MicroBiology MCQs with Answer and Explnation | Chapter 62

Answer: Lactophenol cotton blue

Lactophenol cotton blue is a stain commonly used to demonstrate fungi in microbiology. It is particularly useful for preserving fungal structures and enhancing their visibility under the microscope. This stain helps highlight fungal elements such as hyphae, conidia, and spores.

The other options are incorrect:

• Albert stain: This stain is used to identify acid-fast bacteria, not fungi.
• Nigerosin: While sometimes used in fungal studies, it’s not as specific or widely used as LPCB.

Answer: Heat labile

Exotoxins are proteins or other molecules secreted by bacteria or fungi that can cause harm to the host organism. These are typically complex molecules and can be denatured (inactivated) by heat.

The other options are incorrect:

• Heat stable: Some toxins can withstand high temperatures, but exotoxins are generally heat labile.
• Part of cell wall: Exotoxins are released by the organism, not part of its cell structure.
• Polymerized complexes: While some toxins may involve complex structures, “polymerized complexes” is not a specific enough term to describe exotoxins.

Answer: Bacteriophages

Bacteriophages, also known as phages, are viruses that specifically infect and replicate only within bacterial cells. They are incredibly abundant in the environment and play a significant role in regulating bacterial populations.

The other options are incorrect:

• Bacterial viruses: This is a redundant term. All viruses that infect bacteria are specifically bacteriophages.
• Bacterial pathogens: These are bacteria that cause disease, not viruses that attack bacteria.
• Various: While there are many different types of viruses, bacteriophages are the specific category that target bacteria.

Answer: 0.015–0.2 ìm

Viruses are incredibly small particles. While there is some variation, most viruses fall within the range of 0.015 micrometers (nm) to 0.2 micrometers (µm) in diameter.

The other options are incorrect:

• 0.02–0.2 ìm: This range is acceptable, but 0.015-0.2 µm is a more precise range that captures the vast majority of viruses.
• 0.5–10 ìm: This range is too large. While some giant viruses can approach this size, most viruses are significantly smaller.
• 0.1–100 ìm: Similar to 0.5-10 µm, this range is too broad and encompasses many structures larger than viruses, such as bacteria.

Answer: Binary-fission

Binary fission is the primary method of reproduction for bacteria. It’s a rapid asexual process where a single bacterial cell replicates its DNA, grows in size, and then divides into two identical daughter cells.

The other options are incorrect:

• Mitosis: Mitosis is a cell division process used by eukaryotes (organisms with a nucleus) to produce genetically identical daughter cells. Bacteria are prokaryotes (lack a nucleus) and don’t undergo mitosis.
• Meiosis: Meiosis is a cell division process in eukaryotes that results in daughter cells with half the number of chromosomes compared to the parent cell. This is for sexual reproduction to create genetic variation, which bacteria don’t utilize in binary fission.
• Conjugation: Conjugation is a form of horizontal gene transfer in bacteria, where genetic material is exchanged between two bacterial cells. While it can introduce some genetic variation, it’s not the primary method of reproduction.

Answer: Bacilli

Bacilli (singular: bacillus) refers to rod-shaped bacteria. This is a very common bacterial morphology, with many familiar types of bacteria being bacilli-shaped.

The other options are incorrect:

• Cocci: Cocci are spherical shaped bacteria.
• Comma forms: These are bacteria with a curved, comma-like shape, known as vibrios.
• Pleomorphic forms: These refer to bacteria that can have various shapes and are not consistent in form.

Answer: Mycoplasmas

A cell wall is a rigid structure surrounding most bacteria, providing shape, support, and protection. However, mycoplasmas are a unique exception. They lack a cell wall entirely, making them more flexible and able to squeeze through very small spaces.

The other options are incorrect:

• Mycobacteria: These bacteria have a thick cell wall containing complex components like mycolic acids.
• Clostridia: This is a group of rod-shaped bacteria with a cell wall, known for some species forming heat-resistant spores.
• Rickettsia: These are small, parasitic bacteria that also possess a cell wall.

