Microbiology MCQs with Answer and Explnation | Chapter 4

Answer: Cell-wall

A cell wall is a rigid structure that surrounds the cell membrane and provides support and protection for the cell. Parasitic microorganisms need a cell wall to be able to invade and survive within their host cells.

The other options are not essential for parasitic forms of microorganisms:

• A capsule is a slimy layer that surrounds the cell wall of some bacteria. It can help to protect the bacteria from the host’s immune system, but it is not essential for parasitism.
• Endospores are dormant structures that are produced by some bacteria. They allow the bacteria to survive in harsh conditions, but they are not essential for parasitism.
• Flagella are hair-like appendages that are used by some bacteria to move around. They can help parasitic bacteria to spread within their host, but they are not essential for parasitism.

Answer: Eukaryotes

The correct answer is eukaryotes. Cytoplasmic streaming, also known as cyclosis, is a phenomenon predominantly observed in eukaryotic cells. It involves the movement of cytoplasmic components, such as organelles and nutrients, within the cell. This movement aids in distributing essential materials throughout the cell and is particularly noticeable in plant cells.

The other answer options are incorrect:

• Prokaryotes: Cytoplasmic streaming is not a common phenomenon in prokaryotic cells. Prokaryotes lack membrane-bound organelles and complex internal structures, which limit their ability to exhibit cytoplasmic streaming as observed in eukaryotic cells.
• Animals: While some movement of cytoplasm may occur in certain animal cells, cytoplasmic streaming is not a defining or widely recognized feature of animal cells. It is more prominently observed in plant cells due to their large central vacuoles and the need to distribute nutrients across the cell.

Answer: Electron acceptors

Cytochromes are electron acceptors. They are heme-containing proteins found in the electron transport chain of the mitochondria. They play a crucial role in transferring electrons during cellular respiration.

Other options are Incorrect :

1. ATP acceptors: Cytochromes do not directly accept ATP. They are involved in the transfer of electrons, not ATP molecules.
2. Oxygen acceptors: While cytochromes are involved in the electron transport chain that ultimately leads to oxygen being the final electron acceptor, they themselves are not primarily oxygen acceptors.
3. Protein acceptors: Cytochromes are proteins themselves and function as electron carriers, not acceptors of other proteins.

Answer: Eukaryotes

Histones are found in eukaryotes. They are proteins that bind to DNA, forming complexes known as nucleosomes, which help organize and regulate the structure of chromatin within the cell nucleus. These structures are essential for packing DNA efficiently into the cell and regulating gene expression.

Incorrect options:

1. Prokaryotes: Histones are not typically found in prokaryotes. Prokaryotic cells lack histones and nucleosomes; instead, they have different mechanisms for organizing their DNA.
2. Viruses: Viruses do not have histones. They are non-cellular entities that lack the structures found in both eukaryotes and prokaryotes.

Answer: Prophage

A prophage is a bacteriophage genome that has been integrated into the bacterial chromosome. Prophages are not immediately active, and they do not lyse (burst) their host cells. Instead, they replicate along with the bacterial DNA and are passed on to daughter cells during cell division. Prophages can remain inactive for many generations, but under certain conditions, they can become active and enter the lytic cycle, resulting in the production of new viruses and the lysis of the host cell.

The other options are not correct:

• Metaphage is a term used to describe a group of bacteriophages that can work together to infect and lyse a bacterial cell.
• Temperate phage is another term for a bacteriophage that can enter the lysogenic cycle and form a prophage.
• Bacteriophage is a general term for a virus that infects bacteria.

Answer: Rhodococcus agilis

All of the other options are non-motile cocci. Rhodococcus agilis is a Gram-positive, aerobic, motile coccus that is found in soil and water. It is not typically pathogenic to humans.

Here is a table summarizing the motility of the cocci listed in the question:

Answer: Chondroids

Mesosomes are invaginations of the plasma membrane in prokaryotes, particularly bacteria. They were once thought to be analogous to mitochondria in eukaryotes, but it is now known that they are not true organelles. Mesosomes are produced by the chemical fixation techniques used to prepare samples for electron microscopy, and they are not found in bacteria that have been prepared using freeze-fracture fixation.

The other options are not correct:

• Chloroplasts are organelles found in plant cells that are responsible for photosynthesis.
• Mitochondria are organelles found in eukaryotic cells that are responsible for cellular respiration.
• Golgi complex is an organelle found in eukaryotic cells that is responsible for modifying and packaging proteins.

