MicroBiology MCQs with Answer and Explnation | Chapter 48

Answer: TPHA

TPHA is a specific treponemal test used to confirm the presence of Treponema pallidum, the bacteria causing syphilis. Unlike non-treponemal tests like VDRL and Kahn’s, which detect antibodies that can arise from various inflammatory conditions, TPHA directly detects antibodies specific to T. pallidum, providing a more reliable diagnosis.

The other options are incorrect:

• VDRL (Venereal Disease Research Laboratory) and Kahn’s test: These are non-treponemal tests. While they can be good initial screening tests for syphilis due to their sensitivity, they can also produce false positives due to other conditions. Therefore, a positive result on these tests requires confirmation with a specific treponemal test like TPHA.
• Widal test: This test detects antibodies against Salmonella Typhi and Salmonella Paratyphi, bacteria responsible for typhoid and paratyphoid fever. It has no relevance to syphilis or T. pallidum.

Answer: Most common is animals

While Streptococcus bacteria are commonly found in both humans and animals, they are actually more prevalent in animals, particularly in various animal species’ upper respiratory tracts and intestines. Although several Streptococcus species can cause infections in humans, many others contribute to the normal microbiota of animals.

The other options are incorrect:

• It’s a group of lactic acid production bacteria: This statement is true. Streptococcus bacteria are well-known for producing lactic acid during fermentation, contributing to various food products like yogurt and cheese.
• Shows adherence to dental enamel: This statement is also true. Streptococcus mutans, a specific type of Streptococcus, is notorious for adhering to tooth enamel and contributing to dental plaque formation.
• Most common in humans: This statement is incorrect, as explained above. While some Streptococcus species cause common human infections, animals generally harbor a wider diversity and higher overall abundance of these bacteria.

Answer: Binary fission

The vast majority of bacteria reproduce asexually through binary fission. This process involves a single bacterial cell replicating its DNA, elongating, and then dividing into two identical daughter cells. Binary fission is an efficient and rapid mode of reproduction, allowing bacterial populations to grow exponentially under favorable conditions.

The other options are incorrect:

• Budding: This mode of reproduction is typically seen in yeast and some fungi, where a small outgrowth forms on the parent cell and eventually detaches to become a new individual. It is not a common reproductive method for bacteria.
• Sporing: While some bacteria, like Bacillus and Clostridium, can form spores under harsh conditions, this is not their primary mode of reproduction. Spores are dormant structures that allow bacteria to survive unfavorable environments, but they do not directly produce new individuals.
• Bacterial components produced by host cells: This statement is entirely inaccurate. Bacteria are self-replicating organisms and do not rely on host cells for any part of their reproduction process. They synthesize all necessary components within themselves using their own genetic information.

Answer: Pseudomonas aeruginosa

The description of an oxidase-positive, gram-negative rod producing a bluish-green pigment, growing in culture from an infected burn wound, and showing susceptibility to gentamicin, ticarcillin, and tobramycin, is indicative of Pseudomonas aeruginosa.

The other options are incorrect:

• Escherichia coli: Escherichia coli is a gram-negative rod, but it is oxidase-negative, and it does not typically produce a bluish-green pigment. It also may not exhibit the described antibiotic susceptibility profile.
• Klebsiella pneumoniae: Klebsiella pneumoniae is a gram-negative rod, but it is oxidase-negative and does not produce the characteristic bluish-green pigment associated with the described organism.
• Proteus mirabilis: Proteus mirabilis is a gram-negative rod, but it is oxidase-negative and does not produce the bluish-green pigment. Its antibiotic susceptibility profile may also differ.

Answer: Treponema pallidum

Treponema pallidum is the causative organism of syphilis. It is a spirochete bacterium and is oxidase-negative. Syphilis is a sexually transmitted infection caused by this bacterium.

The other options are incorrect:

• Borrelia burgdorferi: Borrelia burgdorferi is the causative agent of Lyme disease, not syphilis. It is transmitted through the bite of infected ticks.
• Chlamydia trachomatis: Chlamydia trachomatis is a bacterium that causes various sexually transmitted infections, but it is not the causative agent of syphilis.
• Leptospira interrogans: Leptospira interrogans is responsible for leptospirosis, a bacterial infection typically transmitted through contact with contaminated water or soil. It is not the causative agent of syphilis.

Answer: Study of organisms that are not visible to naked eyes

Microbiology is the scientific field concerned with the study of microorganisms, also known as microbes. These microbes are living organisms too small to be seen with the unaided human eye, typically measured in micrometers (millionths of a meter). They include diverse groups like bacteria, archaea, viruses, fungi, protozoa, and some algae. Microorganisms play crucial roles in various aspects of life, including decomposition, nutrient cycling, disease, and food production.

The other options are incorrect:

• Study of molecules that are visible to human eyes: This description falls under the field of macromolecular biology or biochemistry, which deal with the structure and function of molecules visible to the naked eye, not whole organisms.
• Study of animals and their family: This definition aligns with zoology, which focuses on the study of animals, their classification, behavior, and evolution. While some larger microorganisms like amoebas might fall under the zoological umbrella, microbiology encompasses a much broader range of microscopic life forms.
• Study of microscope: This refers to microscopy, a technique used to visualize objects too small for the naked eye. While microscopes are essential tools in microbiological research, they are simply instruments, not the subject of study in microbiology itself.