Answer: 10-25 nm

The thickness of a bacterial cell wall typically falls within the range of 10-25 nanometers (nm). This cell wall provides structural support and protection for the bacteria.pen_spark.

The other options are incorrect:

• 9-10 nm: This range falls below the typical thickness of bacterial cell walls. It is too narrow to encompass the variability seen in bacterial cell wall thickness.
• 12-13 nm: This range is narrower than the typical thickness of bacterial cell walls. While some bacterial species may have cell walls in this range, it does not represent the general thickness observed across all bacteria.
• 30-40 nm: This range exceeds the typical thickness of bacterial cell walls. It is much thicker than the usual range observed, and such thickness is not commonly found in bacterial cell walls.

Answer: Gram positive bacteria

Teichoic acids and teichuronic acids are polymers found in the cell wall of gram-positive bacteria. These molecules contribute to the overall structure, rigidity, and positive charge of the gram-positive cell wall.

The other options are incorrect:

• Gram-negative bacteria: The outer membrane of gram-negative bacteria does not contain teichoic or teichuronic acids.
• Fungi: Fungal cell walls are primarily composed of chitin, not teichoic or teichuronic acids.

Answer: Principal sites of respiratory enzymes

Meosomes are specialized structures found in certain prokaryotic cells, particularly bacteria, where they serve as the primary locations for respiratory enzymes. These enzymes are involved in the cellular respiration process, which generates energy for the cell.

The other options are incorrect:

• Kind of ribosomes: Ribosomes are structures within the cytoplasm, separate from the cell membrane, responsible for protein synthesis. Mesosomes are part of the cell membrane.
• Formed during cell lysis: Cell lysis is the bursting or breaking open of a cell. Mesosomes are normal structures in living prokaryotic cells.
• A part of cell wall: Mesosomes are formed by the plasma membrane, which is distinct from the cell wall. The cell wall is a rigid outer layer surrounding the plasma membrane.

Answer: Cell wall

The characteristic shape of bacteria is primarily maintained by the cell wall. The cell wall provides structural support and protection to the bacterial cell, helping it maintain its shape despite changes in environmental conditions or osmotic pressure.

The other options are incorrect:

• Capsule: Capsules are outer layers found in some bacteria, providing protection and aiding in adherence to surfaces, but they do not primarily contribute to maintaining the shape of the bacteria.
• Cell membrane: While the cell membrane plays crucial roles in cellular functions such as transport and metabolism, it does not provide the structural support needed to maintain the shape of the bacteria.
• Slime layer: Similar to capsules, slime layers are outer layers in some bacteria that aid in protection and adherence, but they do not have a significant role in maintaining the characteristic shape of bacteria.

Answer: Polysaccharides

Bacterial capsules are primarily composed of polysaccharides, which are long chains of sugar molecules. These sugar molecules provide the capsule with its structure and contribute to its protective and adhesive properties.

The other options are incorrect:

• Polypeptides: While some bacterial capsules might contain trace amounts of proteins or amino acids, polypeptides (chains of amino acids) are not the main component.
• Polynucleotides: These are chains of nucleotides, the building blocks of DNA and RNA, and are not relevant to the composition of the capsule.
• Polypeptides or polysaccharides: Some rare exceptions exist where the capsule might have both components, but polysaccharides are the overwhelmingly dominant one.

Answer: ‘ L’ form

These are bacteria that have lost their cell wall entirely or have a defective cell wall. They can arise spontaneously or be induced by certain environmental factors or antibiotics. L-forms can be difficult to culture and are often mistaken for other microbes.

The other options are incorrect:

• Mycoplasma: Mycoplasmas are a naturally wall-less bacteria that have adapted to this existence. They are distinct from L-forms, which arise from walled bacteria losing their cell wall.
• Protoplast: Protoplasts are bacterial cells that have had their cell wall removed entirely, typically by enzymes like lysozyme. This is often done in a lab setting for various purposes.
• Spheroplast: These are bacterial cells that have a weakened or partially degraded cell wall. They can be an intermediate stage in the formation of L-forms.