Answer: Staphylococci

Staphylococcus aureus, a common bacterium found on the skin and in the nose of humans, produces enterotoxins that cause staphylococcal food poisoning. These toxins are heat-stable and can withstand cooking temperatures. When ingested, they bind to receptors on the lining of the small intestine, causing inflammation and the production of fluids and electrolytes. This leads to the symptoms of food poisoning, which typically include nausea, vomiting, diarrhea, and abdominal cramps.

The other options are not correct:

• Entamoeba histolytica is a protozoan parasite that causes amoebic dysentery.
• Enterobacteriaceae are a family of bacteria that includes some common pathogens, such as E. coli and Salmonella.
• Enterococci are a group of bacteria that are commonly found in the intestines.

Answer: 10-25 nm

The thickness of a bacterial cell wall ranges from 10 to 25 nanometers (nm). The cell wall provides structural support to the bacterial cell and varies in thickness depending on the type of bacteria and the specific composition of their cell wall.

Incorrect options:

1. 9-10 nm: This range is slightly smaller than the usual thickness of a bacterial cell wall.
2. 30-40 nm: This range is larger than the typical thickness of a bacterial cell wall.
3. 12-13 nm: While closer to the range, it tends to be slightly narrower than the typical thickness observed in bacterial cell walls.

Answer: Lipids are present

The cell wall of Gram-negative bacteria is composed of two layers: a thin peptidoglycan layer and an outer membrane. The peptidoglycan layer is a mesh-like structure that provides strength and rigidity to the cell. The outer membrane is a lipid bilayer that contains lipopolysaccharides (LPS). LPS is a toxic molecule that helps to protect Gram-negative bacteria from the environment.

Incorrect options:

1. Teichoic acids are absent: Teichoic acids are actually absent in the cell walls of gram-negative bacteria, but this doesn’t solely define the cell wall structure of gram-negative bacteria.
2. Thick: Gram-negative bacterial cell walls are not thick; they have a thinner layer of peptidoglycan compared to gram-positive bacteria.

Answer: Polysaccharides

Polysaccharides are long chains of sugar molecules that are linked together. They are a major component of the bacterial cell wall and capsule. Polysaccharides are also found in the cytoplasm of bacteria, where they play a role in energy storage and cell structure.

Polypeptides are long chains of amino acids that are linked together. They are the building blocks of proteins. Proteins are essential for all life, and they play a role in virtually every cellular process.

Polynucleotides are long chains of nucleotides that are linked together. Nucleotides are the building blocks of DNA and RNA. DNA is the genetic material of all living things, and RNA is involved in protein synthesis and other cellular processes.

Answer: Gram positive bacteria

Teichoic acids and teichuronic acids are found in Gram-positive bacteria. They are important components of the cell wall in these bacteria, contributing to its structure and often playing roles in cell division, ion transport, and regulation of cell growth.

The Other Option are Incorrect :

1. Gram-negative bacteria: Teichoic acids and teichuronic acids are not typically found in Gram-negative bacteria; their cell walls have different compositions, including lipopolysaccharides in their outer membranes.
2. Fungi: These acids are not characteristic components of fungal cell walls. Fungal cell walls primarily contain components like chitin, glucans, and other polysaccharides, but not teichoic or teichuronic acids.

Answer: Botulism

Botulism is a rare but serious illness caused by the neurotoxin botulinum, which is produced by the bacterium Clostridium botulinum. Botulinum toxin is the most potent neurotoxin known and can cause paralysis and death.

Botulinum toxin can be found in food that has been improperly canned or preserved. It can also be found in soil and dust, and can contaminate food during preparation.

The symptoms of botulism typically appear within 12 to 72 hours of eating contaminated food. Symptoms include difficulty swallowing, blurred vision, drooping eyelids, and muscle weakness. In severe cases, botulism can cause paralysis of the muscles that control breathing, which can lead to death.

Answer: Chromatophores

In bacteria, pigment-bearing structures are often found in chromatophores. Chromatophores are specialized membrane-bound structures within certain bacteria that contain pigments, allowing these bacteria to carry out photosynthesis or other light-related processes. They help bacteria absorb and utilize light energy for various metabolic functions.

Incorrect options:

1. Protoplast: Protoplast refers to a bacterial cell that has had its cell wall removed, making it more susceptible to osmotic lysis. It doesn’t specifically involve pigment-bearing structures.
2. Chloroplast: Chloroplasts are the organelles found in plant cells and some protists responsible for photosynthesis, not in bacteria.
3. Sphaeroplast: Similar to a protoplast, a sphaeroplast is a bacterial cell whose cell wall has been partially removed, but it doesn’t directly relate to pigment-bearing structures.

