MicroBiology MCQs with Answer and Explnation | Chapter 59

Answer: Flagella at both ends

Amphitrichous refers to the arrangement of flagella on a cell, where there are one or more flagella present at opposite ends of the cell body. This flagellar arrangement allows the bacterium to efficiently change direction by switching which flagellum is actively rotating.

The other options are incorrect:

• Flagella all-round the cell: This describes a different flagellar arrangement called peritrichous, where flagella are distributed around the entire cell.
• Flagella at one end: This describes another arrangement called monotrichous, where there’s only a single flagellum at one end of the cell.
• Flagella in tufts: This doesn’t represent a typical flagellar arrangement. Flagella can be clustered together at the base (polar organelle) in some bacteria, but “tufts” isn’t a commonly used term.

Answer: Peritrichous

Peritrichous refers to the arrangement of flagella on a cell where they are distributed around the entire circumference of the cell body. This allows the bacterium to move smoothly in any direction by coordinating the rotation of its numerous flagella.

The other options are incorrect:

• Amphitrichous: This describes flagella present at opposite ends of the cell, not all around.
• Monotrichous: This refers to a single flagellum located at one end of the cell.
• Lophotrichous: This describes a cluster of flagella at a single pole of the cell, not all around.

Answer: Capsule

India ink is used in a technique called negative staining for microscopy. It doesn’t stain the bacteria itself but darkens the background. This creates a clear halo around structures that prevent the ink from reaching, such as the capsule. A capsule is a gelatinous layer outside the cell wall that can be present in some bacteria.

The other options are incorrect:

• Cell wall: The cell wall is usually rigid and would not be easily distinguished by negative staining with India ink.
• Nucleus: Bacteria lack a true nucleus and their genetic material is free-floating in the cytoplasm. India ink wouldn’t interact with it specifically.
• Flagella: Flagella are very thin and might not be visible under negative staining with India ink.

Answer: Darkfield microscope

A darkfield microscope uses reflected light to illuminate the sample. The light source is angled in a way that it doesn’t directly enter the objective lens. Only light scattered by the sample (reflected light) reaches the lens, making the sample appear bright against a dark background. This technique is particularly useful for visualizing unstained or transparent objects like some bacteria.

The other options are incorrect:

• Light microscope: Regular light microscopes typically use transmitted light, where light shines through the sample and onto the objective lens.
• Phase contrast microscope: While phase contrast microscopy also uses light, it manipulates the phases of light waves to enhance contrast, not relying solely on reflected light.
• Electron microscope: Electron microscopes don’t use visible light at all. They use a beam of electrons to achieve much higher resolution than light microscopes.

Answer: Mesophilic

Mesophiles are bacteria that thrive in moderate temperature ranges, typically between 20°C and 45°C (68°F and 113°F). This range includes the human body temperature (around 37°C) which is why many pathogens that infect humans are mesophiles.

The other options are incorrect:

• Capnophilic: These bacteria require high levels of carbon dioxide (CO2) for growth, not a specific temperature range.
• Psychrophilic: Psychrophiles prefer cold temperatures, typically below 15°C (59°F).
• Thermophilic: Thermophiles grow best at high temperatures, usually above 45°C (113°F).

Answer: Spherical

Cocci (singular: coccus) are a type of bacteria with a spherical or round shape. They can sometimes appear slightly oval but generally maintain a ball-like form.

The other options are incorrect:

• Rod: This describes another bacterial shape category called bacilli, which are elongated and rod-shaped.
• Comma: This describes a specific type of curved rod-shaped bacteria called vibrios, known for their comma-like appearance.
• Spiral: This describes another bacterial shape category called spirilla, which are long and helical (spiral-shaped).

Answer: Coxiella burnetii

The Holder pasteurization method heats liquids at 62.5°C (144.5°F) for 30 minutes. This is effective in eliminating most vegetative bacteria, including Salmonella and Brucella. However, some bacteria, like Coxiella burnetii, can form highly resistant spores that can survive pasteurization at this temperature.

The other options are incorrect:

• Mycobacterium: Mycobacteria, known for their tough cell walls, can also survive Holder pasteurization in some cases.
• Brucella: As mentioned earlier, Brucella is generally inactivated by Holder pasteurization.
• Salmonella: Salmonella is a vegetative bacterium susceptible to pasteurization and wouldn’t survive the Holder method.