Answer: Chondroids

Mesosomes are infoldings of the plasma membrane in bacteria, and an alternative name for them is chondroids. They are not analogous to organelles found in eukaryotic cells, such as mitochondria or chloroplasts.pen_spark

The other options are incorrect:

• Mitochondria: These are the powerhouses of eukaryotic cells, responsible for cellular respiration. Bacteria do not have mitochondria and use the enzymes in their mesosomes for respiration.
• Chloroplasts: These are organelles in plant cells that carry out photosynthesis. Bacteria don’t perform photosynthesis and therefore lack chloroplasts.
• Golgi complex: This organelle is responsible for packaging and modifying proteins in eukaryotic cells. Bacteria lack a Golgi complex and have different mechanisms for protein processing.

Answer: Cell wall

The main difference between Gram-positive and Gram-negative bacteria lies in the structure of their cell walls. Gram-positive bacteria have a thick layer of peptidoglycan in their cell walls, while Gram-negative bacteria have a thinner layer of peptidoglycan surrounded by an outer membrane containing lipopolysaccharides.

The other options are incorrect:

• Nucleus: Bacteria are prokaryotic organisms and lack a true nucleus with a membrane envelope. Their genetic material is found in a single, circular chromosome located in the cytoplasm.
• Cell membrane: Both Gram-positive and Gram-negative bacteria have a cell membrane as the outermost barrier of the cytoplasm.
• Mesosomes: While present in both Gram-positive and Gram-negative bacteria, mesosomes are not the primary differentiating factor between these two groups.

Answer: Serum

Capsule formation in some bacteria can be stimulated by components found in serum, the liquid portion of blood. Serum contains various nutrients, proteins, and other factors that can influence bacterial growth and capsule production.

The other options are incorrect:

• Albumin: While albumin is a protein found in serum, it’s not the specific component that universally triggers capsule formation.
• Charcoal: Charcoal is an inert material and wouldn’t typically stimulate capsule formation.
• Starch: Starch is a carbohydrate and not a known trigger for capsule formation in bacteria.

Answer: Both Fimbria and Cytoskeleton

Bacterial locomotion can be accomplished by both fimbriae and flagella. Fimbriae are short, hair-like appendages that help bacteria adhere to surfaces and aid in locomotion on solid surfaces. Flagella, on the other hand, are long whip-like structures that rotate to propel bacteria through liquid environments.

The other options are incorrect:

• Cytoskeleton: Bacteria lack a true cytoskeleton like the one found in eukaryotic cells. Their movement is driven by structures like flagella and fimbriae.

Answer: Haemaggulation test

Haemagglutination testing specifically checks for the presence of fimbriae (pili) on bacteria. These fimbriae can bind to specific receptors on red blood cells (hemagglutination means “red blood cell clumping”). A positive test with clumping red blood cells indicates the presence of fimbriae and their ability to bind.

The other options are incorrect:

• Culture: While culturing bacteria can help identify the species, it’s not a specific test for fimbriae presence.
• Gram stain: The Gram stain differentiates between Gram-positive and Gram-negative bacteria based on cell wall structure and doesn’t directly assess fimbriae.
• Biochemical reactions: Biochemical tests identify metabolic pathways of bacteria and wouldn’t indicate the presence of fimbriae.

Answer: Salmonella typhi

Salmonella typhi, the causative agent of typhoid fever, is known to be motile bacteria. It possesses flagella, which are hair-like structures that allow it to swim through liquids.

The other options are incorrect:

• Klebsiella pneumoniae: Can be motile or non-motile depending on the strain. Some strains possess flagella and exhibit motility, while others lack them.
• Bacillus anthracis: Non-motile. Bacillus anthracis lacks flagella and does not exhibit motility.
• Shigella flexneri: Generally non-motile. While some rare strains might have minimal motility, Shigella flexneri is primarily non-motile.

Answer: Rhodococcus agilis

Rhodococcus agilis is a motile bacterium. It belongs to the genus Rhodococcus, which is known for its motile species. It typically moves by using flagella.

