MicroBiology MCQs with Answer and Explnation | Chapter 24

Answer: Budding

The most common method of reproduction for unicellular yeast cells is budding. In this process, a small protrusion called a bud forms on the parent cell. This bud grows and eventually breaks away, forming a new daughter cell that is genetically identical to the parent.

The other options are incorrect:

• Sporing: While some yeast species can reproduce by forming spores, this is not the primary mode of reproduction for most unicellular yeasts. Sporing is often triggered by stress conditions and results in the formation of multiple spores, each capable of developing into a new individual under favorable conditions.
• Conidiation: Conidiation is a form of asexual reproduction in which specialized reproductive structures called conidia are produced. This is more common in filamentous fungi than in unicellular yeasts.
• Both Sporing and Conidiation: While both methods can occur in some yeast species, budding remains the predominant and more common reproductive strategy for unicellular yeasts.

Answer: Antiviral proteins

Interferons protect healthy cells by the production of antiviral proteins. Interferons are signaling proteins released by cells in response to viral infections. They induce nearby cells to heighten their antiviral defenses, including the synthesis of proteins that inhibit viral replication.

The other options are incorrect:

• Antibacterial proteins: Interferons are primarily associated with the antiviral response and do not directly produce antibacterial proteins.
• Antifungal proteins: While the immune system may produce antifungal proteins, interferons specifically play a key role in the antiviral response, not the antifungal response.
• Antiprotozoal proteins: Interferons are not known for directly producing antiprotozoal proteins. Their main role is in the defense against viral infections.

Answer: Mycology

Mycology is the branch of microbiology specifically dedicated to the study of fungi. It encompasses various aspects of fungi, including their taxonomy, morphology, physiology, ecology, genetics, and pathogenesis.

The other options are incorrect:

• Protozoology: This branch of microbiology focuses on the study of protozoa, which are single-celled eukaryotic organisms distinct from fungi.
• Phycology: This branch of microbiology deals with the study of algae, which are photosynthetic organisms that are not classified as fungi.
• Biotechnology: This is a broader field encompassing various biological technologies and applications, not solely focused on the study of fungi.

Answer: Cell wall synthesis

Penicillin acts by inhibiting the synthesis of the bacterial cell wall. It specifically inhibits the enzyme transpeptidase, which is responsible for cross-linking peptidoglycan strands, the major structural component of the bacterial cell wall. This inhibition disrupts the cell wall’s integrity and weakens it, eventually leading to the death of the bacteria.

The other options are incorrect:

• RNA synthesis: While some antibiotics target RNA synthesis, penicillin does not. Its primary target is the cell wall.
• Folate synthesis: Folate is a vitamin necessary for DNA synthesis and cell division. Some antibiotics, like sulfonamides, inhibit folate synthesis, but penicillin does not have this effect.
• DNA gyrase: This enzyme is involved in DNA replication and is targeted by some antibiotics, like fluoroquinolones. However, penicillin does not target DNA gyrase.

Answer: Protozoa

Schizogony is a mode of reproduction observed in protozoa. It involves multiple mitotic divisions within a parent cell, resulting in the formation of numerous daughter cells. This process contributes to the rapid multiplication and increased numbers of protozoan organisms.

The other options are incorrect:

• Algae: Algae typically reproduce through various methods such as binary fission, fragmentation, or spore formation. Schizogony is not a characteristic mode of reproduction in algae.
• Fungi: Fungi reproduce through processes like sexual and asexual spore formation, but schizogony is not a mode of reproduction in fungi.
• Embryophyta: Embryophyta, or land plants, reproduce through methods such as seed formation, spore production, and various types of sexual and asexual reproduction. Schizogony is not a mode of reproduction in land plants.

Answer: Pandemic

A pandemic is a disease that affects a large number of people over a wide geographic area, typically crossing multiple countries and continents. It is considered the most widespread level of disease outbreak.

The other options are incorrect:

• Sporadic: This refers to a disease that occurs only occasionally or in isolated instances, affecting a limited number of individuals and not necessarily spreading widely.
• Epidemic: An epidemic is a disease that affects a large number of people within a specific region or population, but its reach is not as extensive as a pandemic.
• Endemic: This describes a disease that is constantly present or usual in a particular area or group of people, meaning it is geographically limited and not actively spreading to new populations.

Answer: Endospore

Endospores are dormant structures formed by certain bacteria under harsh environmental conditions such as extreme heat, dryness, lack of nutrients, or radiation. These structures are highly resistant and can survive for extended periods while the bacteria remain in a metabolically inactive state. When favorable conditions return, the endospore can germinate and resume growth.