Answer: Protein

Exotoxins are toxic proteins secreted by certain bacteria into their environment. These toxins are typically synthesized and released by bacteria during their growth and metabolism. They are potent and can cause damage to host cells even at low concentrations.

The other options are incorrect

• Heat labile: Exotoxins can be heat labile (destroyed by heat), but this is not a defining characteristic. Some exotoxins are heat labile, while others are heat stable.
• More antigenic: Exotoxins can be highly antigenic, but not necessarily more antigenic than other substances. Their antigenicity varies depending on the specific toxin and host response.
• Non-enzymatic: Exotoxins are often enzymatic in nature, meaning they exert their toxic effects through enzymatic activity.

Answer: Neutralized by antitoxin

Antitoxins are antibodies produced by the immune system in response to the presence of exotoxins. These antibodies can neutralize the toxic effects of exotoxins by binding to them, preventing them from interacting with host cells and causing damage.

The other options are incorrect:

• Produced only by gram-positive bacteria: Exotoxins can be produced by both gram-positive and gram-negative bacteria.
• Less potent than endotoxin: Exotoxins can be highly potent, and their potency varies depending on the specific toxin produced.
• Pyrogenic: Exotoxins are not typically pyrogenic (fever-inducing); this is a characteristic of endotoxins.

Answer: Streptococcus pyogenes

Streptococcus pyogenes is generally considered more susceptible to penicillin than the other listed bacteria. However, antibiotic resistance is a growing concern, and susceptibility testing should always be done to determine the most effective treatment.

The other options are incorrect:

• Staphylococcus aureus: While some strains of S. aureus are still susceptible to penicillin, many have developed resistance, particularly to forms like penicillin G.
• Enterococcus faecalis: Enterococci are often naturally resistant to penicillin and require different antibiotics.
• Staphylococcus epidermidis: Similar to S. aureus, susceptibility of S. epidermidis to penicillin varies, and some strains have become resistant.

Answer: Group-B

Group B Streptococcus (GBS), also known as Streptococcus agalactiae, is the leading cause of bacterial meningitis in newborns.

The other options are incorrect:

• Group-A: Group A Streptococcus (GAS), also known as Streptococcus pyogenes, is commonly associated with infections like strep throat and impetigo, but not typically neonatal meningitis.
• Group-C: While Group C Streptococcus can cause some infections, it’s not a common cause of neonatal meningitis.
• Group-D: Group D Streptococcus is a diverse group with varying pathogenicities. Some can cause infections, but they are not a major cause of neonatal meningitis.

Answer: Clostridia

Clostridia are Gram-positive, spore-forming bacteria that include some well-known foodborne pathogens like Clostridium perfringens and Clostridium botulinum. These species can produce toxins that cause food poisoning symptoms.

The other options are incorrect:

• Mycoplasmas: Mycoplasmas are very small bacteria that lack a cell wall and are not classified as Gram-positive or Gram-negative. They are not typically associated with food poisoning.
• Pseudomonas: Pseudomonas are Gram-negative bacteria commonly found in soil and water. While some species can cause opportunistic infections, they are not a major cause of food poisoning.
• All of the above: Neither Mycoplasmas nor Pseudomonas are common causes of foodborne illness.

Answer: Staphylococci

Methicillin-resistant Staphylococcus aureus (MRSA) is the most common type of methicillin-resistant bacteria. Staphylococci are Gram-positive bacteria and include various species, with S. aureus being a prominent one known to develop methicillin resistance.

The other options are incorrect:

• Streptococci: Streptococci are also Gram-positive bacteria, but they are not as commonly associated with developing methicillin resistance compared to Staphylococci.
• Pseudomonas: Pseudomonas are Gram-negative bacteria and are not known for developing methicillin resistance. They typically have different antibiotic resistance profiles.
• Haemophilus: Haemophilus are another group of Gram-negative bacteria with distinct antibiotic resistance patterns, not typically involving methicillin.

Answer: Staphylococcus saprophyticus

While E. coli is the most common organism causing UTIs overall, Staphylococcus saprophyticus is a significant culprit in UTIs affecting sexually active young women.