The other options are incorrect:

• Staphylococcus: Non-motile. Staphylococcus species lack flagella and are non-motile.
• Meningococcus: Non-motile. Neisseria meningitidis, the bacteria causing meningitis, is a non-motile coccus.
• Gonococcus: Non-motile. Neisseria gonorrhoeae, the bacteria causing gonorrhea, is another non-motile coccus.

Answer: Polymetaphosphates

Metachromatic granules, also known as volutin granules or phosphate granules, are cellular inclusions found in some bacteria. They are primarily composed of polymetaphosphates, which are long chains of phosphate molecules. These granules serve as reserve materials for the bacteria, providing a source of phosphorus and energy when needed.

The other options are incorrect:

• Lipids: While bacteria can store lipids for energy, these wouldn’t be the main component of metachromatic granules.
• Proteins: Proteins are not the primary storage molecule in metachromatic granules.
• Polysaccharides: While bacteria can store carbohydrates like glycogen, these wouldn’t be the main component of metachromatic granules

Answer: Methylene blue

Metachromatic granules, also known as volutin granules, can be stained with methylene blue. This stain is commonly used in microbiology to highlight metachromatic granules within bacterial cells, as they appear as reddish-purple granules under the microscope after staining with methylene blue.

The other options are incorrect:

• Saffranine: This stain is often used for eukaryotic cells and might not be specific for metachromatic granules in bacteria.
• Crystal violet: This is a primary stain commonly used in Gram staining to differentiate between Gram-positive and Gram-negative bacteria. It wouldn’t be used specifically for metachromatic granules.
• Pienic acid (likely a misspelling of picric acid): Picric acid is not a typical stain used for bacteria and wouldn’t be suitable for highlighting metachromatic granules.

Answer: Simple binary fission

Bacteria typically multiply by simple binary fission, a process in which a single bacterial cell divides into two identical daughter cells. During binary fission, the bacterial DNA replicates, and the cell elongates before splitting into two separate cells.

The other options are incorrect:

• Spore formation: Spore formation is a survival mechanism for some bacteria under harsh conditions, not their primary mode of reproduction.
• Conjugation: Conjugation is a process of horizontal gene transfer between bacteria, not asexual reproduction. It involves a temporary connection where genetic material is passed from one bacterium to another.
• Gametes: Gametes are sex cells involved in sexual reproduction, which is not typical in bacteria. Bacteria reproduce asexually through binary fission.

Answer: Weakly acid fast

Bacterial spores are weakly acid-fast, meaning they retain certain dyes like carbol fuchsin when subjected to acid-fast staining methods, but the retention is not as strong as observed in acid-fast bacteria like Mycobacterium tuberculosis. This property is due to the waxy nature of their spore coats.

The other options are incorrect:

• Strongly acid fast: Bacterial spores are not strongly acid-fast. While they can retain some acid-fast dyes, their retention is not as strong as observed in acid-fast bacteria like Mycobacterium tuberculosis.
• Alcohol fast: Alcohol fast is not a recognized staining property. Staining techniques such as acid-fast staining and Gram staining involve the use of alcohol for decolorization, but the term “alcohol fast” itself is not applicable to describe bacterial spores.
• Non acid fast: Bacterial spores are weakly acid-fast, meaning they do retain some acid-fast dyes, albeit not as strongly as acid-fast bacteria. Therefore, they cannot be classified as non acid-fast.

Answer: Malachite green

Endospores, the dormant and highly resistant structures produced by certain bacteria, can be stained with malachite green. This staining method is commonly known as the Schaeffer-Fulton staining technique.

The other options are incorrect:

• Safranine: While used as a counterstain in some endospore staining methods like the Schaeffer-Schaudinn technique, safranin alone wouldn’t differentiate spores.
• Crystal violet: This stain is commonly used in Gram staining to differentiate Gram-positive and Gram-negative bacteria. It wouldn’t be used specifically for endospores.
• Methylene blue: While a versatile stain used in various applications, it might not be the most specific for highlighting endospores in some techniques.