Answer: Chromophores

The pigment-bearing structures in bacteria are called “chromophores.” Chromophores are specialized structures or compounds within bacteria that contain pigments responsible for giving bacteria their characteristic colors. These pigments can have various functions, including light absorption, protection against UV radiation, or aiding in photosynthesis.

These Options are Incorrect :

1. Mitochondria: Mitochondria are organelles found in eukaryotic cells that are involved in energy production through cellular respiration. They are not present in bacteria.
2. Plasmids: Plasmids are small, circular DNA molecules found in bacteria but are not pigment-bearing structures.
3. Mesosomes: Mesosomes were previously thought to be structures within bacterial cells, but their existence and function have been debated and are not universally accepted. They are not pigment-bearing structures.

Answer: Lipolytic microbes

The rancidity of stored foods is primarily due to the activity of lipolytic microbes. These microbes break down fats and oils in food, causing them to become rancid by releasing free fatty acids. This process alters the taste, smell, and quality of the food.

These Option are Incorrect :

1. Proteolytic microbes: These microbes break down proteins, not fats, and are not directly responsible for causing rancidity in stored foods.
2. Toxigenic microbes: Toxigenic microbes produce toxins that can cause food poisoning or other illnesses, but they are not directly related to the process of food rancidity.
3. Saccharolytic microbes: Saccharolytic microbes break down carbohydrates (sugars) into simpler compounds. While they play a role in food spoilage, they are not primarily responsible for causing rancidity in stored foods.

Answer: WIDAL test

The test commonly used for the detection of typhoid fever is the Widal test. This test detects antibodies (specifically agglutinins) produced against the Salmonella typhi bacteria, which causes typhoid fever. However, it’s worth noting that the Widal test has limitations and may sometimes yield false-positive or false-negative results, so it’s often complemented with other diagnostic methods for confirmation.

These Options are Incorrect :

1. ELISA (Enzyme-Linked Immunosorbent Assay) and Western blotting: While these are general types of immunoassays used in laboratory testing, they are not typically the primary tests for diagnosing typhoid fever.
2. Western Blotting: Protein blotting technique that can be used to identify specific Salmonella typhi proteins
3. Rosewaller test: There isn’t a widely recognized diagnostic test for typhoid fever called the Rosewaller test.

Answer: Bacteriophages

The viruses that specifically attack bacteria are called bacteriophages. These viruses infect and replicate within bacterial cells, often causing the destruction of the host bacterium during the viral replication cycle.

Incorrect options:

1. Various: While there are various types of viruses that infect different organisms, the specific viruses that infect bacteria are known as bacteriophages.
2. Bacterial viruses: This term is interchangeable with bacteriophages; both refer to viruses that infect bacteria.
3. Bacterial pathogens: While some bacterial pathogens cause diseases in other organisms, they are not viruses; they are bacteria themselves and cause infections in various hosts, including humans and animals.

Answer: Gram positive

Acridine dyes are generally more effective against Gram-positive bacteria. These dyes have an affinity for binding to DNA, and they tend to be more effective against bacteria with thicker peptidoglycan layers, characteristic of Gram-positive bacteria. The dyes can penetrate these cells more easily due to the presence of a thicker cell wall compared to Gram-negative bacteria.

Incorrect options:

1. Gram-negative: Acridine dyes are generally less effective against Gram-negative bacteria due to their outer membrane, which acts as a barrier, making it harder for these dyes to penetrate the cells.
2. Ricke Hsia: There isn’t a recognized association between acridine dyes and Ricke Hsia. Ricke Hsia might refer to a person’s name or something specific not directly related to acridine dyes.
3. Mycoplasma: Mycoplasma are bacteria that lack a cell wall, which makes them inherently less susceptible to some antibiotics or dyes targeting cell wall synthesis. However, acridine dyes might have varied effectiveness against mycoplasma due to their unique cell structure.

Answer: Gram positive bacteria

Bacillus is an example of Gram-positive bacteria. It belongs to the phylum Firmicutes and is characterized by its ability to form endospores. These bacteria have a thick peptidoglycan cell wall, which stains purple in the Gram staining process.