The other options are incorrect:

• Staphylococcus aureus: S. aureus can cause UTIs, but it’s less frequent than other Staphylococcus species on this list.
• Staphylococcus epidermidis: S. epidermidis is more commonly associated with hospital-acquired infections than UTIs.
• Streptococcus viridians: Streptococcus viridians is a group of harmless or minimally pathogenic Streptococci and not a typical cause of UTIs.

Answer: Pseudomonas

Pseudomonas are notorious for their ability to develop resistance to a wide range of antiseptics, disinfectants, and antibiotics. This makes them challenging to treat in healthcare settings.

The other options are incorrect:

• E. coli: While some E. coli strains can develop resistance, they are generally more susceptible to antimicrobials compared to Pseudomonas.
• Staphylococci: Some Staphylococci, like Methicillin-resistant Staphylococcus aureus (MRSA), can be very resistant to antibiotics, but their resistance to antiseptics and disinfectants can vary.
• Streptococci: Similar to Staphylococci, Streptococci can develop antibiotic resistance, but their overall resistance profile is typically lower than Pseudomonas.

Answer: Streptococcus bovis

There’s a well-established association between Streptococcus bovis (formerly Streptococcus bovis biotype I) and colon cancer. This bacterium can enter the bloodstream and potentially cause infective endocarditis in patients with colon cancer.

The other options are incorrect:

• Staphylococcus epidermidis: While S. epidermidis can cause endocarditis, it’s not typically linked to colon cancer.
• Streptococcus sanguis: S. sanguis is a common cause of endocarditis but isn’t specifically associated with colon cancer.
• Streptococcus mutans: S. mutans is primarily associated with dental caries (cavities) and not endocarditis or colon cancer.

Answer: Klebsiella

Klebsiella is a Gram-negative bacterium that belongs to the family Enterobacteriaceae. It is known for its ability to ferment lactose, producing acid and gas. This characteristic is often used in microbiological laboratory tests, such as MacConkey agar, to differentiate Klebsiella from other bacteria.

The other options are incorrect

• Pseudomonas: Pseudomonas is a Gram-negative bacterium that does not ferment lactose. It is commonly found in soil and water and is not typically associated with lactose fermentation.
• Salmonella: Salmonella is a Gram-negative bacterium that does not ferment lactose. It is known for causing foodborne illnesses, such as salmonellosis, and is not typically associated with lactose fermentation.
• Shigella: Shigella is a Gram-negative bacterium that does not ferment lactose. It is known for causing bacillary dysentery (shigellosis) and is not typically associated with lactose fermentation.

Answer: Cholera

Rice-water stool is a hallmark symptom of cholera, an acute diarrheal illness caused by the bacterium Vibrio cholerae. This watery, whitish stool lacks solid matter and resembles the cloudy water used to rinse cooked rice.

The other options are incorrect:

• Bacillary dysentery: While dysentery can cause severe diarrhea with blood and mucus, it typically doesn’t present with the characteristic rice-water stool seen in cholera.
• Salmonella infection: Salmonella infections can cause diarrhea, but the stool appearance is usually not described as rice-watery. It may be bloody or contain mucus.
• Pseudomembranous colitis: This condition, often caused by Clostridium difficile (C. Diff) infection, can cause diarrhea, but the stool is not typically described as rice-watery. It may contain mucus or pseudomembranes (patches of dead tissue).

Answer: Streptococcus mutans

Streptococcus mutans is the primary bacterium associated with dental caries (cavities). It plays a key role in the formation of biofilms on teeth and produces acids that can erode tooth enamel.

The other options are incorrect:

• Streptococcus pyogenes: This bacterium is more commonly associated with infections like strep throat and impetigo, not dental caries.
• Streptococcus faecalis: While S. faecalis can be found in the mouth, it’s not a major culprit in tooth decay.
• Streptococcus agalactiae: Also known as Group B Streptococcus (GBS), this bacterium is associated with newborn infections and not dental cavities.

Answer: Enterotoxigenic Escherichia coli

Enterotoxigenic E. coli (ETEC) is the most common cause of traveler’s diarrhea. It produces toxins that disrupt the function of the intestines, leading to watery diarrhea, cramps, and nausea.