Answer: D. pneumoniae

D. pneumoniae (presumably referring to Diplococcus pneumoniae, now known as Streptococcus pneumoniae) typically does not produce pigment. It is a Gram-positive bacterium known for causing pneumonia and other respiratory infections but does not produce significant pigmentation.

The other options are incorrect:

• Pseudomonas pyocyaneus: Pseudomonas pyocyaneus, now known as Pseudomonas aeruginosa, is a Gram-negative bacterium that produces a blue-green pigment called pyocyanin, which gives it a characteristic color.
• Serratia marcescens: Serratia marcescens is a Gram-negative bacterium known for its production of a red pigment called prodigiosin, which can give it a pink or red coloration.
• Staphylococcus aureus: Staphylococcus aureus is a Gram-positive bacterium that can produce golden-yellow pigment when grown on certain media. This pigment is known as staphyloxanthin.

Answer: Crystal violet, Iodine solution, Alcohol, Saffranine

The Gram-staining procedure is crystal violet, iodine solution, alcohol (or ethanol), and saffranine. This sequence allows for the differentiation of Gram-positive and Gram-negative bacteria based on differences in cell wall structure and permeability to the stain and decolorizing agent.

The other options are incorrect:

• Iodine solution, Crystal Violet, Saffranin, Alcohol: This disrupts the process. Crystal violet should be applied first to stain the bacteria.
• Alcohol, Crystal Violet, Iodine solution, Saffranin: Decolorization (alcohol) should happen after the crystal violet-iodine complex is formed.
• All of these: Not all the listed orders are correct. The specific sequence is crucial for the Gram staining technique to work effectively.

Answer: 95%

Gram staining utilizes 95% ethanol (ethyl alcohol) as the decolorizing agent. This concentration is crucial for the differential staining of Gram-positive and Gram-negative bacteria.

The other options are incorrect:

• 75%: While some variations might exist, 95% is the standard concentration for effective decolorization.
• 60%: This concentration is likely too weak to efficiently decolorize Gram-negative bacteria.
• 25%: This is much too low of an alcohol concentration to function as a decolorizer in Gram staining.

Answer: Violet

Gram-positive bacteria stain violet in the Gram staining procedure. This is because their thick peptidoglycan layer retains the crystal violet-iodine complex used in the staining process.

The other options are incorrect:

• Pink: Pink is typically associated with Gram-negative bacteria that lose the crystal violet-iodine complex during decolorization and are then stained with the counterstain (safranin).
• Both Pink & Violet: Gram staining differentiates between two types, not both colors would be seen in the same bacteria.

Answer: Pink

Gram-negative bacteria appear pink in Gram staining. Their thinner peptidoglycan layer allows the crystal violet-iodine complex to be washed away during the decolorization step with alcohol. These bacteria then take up the counterstain (safranin), resulting in a pink color under the microscope.

The other options are incorrect:

• Violet: Violet is the characteristic color for Gram-positive bacteria that retain the crystal violet-iodine complex.
• Both pink & violet: Gram staining differentiates between two types, not both colors would be seen in the same bacteria.

Answer: Decolorises the cells

In Gram staining, alcohol acts as a decolorizing agent. It selectively removes the crystal violet-iodine complex from the cell walls of Gram-negative bacteria due to their thinner peptidoglycan layer. This allows for differentiation between Gram-positive and Gram-negative bacteria based on their ability to retain the stain.

The other options are incorrect:

• Allows the color: Alcohol actually works in opposition to allowing color. It removes some of the previously applied stain.
• It adds color: Alcohol doesn’t directly add color to the bacteria in Gram staining.

Answer: Gram negative bacteria

Gram-negative bacteria generally have a higher lipid content compared to Gram-positive bacteria. This higher lipid content is due to the presence of an outer membrane in Gram-negative bacteria, which contains lipopolysaccharides (LPS) and lipoproteins, contributing to their higher lipid content.