Incorrect options:

1. Virus: Bacillus is not a virus. Viruses are non-cellular infectious agents that require a host cell to replicate.
2. Viroid: Viroids are infectious RNA molecules that cause disease in certain plants but are distinct from bacteria like Bacillus.
3. Gram-negative bacteria: Bacillus is categorized as Gram-positive bacteria due to its thick peptidoglycan layer in the cell wall, which retains the crystal violet stain in the Gram staining process.

Here is a table summarizing the characteristics of Bacillus bacteria:

Answer: All of above

Aspergillus fumigatus can indeed infect all of the options listed: animals, birds, and humans (man). It is a common species of fungus found in the environment and can cause a range of infections in various animals, including mammals, birds, and humans. In humans, it is known to cause a variety of respiratory infections, especially in individuals with weakened immune systems or underlying lung conditions.

Answer: Rickettsias

Rickettsias are obligate intracellular parasites, meaning that they can only survive and replicate inside the cells of other organisms. They are smaller than bacteria but larger than viruses, and they have a cell wall. Rickettsias can cause a variety of diseases, including typhus, Rocky Mountain spotted fever, and ehrlichiosis.

The other options are not correct:

• Mycoplasmas are bacteria that lack a cell wall.
• Prions are misfolded proteins that can cause neurodegenerative diseases such as Creutzfeldt-Jakob disease and Alzheimer’s disease.
• Viroids are small RNA molecules that can infect plants and cause diseases such as potato spindle tuber viroid.

Here is a table summarizing the characteristics of Rickettsiae:

Answer: Lactophenol cotton blue

The stain commonly used to demonstrate fungi in microscopy is Lactophenol cotton blue. This stain helps visualize fungal structures by highlighting their morphological features, such as spores, hyphae, and fruiting bodies, against a contrasting background.

The Other Options are Incorrect :

1. Albert: There isn’t a commonly recognized staining method named Albert used specifically for demonstrating fungi.
2. Nigerosin: Nigerosin is a stain used in histology and bacteriology to stain acidic structures, but it’s not typically used for demonstrating fungi.

Answer: Measles

Koplik spots observed in the mucous membranes, particularly in the mouth, are a characteristic feature of the disease measles (also known as rubeola). These spots appear as small, white or bluish-white spots surrounded by a red halo and are indicative of an early stage of measles infection.

The other Options are Incorrect :

1. Mumps: Mumps is a viral infection caused by the mumps virus. It typically presents with swelling of the salivary glands (parotitis) but does not produce Koplik spots.
2. Influenza: Influenza, caused by influenza viruses, primarily affects the respiratory system and does not produce Koplik spots.
3. Rubella: Rubella, also known as German measles, is caused by the rubella virus. It doesn’t produce Koplik spots; instead, it can cause a rash and other symptoms.

Here is a table summarizing the characteristics of Koplik spots:

Answer: Hfr

Hfr stands for high-frequency recombination. Hfr cells are formed when the F plasmid integrates into the bacterial chromosome. This integration event can occur by homologous recombination between the F plasmid and the chromosome. Once integrated, the F plasmid can be transferred to other bacteria during conjugation. However, the transfer of the F plasmid is not always complete, and Hfr cells often transfer only a portion of the chromosome to the recipient cell.

Hfr cells are important tools for studying bacterial genetics. They can be used to map the location of genes on the chromosome and to study the process of recombination.

The other terms listed are not correct:

• F– cells are cells that do not have the F plasmid.
• Hbr cells are cells that have the R plasmid, which is a plasmid that encodes resistance to antibiotics.
• C+ cells are cells that have the C plasmid, which is a plasmid that encodes colicins, which are proteins that can kill other bacteria

Answer: ‘L’ form

The cell wall-deficient form of bacteria is often referred to as the ‘L’ form. These are bacterial variants that lack a cell wall and can exhibit various shapes and sizes, often resulting from the loss or alteration of the cell wall structure. This alteration can happen naturally or due to certain treatments, leading to the survival of bacteria without the typical cell wall.

The other options are Incorrect :

1. Protoplast: Protoplasts are bacterial cells that have had their cell wall removed enzymatically but can still retain their cell membrane.
2. Spheroplast: Spheroplasts are similar to protoplasts but may still have residual cell wall material.
3. Mycoplasma: Mycoplasmas are naturally occurring bacteria that lack a cell wall but are not typically considered the same as the ‘L’ form, which refers to variants of bacteria that have lost their cell walls due to changes or treatments.

Here is a table summarizing the characteristics of L-form bacteria:

Answer: Bacilli

Rod-shaped bacteria are known as bacilli. These bacteria have a cylindrical shape resembling a rod or stick and can vary in size and arrangement.

