Microbiology: Chapter 3

Magnification is a measure of how much larger an object appears compared to its actual size. It is commonly expressed as a number combined with "X" to indicate the number of times larger the object appears. For example, a magnification of 5X means that the object appears five times larger than its actual size. Therefore, it is true that magnification can be expressed as a number combined with "X" (times).

The gram stain, developed by Hans Christian Gram in 1884, is a commonly used laboratory technique to aid in bacterial identification. It involves staining bacterial cells with crystal violet dye, followed by a series of washes and counterstains. The stain helps to differentiate bacteria into two major groups: gram-positive and gram-negative, based on their cell wall composition. This information is valuable in determining appropriate treatment options for bacterial infections. Therefore, the statement "The gram stain was developed by Hans Christian Gram in 1884 in order to aid in bacterial identification" is true.

In fluorescence microscopy, specimens are indeed stained with "fluorochromes" that can absorb and radiate UV light. This technique allows for the visualization of specific structures or molecules within the specimen by emitting a different color of light when excited by UV light. Therefore, the statement is true.

The compound light microscope uses visible light because it relies on a series of lenses to magnify the specimen. These lenses focus the light onto the specimen, allowing it to be viewed by the observer. Since visible light is used, it means that the microscope can only magnify objects that are within the visible light spectrum. This is in contrast to other types of microscopes, such as electron microscopes, which use beams of electrons instead of visible light to magnify the specimen. Therefore, the statement "The compound light microscope uses visible light" is true.

Some bacteria may react differently after a gram stain procedure due to a structural difference in their cell wall. Gram staining is a method used to differentiate bacteria into two groups: gram-positive and gram-negative, based on their cell wall composition. Gram-positive bacteria have a thick layer of peptidoglycan in their cell wall, which retains the crystal violet stain 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, the structural difference in the cell wall can cause bacteria to react differently in a gram stain procedure.

The correct statement for magnification is the ability to make objects appear larger. Magnification refers to the process of enlarging the size of an object or image, allowing for a closer and more detailed view. It is commonly used in various fields such as microscopy, photography, and optics to enhance visibility and study minute details that may not be visible to the naked eye.

Resolving power refers to the ability of an optical system to distinguish between two closely spaced objects or details. It is determined by the wavelength of light employed for viewing. The shorter the wavelength of light used, the higher the resolving power. This is because shorter wavelengths allow for greater detail to be observed and smaller gaps to be resolved. Therefore, the correct answer is "the wavelength of light employed for viewing".

The first step in performing a gram stain procedure is to apply a basic dye, which stains all the cells one color (blue or purple) and is referred to as the primary stain. This step helps to differentiate between gram-positive and gram-negative bacteria based on the differences in their cell wall structures. Gram-positive bacteria retain the primary stain, while gram-negative bacteria do not. This initial staining is crucial for the subsequent steps in the gram stain procedure.

Resolution refers to the ability to show detail in an image or display. It is a measure of the clarity and sharpness of the image, indicating how well-defined and distinct the individual elements or pixels are. A higher resolution means that more detail can be seen, while a lower resolution may result in a less clear and more pixelated image. Therefore, the statement "The ability to show detail" accurately describes resolution.

The given answer is correct because simple stain, differential stain, and Gram stain are all staining techniques used in microbiology and histology. Staining techniques are used to enhance the visibility of cells or tissues under a microscope by adding color to them. Simple stain involves using a single dye to stain all cells the same color, making them easier to see. Differential stain involves using multiple dyes to distinguish different types of cells or structures. Gram stain is a specific type of differential stain used to classify bacteria into Gram-positive and Gram-negative based on differences in cell wall composition.

After a gram stain procedure, gram-positive cells retain the purple crystal violet stain, while gram-negative cells lose the stain and take up the red counterstain. This is because gram-positive cells have a thick peptidoglycan layer in their cell wall that retains the crystal violet dye, while gram-negative cells have a thin peptidoglycan layer that allows the crystal violet to be washed out and the red counterstain to be absorbed. Therefore, the statement that gram-positive cells should look purple and gram-negative cells should look red after a gram stain procedure is true.

Transmission Electron Microscopy (TEM) is the best choice that fits the given description. In TEM, a beam of electrons passes through a thin sample, similar to how light passes through a sample in light microscopy. TEM requires samples to be very thin in order to allow the electrons to pass through. It can achieve high magnification and resolution, up to 1,000,000 times and 1 nanometer, respectively. This technique is similar in concept to brightfield microscopy, where the sample is illuminated with light and observed through a lens system.