The other options are incorrect:

• Enteroinvasive E. coli (EIEC): This type of E. coli causes dysentery-like symptoms with bloody diarrhea, which is less frequent in traveler’s diarrhea.
• Enterohemorrhagic E. coli (EHEC): EHEC is known for causing bloody diarrhea and can be associated with more severe complications. It’s not the most typical cause of traveler’s diarrhea.
• Enteropathogenic E. coli (EPEC): EPEC can cause diarrhea, particularly in children, but it’s less prevalent than ETEC in traveler’s diarrhea.

Answer: Those wearings socks and shoes

Tinea pedis (athlete’s foot) thrives in warm, moist environments. Wearing socks and shoes creates a perfect environment for fungal growth, especially if the shoes are not breathable or if the feet sweat excessively.

The other options are incorrect:

• People of cold countries: While cold weather can contribute to sweaty feet if people wear warm socks and shoes indoors, colder climates generally reduce the risk of tinea pedis.
• Those walking barefoot: Walking barefoot can increase the risk of contracting the fungus from contaminated surfaces, but it doesn’t necessarily create the ideal environment for fungal growth on the feet themselves.
• Hospitalized people: Hospitalization can increase the risk of some infections, but tinea pedis is not as common in hospital settings unless there are specific risk factors like immunosuppression or poor hygiene. However, hospital staff who wear shoes and socks for extended periods could be at risk.

Answer: Borrelia burgdoferi

Lyme disease is a tick-borne illness caused by the bacterium Borrelia burgdorferi. It is transmitted to humans through the bite of infected black-legged ticks (Ixodes scapularis in North America and Ixodes ricinus in Europe). The disease can lead to a variety of symptoms, including fever, fatigue, joint pain, and characteristic skin rash called erythema migrans.

The other options are incorrect:

• Borrelia vincenti: This bacterium is not associated with Lyme disease. It’s part of the normal human flora but can be involved in a gum infection called Vincent’s gingivitis.
• Borrelia recurrentis: This bacterium causes relapsing fever, a tick-borne illness with different symptoms than Lyme disease.
• Leptospira interrogans: This bacterium causes leptospirosis, an infection spread through contact with contaminated water or animal urine. It has distinct symptoms from Lyme disease.

Answer: Neurotoxin

Botulism intoxication is caused by a neurotoxin produced by the bacterium Clostridium botulinum. This neurotoxin specifically targets the nervous system, causing paralysis.

The other options are incorrect:

• Endotoxin: Endotoxins are lipopolysaccharides found in the outer membrane of Gram-negative bacteria. They can cause fever and inflammation, but they are not the primary cause of botulism intoxication.
• Mycotoxin: Mycotoxins are toxins produced by fungi. While some mycotoxins can affect the nervous system, they are not responsible for botulism.

Answer: Louis Pasteur

Louis Pasteur made significant contributions to the field of microbiology, including the development of the germ theory of disease, pasteurization, and vaccines. His work laid the foundation for modern microbiology and the understanding of infectious diseases.

The other options are incorrect:

• Robert Koch: Robert Koch made pioneering contributions to the field of bacteriology, including the identification of specific bacteria responsible for diseases such as tuberculosis and cholera. However, he is not known as the ‘father of microbiology.’
• Alexander Fleming: Alexander Fleming discovered the first antibiotic, penicillin, which revolutionized medicine. However, he is not known as the ‘father of microbiology.’
• Edward Jenner: Edward Jenner developed the smallpox vaccine, which was the first successful vaccine to prevent a disease. However, he is not known as the ‘father of microbiology.’

Answer: Klebsiella

Klebsiella is a non-motile bacterium. It lacks flagella, which are the whip-like structures that bacteria use for motility. Instead, Klebsiella species are typically non-motile and rely on other mechanisms for movement.

The other options are incorrect:

• E. coli: Escherichia coli is a motile bacterium. It possesses flagella that allow it to move through its environment.
• Vibrio: Vibrio species are motile bacteria. They have a single polar flagellum that enables them to move in liquid environments.
• Proteus: Proteus species are highly motile bacteria. They exhibit a characteristic swarming motility on solid surfaces, facilitated by peritrichous flagella.

Answer: hot air oven

Oils and grease cannot withstand the high moisture environment of an autoclave. Vaccine baths are not a general sterilization method. Hot air ovens, however, provide dry heat effective for sterilizing heat-stable materials like oils and grease.