The other options are Incorrect :

1. Cocci: Cocci are spherical-shaped bacteria, not rod-shaped.
2. Pleomorphic forms: Pleomorphic bacteria can have various shapes (pleomorphism), including rods, cocci, and other forms, but the term doesn’t specifically denote rod-shaped bacteria.
3. Comma forms: Comma-shaped bacteria refer to a specific shape, typically seen in Vibrio species, which are curved or comma-shaped, not strictly rod-shaped.

Here is a table summarizing the characteristics of bacilli:

Answer: Heat labile

Exotoxins are heat-labile proteins secreted by certain bacteria. They are not part of the bacterial cell wall but are rather released into the surrounding environment. These toxins are usually proteins and can be highly potent, causing damage to host cells or tissues.

Incorrect options:

1. Part of cell wall: Exotoxins are not components of the bacterial cell wall. They are secreted by bacteria as part of their pathogenic mechanisms.
2. Polymerized complexes: Exotoxins are typically proteins and are not specifically known for being polymerized complexes.
3. Heat stable: Exotoxins are heat-labile, meaning they are susceptible to being denatured or inactivated by heat.

Here is a table summarizing the characteristics of exotoxins:

Answer: Treponema pallidum

Treponema pallidum is the bacteria that causes syphilis. It is a spiral-shaped bacteria, also known as a spirochete. Spirochetes are unique in that they have flagella inside their cell membranes, which allows them to move in a corkscrew-like fashion.

Treponema pallidum is a very difficult bacteria to grow in the laboratory, which is why syphilis was so difficult to diagnose and treat in the past. Today, syphilis can be easily diagnosed and treated with antibiotics.

The other options are not spirochetes:

• Gonococci are the bacteria that cause gonorrhea. They are cocci-shaped bacteria, which means that they are round.
• Strphylococci are the bacteria that cause a variety of infections, including skin infections, pneumonia, and sepsis. They are cocci-shaped bacteria.
• Streptococci are the bacteria that cause a variety of infections, including strep throat, scarlet fever, and pneumonia. They are cocci-shaped bacteria.

Here is a table summarizing the characteristics of spirochetes, gonococci, streptococci, and staphylococci:

Answer: H.C. Gram

Hans Christian Gram was a Danish bacteriologist who developed the Gram staining technique in 1884. The Gram stain is a method of staining bacteria that differentiates them into two large groups: gram-positive bacteria and gram-negative bacteria. The stain is based on the difference in the composition of the cell walls of gram-positive and gram-negative bacteria.

Gram-positive bacteria have a thick peptidoglycan layer in their cell wall, which retains the crystal violet stain used in the Gram staining procedure. Gram-negative bacteria have a thinner peptidoglycan layer and an outer membrane, which decolorize during the Gram staining procedure.

The Gram stain is a simple and inexpensive test, and it is one of the most important tools used in microbiology. It is used to identify bacteria, diagnose infections, and guide treatment decisions.

The other answer choices are not correct:

• A.H. Gram and N.C. Gram are not real people.
• H.A. Gram is a misspelling of H.C. Gram.

Answer: Lysogen

A bacterium containing a prophage is called a lysogen. When a bacteriophage integrates its DNA into the bacterial chromosome, the bacterium harboring this prophage is referred to as a lysogen. The prophage remains dormant within the bacterial genome until conditions trigger its activation, leading to the lytic cycle where new phages are produced and released.

Incorrect options:

1. Lytic: The lytic cycle refers to the phase in the viral life cycle where the virus actively replicates within the host and leads to the host cell’s lysis and release of new viral particles.
2. Lytogen: This term is not commonly used in microbiology to describe bacteria containing prophages.

Here is a table summarizing the characteristics of lysogens:

Answer: Binary-fission

Bacterial cell multiplication primarily occurs through binary fission. In this process, a single bacterial cell replicates its genetic material and then divides into two identical daughter cells. This method of asexual reproduction is the most common way bacteria increase their numbers.

Incorrect options:

1. Conjugation: Conjugation involves the transfer of genetic material (plasmids) between two bacterial cells but doesn’t directly result in cell multiplication.
2. Meiosis: Meiosis is a type of cell division that occurs in sexually reproducing organisms to produce gametes (sex cells) with reduced genetic material, not in bacteria.
3. Mitosis: Mitosis is a form of cell division seen in eukaryotic cells where a single cell divides into two identical daughter cells, but this process does not occur in bacteria.