The other options are incorrect:

• Gram positive bacteria: Gram-positive bacteria typically have a lower lipid content compared to Gram-negative bacteria. They lack the outer membrane found in Gram-negative bacteria, which contains significant lipid components.
• Same in both: Lipid content is not the same in both Gram-negative and Gram-positive bacteria. Gram-negative bacteria generally have a higher lipid content due to the presence of an outer membrane containing lipopolysaccharides.

Answer: Thick in Gram positive than Gram negative

The key difference between Gram-positive and Gram-negative bacteria lies in their cell wall composition. Gram-positive bacteria boast a thicker cell wall compared to Gram-negative bacteria. This thicker wall is primarily made up of peptidoglycan, offering Gram-positive bacteria greater rigidity and protection.

The other options are incorrect:

• Thick in Gram negative than Gram positive: Gram-negative bacteria have a thinner peptidoglycan layer and an outer membrane, resulting in a less robust cell wall.
• Equal in both: The thickness of the cell wall is a defining characteristic that differentiates these two bacterial groups.
• In Gram negative cell-wall is absent: Gram-negative bacteria do have a cell wall, but it’s thinner than the one found in Gram-positive bacteria. Their cell wall also includes an outer membrane, which is absent in Gram-positive bacteria.

Answer: 1-5 %

Gram-positive bacteria have a lower lipid content in their cell walls compared to their overall cell composition. This lipid content typically falls within the range of 1-5%.

The other options are incorrect:

• 1-10%: While the lipid content can vary slightly and some bacteria might reach near 10%, 1-5% is a more precise estimate for most Gram-positive bacteria.
• 2-8%: Similar to 1-10%, this range might encompass some Gram-positive bacteria, but 1-5% is a more well-established range.

Answer: Gram negative

Rickettsiae, which are a group of obligate intracellular bacteria, typically respond to staining techniques as Gram-negative. This means they appear pink or red after Gram staining due to the thinner peptidoglycan layer in their cell wall, which is not well-retained by the crystal violet-iodine complex.

The other options are incorrect:

• Gram positive: This option is incorrect because Rickettsiae do not respond to staining techniques as Gram-positive. Gram-positive bacteria retain the crystal violet-iodine complex, appearing violet or purple after Gram staining.
• Between positive and negative: This option is incorrect because Rickettsiae typically respond as Gram-negative, rather than exhibiting characteristics that are in between Gram-positive and Gram-negative bacteria.

Answer: Elementary bodies and Reticulate bodies

Elementary bodies (EBs) and reticulate bodies (RBs). Elementary bodies are the infectious, dormant form of Chlamydiae that are released from infected host cells and are responsible for transmission between hosts. Reticulate bodies are the non-infectious, replicative form of Chlamydiae that multiply within host cells.

The other options are incorrect:

• Complex structures: While Chlamydiae have a unique lifecycle, they wouldn’t be described as generally “complex structures” compared to other bacteria.
• Elementary bodies: Chlamydiae need both EBs for transmission and RBs for replication within the host cell.

Answer: Giminez stains

Chlamydiae can be stained better with Gimenez stains. Gimenez staining is a specific staining technique developed for the visualization of Chlamydiae. It involves using a combination of basic and acidic dyes, producing distinct coloration that enhances the visibility of Chlamydiae under the microscope.

The other options are incorrect:

1. Ziehl Neelsen staining: Ziehl-Neelsen staining is primarily used for the detection of acid-fast bacteria like Mycobacterium tuberculosis.
2. Castaneda & Machiavello stains: Castaneda and Machiavello stains are not commonly used for staining Chlamydiae. These staining techniques are typically used for other purposes, such as staining fungal elements or specific structures in histopathology, and may not be suitable for staining Chlamydiae effectively.
3. Both Ziehl Neelsen staining and Gimenez stains: While Gimenez stains are indeed suitable for staining Chlamydiae, Ziehl-Neelsen staining is not optimal for this purpose.

Answer: Saphrophytes

Molds that obtain nutrition from dead and decaying matter are called saprophytes. These organisms play a crucial role in the decomposition of organic matter, breaking it down into simpler compounds and recycling nutrients back into the ecosystem.