Answer: Antoni van Leeuwenhoek

Antoni van Leeuwenhoek is widely recognized as the “Father of Microbiology” due to his pioneering work in the 17th century. He developed incredibly powerful single-lens microscopes and used them to make groundbreaking discoveries about the microscopic world. He was the first to observe and describe various microorganisms, including bacteria, protozoa, and even sperm cells, laying the foundation for the field of microbiology.

The other options are incorrect:

• Edwin John Butler: Though a renowned Indian mycologist and plant pathologist, his contributions primarily focused on the study of fungi and plant diseases, not the broader field of microbiology.
• Ferdinand Cohn: A significant figure in bacteriology, he contributed to the classification and understanding of bacteria, but his work came later in the 19th century after Leeuwenhoek’s initial discoveries.
• Robert Koch: Another highly influential bacteriologist known for his postulates establishing the germ theory of disease, his work built upon the foundation laid by Leeuwenhoek and further advanced the field of microbiology in the late 19th century.

Answer: Cyanobacteria

Cyanobacteria are the microorganisms among the options that perform photosynthesis by utilizing light. They are a group of bacteria capable of photosynthesis and are often referred to as blue-green algae.

The other options are incorrect:

• Cyanobacteria, Fungi, and Viruses: Fungi and viruses do not perform photosynthesis. Fungi are heterotrophic organisms, obtaining nutrients through absorption, while viruses lack cellular structures and metabolic processes necessary for photosynthesis.
• Viruses: Viruses are not capable of photosynthesis. They lack the cellular machinery and structures required for independent metabolic processes and energy production.
• Fungi: Fungi are heterotrophic organisms that obtain nutrients by absorbing organic material from their environment. They do not possess the capability for photosynthesis.

Answer: Condenser lens

The condenser lens in a compound microscope plays a crucial role in gathering and focusing light rays onto the specimen. It is located beneath the stage and above the light source. By adjusting the condenser lens, you can control the intensity and concentration of light illuminating the specimen, leading to a clearer and more detailed image.

The other options are incorrect:

• Magnifying lens: While magnifying lenses within the objective and eyepiece contribute to the overall magnification of the image, they do not directly focus light on the specimen.
• Objective lens: The objective lens is located closest to the specimen and provides the initial magnification. However, it relies on the light already focused by the condenser lens to create a clear image.
• Eyepiece lens: The eyepiece lens further magnifies the image formed by the objective lens, but it does not manipulate the light rays themselves.

Answer: All of the mentioned

Microorganisms, particularly bacteria, yeasts, and fungi, play a crucial role in the production of various food items. They utilize their metabolic processes to transform ingredients into desired products with distinct flavors, textures, and nutritional profiles.

• Alcoholic beverages: Yeasts ferment sugars present in fruits and grains, converting them into alcohol and carbon dioxide. This process forms the basis for producing beers, wines, and spirits.
• Fermented dairy products: Bacteria like Lactobacillus and Streptococcus ferment lactose (milk sugar) into lactic acid, giving rise to yogurt, cheese, kefir, and other fermented dairy products.
• Breads: Yeasts ferment sugars in dough, producing carbon dioxide that causes the bread to rise. Additionally, some bread-making processes involve bacteria that contribute to flavor development.

Answer: 0.5 to 1.0 micrometer in diameter

Bacterial cells are incredibly tiny, much smaller than human cells. Their size typically ranges from 0.5 to 1.0 micrometer (μm) in diameter, which is equivalent to 0.0005 to 0.001 millimeters. This means they are invisible to the naked eye and require microscopes for visualization.

The other options are incorrect:

• 1mm in diameter: This is 1,000 times larger than the typical size of a bacterial cell. It is closer to the size of some of the largest eukaryotic cells, like amoebas or certain plant cells.
• 2mm in diameter: Similar to the previous option, this is significantly larger than the typical bacterial size.
• 2 micrometer in diameter: While closer to the actual range, this is still slightly larger than the average diameter of most bacterial cells.

Answer: Shortest wavelength of visible light used and an objective with the maximum numerical aperture

The resolution in light microscopy is determined by the wavelength of the light used and the numerical aperture of the objective lens. Shorter wavelengths provide higher resolution, and a higher numerical aperture allows for better light-gathering ability. Therefore, using the shortest wavelength of visible light and an objective with the maximum numerical aperture together will result in the greatest resolution in light microscopy.

The other options are incorrect:

• Shortest wavelength of visible light used: Incorrect because shorter wavelengths actually contribute to higher resolution, not lower.
• Longest wavelength of visible light used: Incorrect because longer wavelengths result in lower resolution in light microscopy.
• An objective with minimum numerical aperture: Incorrect because a higher numerical aperture is essential for achieving better resolution.