Here is a table summarizing the different types of cell division:

Answer: Virulent

A bacteriophage capable of only lytic growth is called a virulent bacteriophage. Virulent phages exclusively undergo the lytic cycle upon infecting a bacterial host, leading to the destruction of the host cell as new phages are released.

Incorrect options:

1. Temperate: Temperate phages have the ability to undergo both the lytic and lysogenic cycles. They can integrate their DNA into the host genome and remain dormant (lysogenic) or initiate the lytic cycle.
2. Avirulent: Avirulent typically refers to organisms that lack the ability to cause disease or have reduced pathogenicity, but it is not a specific term used for bacteriophages that exhibit solely lytic growth.

Here is a table summarizing the different types of bacteriophages:

Answer: Influenza

Influenza is an example of a common airborne epidemic disease. It spreads easily through the air via droplets from coughs or sneezes of infected individuals. Influenza viruses can cause seasonal epidemics that affect large populations.

Incorrect options:

1. Typhoid: Typhoid fever is typically transmitted through contaminated food or water, not primarily through airborne transmission.
2. Malaria: Malaria is transmitted through the bite of infected mosquitoes and is not considered primarily an airborne disease.
3. Encephalitis: Encephalitis can be caused by various factors, including viruses transmitted by mosquitoes or ticks, but it is not primarily transmitted through airborne routes.

Answer: Attenuation

Virulence of microorganisms can be reduced by attenuation. Attenuation is a process of weakening the virulence or pathogenicity of a microorganism, typically done intentionally in vaccine development. This method involves modifying the microorganism so that it retains the ability to stimulate an immune response but is less capable of causing disease.

Incorrect options:

1. A virulence: This term does not directly denote a process to reduce virulence. It might refer to the absence of virulence or the state of being non-pathogenic.
2. Freezing: Freezing microorganisms does not inherently reduce their virulence. Some microorganisms might survive freezing, retaining their virulence upon thawing.
3. Inactivation: Inactivation often involves killing or rendering microorganisms non-viable, which might reduce their ability to cause infection, but it’s not specifically aimed at reducing their virulence while maintaining their ability to stimulate an immune response.

Answer: Infectious virus particles

Virion refers to infectious virus particles. It’s the complete, infectious form of a virus, consisting of the viral genome (either DNA or RNA) surrounded by a protein coat called the capsid. The virion is the fully assembled and functional virus particle capable of infecting host cells and replicating within them.

Incorrect options:

1. Non-infectious particles: Virions are infectious and capable of causing infection.
2. Defective virus particles: Defective virus particles have mutations or structural abnormalities that reduce their ability to replicate or cause infection. Virions, by definition, are functional and infectious.
3. Incomplete particles: Incomplete particles lack certain components needed for infectivity. Virions are complete and infectious viral particles.

Answer: Entamoeba histolytica

Amoebic dysentery in humans is caused by Entamoeba histolytica, a parasitic amoeba. This protozoan is responsible for causing intestinal infections, leading to symptoms such as severe diarrhea (often with blood and mucus), abdominal pain, and fever.

Incorrect options:

1. Paramecium: Paramecium is a genus of single-celled ciliates, not responsible for amoebic dysentery.
2. Yeast: Yeast is a type of fungus and is not associated with causing amoebic dysentery.
3. Plasmodium: Plasmodium species are protozoan parasites responsible for causing malaria, not amoebic dysentery.

Here is a table summarizing the organisms and their associated diseases:

Answer: Kleb’s – lofflers bacillus

Diphtheria bacillus is otherwise known as Klebs-Löffler bacillus. It’s named after the bacteriologists Edwin Klebs and Friedrich Löffler, who identified and characterized the bacterium Corynebacterium diphtheriae as the causative agent of diphtheria in the late 19th century.

Incorrect options:

1. Koch’s bacillus: Koch’s postulates are criteria used to establish a causative relationship between a microorganism and a disease. The term doesn’t refer to diphtheria bacillus.
2. Frösch bacillus: There isn’t a widely recognized bacterium known as “Frösch bacillus” associated with diphtheria.
3. Friedländer’s bacillus: This term is used for another bacterium, Klebsiella pneumoniae, identified by Carl Friedländer, but it’s not related to diphtheria.

Here is a table summarizing the different names for the diphtheria bacillus:

Answer: Iodine

The mordant used in Gram staining is iodine. In the Gram staining process, iodine serves as a mordant that enhances the interaction between the crystal violet (the primary stain) and the bacterial cells, aiding in the formation of the crystal violet-iodine complex within Gram-positive bacteria.