The other options are incorrect:

• Parasites: Parasites obtain nutrients from living organisms by harming or feeding off the host. Molds typically don’t have a direct parasitic relationship with a living host.
• Commensals: Commensals live in close association with another organism, but neither benefits nor harms the other. Molds primarily focus on obtaining nutrients from dead and decaying matter, not establishing commensal relationships.

Answer: 0o – 35oC

Most molds are capable of growing in the temperature range between 0°C and 35°C. This temperature range encompasses the optimal conditions for mold growth, allowing them to thrive and reproduce efficiently.

The other options are incorrect:

• 0°C – 25°C: This option is too narrow. While some molds can grow at temperatures as low as 0°C, many molds can also grow at temperatures higher than 25°C.
• 10°C – 25°C: This option is also too narrow. While many molds can grow within this range, it excludes temperatures below 10°C and above 25°C, limiting the range of conditions where molds can grow.
• 10°C – 35°C: This option includes temperatures suitable for mold growth, but it excludes the lower limit of 0°C, which is important because some molds are capable of growth at temperatures close to freezing.

Answer: Simple staining

Simple staining utilizes a single stain to color all the cells in a specimen. This provides basic information about cell size, shape, and sometimes internal structures, depending on the stain used. It’s a quick and straightforward technique for initial visualization.

The other options are incorrect:

• Negative staining: This technique uses a stain that doesn’t penetrate the cells but colors the background instead. The cells appear unstained against the dark background.
• Differential staining: This involves using multiple stains to differentiate between different types of cells based on their varying affinities for the stains. It provides more detailed information than simple staining.

Answer: Negative staining

In negative staining, the stain doesn’t penetrate the cells but instead coats the background. This creates a dark contrast against which the unstained cells become visible. It’s a useful technique for highlighting the shape and sometimes external features of cells.

The other options are incorrect:

• Simple staining: Simple staining involves applying a single stain directly to the cells themselves, coloring them all the same hue.
• Differential staining: This technique utilizes multiple stains to differentiate between different cell types based on their varying affinities for the individual stains.
• None of these: Negative staining has a distinct characteristic of staining the background, not the sample itself.

Answer:

Differential staining is a staining technique in which more than one stain is used to differentiate between different structures or types of microorganisms within a single specimen. Examples include Gram staining, acid-fast staining, and endospore staining.

The other options are incorrect:

• Simple staining: Simple staining utilizes only one stain to color all cells in the sample with a single hue. It doesn’t involve differentiation between cell types.
• Negative staining: Negative staining uses just one stain, but it stains the background instead of the cells themselves. The cells appear as unstained objects against the dark backdrop.

Answer: All of these

Bacteria can utilize various inorganic forms of nitrogen for their growth and metabolism. Here’s a breakdown of the options:

• Nitrates (NO3-): Many bacteria possess enzymes that allow them to convert nitrates to nitrites and then ultimately to ammonia, a usable form of nitrogen for cellular processes.
• Nitrites (NO2-): Some bacteria can directly take up and utilize nitrites for their nitrogen needs.
• Ammonium salts (NH4+): Ammonium is the preferred nitrogen source for many bacteria. It can be readily incorporated into amino acids and other nitrogenous compounds essential for growth.

Answer: Extreme thermophiles

Archaea (formerly called archaebacteria) are a domain of single-celled organisms known for thriving in extreme environments. Extreme thermophiles are a type of archaea that can live in very high temperatures, often exceeding what other organisms can tolerate, like around hydrothermal vents or hot springs.

The other options are incorrect:

• Halophiles: These are organisms that thrive in very salty environments, but not necessarily hot ones.
• Red extreme halophiles: This is a specific type of halophile that also has a red pigment, but again, not necessarily heat-loving.
• Osmophiles: These organisms can survive in environments with very high or low concentrations of water, but not necessarily extreme temperatures.