The other options are incorrect:

• Capsule: A capsule is a slimy layer surrounding the cell wall of some bacteria. While it can provide some protection against environmental stresses, it is not as resistant as an endospore and does not allow the bacteria to enter a dormant state.
• Cyst: Cysts are dormant structures formed by some protozoa and other eukaryotes under similar conditions as endospores. However, the structure and function of cysts are different from those of endospores.
• Bud: A bud is a small protrusion on the surface of a yeast cell that eventually breaks off to form a new daughter cell. This is a normal mode of reproduction for yeast and not related to dormancy mechanisms.

Answer: anaerobic

Many clostridial diseases require an anaerobic environment, meaning an environment with little to no oxygen, for their development. This is because Clostridium bacteria are strict anaerobes, which means they cannot survive in the presence of oxygen. They typically thrive in environments like the gastrointestinal tract, soil, and decaying organic matter, where oxygen levels are low.

The other options are incorrect:

• Living tissue: While some clostridial diseases can occur in living tissues, they are not dependent on this specific environment for their development.
• Aerobic: Aerobic environments are rich in oxygen, which is detrimental to the growth and survival of clostridial bacteria.
• Low-pH: While some clostridial bacteria can tolerate acidic environments, this is not the primary requirement for their development. Anaerobic conditions remain the crucial factor for clostridial growth.

Answer: Log phase

The log phase, also known as the exponential phase, is the period of rapid bacterial growth. During this phase, bacteria are actively dividing and their population increases exponentially. This rapid growth occurs because the environmental conditions are optimal for bacterial multiplication, with sufficient nutrients and favorable temperature and pH.

The other options are incorrect:

• Lag phase: The lag phase precedes the log phase and is a period of adaptation for bacteria as they adjust to new environmental conditions. During this phase, bacterial growth is slow or even absent.
• Death phase: The death phase occurs at the end of the bacterial growth cycle when the population starts to decline due to nutrient depletion, accumulation of waste products, or other unfavorable conditions.
• Stationary phase: The stationary phase is reached when the bacterial population stabilizes and the rate of cell division equals the rate of cell death. This phase occurs when resources become limited or environmental conditions become less favorable.

Answer: Mycelia

A group of fungal hyphae is called mycelia. Hyphae are thread-like structures that form the body of a fungus, and mycelium (plural: mycelia) refers to the mass of hyphae that collectively make up the fungal organism. Mycelia are involved in nutrient absorption and play a crucial role in the life cycle and ecological functions of fungi.

The other options are incorrect:

• Filtering body: “Filtering body” is not a recognized term in mycology. Fungi obtain nutrients through absorption, facilitated by the mycelium, rather than by filtering.
• Conidia: Conidia are asexual spores produced by certain fungi, but they are not the term used to describe a group of fungal hyphae.
• Yeast: Yeasts are unicellular fungi, and they do not form mycelia. Mycelia are characteristic of multicellular fungi with a filamentous structure, not yeast.

Answer: Mesophiles

Most human pathogenic bacteria are mesophiles. Mesophiles are bacteria that grow optimally in moderate temperatures, typically within the range of 20 to 45 degrees Celsius (68 to 113 degrees Fahrenheit). These temperatures are consistent with the conditions found in the human body, making mesophiles well-adapted to survive and cause infections in the human host.

The other options are incorrect:

• Psychrophiles: Psychrophiles are bacteria that thrive in cold temperatures. They are not commonly associated with human pathogens, as the human body is warmer than the environments preferred by psychrophiles.
• Psychrotrophes: Psychrotrophes can grow in both cold and moderate temperatures. However, the term is not typically used to describe bacteria that are significant human pathogens.
• Thermophiles: Thermophiles are bacteria that prefer high temperatures. They are not commonly associated with human pathogens, as the human body is not within their preferred temperature range.

Answer: Thymine

DNA (deoxyribonucleic acid) contains the nitrogenous base thymine. Thymine is one of the four nitrogenous bases present in DNA, alongside adenine (A), cytosine (C), and guanine (G). These bases form complementary base pairs (A with T, and C with G), providing the genetic code that directs the synthesis of proteins and other cellular functions.

The other options are incorrect:

• Alanine: Alanine is an amino acid, not a nitrogenous base found in DNA. Amino acids are the building blocks of proteins.
• Uracil: Uracil is a nitrogenous base found in RNA (ribonucleic acid) but is not present in DNA. In DNA, thymine replaces uracil.
• Arginine: Arginine is an amino acid and is not a component of the nitrogenous bases in DNA. It is involved in protein synthesis but is not part of the genetic code in nucleic acids.

Answer: Active artificial acquired immunity

The type of immunity achieved through vaccination is active artificial acquired immunity. This form of immunity results from the stimulation of the immune system by exposure to antigens, often through vaccines. The body responds by producing its own immune response, including the generation of memory cells, providing protection against future encounters with the pathogen.