The other options are incorrect:

• Autoclave: Autoclaves use high-pressure steam for sterilization, which can damage oils and grease.
• Vaccine Bath: Vaccine baths are specifically designed for storing and activating vaccines, not general sterilization.
• None of These: While some options may not be ideal, a hot air oven is a viable method for sterilizing oils and grease.

Answer: agar

Agar is a complex carbohydrate extracted from red algae, commonly used as a solidifying agent in culture media. It allows for the creation of a solid surface for microorganism growth and isolation, while remaining inert to most microbes.

The other options are incorrect:

• Peptone: Peptone is a broken-down protein source providing essential nutrients for microbial growth in culture media.
• Meat Extract: Similar to peptone, meat extract is another source of nutrients for microbes, but it doesn’t solidify the media.
• Sodium Chloride: Sodium chloride (table salt) is often added to culture media to maintain a specific ionic balance for optimal microbial growth, but it has no solidifying properties.

Answer: Bile salt

Bile salts are a key component of MacConkey Agar that specifically inhibit the growth of gram-positive bacteria. Their detergent-like properties disrupt the cell membranes of gram-positive bacteria, while gram-negative bacteria have outer membranes that offer some protection.

The other options are incorrect:

• Peptone: Peptone is a source of nutrients (amino acids) for bacterial growth in MacConkey Agar and doesn’t inhibit any bacteria.
• Neutral Red: Neutral red is a pH indicator dye in MacConkey Agar. It helps differentiate lactose-fermenting from non-fermenting bacteria based on a color change, not inhibiting growth.
• Agar: Agar is the solidifying agent in MacConkey Agar, providing a solid surface for bacterial growth, but doesn’t target specific bacterial types.

Answer: VR medium

VR Medium (Virus Transport Medium) is specifically designed for transporting viruses, chlamydiae, and mycoplasma. While some bacteria might survive short periods in VR Medium, it’s not generally used for routine bacterial transport.

The other options are incorrect:

• Thioglycollate medium: This medium is designed for culturing a wide variety of bacteria, including both aerobic and anaerobic types, by providing different oxygen environments within the tube.
• Stuart’s medium: This is a popular transport medium used for a broad range of bacteria, particularly those requiring a moist environment.
• Amies medium: Another frequently used transport medium, Amies medium contains nutrients and buffers to maintain bacterial viability during transport to the lab for analysis.

Answer: Citrate utilisation test

The IMViC tests are a set of four biochemical tests used to identify and differentiate between certain groups of Gram-negative bacteria, particularly members of the Enterobacteriaceae family. Citrate utilization is one of the four tests included in the IMViC battery.

The other options are incorrect:

• Coagulase test: This test identifies bacteria that can produce coagulase, an enzyme that clots blood plasma. It’s not part of the IMViC set.
• Catalase test: This test detects the presence of the catalase enzyme, which breaks down hydrogen peroxide. While helpful for initial identification, it’s not specific to the IMViC group.
• None of the above: This is incorrect because Citrate utilization is indeed a part of the IMViC tests.

Answer: haemophilus

Haemophilus bacteria require both X (hemin) and V (nicotinamide adenine dinucleotide, NAD) factors for their growth. These factors are often supplied in specialized growth media for the cultivation of Haemophilus species.

The other options are incorrect:

• Staphylococcus: Most Staphylococcus species are not dependent on X and V factors for growth. They can generally grow on basic media without these supplements.
• Brucella: Brucella species also don’t typically require X and V factors. They can grow on enriched media with essential nutrients.
• Salmonella: Similar to Staphylococcus and Brucella, Salmonella species are not obligately dependent on X and V factors for growth.

Answer: fungus

Mycology is a specific branch of biology dedicated to the study of fungi, including their characteristics, classification, ecology, and impact on various environments.

The other options are incorrect:

• Bacteria: Bacteriology is the field of study focused on bacteria.
• Immunity: Immunology is the branch concerned with the body’s immune system and its response to pathogens.
• Parasites: Parasitology deals with the study of parasites and their relationship with their hosts.

Answer: Proteus

Proteus bacteria are known for their characteristic swarming growth pattern on agar plates. This swarming growth is due to their ability to produce flagella and move rapidly across the surface of the agar.