Incorrect options:

1. Saffranin: Saffranin is a counterstain used in Gram staining to colorize Gram-negative bacteria after the initial staining process.
2. Crystal Violet: Crystal violet is the primary stain used in Gram staining to initially colorize all bacteria before differentiation between Gram-positive and Gram-negative bacteria occurs.

Here is a table summarizing the different steps in Gram staining and the substances used:

Answer: 0.02–0.2 ìm

The size of virus particles typically ranges from 0.02 to 0.2 micrometers (µm). Viruses are extremely small and can vary in size, with some of the largest viruses nearing the upper end of this range and some of the smallest viruses being closer to the lower end.

Incorrect options:

1. 0.1–100 µm: This range is broader than the typical size range of viruses and includes sizes larger than what viruses usually measure.
2. 0.5–10 µm: This range includes larger particles that are not representative of most virus sizes.
3. 0.015–0.2 µm: The lower end of this range is closer to the actual size range of viruses, but 0.015 µm would be unusually small for most viruses.

Here is a table summarizing the size range of different types of viruses:

Answer: Prophage

The viral genome that can become integrated into the bacterial genome is called a prophage. When a bacteriophage inserts its DNA into the bacterial chromosome, it becomes a prophage, and the bacterium containing this integrated phage DNA is referred to as a lysogen.

Incorrect options:

1. Bacteriophage: Bacteriophages are viruses that infect bacteria but may not necessarily integrate into the bacterial genome. A bacteriophage becomes a prophage upon integration.
2. Temperate phage: Temperate phages are bacteriophages that can switch between a lytic and lysogenic cycle, with the lysogenic cycle involving integration into the bacterial genome. The integrated form is then termed a prophage.
3. Metaphage: There isn’t a widely recognized term “metaphage” used in the context of viral integration into the bacterial genome.

Here is a table summarizing the different types of bacteriophages:

Answer: Cell wall

The characteristic shape of bacteria is primarily maintained by the cell wall. The cell wall provides structural support and determines the shape of the bacterium. Different bacterial species have distinct cell wall compositions, which contribute to their varied shapes, such as cocci (spherical), bacilli (rod-shaped), spirilla (spiral-shaped), etc.

Incorrect options:

1. Slime layer: The slime layer (or glycocalyx) is a viscous, gel-like layer outside the cell wall that helps bacteria adhere to surfaces, but it doesn’t primarily contribute to maintaining the characteristic shape.
2. Capsule: Capsules are layers outside the cell wall that protect bacteria from phagocytosis and desiccation, but they don’t play a significant role in determining the basic shape of the bacterium.
3. Cell membrane: While the cell membrane is vital for various cellular functions, it’s not the primary structure responsible for maintaining the characteristic shape of the bacterium.

Answer: Principal sites of respiratory enzymes

Mesosomes are internal structures found in some bacterial cells. These structures were initially thought to be involved in various functions, such as DNA replication, cell division, and as sites for respiratory enzymes. However, their existence and function have been debated, and they are not universally accepted as distinct structures in bacterial cells. Their presence might be artifacts resulting from sample preparation for electron microscopy rather than being actual cell components.

Incorrect options:

1. Kind of ribosomes: Mesosomes are not a type of ribosome. Ribosomes are cellular structures responsible for protein synthesis.
2. Lysis A part of cell wall: Mesosomes are not directly associated with the process of cell lysis or a specific part of the cell wall.
3. Formed during cell: It’s unclear what “formed during cell” refers to. Mesosomes, if present, would be internal structures within bacterial cells, not necessarily formed during a particular phase of cell growth or division.

Answer: S. typhi

Salmonella typhi is the causative agent of typhoid fever, a serious bacterial infection that can be fatal if not treated. It is a Gram-negative, rod-shaped bacterium that is motile by peritrichous flagella.

Klebsiella pneumoniae, Bacillus anthracis, and Shigella are also Gram-negative, rod-shaped bacteria, but they are non-motile.

Answer: 2 – 8%

Moderate anaerobes typically require oxygen in lower amounts than obligate aerobes but more than strict anaerobes. They can tolerate and grow in the presence of limited oxygen levels, roughly around 2-8%. This oxygen range allows them to survive and even use oxygen when available, but they can also switch to fermentation in the absence of oxygen.

