Question 1

Which type of microscope shows cells against a white background?

Accepted Answer

Bright-field microscopes show cells against a white background, which results from the light passing through the specimen and being absorbed, refracted, or reflected by different structures within the cell.

Question 2

Which of the following parts of a microscope magnifies the specimen to produce a real image of the specimen?

Accepted Answer

The objective lens is the part of the microscope that magnifies the specimen to produce a real image of the specimen. The ocular lens further magnifies the real image produced by the objective lens. The body provides support for the various parts of the microscope, the condenser focuses the light onto the specimen, and the nosepiece holds and rotates the objective lenses.

Question 3

A nutrient medium that contains at least one ingredient that is not chemically defined is termed ______.

Accepted Answer

A complex medium contains at least one ingredient that is not chemically defined, meaning that it cannot be described by its chemical formula. Examples of complex media include nutrient agar and tryptic soy agar, which both contain a mixture of nutrients derived from plant or animal sources. Enriched media contain additional nutrients to support the growth of fastidious organisms, reducing media contain compounds that chemically reduce oxygen, and synthetic media contain only chemically-defined ingredients.

Question 4

All of the following are diameters of cells that would be resolved in a microscope with a limit of resolution of 0.2 µm except ______.

Accepted Answer

The limit of resolution is the smallest distance between two objects that can be distinguished as separate entities. In this case, the limit of resolution is 0.2 µm. Therefore, any cell with a diameter less than 0.2 µm will not be resolved in the microscope. Choice B is 0.1 µm, which is less than the limit of resolution, so it will not be resolved in the microscope.

Question 5

Which term refers to the microscope's ability to show two separate objects as discrete and distinct?

Accepted Answer

Resolution refers to the microscope's ability to differentiate between two separate objects and show them as discrete and distinct.

Question 6

Scattering of peripheral light rays through the glass slide under very high magnification can be prevented by ______.

Accepted Answer

Scattering of peripheral light rays through the glass slide can be prevented by using immersion oil, which has the same refractive index as the glass slide and helps to focus the light rays more precisely onto the sample being observed. The other options, such as the condenser, ocular, and cover slip do not directly affect peripheral light scattering.

Question 7

If a microbiologist is studying a specimen at a total magnification of 950X, what is the magnifying power of the objective lens if the ocular lens is 10X?

Accepted Answer

Total magnification = magnification of objective lens x magnification of ocular lens.
So, magnification of the objective lens = total magnification / magnification of ocular lens.
Therefore, magnification of the objective lens = 950X / 10X = 95X.

Question 8

A nutrient medium that has all of its chemical components identified and their precise concentrations known and reproducible is termed ______.

Accepted Answer

A defined medium has all of its chemical components identified and their precise concentrations known and reproducible. A reducing medium is one in which oxygen is chemically removed from the medium. An enriched medium has been supplemented with specific growth factors, such as blood or serum. A complex medium contains a variety of organic compounds in partially digested form, and their precise concentrations are not known.

Question 9

Which of the following parts of the microscope magnifies the specimen to produce the virtual image of the specimen?

Accepted Answer

The ocular lens, also known as the eyepiece, is the part of the microscope that magnifies the specimen to produce the virtual image that is viewed by the observer.

Question 10

The simple microscopes used by the earliest practitioners of microscopy contained which of the following?

Accepted Answer

The earliest microscopes used by early practitioners only contained a magnifying lens, which allowed for basic observation of small objects. The other components listed were not incorporated until later developments in microscopy.

Question 11

The specimen preparation technique that is best for viewing cell motility is the ______.

Accepted Answer

The hanging drop technique allows for live observation of cell motility, making it the best choice for this purpose. Option A and B are stains that do not allow for live observation, while option C is a stain that highlights the background instead of the cells themselves. Option E involves fixing and staining the cells, which can disrupt and alter their natural motility.

Question 12

The _____ of the microscope holds and allows selection of the objective lenses.

Accepted Answer

The nosepiece is the part of the microscope that holds the objective lenses and allows selection between them. The ocular is the eyepiece that you look through, the condenser is the lens that focuses light onto the specimen, and the stage is the platform on which the specimen sits.

Question 13

The type of microscopy in which you would observe brightly illuminated specimens against a black background is ______.

Accepted Answer

Dark-field microscopy uses a special condenser that produces a hollow cone of light that allows only oblique rays to enter the objective lens. This produces a brightly illuminated specimen against a dark or black background.

Question 14

Who invented the first crude microscope by grinding glass?

Accepted Answer

Antonie van Leeuwenhoek, a Dutch tradesman and scientist, invented the first crude microscope by grinding glass in the late 1600s. He was the first to see microorganisms and is often considered the father of microbiology.

Question 15

Eosin-methylene blue agar, or EMB, is a commonly used bacteriological medium for growing gram-negative bacteria from complex environments.It contains two dyes, eosin and methylene blue, as well as the sugar lactose.Eosin is a pH indicator that changes color when the medium is acidic, while methylene blue inhibits the growth of most gram-positive bacteria.If an organism consumes lactose, acid will be produced, causing the bacterial colonies to change color. Based upon this description, this medium is ______.

Accepted Answer

Eosin-methylene blue agar is both differential and selective. It is selective because it inhibits the growth of gram-positive bacteria through the use of methylene blue. It is differential because it allows the differentiation of lactose-fermenting (pink to red colonies) from non-lactose fermenting (colorless colonies) gram-negative bacteria through the use of eosin as a pH indicator.

Question 16

The wavelength of light used and the numerical aperture governs ______.

Accepted Answer

The resolution of an optical system is determined by the wavelength of the light used and the numerical aperture. Numerical aperture is a measure of the light-gathering capacity of a lens or microscope objective. Therefore, the wavelength of light used and the numerical aperture govern resolution.

Question 17

A scanning confocal microscope

Accepted Answer

A scanning confocal microscope scans narrow planes of a specimen using laser beams and can build a three-dimensional image of the specimen. It does not produce electron micrographs or use ultraviolet light to form a specimen image. Instead, it uses dyes that emit visible light when excited by the laser.

Question 18

Magnification is achieved in a compound microscope through the initial magnification of the specimen by the _____ lens.This image is then projected to the _____ lens that will further magnify the specimen to form a virtual image received by the eye.

Accepted Answer

The initial magnification of the specimen is achieved by the objective lens in a compound microscope, and this image is then further magnified by the ocular lens to form a virtual image received by the eye.

Question 19

All of the following pertain to the fluorescence microscope except

Accepted Answer

The fluorescence microscope uses visible light to produce a specimen image, not electrons.

Answer: B
 While the fluorescence microscope can be used in medical applications, such as detecting fluorescently labeled pathogens, it is not typically used to directly diagnose infections.

Therefore, the correct choices are C and B.

Question 20

Which type of microscopy transforms the subtle variations in cell density into differences in light intensity, allowing for increased internal detail without staining?

Accepted Answer

Phase-contrast microscopy enhances contrast by transforming subtle variations in cell density into differences in light intensity, allowing for increased internal detail without staining. This is achieved by altering the phase of the light passing through the specimen.

Quiz 3: Tools of the Laboratory: Methods for the Culturing of Microscopic Analysis of Microorganisms