The other options are incorrect:

• Active natural acquired immunity: Active natural acquired immunity results from natural exposure to pathogens, leading to the development of an immune response. It does not involve vaccination.
• Passive artificial acquired immunity: Passive artificial acquired immunity involves the administration of pre-formed antibodies or antitoxins. It does not involve the activation of the individual’s immune system through vaccination.
• Passive natural acquired immunity: Passive natural acquired immunity occurs naturally through the transfer of antibodies from mother to baby, such as through breastfeeding. It is not related to vaccination.

Answer: Hypertonic

Shrinkage of the cell occurs in a hypertonic environment. In a hypertonic solution, the concentration of solutes is higher outside the cell compared to inside. Water moves out of the cell, causing it to shrink or undergo plasmolysis.

The other options are incorrect:

• Hypotonic: In a hypotonic solution, the concentration of solutes is lower outside the cell compared to inside. Water moves into the cell, causing it to swell or undergo cytolysis.
• Isotonic: In an isotonic solution, the concentration of solutes is the same inside and outside the cell. There is no net movement of water, and the cell maintains its shape.

Answer: Prokaryotic

Bacteria are prokaryotic organisms, meaning they lack a membrane-bound nucleus and other organelles characteristic of eukaryotic cells. Their genetic material is single-stranded and circular, located in the cytoplasm rather than within a nucleus. Prokaryotes are the simplest and most abundant type of organism on Earth.

The other options are incorrect:

• Eukaryotic: Eukaryotic cells have a true nucleus and membrane-bound organelles such as mitochondria, Golgi apparatus, and endoplasmic reticulum. Bacteria do not possess these features.
• Acellular: Acellular organisms are non-living entities that lack cellular structure and organization. Bacteria are living organisms with complex cellular structures.
• May be prokaryotic or eukaryotic: This statement is incorrect. All bacteria are prokaryotic without exception.

Answer: Acetylcholine

Botulin toxin prevents the release of acetylcholine, a chemical that acts as a neurotransmitter. Acetylcholine is responsible for initiating the signal for muscle contraction. When botulin toxin binds to the presynaptic nerve terminal, it blocks the release of acetylcholine into the synapse, preventing muscle contraction.

The other options are incorrect:

• Serotonin: Serotonin is a neurotransmitter associated with mood, sleep, and pain perception. It is not involved in muscle contraction.
• Dopamine: Dopamine is another neurotransmitter involved in movement, reward, and learning. It does not directly initiate muscle contraction.
• Norepinephrine: Norepinephrine is a hormone and neurotransmitter involved in the fight-or-flight response and alertness. It can indirectly affect muscle contraction through its effects on the nervous system, but it is not the primary neurotransmitter responsible for initiating muscle contraction.

Answer: Erysipeloid

Erysipeloid is an infection caused by the bacterium Erysipelothrix rhusiopathiae. This bacterium is commonly found in pigs, sheep, and other animals, and it can be transmitted to humans through contact with infected animals or their tissues. In humans, erysipeloid typically causes a skin infection characterized by redness, swelling, and pain.

The other options are incorrect:

• Anthrax: Anthrax is another bacterial infection that can be transmitted to humans from animals. However, it is typically caused by a different bacterium, Bacillus anthracis, and has different clinical manifestations compared to erysipeloid.
• Diphtheria: Diphtheria is a bacterial infection caused by Corynebacterium diphtheriae. It affects the throat and respiratory tract and can cause serious complications.
• Tuberculosis: Tuberculosis is a bacterial infection caused by Mycobacterium tuberculosis. It primarily affects the lungs but can also spread to other organs.

Answer: Dislocated shoulder

A dislocated shoulder does not predispose to gas gangrene. Gas gangrene is a serious and potentially life-threatening infection caused by Clostridium bacteria, and it is commonly associated with contaminated wounds, such as surgical incisions, compound fractures, and puncture wounds. However, a dislocated shoulder, which involves the displacement of the shoulder joint, is not typically associated with the conditions conducive to gas gangrene.

The other options are incorrect:

• Surgical incisions: Surgical incisions can provide an entry point for bacteria, including Clostridium, leading to infections such as gas gangrene.
• Compound fractures: Compound fractures involve a break in the bone that protrudes through the skin, providing an open wound susceptible to bacterial infection, including gas gangrene.
• Puncture wounds: Puncture wounds, especially those with contamination, can introduce bacteria into deep tissues, potentially leading to gas gangrene.

Answer: infection, disease

In general, humans are rather prone to infection with the tubercle bacillus (Mycobacterium tuberculosis) but are resistant to developing the disease tuberculosis (TB) in many cases. While individuals may become infected with the bacteria, the immune system can control the infection, and only a portion of those infected progress to develop active TB disease.

The other options are incorrect:

• Disease, infection: This option is reversed. Humans are prone to infection with the tubercle bacillus, and not everyone infected progresses to develop the disease.
• TB, Leprosy: This option introduces leprosy, which is caused by Mycobacterium leprae. The original statement focuses specifically on tuberculosis.
• Leprosy, TB: This option is reversed, and it introduces leprosy. The original statement is about humans’ susceptibility to infection with the tubercle bacillus and resistance to developing TB in many cases.

Answer: Plasmodium

Malaria is caused by a single-celled parasite belonging to the genus Plasmodium. Several species within this genus can infect humans and cause various forms of malaria, with Plasmodium falciparum being the most prevalent and deadly.

The other options are incorrect:

• Paramecium: Paramecium is a genus of free-living ciliates, which are protozoa but not parasites. They are not known to cause any diseases in humans.
• Pseudomonas: Pseudomonas is a genus of bacteria, not parasites. Some species of Pseudomonas can cause opportunistic infections, but they are not associated with malaria.
• Pasteurella: Pasteurella is a genus of bacteria that can cause various diseases in animals and humans, including plague and tularemia. However, they are not associated with malaria.

Answer: Lag phase

The first phase of a bacterial growth curve is the lag phase. During this phase, bacteria are adjusting to their new environment and preparing for exponential growth. They are not dividing actively, but they are engaging in metabolic activities like synthesizing enzymes and acquiring nutrients. The length of the lag phase depends on several factors, including the bacterial species, the composition of the growth medium, and the temperature.

The other options are incorrect:

• Log phase: The log phase, also known as the exponential phase, follows the lag phase. During this phase, bacteria are actively dividing and their population increases exponentially.
• γ phase: This term is not commonly used to describe phases in bacterial growth. It is possible that it is a typo for another phase, such as the stationary phase or the death phase.
• Exponential: This is another term for the log phase, where bacterial growth is exponential.

Answer: Endoflagella

Spirochetes are unique bacteria that move using endoflagella. These are long, thin, helical filaments located within the periplasmic space, the narrow gap between the inner and outer membranes of the bacterium. The rotation of the endoflagella causes the spirochete’s cell body to rotate and/or undulate, allowing it to move forward in a corkscrew-like fashion.

The other options are incorrect:

• Pseudopodia: Pseudopodia are temporary, finger-like extensions of the cytoplasm used for movement by some protozoa and amoeba but not by spirochetes.
• Axial filament: This term is sometimes used interchangeably with endoflagella, but it specifically refers to the flagellum found in some spirochetes like Treponema pallidum. Regardless, both terms describe the same structure responsible for spirochete movement.
• Both Pseudopodia and Endoflagella: While spirochetes possess endoflagella, they do not use pseudopodia for movement.

Answer: Only living inside cells

Viruses are not truly living organisms in the traditional sense. They lack many of the key characteristics of life, such as the ability to grow, reproduce on their own, and metabolize. However, they do exhibit some characteristics of living things, such as having genetic material and the ability to evolve.

The other options are incorrect:

• Living: While viruses possess some properties of living organisms, they lack essential characteristics like independent growth and metabolism. Therefore, they are not considered truly living.
• Non-Living: Although viruses lack some key features of life, their ability to replicate within living cells and their complex structure suggest they are not entirely non-living entities.
• Capsular: This term refers to a specific layer of polysaccharides surrounding certain bacterial cells, not a general characteristic of viruses.

Answer: Mycoplasma

All of the following prokaryotes are bounded by a cell wall EXCEPT Mycoplasma. Mycoplasma is a unique prokaryote that lacks a cell wall. Instead, it has a flexible cell membrane and relies on sterols for stability. Spirochetes, Actinomycetes, and Streptococcus are prokaryotes that have cell walls.

The other options are incorrect:

• Spirochetes: Spirochetes are a group of bacteria characterized by their spiral shape and do have a cell wall.
• Actinomycetes: Actinomycetes are a group of bacteria that have a cell wall and are known for their filamentous growth.
• Streptococcus: Streptococcus is a genus of bacteria, and members of this genus have a cell

Answer: Macrophages

Tubercles are granulomas formed in response to Mycobacterium tuberculosis infection. They consist of a central core containing TB bacilli (Mycobacterium tuberculosis) and enlarged macrophages.

The other options are incorrect:

• Neutrophils: Neutrophils are not typically associated with the granulomas in tuberculosis. They are more commonly involved in acute inflammatory responses.
• Lymphocytes: While lymphocytes, particularly T cells, play a crucial role in the immune response against tuberculosis, they are not the primary cells found in the central core of tubercles.
• Eosinophils: Eosinophils are white blood cells that are more commonly associated with parasitic infections and allergic reactions. They are not typically a major component of the granulomas formed in tuberculosis.