Incorrect options:

1. 0%: This percentage indicates the absence of oxygen, which is not suitable for moderate anaerobes. They require at least a limited amount of oxygen for growth.
2. < 0.5%: This minimal amount of oxygen would be too low for moderate anaerobes, as they generally require slightly higher levels to sustain growth.
3. 5-10%: This range is higher than what moderate anaerobes typically require. They prefer lower oxygen concentrations for optimal growth.

Answer: All of These

Lymphocytes are white blood cells that play a vital role in the immune system. They can produce interferon in response to viral infection.
Lymphoblasts are immature lymphocytes. They can also produce interferon in response to viral infection.
Fibroblasts are cells that produce collagen and other proteins that make up connective tissue. They can also produce interferon in response to viral infection.
Interferon is a signaling protein that helps to protect cells from viral infection. It is produced by a variety of cells in the body, including lymphocytes, lymphoblasts, and fibroblasts. When a cell is infected with a virus, it produces interferon, which signals to other cells to produce antiviral proteins. This helps to protect the body from the spread of the virus.

Here is a table summarizing the sources of different types of interferon:

Answer: Differential staining

Gram staining is an example of differential staining. This laboratory technique allows for the differentiation of bacteria into two major groups, Gram-positive and Gram-negative, based on differences in their cell wall compositions. The staining process involves multiple steps and different dyes to distinguish between these two categories of bacteria.

Incorrect options:

1. Simple staining: Simple staining uses a single dye to colorize microorganisms for better visualization under a microscope. Gram staining, in contrast, involves multiple dyes and a multistep process to differentiate bacteria.
2. Negative staining: Negative staining involves using acidic dyes to color the background while leaving the microorganisms unstained, creating a contrast. Gram staining does not utilize negative staining; it specifically aims to differentiate bacteria based on their cell wall characteristics.

Here is a table summarizing the different types of staining techniques and their applications:

Answer: Lysosomes

Autolysis, the process of self-destruction or self-digestion of cells or tissues, is primarily carried out by lysosomes. Lysosomes contain digestive enzymes that break down cellular components or foreign materials, and in certain conditions or after cell death, they can cause autolysis by releasing these enzymes, leading to the breakdown of cellular structures.

Incorrect options:

1. Peroxisomes: Peroxisomes are involved in various metabolic processes, including breaking down fatty acids, but they are not primarily responsible for autolysis.
2. Golgi bodies: Golgi bodies are responsible for modifying, sorting, and packaging proteins and lipids, not for autolysis.
3. Mitochondria: Mitochondria are known as the powerhouses of the cell, producing energy in the form of ATP through cellular respiration. They are not directly involved in autolysis.

Here is a table summarizing the functions of the different organelles listed:

Answer: Ordinarily an aerobe but can grow in absence of O2

A facultative anaerobe is ordinarily an anaerobe but has the capability to grow in the presence of oxygen (O2). These microorganisms can switch between aerobic respiration when oxygen is available and anaerobic metabolism in the absence of oxygen, exhibiting adaptability to both oxygen-rich and oxygen-poor environments.

Incorrect options:

1. Only grow in the presence of O2: This describes obligate aerobes, organisms that require oxygen for growth and cannot survive in the absence of oxygen.
2. Only grow anaerobically: This refers to obligate anaerobes that can only grow in the absence of oxygen and are inhibited or killed in its presence.
3. Ordinarily an aerobe but can grow in absence of O2: This describes aerotolerant anaerobes, which can survive in the presence of oxygen but do not utilize it for growth. Facultative anaerobes, in contrast, can utilize oxygen if it’s available.

Here is a table summarizing the different types of organisms and their oxygen requirements:

Answer: Transduction

The recombination process occurring through the mediation of phages is called transduction. Transduction involves the transfer of bacterial genes from one bacterium to another by a bacteriophage (virus that infects bacteria) acting as a vector. During the phage life cycle, bacterial DNA may be mistakenly packaged into the phage capsid, and when this phage infects another bacterium, it transfers the bacterial DNA, resulting in recombination in the recipient cell.

Incorrect options:

1. Transfection: Transfection involves the introduction of foreign DNA into eukaryotic cells, typically using techniques like electroporation or chemical methods.
2. Conjunction: Conjunction is the process of genetic transfer in bacteria that involves direct cell-to-cell contact via a conjugation bridge, mediated by plasmids.
3. Transformation: Transformation is the genetic alteration of a cell resulting from the direct uptake and incorporation of exogenous genetic material (usually DNA) from the surroundings into the cell.

Here is a table summarizing the different types of horizontal gene transfer: