Microbiology Chapter 2 Quiz Questions

Light rays are refracted (bent) when they cross the interface between materials with different refractive indices. This is a well-known phenomenon in physics, where light changes direction as it passes from one medium to another. The amount of bending depends on the refractive indices of the materials involved. Therefore, it is true that light rays are refracted when they cross the interface between materials with different refractive indices.

To view a specimen with a total magnification of 400, the ocular magnification of 10 needs to be multiplied by the objective magnification. Therefore, the objective magnification must be 40 in order to achieve a total magnification of 400.

The total magnification is determined by multiplying the magnification of the objective lens by the magnification of the ocular lens. In this case, the objective lens has a magnification of 45 and the ocular lens has a magnification of 10. Therefore, the total magnification is 45 x 10 = 450.

Confocal microscopes are indeed capable of creating three-dimensional images of cell structures when used in combination with specialized computer software. This is achieved by capturing multiple images of the sample at different focal planes and then reconstructing them into a three-dimensional representation. This technology has greatly advanced the field of cell biology by allowing researchers to visualize and study cellular structures in greater detail.

In the Gram-staining procedure, the mordant is iodine. A mordant is a substance that helps to fix or attach a stain to a specimen. In Gram staining, iodine is used as a mordant to form a complex with crystal violet dye, which helps to stabilize the dye and prevent it from being easily washed away. This complex is then trapped within the thick peptidoglycan layer of Gram-positive bacteria, resulting in the retention of the purple color. In Gram-negative bacteria, the iodine complex is washed away during the decolorization step, leading to the uptake of the counterstain (safranin) and the pink coloration.

Mordants are substances that are used in staining techniques to enhance the binding between a stain and the specimen. They achieve this by forming a complex with the stain and the specimen, creating a stronger and more durable bond. This increased binding allows for better retention of the stain on the specimen, resulting in clearer and more visible staining. Therefore, the statement that mordants increase the binding between a stain and specimen is true.

After the secondary stain has been added, gram-positive organisms retain the purple color of the primary stain and appear purple. On the other hand, gram-negative organisms lose the purple color and take on the pink color of the secondary stain, appearing pink.

The Gram-staining procedure is a method used to differentiate bacteria into two groups: Gram-positive and Gram-negative. In this procedure, the primary stain is crystal violet. Crystal violet is a purple dye that is applied to the bacteria, allowing them to retain the color. After the crystal violet stain, a series of steps including iodine, alcohol, and safranin are used to further differentiate and stain the bacteria. However, crystal violet is the initial and primary stain used in the Gram-staining procedure.

The counterstain in the Gram-staining procedure is safranin. Gram staining is a technique used to differentiate bacteria into two groups: Gram-positive and Gram-negative. Crystal violet is the primary stain used to stain all bacteria, and iodine is used as a mordant to enhance the staining. After applying alcohol as a decolorizer, Gram-positive bacteria retain the crystal violet stain while Gram-negative bacteria do not. Finally, safranin is used as a counterstain to stain the Gram-negative bacteria pink or red, allowing for easy differentiation between the two groups.

The correct answer is "simple" because the question is asking for the term used to describe the procedure of using a single stain to visualize microorganisms. The term "simple" accurately describes this procedure, as it involves using only one stain instead of multiple stains.

The Gram-staining procedure is an example of differential staining. This technique is used to differentiate bacteria into two major groups, Gram-positive and Gram-negative, based on their cell wall composition. The staining process involves multiple steps, including the application of a crystal violet dye, iodine treatment, decolorization with alcohol or acetone, and counterstaining with safranin. Gram-positive bacteria retain the crystal violet stain and appear purple, while Gram-negative bacteria lose the stain and appear pink or red after counterstaining. This staining technique is crucial for identifying and classifying bacteria in microbiology.

The total magnification is determined by multiplying the magnification of the objective lens by the magnification of the ocular lens. In this case, the objective lens has a magnification of 30 and the ocular lens has a magnification of 20. Therefore, the total magnification is 30 x 20 = 600.