Answer: Nitrobacter

Nitrification is a two-step process in the nitrogen cycle. Nitrosomonas bacteria convert ammonia into nitrite. Nitrobacter then takes over and converts the nitrite into nitrate, a more usable form of nitrogen for plants.

The other options are incorrect:

• Nitrosomonas: As mentioned above, these bacteria convert ammonia, not nitrite.
• Nitrosocytes: This term isn’t commonly used in microbiology. It might be a misspelling of Nitrosomonas.
• Azatobacter: These bacteria are nitrogen fixers, meaning they convert atmospheric nitrogen gas into a usable form for plants. They are not involved in the conversion of nitrite to nitrate.

Answer: Hydrogen – Oxydising bacteria

Bacillus Schlegelli is a type of bacteria classified as a facultatively chemolithoautotrophic organism. This means it can get its energy from oxidizing molecules like hydrogen (H2) for growth, but can also utilize organic compounds if available.

The other options are incorrect:

• Sulphur-Oxidizing Bacteria: These bacteria use sulfur compounds (like hydrogen sulfide) as their energy source. While Bacillus Schlegelli might be able to utilize some sulfur compounds in certain conditions, it’s not its primary energy source.
• Iron-Oxidizing Bacteria: These bacteria derive energy from the oxidation of iron compounds. Bacillus Schlegelli doesn’t have this specific metabolic capability.
• Nitrite-Oxidizing Bacteria: These bacteria specialize in converting nitrite (NO2-) to nitrate (NO3-). Bacillus Schlegelli isn’t known for this particular process.

Answer: Heterotrophes

Bacteria are classified based on their energy and carbon source. Heterotrophs obtain their energy by breaking down organic compounds made by other organisms (plants, animals, or other microbes). They cannot synthesize their own food from inorganic materials like sunlight or inorganic chemicals.

The other options are incorrect:

• Chemotrophs: This term refers to organisms that get their energy from chemical reactions, which can be organic or inorganic. Heterotrophs are a specific type of chemotroph that relies on organic sources.
• Phototrophs: These organisms use light energy (like sunlight) to power their growth. They don’t necessarily depend on organic sources.
• Organotrophs: This term is very similar to heterotrophs and is sometimes used interchangeably.

Answer: Saprophytes

The vast majority of bacteria are saprophytes. These bacteria obtain their nutrients by decomposing dead organic matter from plants, animals, or other microbes. They play a crucial role in nutrient cycling by breaking down complex molecules into simpler forms that can be used by other organisms.

The other options are incorrect:

• Symbionts: These are organisms that live in a close relationship with another organism, where both benefit in some way.
• Commensals: These organisms live on or with another organism without harming or benefiting it.
• Parasites: These organisms live in or on another organism and derive nutrients at the expense of the host, often causing harm. Parasitic bacteria are a minority compared to saprophytes.

Answer: All of these

A symbiont refers to any organism participating in a symbiotic relationship. Symbiosis is a close and long-term biological interaction between two different species. So, symbionts can be:

• Bacteria in symbiotic association: Many bacteria form symbiotic relationships with other organisms, like plants or animals. For example, gut bacteria in humans aid digestion.
• The group of fungi in symbiotic association: Fungi also engage in symbiosis, like mycorrhizae which help plants absorb nutrients.
• The groups participating in symbiotic association: This broadly encompasses all the different types of organisms that can be involved in a symbiotic relationship, including bacteria, fungi, plants, and animals.

Answer: Lichens

Lichens are one of the best examples of symbiotic association. They are formed through a mutualistic relationship between a fungus (usually an ascomycete) and a photosynthetic partner (often a green alga or cyanobacterium). The fungus provides structural support and protection, while the photosynthetic partner provides nutrients through photosynthesis.

The other options are incorrect:

• E. coli in the intestine of man: While E. coli can be part of the normal gut microbiota in humans and may exhibit a form of symbiosis, it is not typically regarded as the best example of symbiotic association.
• Normal flora of skin: The normal flora of the skin consists of various bacteria, fungi, and other microorganisms that inhabit the skin surface. While they can have symbiotic relationships with the human host.