Yes, if a microscope magnifies a specimen by 100X, it means that the object will appear 100 times larger than its actual size. This is because the magnification factor indicates how many times larger the object will appear when viewed through the microscope. Therefore, the statement "True" is correct.

Scanning Electron Microscopy (SEM) is the best choice that fits the given description. In SEM, electrons are used to scan the surface of the specimen, resulting in a three-dimensional image. SEM provides high-quality pictures and magnifications up to 10,000X, with a resolution of 20nM. This technique is similar in concept to darkfield microscopy, where the specimen is illuminated from the side, resulting in a bright image against a dark background. Therefore, SEM is the correct answer based on the provided information.

It has two types

A basic dye relates to the statement "chromophore is positive ion" because basic dyes are cationic in nature, meaning they carry a positive charge. The chromophore, which is the part of the dye molecule responsible for its color, is positively charged in basic dyes. This positive charge allows the dye to bind to negatively charged components, such as cell walls or proteins, resulting in a colored stain. Acidic dyes, on the other hand, are anionic and have a negative charge, making them unsuitable for the given statement.

A chromophore is a chemical group or moiety that is responsible for the color of a compound. In the given statement, it is stated that the chromophore is a negative ion. Acidic dyes are colored compounds that are negatively charged and are attracted to positively charged substances. Therefore, an acidic dye is more likely to have a chromophore that is a negative ion, making it the correct answer. Basic dyes, on the other hand, are positively charged and are attracted to negatively charged substances, so they would not be related to a negative ion chromophore.

A simple stain is a staining procedure that uses a single basic dye to highlight the entire organism. This means that the dye will color the entire bacteria, making it easier to visualize and study under a microscope. It does not involve dividing bacteria into groups based on their reaction to the staining procedure or categorizing them into positive and negative groups. The focus of a simple stain is on staining the organism uniformly, rather than on any classification or grouping.

The final step in a gram staining procedure is to apply a basic stain, safranin, which colors the unstained bacteria red or pink. This step is known as a counterstain and helps to differentiate between Gram-positive and Gram-negative bacteria. The safranin stain allows the unstained bacteria to be visible and helps in the final identification of the bacteria under the microscope.

Special stains are used to visualize microbial capsules, color the background, highlight endospores, and highlight flagella. These stains have specific properties that allow them to selectively bind to certain structures or components in microorganisms, making them visible under a microscope. By using different special stains, scientists can enhance the visibility of different microbial structures and features, such as capsules, endospores, and flagella. Therefore, the correct answer is "All of these."

The third step in the procedure for an Acid-fast stain is to wash the preparation with acid-alcohol. This is a decolorizing agent that removes the stain from some bacteria that do not have a waxy substance. This step helps to differentiate between acid-fast bacteria, which retain the primary dye (carbolfuchsin) and appear red, and non-acid-fast bacteria, which lose the stain and appear colorless.

The Acid-Fast Stain is the correct answer because it is specifically designed to identify bacteria of the genus Mycobacterium, which includes the bacteria that cause tuberculosis. This staining technique uses a combination of dyes and heat to penetrate the unique cell wall of these bacteria, allowing them to retain the stain even after being washed with an acid-alcohol solution. This characteristic distinguishes Mycobacterium from other bacteria and helps in the diagnosis of tuberculosis.

acid-fast cells look red, and non acid-fast cells are blue

The third step in performing a gram stain procedure is to wash the preparation with alcohol. This step serves as a decolorizing agent, which removes the stain from some bacteria. By using alcohol, the dye is stripped away from certain bacteria, allowing for differentiation between different types of bacteria based on their staining characteristics. This step is crucial in the gram stain procedure as it helps to classify bacteria into gram-positive or gram-negative categories.

Darkfield microscopy is a type of microscopy where a specimen appears light against a dark background and does not require staining. In darkfield microscopy, the specimen is illuminated with a hollow cone of light, causing only the scattered light to enter the objective lens. This creates a contrasting image where the specimen appears bright against a dark background. Darkfield microscopy is particularly useful for observing live, unstained specimens, as it enhances the visibility of transparent or low-contrast samples.