India ink is commonly used in microbiology to perform negative staining, a technique that allows the visualization of capsules surrounding bacterial cells. The ink particles are repelled by the capsule material, creating a dark background against which the capsules appear as clear halos. This technique is particularly useful for identifying encapsulated bacteria such as Streptococcus pneumoniae, which causes pneumonia and other infections. Therefore, the statement that negative staining with India ink can be used to reveal the presence of capsules surrounding bacterial cells is true.

Immersion oil is used in microscopy to improve the resolution and clarity of the image. It has a similar refractive index to glass, which reduces the amount of light that is lost or scattered as it passes through the specimen. This allows more light to pass through the objective lens, resulting in a brighter and clearer image. Therefore, it is true that immersion oil increases the amount of light passing through a specimen and entering the objective lens.

Scanning electron microscopes use electrons to create an image of a specimen. These electrons are derived from atoms within the specimen itself, rather than the electrons used to bombard the specimen. This is true because the electrons used for imaging are secondary electrons that are emitted from the specimen's surface when it is bombarded with the primary electron beam.

In the Gram-staining procedure, the decolorizer is ethanol or acetone. This step is crucial in differentiating between Gram-positive and Gram-negative bacteria. The decolorizer removes the crystal violet stain from the Gram-negative bacteria, making them colorless, while the Gram-positive bacteria retain the stain. This allows for the differentiation and classification of bacteria based on their cell wall composition.

A substage condenser is a component of a light microscope that is used to focus light onto the specimen. By focusing the light, the condenser increases the resolution of the microscope. This means that the microscope is able to produce a clearer and more detailed image of the specimen. Therefore, the statement "A substage condenser is used to focus light onto the specimen, which increases the resolution of a light microscope" is true.

The explanation for the given correct answer is that viruses are extremely small and cannot be seen with a light microscope, which uses visible light to magnify objects. The electron microscope, on the other hand, uses a beam of electrons to create a highly magnified image, allowing us to view viruses and other tiny particles that are not visible with a light microscope. Therefore, it was only after the invention of the electron microscope that we were able to see viruses.

Gram staining is a common technique used to classify bacteria into two major groups based on their cell wall composition. These groups are referred to as Gram-positive and Gram-negative bacteria. Gram-positive bacteria have a thick layer of peptidoglycan in their cell walls, which retains the crystal violet stain used in the Gram staining process and appears purple under a microscope. On the other hand, Gram-negative bacteria have a thinner peptidoglycan layer and an outer membrane, which does not retain the stain and appears pink or red. Therefore, it can be said that Gram staining divides bacterial species into roughly two equal groups.

Immersion oil is actually used to increase the resolution and clarity of a specimen under a microscope. It has a higher refractive index than air, which reduces the amount of light that is scattered and allows more light to enter the objective lens. This improves the sharpness and detail of the image. It does not have any effect on preventing the specimen from drying out.

Heat-fixing is a process in which smears of microorganisms are subjected to heat in order to attach them firmly to the slide. This helps in preventing the smears from being washed off during subsequent staining and washing steps. Heat-fixing also helps in preserving the overall morphology of the microorganisms, making it easier to visualize their internal structures under a microscope. Therefore, the correct answer is "attach it firmly to the slide."

If the decolorizer is not left on long enough in the Gram-staining procedure, gram-positive organisms will retain the crystal violet stain and appear purple, while gram-negative organisms will lose the crystal violet stain and appear purple as well.

Scanning tunneling electron microscopes use a fine-tipped probe to scan the surface of a specimen. As the probe moves across the surface, a small electric current flows between the probe and the specimen due to the quantum mechanical phenomenon called tunneling. This current is used to create a three-dimensional image of the specimen with atomic-level resolution. Therefore, the statement that scanning tunneling electron microscopes create a three-dimensional image of specimens at atomic level resolution is true.

A microscope that exposes specimens to ultraviolet, violet, or blue light and forms an image with the light emitted at a different wavelength is called a fluorescence microscope. This type of microscope uses fluorescent dyes or proteins to label specific structures or molecules within the specimen, which then emit light of a different color when excited by the specific wavelength of light used. This allows for the visualization and study of specific cellular components or processes.