Answer: Transcription

Transcription is the process of converting DNA (genetic information) into RNA. During transcription, a specific segment of DNA serves as a template for the synthesis of a complementary RNA molecule.

The other options are incorrect:

• Transduction: Transduction is a process in molecular biology that involves the transfer of genetic material from one bacterium to another by a bacteriophage (a type of virus). It is not related to the conversion of DNA to RNA.
• Translation: Translation is the process of synthesizing proteins from RNA. It occurs in the ribosomes, where the information encoded in mRNA (messenger RNA) is used to build a corresponding polypeptide chain. It does not involve the direct conversion of DNA to RNA.
• Replication: Replication is the process of copying DNA to produce an identical copy. It occurs during cell division and is responsible for ensuring that genetic information is passed on to daughter cells. It does not directly involve the conversion of DNA to RNA.

Answer: Double hydrogen bonds

Adenine (A) and Thymine (T) form a specific base pair in DNA due to the presence of two hydrogen bonds between them. These hydrogen bonds are crucial for maintaining the stability and accuracy of DNA structure and function.

The other options are incorrect:

• Single hydrogen bond: While hydrogen bonds are important for base pairing, one bond wouldn’t be sufficient for the stability and specificity required for DNA structure and function.
• Triple hydrogen bonds: The specific chemical structures of Adenine and Thymine only allow for the formation of two hydrogen bonds between them. Triple hydrogen bonds are characteristic of the Guanine (G) and Cytosine (C) base pair in DNA.
• Both “Single hydrogen bonds” and “Triple hydrogen bonds”: This option is inaccurate as it combines incorrect information with the correct answer.

Answer: All of these

Fungi have remarkable reproductive versatility, utilizing various methods to spread and ensure survival. While each option listed plays a role:

• Sexual Spores: Fungi form specialized reproductive structures called fruiting bodies that produce spores through sexual fusion of compatible mating types. These spores can then germinate and grow into new individuals.
• Fragmentation: Many fungi can reproduce asexually by simply separating into smaller pieces, each capable of growing into a new organism. This can occur through mycelial fragmentation or budding.
• Asexual Spores: Aside from sexual spores, fungi produce various types of asexual spores, such as conidia, chlamydospores, and sporangiospores. These spores are not directly involved in sexual reproduction but allow the fungi to disperse and colonize new habitats.

Answer: Mycobacterium bovis

The BCG (Bacille Calmette-Guérin) vaccine, used for tuberculosis (TB) control, is based on the attenuated strain of Mycobacterium bovis. It provides some protection against severe forms of TB, particularly in children.

The other options are incorrect:

• Mycobacterium tuberculosis: This is incorrect in the context of the BCG vaccine. The BCG vaccine is not based on Mycobacterium tuberculosis, the causative agent of TB, but rather on a related species, Mycobacterium bovis.
• Mycobacterium avium complex: This is incorrect. The BCG vaccine is not derived from Mycobacterium avium complex, which includes several species of mycobacteria but is not used in the BCG vaccine.
• Mycobacterium paratuberculosis: This is incorrect. The BCG vaccine is not based on Mycobacterium paratuberculosis, which is associated with Johne’s disease in animals, not TB in humans.

Answer: Bacteria

Antibiotics are specifically designed to target and kill bacteria. They work by disrupting essential bacterial processes, like cell wall synthesis or protein production, leading to the bacteria’s death or preventing their growth.

The other options are incorrect:

• Virus: Viruses are much smaller and simpler than bacteria and have different cellular machinery. Antibiotics cannot target viruses effectively.
• Algae: Algae are photosynthetic organisms, like plants, and have complex cell structures that are not affected by antibiotics.
• Protozoa: Protozoa are single-celled organisms, but they are much larger and more complex than bacteria. While some antibiotics can affect them, they are not the primary target for these drugs.

Answer: HSV-2

Genital herpes is primarily caused by the herpes simplex virus type 2 (HSV-2). While HSV-1, the virus responsible for oral cold sores, can also occasionally cause genital herpes, it’s significantly less common and typically through oral-genital contact.

The other options are incorrect:

• HSV-1: As mentioned, HSV-1 can cause genital herpes, but it’s not the main culprit. The risk of transmission from oral-genital contact is lower compared to HSV-2.
• HSV-3: This virus is associated with varicella-zoster virus (VZV), causing chickenpox and shingles. It doesn’t cause genital herpes.
• HSV-4: This virus is relatively rare and primarily linked to Epstein-Barr virus (EBV), associated with mononucleosis. It doesn’t typically cause genital herpes.

Answer: Enriched media

Blood agar is an example of enriched media. It is a type of solid growth medium that contains nutrients like blood (usually sheep’s blood) to support the growth of a wide variety of microorganisms, including fastidious bacteria that require additional nutrients not provided by general-purpose media.