The other options are incorrect:

• E. coli: Escherichia coli (E. coli) does not typically exhibit swarming growth. It often forms colonies with a distinct morphology but does not display the rapid and expansive movement seen in swarming bacteria like Proteus.
• Salmonella: Salmonella bacteria do not typically exhibit swarming growth. They may form colonies with various characteristics on agar plates, but they do not display the swarming behavior characteristic of Proteus.
• All the Above: This option suggests that all three bacteria listed (E. coli, Salmonella, and Proteus) exhibit swarming growth, which is incorrect. Only Proteus bacteria are known for their swarming growth behavior.

Answer: Leeuwenhoek

The passage describes observing “green streaks, spirally wound serpent-wise” which aligns with early descriptions of bacteria observed by Antoni van Leeuwenhoek. He is considered a pioneer in microbiology for his use of self-made microscopes to examine microorganisms.

The other options are incorrect:

• A. Jenner: Edward Jenner is known for his work on developing the smallpox vaccine, not observations of microorganisms.
• B. Pasteur: Louis Pasteur made significant contributions in microbiology, including germ theory and pasteurization, but the quote doesn’t reflect his specific discoveries.
• C. Koch: Robert Koch developed postulates to link specific microbes to specific diseases. While his work was crucial, it doesn’t correspond to the descriptive nature of the quote.

Answer: Immobilization

In the biogeochemical cycle, immobilization refers to the process where microorganisms take up elements like carbon and convert them into organic forms, making them temporarily unavailable for other organisms. In this scenario, the elemental carbon is being utilized by microbes and locked up in their biomass.

The other options are incorrect:

• Dissimilation: This refers to the breakdown of complex organic molecules into simpler ones for energy production. While it can involve carbon, it doesn’t necessarily involve immobilization.
• Decomposition: This is a broader term encompassing the breakdown of organic matter by various processes, including by microorganisms. Immobilization can be a part of decomposition, but it specifically focuses on the capture of elements.
• Neutralization: This term refers to the chemical reaction between an acid and a base, resulting in a neutral solution. It’s not relevant to the process of capturing carbon by microorganisms.

Answer: John Tyndall

John Tyndall conducted experiments demonstrating that open tubes of broth remained sterile when air was filtered to remove dust particles. This provided strong evidence against spontaneous generation and supported the idea that microbes in the air are responsible for broth contamination.

The other options are incorrect:

• Abbc Spallanzani: Spallanzani also performed experiments with boiled broths, but his methods didn’t definitively address the role of dust.
• Francisco Redi: Redi’s experiments disproved spontaneous generation in maggots but didn’t directly address airborne microbes.
• Pasteur: While Louis Pasteur famously disproved spontaneous generation, his experiments focused on different methods, not specifically filtering air.

Answer: Bradyrhizobium

Bradyrhizobium, particularly species like Bradyrhizobium japonicum and B. elkanii, form a symbiotic relationship with soybeans. These bacteria fix atmospheric nitrogen into a usable form (ammonium) that the soybean plant can utilize for growth and development. This symbiosis is crucial for soybean production as it reduces the need for external nitrogen fertilizers.

The other options are incorrect:

• Azatobactor paspali: While Azatobactor is a free-living nitrogen-fixing bacterium, it doesn’t establish a symbiotic relationship with soybeans specifically.
• Nostoc: Nostoc is a filamentous cyanobacteria that can fix nitrogen, but it’s not typically associated with symbiosis with soybeans.

Answer: Cyanophyceae

Spirulina belongs to the phylum Cyanophyceae, also known as Cyanobacteria. This group of photosynthetic bacteria is known for its characteristic blue-green pigmentation.

The other options are incorrect:

• Xanthophyceae: This phylum comprises yellow-green algae, distinct from the blue-green pigmentation of Spirulina.
• Rhodophyceae: Red algae are classified under Rhodophyceae and differ from Spirulina in terms of pigments and cell structure.
• Pheophyceae: This phylum includes brown algae, again differing from the characteristics of Spirulina.

Answer: Luciferase

Luciferase is the key enzyme responsible for bioluminescence in bacteria and many other organisms. It catalyzes a reaction between luciferin (a light-emitting molecule) and oxygen, resulting in the release of light.