A differential stain is a staining procedure that divides bacteria into groups based on their reaction to the staining process. This is the most popular definition for a differential stain. It allows for the differentiation of different types of bacteria based on their staining characteristics, such as the ability to retain or not retain the stain. By dividing bacteria into groups, it helps in the identification and classification of different bacterial species.

The second step in performing a gram stain procedure is to wash off the dye and apply iodine, the mordant. This step is important because after the wash, all cells will appear purple. The primary stain applied in the first step stains all the cells one color (blue or purple), but it is the application of iodine as a mordant that helps to fix the stain and make it more resistant to removal. This step is crucial in differentiating between gram-positive and gram-negative bacteria, as the color retention varies between the two types.

The first step in the procedure for an Acid-fast stain is to apply a basic dye (carbolfuchsin). This dye stains all the cells red and is called the primary dye. This step is important because it allows the dye to bind to the cell walls of bacteria that contain a certain type of wax, which is characteristic of acid-fast bacteria. By staining all the cells red, the acid-fast bacteria can be distinguished from other bacteria during the subsequent steps of the staining procedure.

Resolution refers to the ability of an optical system to distinguish between two adjacent points. It determines the level of detail that can be observed or captured by the system. A higher resolution means that the system can distinguish smaller details and provide a clearer and more detailed image. Magnification, on the other hand, refers to the increase in apparent size of an object, while resolving power is another term used synonymously with resolution in the context of optical systems.

All of these options (10X, 40X, 4X, and 100X) are common objective lenses found on a compound microscope. Different objective lenses have different magnification powers, and they are used to view specimens at different levels of detail. The 10X lens provides low magnification, the 40X lens provides medium magnification, the 4X lens provides high magnification, and the 100X lens provides the highest magnification. By having a range of objective lenses, users can choose the appropriate lens based on the level of magnification required for their observation.

Dyes are salts composed of a positive and negative ion. Salts are formed when a positive ion (cation) and a negative ion (anion) combine together. In the case of dyes, the positive and negative ions are responsible for the coloration of the dye. These ions interact with the molecules they come into contact with, causing the dye to bind and color the material. This combination of positive and negative ions allows dyes to have their characteristic coloring properties.

Eukaryotic cells are typically larger than prokaryotic cells. The size range of 10-100 micrometers is consistent with the size of eukaryotic cells, which can vary depending on the specific type of cell. This range allows for the presence of various organelles and structures within the cell, such as the nucleus, mitochondria, and endoplasmic reticulum. The other options, 1-5 micrometers and 50-100 nanometers, are too small to accommodate these organelles and are more characteristic of prokaryotic or subcellular structures.

The gram stain is a staining procedure used to divide bacteria into two large groups, a positive and a negative. This classification is based on the ability of bacteria to retain a specific stain called crystal violet. Gram-positive bacteria retain the stain and appear purple, while gram-negative bacteria do not retain the stain and appear pink or red when counterstained with a different dye. This classification is important in microbiology as it helps in identifying and characterizing different types of bacteria.

A virus is typically measured in nanometers, specifically in the range of 50-100 nanometers. This measurement refers to the size of the virus particle, which is extremely small and can only be seen under a microscope. The given answer accurately describes the size range of a virus, highlighting their minuscule dimensions.

Bacteria are very small microorganisms that can only be seen under a microscope. They typically range in size from 1 to 5 micrometers, which is equivalent to 0.001 to 0.005 millimeters. This size range allows bacteria to be easily transported through the air, water, and even on surfaces. It also enables them to quickly reproduce and colonize various environments, making them highly adaptable and ubiquitous in nature.

Basic dyes have a positive charge, which allows them to bind to bacterial structures that are negatively charged. This binding helps in staining the bacterial structures, making them more visible under a microscope. Therefore, the correct answer is that basic dyes bind to bacterial structures.

Acidic dyes have a negative charge, which repels the negatively charged bacteria. This repulsion causes the acidic dyes to avoid binding to the bacteria, resulting in a negative staining.

The fourth step in the procedure for an Acid-fast stain is to apply a basic stain, methylene blue, which will color the unstained bacteria blue. This step is referred to as a counterstain, as it helps to differentiate between the stained bacteria and the unstained bacteria. By applying the methylene blue, the unstained bacteria can be easily identified and observed under a microscope.

