Chapter 3 HW

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

25 nm

2.5 nm

2500 nm

250 nm

25,000 nm

250 nm

A paramecium is approximately 150 micrometers in length. What is this measurement expressed in millimeters (mm)?
A paramecium is approximately 150 micrometers in length. What is this measurement expressed in millimeters (mm)?
1.5 mm
0.015 mm
1500 mm
0.15 mm
15 mm

0.15 mm

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

Visible light is only good at wavelengths below 390 nm.
Anything smaller than 200 nm cannot interact with visible light.
The lenses only go to 100 X magnification power.
It is too easy to lose on the stage.

Anything smaller than 200 nm cannot interact with visible light.

What happens to the light rays when they hit the specimen?
They are focused into a small area towards the objective lens.
They are absorbed by the stage.
They are reflected, refracted, or absorbed by the specimen.
They are diverted to the ocular lens.

They are reflected, refracted, or absorbed by the specimen

What is the role of the ocular lens?
What is the role of the ocular lens?
To adjust the wavelength of light
To recreate the image in the viewer’s eye
To do the bulk of the magnification
To focus the light to a high intensity in a small area

To recreate the image in the viewer’s eye

What is meant by light rays being divergent?
It is spreading out
It is coming together to a focused beam
It is heading upwards

It is spreading out

In a typical brightfield microscope (seen in the animation), at which point does magnification begin?
The stage
The objective lens
The lamp
The condenser lens
The ocular lens

The objective lens

While staining a mixed culture of Gram-positive and Gram-negative bacteria, switching the order of steps 2 and 3 would result in ______________________.
all bacteria appearing pink
all bacteria appearing purple
all bacteria appearing clear
a change in the Gram reaction; Gram-negative cells would appear purple while Gram-positive cells would appear pink.

all bacteria appearing pink

Which structural feature of Gram-positive bacteria enhances their ability to retain the crystal violet dye?

a thin peptidoglycan layer
a thick peptidoglycan layer
an outer membrane
All of the above contribute to a Gram-positive cell’s ability to retain crystal violet.

a thick peptidoglycan layer

What would you anticipate seeing if you accidentally switched crystal violet and safranin while performing a Gram stain?

All bacteria would appear purple.
All bacteria would appear pink.
Gram-positive bacteria would appear pink and Gram-negative bacteria would appear purple.
Gram-positive bacteria would appear purple and Gram-negative bacteria would appear pink.

All bacteria would appear purple.

What would you expect to see if you forgot to perform step 2 of the Gram stain procedure?

All bacteria would appear pink.
All bacteria would appear purple.
Gram-positive cells would appear purple and Gram-negative cells would appear pink.
Gram-positive cells would appear pink and Gram-negative cells would appear purple.

All bacteria would appear pink.

Which of the following measurements is correctly matched with microorganisms of that size?

viruses–1 centimeter
bacteria–2 micrometers
viruses–10 micrometers
bacteria–10 nanometers

bacteria–2 micrometers

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

The fluorescent screen adds another magnification step.

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

They are capable of producing 3-dimensional images, which light microscopes cannot do.

The copper grid used in electron microscopy provides enhanced resolution.

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

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

Condenser lens
Eyepiece lens
Objective lens
Projector lens

Projector lens

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

A light microscope
A scanning electron microscope
A light microscope, transmission electron microscope, and scanning electron microscope can all view ribosomes inside a cell.
A transmission electron microscope

A transmission electron microscope

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

They both utilize white light to magnify the specimen.
They both employ the use of objective lenses.
Both microscopes require an internal camera to visualize the specimen.
Both microscopes have a resolving power of 0.01 nm.

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

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

What is the role of lenses in microscopy?

Lenses are only used to magnify specimens that are smaller than whole red blood cells.
Lenses focus either light or electrons to create a magnified image of a specimen.
Lenses increase the contrast to determine structural differences in stained specimens.

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

What does resolution mean?

a measure of the ability of a medium to bend light
the ability of a microscope to stay in focus when the objective lenses are moved from low power to high
the total magnification of the visual image seen
the ability of a microscope to distinguish fine details and differentiate between two very close objects

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

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?

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

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

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

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

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

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.
Images produced by light microscopes can be in color, whereas electron microscope images are black and white unless they are artificially colored.
The electron microscope has greater resolution than the light microscope.
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.

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

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

2000×

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

darkfield microscopy
transmission electron microscopy
scanning electron microscopy
fluorescent microscopy

darkfield microscopy

What is the role of iodine in the Gram stain process?

Iodine is a mordant in the Gram stain technique, which functions to intensify the primary stain.
Iodine is a pink dye that acts as the primary stain in the Gram stain technique.
Iodine is the decolorizer removing the primary stain after the first step in the Gram stain technique.
Iodine is a basic purple dye, which acts as the primary stain in the Gram stain technique.

Iodine is a mordant in the Gram stain technique, which functions to intensify the primary stain.

A student creates a Gram stain on a bacterial sample that has a mix of gram-negative and gram-positive organisms. The student accidentally forgets the decolorizer step. What would the outcome of the Gram stain be?

The Gram stain would show pink (gram-negative bacteria) and purple (gram-positive bacteria).
All organisms would appear purple (gram-positive).
All organisms would appear colorless.
All organisms would appear pink (gram-negative).

All organisms would appear purple (gram-positive).

Consider the following situations, and determine when a simple stain could be used instead of a Gram stain.

An unknown species of bacteria is being characterized and identified.
A specimen is suspected to contain multiple species of bacteria.
A wound specimen is being examined.
A microbiologist is trying to determine whether a specimen contains bacteria or fungi.

A microbiologist is trying to determine whether a specimen contains bacteria or fungi.

Which of the following staining procedures is matched with the principal use for that stain?

negative stain used to differentiate cell wall components
flagella stain used to distinguish dormant structures formed during adverse environmental conditions
endospore stain to visualize flagella
acid-fast stain for microbes with waxy cell walls

acid-fast stain for microbes with waxy cell walls