The other options are incorrect:

• Enrichment media: Enrichment media usually contain specific nutrients to enhance the growth of a particular group of bacteria, often used for the isolation of specific pathogens. Blood agar is more accurately classified as enriched media.
• Selective media: Selective media are designed to encourage the growth of specific microorganisms while inhibiting the growth of others. Blood agar is not primarily designed for selectivity but for providing additional nutrients.
• General purpose media: General purpose media support the growth of a broad range of microorganisms without providing specific enhancements or inhibitory factors. Blood agar, with its enriched composition, goes beyond the characteristics of general-purpose media.

Answer: Non-sense mutation

A non-sense mutation is a type of genetic mutation that changes a codon specifying an amino acid into a termination codon. Termination codons (UAG, UAA, UGA) signal the ribosome to stop protein synthesis, resulting in a truncated and often non-functional protein. This can have significant consequences for the cell and organism.

The other options are incorrect:

• Mis-sense mutation: This type of mutation changes a codon to code for a different amino acid, not a stop codon. This can also affect protein function, but in a different way than a non-sense mutation.
• Reverse mutation: This mutation reverses a previous mutation, not necessarily creating a termination codon. It can restore the original sequence or create a new mutation.
• Frame shift mutation: This mutation inserts or deletes one or more nucleotides, causing a shift in the reading frame and potentially creating stop codons, but not directly introducing one.

Answer: Obligate anaerobe

The gas gangrene bacillus, also known as Clostridium perfringens, is a strict obligate anaerobe. This means it requires a complete absence of oxygen to survive and grow. The bacteria produce toxins that cause tissue death and gas formation in the affected area, leading to the severe symptoms of gas gangrene.

The other options are incorrect:

• Facultative anaerobe: These bacteria can grow with or without oxygen. While some Clostridium species are facultative anaerobes, C. perfringens is specifically an obligate anaerobe.
• Obligate aerobe: These bacteria require oxygen for growth and cannot survive in its absence. This is the opposite of C. perfringens, which needs an anaerobic environment.
• Facultative aerobe: As mentioned above, this option is inaccurate for C. perfringens.

Answer: Mechanical vector

A mechanical vector is an organism that only transports a pathogen from one host to another without being involved in the pathogen’s life cycle. Unlike biological vectors, mechanical vectors do not play a role in the replication or development of the pathogen.

The other options are incorrect:

• Biological vector: Biological vectors are organisms that not only transmit a pathogen but also play a role in the pathogen’s life cycle. The pathogen may replicate or undergo developmental stages within the biological vector.
• Biological reservoir: A biological reservoir is a host (human or animal) in which a pathogen can persist and potentially reproduce, serving as a source of infection. It is not specifically involved in transmitting the pathogen.
• Biological carrier: The term “biological carrier” is not commonly used in the context of disease transmission. Carriers typically refer to individuals who harbor a pathogen without showing symptoms but can still spread the infection to others.

Answer: Pseudomonas

Pseudomonas is a genus of bacteria that is important as decomposers and is involved in bioremediation. These bacteria are known for their metabolic versatility, including the ability to break down and utilize a wide range of organic compounds, making them valuable in the process of bioremediation, which aims to clean up environmental pollutants.

The other options are incorrect:

• Brucella: Brucella is a genus of bacteria known for causing brucellosis, a zoonotic infectious disease. It is not typically associated with decomposition or bioremediation.
• Francisella: Francisella is a genus of bacteria that includes species causing diseases like tularemia. It is not commonly involved in decomposition or bioremediation processes.
• Bordetella: Bordetella is a genus of bacteria, and species within this genus are known for causing respiratory infections in humans and animals, such as whooping cough. They are not typically involved in decomposition or bioremediation.

Answer: Cerebrospinal fluid

Brucellosis is not typically spread through human-to-human contact, and transmission usually occurs from direct or indirect contact with infected animals or their products. Among the options listed, cerebrospinal fluid is not considered a common route of transmission for brucellosis.

The other options are incorrect:

• Blood: Brucellosis can be transmitted through contact with infected blood, especially if there are open wounds or mucous membranes present. This mode of transmission is more relevant to occupational exposure in certain settings.
• Urine: Brucellosis can be transmitted through contact with contaminated urine from infected animals. However, human-to-human transmission via urine is not a common route.
• Placenta: Brucella species have the ability to cross the placenta, leading to transmission from mother to fetus. This is an important route of transmission, especially in cases of pregnant women with brucellosis.

Answer: Urease

Helicobacter pylori, a bacteria that colonizes the stomach lining, possesses a crucial enzyme called Urease. This enzyme plays a vital role in helping H. pylori neutralize the acidic environment of the stomach, creating a more favorable niche for its survival.

