Question 1

Which type of microscope shows cells against a bright background but also differentiates intracellular structures of unstained cells based on their varying densities?

Accepted Answer

Phase contrast microscopy is the only type of microscope among the given options that can differentiate intracellular structures in unstained cells based on their varying densities. It achieves this by using changes in the phase of light passing through the specimen to create contrast. However, it still shows cells against a bright background, unlike dark field or differential interference microscopy, which use oblique or polarized light, respectively, and present a dark or colored background. Electron microscopy is not among the given options, but it provides high-resolution images of cell structures but requires fixed and coated specimens and a vacuum chamber. Bright field microscopy is the most basic and widely available type, but it only shows cells and their features as dark objects on a bright background, which limits its usefulness in studying transparent or colorless specimens.

Question 2

Which of the following magnifies the specimen to produce its virtual image?

Accepted Answer

The ocular lens, also known as the eyepiece, produces a virtual image by magnifying the image formed by the objective lens. The condenser is responsible for focusing the light onto the specimen, the body holds the various parts of the microscope together, and the iris diaphragm controls the amount of light that enters the microscope.

Question 3

A microbiologist inoculates Staphylococcus aureus into a culture medium. Following incubation, both Staphylococcus aureus and Staphylococcus epidermidis are determined to be growing in this culture. What is the most likely explanation?

Accepted Answer

The presence of both Staphylococcus aureus and Staphylococcus epidermidis suggests contamination of the culture medium, as these two species are commonly found together as normal skin flora.

Question 4

A microbiologist must culture a patient's feces for intestinal pathogens. Which of the following would likely be present in selective media for analyzing this fecal specimen?

Accepted Answer

Bile salts are often added to selective media for intestinal pathogens because they inhibit the growth of Gram-positive bacteria while allowing the growth of Gram-negative bacteria like enteric pathogens. NaCl, sheep red blood cells, thioglycollic acid, and peptone are not typically added to selective media for this purpose.

Question 5

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

Accepted Answer

The answer of All of the following are diameters of...

Question 6

Which of the following magnifies the specimen to produce its real image?

Accepted Answer

The objective lens is responsible for magnifying the specimen to produce its real image. The condenser focuses the light onto the specimen, the ocular lens further magnifies the image, the body connects the objective lens to the eyepiece, and the nosepiece holds and rotates the objective lenses.

Question 7

A reducing media is used to culture

Accepted Answer

A reducing media is used to culture anaerobic organisms, as it contains substances that help remove oxygen from the medium and create an anaerobic environment. This type of media can be used to culture organisms that cannot survive in the presence of oxygen.

Question 8

Which type of medium is able to distinguish different species or types of microorganisms based on an observable change in the colonies or in the medium?

Accepted Answer

Differential media can differentiate between different species or types of microorganisms by producing observable changes in the colonies or in the medium. Selective media are designed to only grow specific types of microorganisms while inhibiting others. Enumeration media contain nutrients that promote the growth of a particular group of microorganisms so that they can be counted. Enriched media contain nutrients that promote the growth of fastidious or nutritionally deficient microorganisms. Reducing media are used to culture anaerobic microorganisms.

Question 9

Bacteria that require special growth factors and complex nutrients are termed ________.

Accepted Answer

Fastidious bacteria are those that require special growth factors and complex nutrients to grow. This is in contrast to non-fastidious bacteria, which can grow on simple nutrient media. Options A, B, D, and E describe different types of microbial metabolic processes, but do not relate to the nutrient requirements of bacteria.

Question 10

The type of microscope in which you would see brightly illuminated specimens against a black background is ________.

Accepted Answer

Dark field microscopy uses oblique illumination to create bright specimens against a dark background.

Question 11

For which bacterial genus does mannitol salt agar differentiate between species?

Accepted Answer

Mannitol salt agar is a selective and differential medium used to differentiate between different species of Staphylococcus. It contains high levels of salt, making it selective for Staphylococcus species, and the medium also contains mannitol, which can be fermented by some Staphylococcus species, leading to a change in pH and the production of yellow colonies.

Question 12

An enveloped virus measures 0.02 micrometers (μm) in diameter. What is the diameter of this virus in nanometers (nm)?

Accepted Answer

To convert micrometers (μm) to nanometers (nm), we multiply by 1000. Therefore, the diameter of the virus in nanometers is 0.02 μm x 1000 nm/μm = 20 nm.

Question 13

Newly inoculated cultures must be ________ at a specific temperature to encourage growth.

Accepted Answer

Newly inoculated cultures must be incubated at a specific temperature to provide an optimal growth environment for the organisms.

Question 14

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 for easy selection and changing of them. The stage is where the specimen is placed, the condenser helps to focus the light onto the specimen, the objective lenses provide different levels of magnification, and the ocular lens is the eyepiece that the viewer looks through to see the magnified specimen.

Question 15

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 done by the objective lens, and the further magnification is achieved through the ocular lens. Therefore, the correct answer is C, where objective lens projects to the ocular lens.

Question 16

Which of the following controls the amount of light entering the specimen?

Accepted Answer

The iris diaphragm controls the opening through which light enters the specimen, allowing the operator to adjust the amount of light that reaches the specimen.

Question 17

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

The total magnification is the product of the ocular lens magnification and the objective lens magnification. Given a total magnification of 950x and an ocular lens of 10x, the objective lens must be 95x (950 ÷ 10 = 95).

Question 18

Which of the following characteristics refers to the microscope's ability to show two separate entities as separate and distinct?

Accepted Answer

Resolving power, also known as resolution, refers to the ability of a microscope to distinguish between two separate entities as separate and distinct. Magnification and refraction are also important characteristics of microscopes, but they do not specifically refer to this ability to resolve separate entities. Therefore, choice A is the best answer.

Question 19

A rod-shaped bacterium is measured as 0.3 micrometers (μm) in length using an ocular micrometer. Your instructor wants you to report the length in millimeters (mm) to test your understanding of metric conversions. What is the length of the organism in millimeters?

Accepted Answer

1 micrometer (μm) is equal to 0.001 millimeters (mm), so 0.3 μm is equal to 0.0003 mm.

Question 20

Differential media results in which of the following growth characteristics?

Accepted Answer

Differential media is designed to distinguish between different types of microorganisms based on their growth characteristics. This can include different color colonies, changes in media color post incubation, precipitates, and the production of gas bubbles. Therefore, all of the choices listed are correct.

Quiz 2: Tools of the Laboratory: Methods for the Culturing and Microscopic Analysis of Microorganisms