Prior to staining, the microbe must be fixed to ensure that it adheres to the slide and does not wash away during the staining process. Creating a smear of the microbe is also necessary as it helps to spread the microbe evenly on the slide, allowing for better visualization and staining of the microbe.

The maximum resolving power of a compound microscope refers to its ability to distinguish between two closely spaced objects. In this case, the maximum resolving power is given as 200 nanometers, indicating that the microscope can differentiate between objects that are at least 200 nanometers apart.

The maximum magnification, on the other hand, refers to the degree of enlargement that the microscope can provide. Here, the maximum magnification is stated as 2,000X, meaning that the microscope can make objects appear 2,000 times larger than their actual size.

Therefore, the correct answer is 200 nanometers and 2,000X, as it accurately represents the maximum resolving power and maximum magnification of a compound microscope.

Mordant is a substance that enhances the binding of a dye to a sample by forming a complex with the dye. Simple staining involves the use of a single dye to color the entire sample, while differential staining uses multiple dyes to differentiate between different components of the sample. Gram staining is a type of differential staining used to classify bacteria into Gram-positive and Gram-negative based on differences in their cell walls. Since all three types of staining techniques involve the use of dyes and can benefit from the use of a mordant, the correct answer is "All of these."

When specimens observed under a compound microscope are stained, the refractive index of the specimen and the medium are increased. Staining helps to enhance the contrast and visibility of the specimen by increasing the refractive index of both the specimen and the medium. This allows for better resolution and clarity when viewing the specimen under the microscope.

Electron microscopy is a technique used to visualize the structure and composition of materials at a very high magnification. There are two main types of electron microscopy: transmission electron microscopy (TEM) and scanning electron microscopy (SEM). In TEM, a beam of electrons is transmitted through a thin sample, and the resulting image shows the internal structure of the sample. SEM, on the other hand, uses a focused beam of electrons to scan the surface of a sample, providing a detailed three-dimensional image. Both techniques have their own advantages and are used in various scientific fields for different purposes.

Electron microscopy uses a beam of electrons instead of visible light, which allows for much greater magnification and resolution. Electromagnets act as lenses to focus the electron beam. This technique does not require staining. Therefore, the correct answer is that all of these statements are true.

Safranin is a dye commonly used in microbiology to stain bacterial cells. It is a basic dye that has an affinity for acidic components in the cell. In this case, safranin colors the entire bacterium except for the capsule. Capsules are a protective layer surrounding some bacterial cells, composed of polysaccharides or proteins. The capsule is often not easily stained by dyes, including safranin, due to its composition and structure. Therefore, while the rest of the bacterium takes up the safranin stain, the capsule remains unstained and appears as a clear area around the bacterium when viewed under a microscope.

Fluorescence microscopy is not the correct answer for this question. The correct answer is Darkfield microscopy. In darkfield microscopy, a specimen appears bright against a dark background, which enhances the visibility of certain structures and is commonly used for diagnostic purposes. Fluorescence microscopy, on the other hand, uses fluorescence to visualize specific molecules or structures within a specimen.

Capsules are related to the virulence of pathogens. Pathogens, such as bacteria, can have a capsule, which is a protective layer outside their cell wall. This capsule helps the pathogens evade the host's immune system by preventing phagocytosis and complement activation. It also aids in the attachment of the pathogen to host cells and protects it from environmental stresses. The presence of a capsule is often associated with increased virulence, as it enhances the pathogen's ability to cause disease and establish infection in the host.

The second step in the procedure for an Acid-fast stain is to apply a basic dye (carbolfuchsin). This dye stains all the cells red and is called the primary dye.

Immersion oil must be used under high magnification to reduce loss of light because it helps to prevent the scattering of light as it passes through the slide, thus improving the amount of light that reaches the objective lens. Additionally, oil has a refractive index similar to the microscope slide, which helps to minimize the loss of light due to reflection at the air-glass interface. Finally, using immersion oil can create better resolution by reducing the diffraction of light, allowing for clearer and more detailed images to be observed.

Charge repulsion refers to the phenomenon where like charges repel each other. In the context of acidic dyes and bacteria staining, when acidic dyes are used, they carry a negative charge. Bacteria, on the other hand, have negatively charged surfaces. Due to charge repulsion, the negatively charged acidic dyes are repelled by the negatively charged bacteria, resulting in a negative staining effect. Therefore, "charge repulsion" is another term used to describe the situation when acidic dyes cause a negative staining with bacteria.