The other options are incorrect:

• Coagulase: This enzyme helps certain bacteria clump together and form clots, which is not relevant to H. pylori’s acid tolerance.
• Hyaluronidase: This enzyme breaks down hyaluronic acid, a component of connective tissues, and doesn’t directly neutralize stomach acid.
• DNase: This enzyme degrades DNA and doesn’t contribute to H. pylori’s survival in the acidic stomach.

Answer: Sterilization

Sterilization is the technique used to kill or eliminate all forms of microorganisms, including bacteria, viruses, fungi, and spores. It aims to achieve a complete absence of viable microorganisms, making an object or environment entirely free from microbial life.

The other options are incorrect:

• Disinfection: Disinfection is a process that aims to reduce the number of pathogenic microorganisms on surfaces or in substances to a level that is considered safe for public health. However, it does not necessarily eliminate all microorganisms.
• Antisepsis: Antisepsis involves the application of antimicrobial agents to living tissues, such as skin or mucous membranes, to prevent or inhibit the growth of microorganisms. It is not aimed at killing all microorganisms and is generally used to reduce the risk of infection.
• Pasteurization: Pasteurization is a process that involves heating liquids, such as milk or juice, to a specific temperature to kill or inactivate certain harmful microorganisms. However, it does not achieve complete sterilization as it may not eliminate all spores or heat-resistant microorganisms.

Answer: Red pulp

Red pulp is a component of the spleen, not the lymph node. The red pulp in the spleen is involved in the filtration and storage of red blood cells, but it is not a structure found in lymph nodes.

The other options are incorrect:

• Lymphoid follicle: Lymphoid follicles are structures found in lymph nodes and other lymphoid organs. They contain B cells and are important in the immune response.
• B cells: B cells are a type of lymphocyte that is commonly found in lymph nodes. They play a crucial role in the adaptive immune response, producing antibodies against specific pathogens.
• T cells: T cells, another type of lymphocyte, are also found in lymph nodes. They are involved in cell-mediated immunity and play a role in coordinating the immune response.

Answer: Cord factor

The virulence of tubercle bacillus (Mycobacterium tuberculosis) is due in part to the presence of a cell wall component called “cord factor.” Cord factor helps the bacterium resist destruction by lysosomes and macrophages, contributing to the pathogenicity of M. tuberculosis.

The other options are incorrect:

• Exotoxin: Exotoxins are toxic substances released by bacteria into their environment. They are not directly associated with the virulence of tubercle bacillus and avoiding destruction by lysosomes/macrophages.
• Enterotoxin: Enterotoxins are toxins that affect the intestines, causing symptoms like diarrhea. They are not specific to Mycobacterium tuberculosis and are not involved in avoiding destruction by lysosomes/macrophages.
• Endotoxin: Endotoxins are lipopolysaccharides found in the outer membrane of certain bacteria. While M. tuberculosis has cell wall components, the term “endotoxin” is more commonly associated with Gram-negative bacteria and may not directly contribute to the virulence of M. tuberculosis.

Answer: Lepromatous

Lepromatous leprosy is the form of the disease most closely associated with severe disfigurement of the face and other parts of the body. This is due to the extensive nerve damage and tissue destruction caused by the Mycobacterium leprae bacteria.

The other options are incorrect:

• Tuberculoid leprosy: This form of leprosy is characterized by granulomas, which are localized areas of inflammation. While some nerve damage can occur, it is typically less severe than in lepromatous leprosy, and facial disfigurement is less common.
• Borderline leprosy: This is an intermediate form of leprosy that can exhibit characteristics of both tuberculoid and lepromatous leprosy. Facial disfigurement may occur, but it is typically less severe than in lepromatous leprosy.
• Papular leprosy: This form of leprosy is characterized by raised, red bumps on the skin. While some nerve damage can occur, it is typically limited, and facial disfigurement is uncommon.

Answer: Corynebacterium

Diphtheria is caused by the bacterium Corynebacterium diphtheriae. This bacterium produces a toxin that can lead to the formation of a pseudomembrane in the throat and cause respiratory and systemic symptoms.

The other options are incorrect:

• Staphylococcus: Staphylococcus aureus is a bacterium known for causing various infections, but it is not the causative agent of diphtheria.
• Bacillus: Bacillus species, such as Bacillus cereus or Bacillus anthracis, can cause different diseases, but they are not responsible for diphtheria.
• Clostridium: Clostridium species, including Clostridium difficile and Clostridium tetani, are associated with specific diseases, but they do not cause diphtheria.

Answer: Propionibacterium

Propionibacterium species reside in the sebaceous glands of human skin. These bacteria are part of the normal skin microbiota and play a role in maintaining a healthy skin environment.

