anything smaller than 200 nm cannot interact with visible light.

Which of the following staining procedures is correctly matched with the principal use for that particular stain? - Flagella stain used to detect capsules - Acid-fast stain for microbes with capsules - Negative stain used to differentiate cell wall components - Endospore stain to distinguish dormant structures formed during adverse environmental conditions

Endospore stain to distinguish dormant structures formed during adverse environmental conditions

Before cells are stained, the specimen must be fixed. Fixing a specimen accomplishes all of the following EXCEPT which one? - Fixation preserves cellular structure in the natural state, with minimum distortion. - Fixation differentiates the various cells being observed. - Fixation attaches cells to the slide so that they will not wash off during the staining process. - Fixation kills the cells that are being stained for observation.

Fixation differentiates the various cells being observed.

Which of the following steps is common to both the Gram stain and the acid-fast stain? - Heat fixation of the smear before staining - The application of iodine as a mordant - Steam exposure for stain penetration - Acid-alcohol for decolorizing - The use of methylene blue as a counterstain

Heat fixation of the smear before staining

A student is observing an object that displays the internal detail on a virus at great magnification. Which type of microscope is used for this image?

Transmission electron microscope

(T/F) The limit of resolution of the compound microscope illuminated with visible light is approximately 0.2 μm.

True

used for initial focusing; should never be used when the high-power objective lens or oil immersion objective lens is in place

coarse focus knob

Through which structure would the light pass before it reaches the specimen affixed to the stage?

condenser

used to focus the light from the illuminator onto the slide

condenser lens

Which of the following correctly traces the path of light through the compound microscope?

light source; condenser; specimen; objective lens; ocular lens