The other options are incorrect:

• Coenzyme Q: Coenzyme Q is involved in the electron transport chain for cellular respiration, not light emission.
• Lactose dehydrogenase: This enzyme plays a role in lactose metabolism and doesn’t participate in bioluminescence.
• Carboxylase reductase: This enzyme is involved in various metabolic processes but not in light production.

Answer: All of the above

Nitrogen fixation, the process of converting atmospheric nitrogen (N₂) into usable nitrogen compounds, can occur through several mechanisms:

• Biological process: Nitrogen-fixing bacteria like Rhizobium and Azotobacter have the enzyme nitrogenase, which allows them to fix nitrogen gas into ammonia (NH₃). This is a crucial step in the nitrogen cycle and provides a vital source of nitrogen for plants and ecosystems.
• Lightning: During lightning strikes, the immense heat and energy can break the strong triple bond in N₂ molecules, allowing them to combine with oxygen (O₂) to form nitrogen oxides (NOₓ). These nitrogen oxides eventually dissolve in water and are converted into nitrates (NO₃⁻) and nitrites (NO₂⁻) that can be utilized by plants and microbes.
• Ultraviolet light: High-energy ultraviolet (UV) radiation from the sun can also split N₂ molecules in the upper atmosphere. However, this contributes a much smaller amount of fixed nitrogen compared to biological processes and lightning.

Answer: Aspergillus

Aspergillus is the most serious threat in a bone marrow transplant unit. It is a mold commonly found in the environment, especially in soil and decaying organic matter. Immunocompromised patients, such as those undergoing bone marrow transplants, are at increased risk of developing invasive aspergillosis, a severe fungal infection that can be life-threatening.

The other options are incorrect:

• Candida albicans: While Candida albicans is a common fungal pathogen, it’s generally less aggressive than Aspergillus in bone marrow transplant settings.
• Blastomyces: Blastomycosis is a fungal disease, but it’s less frequent than aspergillosis in bone marrow transplant units.
• Cryptococcus: Similar to Blastomyces, Cryptococcus infections are less common compared to Aspergillus in this specific context.

Answer: Neuberg chamber

A Neuberg chamber, also known as a hemocytometer, is a specialized counting chamber used for performing direct microscopic counts of blood cells, bacteria, and other microscopic particles in a suspension. It has a specific engraved grid that allows for counting cells within a defined volume of the suspension.

The other options are incorrect:

• Anaerobic chamber: An anaerobic chamber is an environment designed to maintain anaerobic (oxygen-free) conditions. It’s not directly used for cell counting but can be used to cultivate or maintain anaerobic microbes before counting.
• Mineral oil: Mineral oil can be used for some microscopy techniques, but it’s not typically used for direct cell counting with a Neuberg chamber. It might interfere with the counting process or damage the cells.
• Olive oil: Olive oil is not suitable for use in microscopy. It can damage cells and is not optically clear for proper visualization under a microscope.

Answer: Zymase

Zymase is a complex of enzymes, not a single enzyme, responsible for converting sugars like glucose into ethanol and carbon dioxide during alcoholic fermentation.

The other options are incorrect:

• Ketolase: Ketolase is an enzyme involved in breaking down ketone bodies, not in the fermentation of sugars to alcohol.
• Peroxidase: Peroxidase is an enzyme that uses hydrogen peroxide to oxidize various substrates. It’s not involved in alcoholic fermentation.
• Oxidase: Oxidases are enzymes that transfer electrons to oxygen, not involved in the fermentation process which is anaerobic (without oxygen).

Answer: Ascospores

Ascospores are sexual spores produced by fungi within a sac-like structure called an ascus. They arise from the fusion of two haploid nuclei during sexual reproduction in certain fungal groups.

The other options are incorrect:

• Conidia: Conidia are asexual spores produced by fungi through a process called mitosis. They bud or fragment from specialized hyphae called conidiophores and do not involve sexual reproduction.
• Sporangiospores: Similar to conidia, sporangiospores are asexual spores produced within a structure called a sporangium. They are released when the sporangium breaks open and don’t involve sexual fusion.
• None of these: While some of the options are incorrect, Ascospores are indeed produced sexually in fungi.