The other options are incorrect:

• Bacillus: While Bacillus species are diverse and can be found in various environments, they are not specifically known for residing in sebaceous glands in human skin.
• Erysipelothrix: Erysipelothrix species are associated with infections in animals and can occasionally cause human infections, but they are not known for residing in sebaceous glands.
• Corynebacterium: Corynebacterium species are part of the skin microbiota, but they are not specifically associated with sebaceous glands. Some species may inhabit other regions of the skin.

Answer: Pox virus

While some Parvovirus and Picornavirus species are relatively large compared to other viruses, Poxvirus holds the title for the largest virus in terms of both diameter and genome size. Poxviruses are known for their complex structure and double-stranded DNA genome, contributing to their substantial size.

The other options are incorrect:

• Parvovirus: These viruses are generally small, with a single strand of DNA. While some species like B19 parvovirus can be larger, they still fall short of the Poxvirus size.
• Picornavirus: These viruses are also relatively small, with single-stranded RNA genomes. Some like enteroviruses can be slightly larger, but not comparable to Poxviruses.
• HIV: While HIV has a complex genome, its overall size is considerably smaller than Poxviruses. It is a retrovirus with a single-stranded RNA genome.

Answer: Malachite green

Endospores are highly resistant structures formed by some bacteria to survive harsh conditions like heat, dryness, and radiation. They are difficult to stain with standard dyes due to their thick and impermeable coats. However, malachite green is a specific dye that can penetrate the endospore wall and stain the dormant bacteria within.

The other options are incorrect:

• Safranin: This is another dye commonly used in microbiology, but it is not effective for staining endospores due to their unique structure.
• Methylene blue: While some protocols utilize methylene blue in combination with other dyes for endospore staining, it is not as effective as malachite green alone.
• Crystal Violet: Similar to Safranin, Crystal Violet struggles to penetrate the endospore coat and is not a reliable option for endospore staining.

Answer: Polio virus

Poliovirus is an RNA virus, not a DNA virus. The other options—Parvovirus, Poxvirus, and Hepatitis B Virus—are DNA viruses.

The other options are incorrect:

• Parvo virus: Parvovirus is a DNA virus. It has a single-stranded DNA genome.
• Pox virus: Poxviruses, such as the variola virus (smallpox virus), are DNA viruses. They have a large, double-stranded DNA genome.
• Hepatitis B Virus: Hepatitis B Virus is a DNA virus with a partially double-stranded DNA genome. It is classified as a Hepadnavirus.

Answer: Dimorphic

Fungi that can exist in both a mold (filamentous hyphal) form and a yeast form, depending on environmental conditions, are referred to as dimorphic fungi. The ability to switch between these two forms is often associated with certain pathogenic fungi.

The other options are incorrect:

• Hyphae: Hyphae are the thread-like structures that make up the fungal mycelium. While some fungi have hyphal forms, this term does not specifically describe fungi that can exist as both molds and yeasts.
• Tinea pedis: Tinea pedis refers to a fungal infection commonly known as athlete’s foot. It does not describe fungi that can exist in both mold and yeast forms.
• Spore forming: The ability to form spores is a characteristic of many fungi, but it does not specifically refer to the ability to exist in both mold and yeast forms (dimorphism).

Answer: Bacteriophages

Viruses that infect and attack bacteria are called bacteriophages. Bacteriophages are viruses specifically designed to infect bacterial cells, and their name is derived from “bacteria” and “phage” (meaning “to eat”).

The other options are incorrect:

Bacterial viruses: This term is somewhat redundant, as all viruses that infect bacteria can be referred to as bacteriophages. The more common and specific term is “bacteriophage.”
Bacterial pathogens: Bacterial pathogens are bacteria that cause diseases. The term does not specifically refer to viruses that infect bacteria.
Virions: Virions are complete virus particles outside of a host cell, encompassing the genetic material and protein coat. While all viruses, including bacteriophages, exist as virions, the term is not specific to viruses that attack bacteria.

Answer: All of these

Fungal hyphae can exhibit various characteristics. They may be septate (divided into distinct cells by septa or cross-walls), non-septate (coenocytic, lacking cross-walls), and branched. Therefore, fungal hyphae can be septate, non-septate, or branched, or they may possess a combination of these features.

The other options are incorrect:

• Septate: This is not incorrect, as fungal hyphae can indeed be septate. However, the correct answer is more inclusive, as fungal hyphae can also be non-septate and branched.
• Non-septate: This is not incorrect, as fungal hyphae can be non-septate. However, the correct answer is more comprehensive, including the fact that they can also be septate and branched.
• Branched: This is not incorrect, as fungal hyphae can be branched. However, the correct answer is more comprehensive, encompassing the fact that they can also be septate and non-septate.