As the magnification of a series of objective lenses increases, the working distance decreases. This is because as the magnification increases, the lenses need to be closer to the object being observed in order to achieve a higher level of detail. Therefore, the working distance, which is the distance between the lens and the object, decreases as the magnification increases.

A staining procedure that divides organisms into different groups based on their individual reactions is referred to as differential staining. This technique allows for the differentiation and identification of different types of organisms or structures within organisms based on their staining characteristics. By using different stains or dyes, specific structures or components can be highlighted or differentiated, providing valuable information for classification and identification purposes.

The working distance refers to the distance between the specimen and the objective lens when the specimen is in focus. This distance is important because it determines the amount of space available for manipulating the specimen or inserting additional tools or equipment. A longer working distance allows for more flexibility and ease of use, while a shorter working distance may require more precision and careful handling of the specimen.

A dark field microscope is an instrument that produces a bright image of the specimen against a dark background. This is achieved by blocking the direct light that would normally pass through the specimen, and instead only capturing the light that is scattered or refracted by the specimen. This technique enhances the contrast between the specimen and its surroundings, making it easier to observe and analyze.

The focal point is the point at which a lens focuses parallel beams of light. When parallel rays of light pass through a lens, they converge at a single point called the focal point. This is where the light rays come together after passing through the lens and is an important concept in understanding how lenses work.

The explanation for the given correct answer is that magnification refers to the ability of a microscope to enlarge an image, while resolution refers to the ability to distinguish between two separate points in an image. Even if a microscope has a high magnification power of 10,000x, it does not guarantee a sharp image if the resolution is poor. Resolution depends on factors such as the quality of the lenses and the wavelength of light used. Therefore, it is possible to have high magnification but low resolution, resulting in a blurry image.

Flagella are thin, whip-like structures that are difficult to observe under light microscopy due to their small size. In order to make them more visible, it is necessary to increase their thickness. This can be achieved by staining the flagella, which involves adding a dye or a specific chemical to the sample. The stain increases the contrast between the flagella and the surrounding environment, making them easier to observe and study under a light microscope. Therefore, the statement is true.

The statement is true because the resolution of a light microscope depends on the numerical aperture (NA) of the objective lens and the wavelength of light used. The formula for resolution is given by the Rayleigh criterion, which states that the minimum resolvable distance is approximately equal to half the wavelength of light divided by the numerical aperture. In this case, the numerical aperture is 0.65 and the wavelength of light is 420 nm, so the resolution is approximately 322 nm. Since the objects are 400 nm apart, they can be distinguished by the microscope.

The resolution actually increases when the wavelength of the illuminating light decreases. This is because resolution is determined by the ability of a microscope or imaging system to distinguish between two closely spaced objects. According to the Rayleigh criterion, the resolution is inversely proportional to the wavelength of the light used. Therefore, shorter wavelengths of light (such as blue or ultraviolet light) provide better resolution compared to longer wavelengths (such as red or infrared light).

Fixation is the process by which internal and external structures of cells and organisms are preserved and maintained in position. It involves treating the cells or tissues with a fixative, such as formaldehyde, which helps to prevent decay and maintain the structure of the cells. Fixation is an important step in various biological techniques, including histology and electron microscopy, as it allows for the preservation of cellular structures and the ability to study them under a microscope. It helps to prevent the loss of cellular components and maintains the integrity of the sample for further analysis.

Freeze-etching is a technique used to observe frozen specimens under a transmission electron microscope. It involves freezing the specimen and then fracturing it along lines of weakness, typically the lipid bilayer membranes. This technique allows for the visualization of the internal structures and surfaces of the specimen, providing valuable information about its morphology and organization. Freeze etching is another term used to describe this process.

After the decolorizer has been added, gram-positive organisms retain the purple stain because their cell walls have a thick layer of peptidoglycan which traps the crystal violet dye. On the other hand, gram-negative organisms lose the purple stain because their cell walls have a thinner layer of peptidoglycan and are easily decolorized by the alcohol in the decolorizer. As a result, gram-negative organisms appear colorless after the decolorizer has been added.