Answer: Griffith

Frederick Griffith discovered bacterial transformation in 1928. His experiments demonstrated that genetic material (later identified as DNA) could be transferred between Streptococcus pneumoniae strains, altering their characteristics. This discovery laid the groundwork for understanding horizontal gene transfer in bacteria.

The other options are incorrect:

• Ederberg and Tatum: Joshua Lederberg and Edward Tatum are credited with demonstrating bacterial conjugation, another mechanism of horizontal gene transfer, in the 1940s.
• Beadle and Tatum: George Beadle and Edward Tatum (mentioned above) are known for their work on one gene-one enzyme hypothesis in Neurospora crassa, not bacterial transformation.

Answer: A.V. Leeuwenhock

Antoni van Leeuwenhoek is widely recognized as the “Father of Microbiology” for his pioneering work in the 17th century. He used self-made microscopes with incredibly high magnification for the time, allowing him to observe and describe microorganisms for the first time. This opened a new era in understanding the microbial world.

The other options are incorrect:

• Louis Pasteur: While Louis Pasteur made significant contributions to microbiology, including germ theory and pasteurization, Leeuwenhoek’s earlier work laid the foundation for the field.
• Lister: Joseph Lister is credited as a pioneer in antiseptic surgery, but Leeuwenhoek’s focus on observing and understanding microorganisms is more central to the field of microbiology.
• Robert Koch: Robert Koch developed postulates to link specific microorganisms to specific diseases. His work was crucial, but Leeuwenhoek’s role in discovering and describing microbes themselves holds a more foundational place in microbiology.

Answer: Lord Lister

Lord Lister (Joseph Lister) is credited with pioneering the antiseptic method in surgery. He introduced the use of carbolic acid (phenol) to sterilize surgical instruments, dressings, and the surgical environment. This significantly reduced post-surgical infections and revolutionized surgical practices.

The other options are incorrect:

• Lwanowski: While there may have been other historical figures contributing to antiseptic practices, Lwanowski is not a widely recognized name in this context.
• Edward Jenner: Edward Jenner is famous for developing the smallpox vaccine, a major contribution to immunology, but not directly related to the antiseptic method.
• Beijerinck: Martinus Beijerinck was a microbiologist known for his work on viruses and nitrogen fixation. He wasn’t a key figure in developing the antiseptic method.

Answer: Koch

Robert Koch is widely considered the “Father of Medical Microbiology” for his groundbreaking work in the late 19th century. He developed Koch’s postulates, a set of criteria to establish a causal relationship between a specific microorganism and a specific disease. This approach revolutionized the field of microbiology and laid the foundation for understanding infectious diseases.

The other options are incorrect:

• Pasteur: While Louis Pasteur made significant contributions to microbiology, including germ theory and pasteurization, Koch’s work specifically focused on linking microbes to diseases.
• Jenner: Edward Jenner is known for developing the smallpox vaccine, a major advancement in immunology, but not directly related to medical microbiology.
• A.L.Hock: A.L.Hock is likely not a well-known figure in microbiology. The answer choices seem to focus on more prominent historical figures in the field.

Answer: Absence of nuclear envelope

The defining characteristic of prokaryotic organisms is the absence of a nuclear envelope. This means their genetic material (DNA) is not enclosed within a membrane-bound nucleus but rather exists freely in the cytoplasm.

The other options are incorrect:

• Absence of locomotion: Not all prokaryotes are motile, but some, like bacteria with flagella, can move.
• Absence of nuclear material: All living organisms, including prokaryotes, possess genetic material (DNA) for carrying hereditary information.
• Absence of protein synthesis: Protein synthesis is essential for all living organisms, and prokaryotes have ribosomes for this process.

Answer: Oxysomes

The stalked particles on the cristae of mitochondria are called oxysomes. These are another term for the complexes containing ATP synthase, an enzyme crucial for ATP (adenosine triphosphate) production in cellular respiration. The stalk and head structure of these complexes give them a characteristic stalked appearance.

The other options are incorrect:

• Glyoxysomes: These are specialized organelles found in some plants and fungi, involved in the conversion of fats to carbohydrates. They are not present in mitochondria.
• Peroxisomes: These are separate organelles with distinct functions like breaking down fatty acids and detoxification. They are not located on the cristae of mitochondria.
• Spherosomes: This term can refer to various storage organelles in plants and some protists, not specific to mitochondria.