A transmission electron microscope is the best tool for visualizing small internal cell structures because it uses a beam of electrons to create a detailed image of the specimen. Unlike a light microscope, which uses visible light, the transmission electron microscope has a much higher resolution and can magnify the image up to a million times. This allows for the visualization of very small structures within the cell, such as organelles and macromolecules. A dark-field microscope is used to observe transparent or unstained specimens, while a flagellar microscope is specifically designed to observe flagella.

Immersion oil is used to increase the resolution achieved with some microscope lenses because it increases the refractive index between the specimen and the objective lens. By placing a drop of immersion oil between the lens and the specimen, the refractive index of the oil matches that of the glass lens, reducing the amount of light that is scattered or lost at the interface. This allows for better light transmission and improved resolution, allowing finer details of the specimen to be observed.

A phase-contrast microscope is an instrument that is used to magnify slight differences in the refractive index of cell structures. It allows for the visualization of transparent or unstained samples by enhancing the contrast between the different parts of the cell. This technique is particularly useful for studying living cells or observing dynamic processes within cells.

Acid-fast organisms like Mycobacterium tuberculosis have cell walls composed of lipids called mycolic acids. These lipids provide a protective barrier for the organism and contribute to its acid-fast properties. Lipids are a type of biomolecule that are insoluble in water and play important roles in cell structure and function. In the case of acid-fast organisms, the presence of mycolic acids in their cell walls helps to differentiate them from other bacteria.

Before the decolorizer is used, gram-positive organisms retain the primary stain (crystal violet) and appear purple. Gram-negative organisms also retain the primary stain and appear purple. Therefore, both gram-positive and gram-negative organisms are stained purple at this stage.

The focal length is the distance between the center of a lens and the point at which it focuses parallel beams of light.

Confocal microscopes exhibit improved contrast and resolution by blocking out stray light with an aperture located above the objective lens. This aperture acts as a barrier, preventing unwanted light from entering the microscope and reducing background noise. By blocking out stray light, the microscope is able to capture clearer and more focused images of the specimen, resulting in improved contrast and resolution.

Basic dyes such as methylene blue bind to cellular molecules that are negatively charged. This is because basic dyes have a positive charge and are attracted to molecules with a negative charge. The binding occurs through electrostatic interactions between the positive and negative charges, allowing the dye to attach to the cellular molecules.

Both the Gram stain and Acid-fast stain are considered to be differential staining procedures. Differential staining is a technique used to distinguish between different types of microorganisms or different parts of the same microorganism based on their staining properties. The Gram stain differentiates bacteria into Gram-positive and Gram-negative based on the differences in their cell wall composition. The Acid-fast stain is used to identify bacteria that have a waxy cell wall, such as Mycobacterium tuberculosis, which causes tuberculosis.

If the objective lenses of a microscope can be changed without losing focus on the specimen, they are said to be parfocal. This means that when switching between different objective lenses, the specimen remains in focus and there is no need for significant adjustments to be made to the focus knob. This feature is important in microscopy as it allows for efficient and convenient examination of different magnifications without losing focus on the specimen.

The Schaeffer-Fulton procedure is a staining technique commonly used to visualize endospores. Endospores are dormant, highly resistant structures formed by certain bacteria as a way to survive harsh conditions. These structures are not easily stained by conventional staining methods, hence the need for specialized techniques like the Schaeffer-Fulton procedure. This procedure involves the use of heat and multiple dyes to selectively stain the endospores, allowing them to be easily observed and distinguished from other cellular components.

If the decolorizer is left on too long in the Gram-staining procedure, gram-positive organisms will be stained pink and gram-negative organisms will also be stained pink.

The useful magnification of a light microscope is limited by the wavelength of the light source being utilized. This is because the resolution of a microscope is determined by the wavelength of the light used. As the wavelength decreases, the resolution increases, allowing for more detailed observation of the specimen. Therefore, a shorter wavelength light source will provide higher magnification and better resolution in a light microscope.

Negative staining actually does not facilitate the visualization of bacterial capsules. Negative staining is a technique used to visualize the background or the external surface of bacteria, while bacterial capsules are visualized using positive staining techniques. Therefore, the statement is false.