Answer: electron beams and magnetic fields

Unlike optical microscopes that utilize visible light, electron microscopes employ a beam of electrons to illuminate and magnify objects. These electron beams are generated by an electron gun and then focused and manipulated using magnetic fields generated by electromagnets. The interaction of these electrons with the sample reveals information about its structure and composition, allowing for incredibly high magnification and resolution.

The other options are incorrect:

• Light waves: Optical microscopes use light waves for illumination, not electron microscopes.
• Magnetic fields: While magnetic fields are crucial for manipulating the electron beam, they alone wouldn’t be sufficient for generating images.
• Electron beams: While electron beams are indeed essential, they require the guiding and focusing power of magnetic fields to form meaningful images.

Answer: Treponema pallidum

Spirochetes are a group of spiral-shaped bacteria, and Treponema pallidum is one of the examples of spirochetes. Spirochetes are characterized by their helical shape and unique means of motility, often using axial filaments (endoflagella) within their periplasmic space.

The other options are incorrect:

• Streptomyces sp.: Streptomyces sp. is not a spirochete; it belongs to the Actinobacteria group and is known for its filamentous, branching growth.
• Spirillum volutans: Spirillum volutans is a spiral-shaped bacterium, but it is not classified as a spirochete. It belongs to the genus Spirillum.
• Corynebacterium diphtheriae: Corynebacterium diphtheriae is a rod-shaped bacterium and does not have the characteristic spiral shape of spirochetes. It causes diphtheria and belongs to the Corynebacterium genus.

Answer: Amphitrichous

The arrangement of flagella on a bacterial cell is an important taxonomic characteristic and can affect its motility and behavior. Amphitrichous bacteria have two clusters of flagella, one at each pole of the cell. This arrangement allows them to move in a bipolar fashion, meaning they can change direction quickly and efficiently.

The other options are incorrect:

• Monotrichous: These bacteria have only one flagellum, typically at one end of the cell
• Peritrichous: These bacteria have flagella distributed all over their cell surface.
• Lophotrichous: These bacteria have a single cluster of flagella located at one pole or both poles of the cell.

Answer: cytoplasmic membrane

The bacterial respiratory chain, also known as the electron transport chain, is a series of protein complexes embedded within the cytoplasmic membrane. These complexes transfer electrons from various donor molecules, like carbohydrates or proteins, to final electron acceptors, often oxygen. As electrons move through the chain, energy is released and used to create a proton gradient across the membrane. This gradient then powers the production of ATP (adenosine triphosphate), the primary energy currency of the cell.

The other options are incorrect:

• Cell wall: The cell wall provides structural support and protection to the bacterial cell but is not directly involved in energy production.
• Cytoplasm: The cytoplasm houses various cellular components and processes but doesn’t contain the specific protein complexes needed for the respiratory chain.
• Mitochondrial membrane: This membrane surrounds the mitochondria in eukaryotic cells, which contain their own respiratory chain. Bacteria, however, lack mitochondria and utilize a separate respiratory chain located on their cytoplasmic membrane.

Answer: both aerobic and anaerobic cells

Glycolysis is the initial phase of cellular respiration that occurs in the cytoplasm, and it can take place in both aerobic and anaerobic cells. Glycolysis involves the breakdown of glucose into pyruvate, producing ATP and NADH in the process. While glycolysis is followed by different pathways depending on the availability of oxygen, it is a common pathway in both aerobic and anaerobic metabolism.

The other options are incorrect:

• Anaerobic cells only: While anaerobic cells primarily rely on glycolysis for energy production, aerobic cells also use it as the initial step in their energy-generating pathways.
• Aerobic cells only: As mentioned earlier, glycolysis occurs in both aerobic and anaerobic conditions. It serves as the foundation for both aerobic and anaerobic respiration.
• Neither aerobic and anaerobic cells: This option is completely incorrect. Glycolysis is a fundamental process utilized by both types of cells for energy production.

Answer: DNA polymerase I

DNA polymerase I possesses both polymerase and exonuclease activities. Its 5′-nuclease activity specifically degrades nucleotides from the 5′ end of a DNA strand. During DNA replication, this activity is crucial for removing the RNA primer, a short RNA sequence that initiates DNA synthesis on the lagging strand. After removing the primer, DNA polymerase I also fills the gap with DNA nucleotides using its polymerase activity.

The other options are incorrect:

• DNA polymerase III: Primarily responsible for DNA synthesis during replication, not involved in primer removal.
• RNA polymerase: Transcribes DNA into RNA, not involved in DNA replication processes like primer removal.
• DNA polymerase II: Primarily involved in DNA repair mechanisms, not specifically involved in removing RNA primers.

Answer: All of the mentioned

Phosphorus, a vital element for life, has numerous roles in biological systems. It’s found in several key molecules:

• Phospholipids: Form the major constituents of cell membranes, providing structure and fluidity.
• Teichoic acid: Found in the cell walls of certain bacteria, contributing to structure and immune defense.
• Nucleotides: The building blocks of DNA and RNA, responsible for genetic information storage and transfer.

Answer: Mesophile

Staphylococcus aureus is classified as a mesophile because it thrives at moderate temperatures, typically between 30°C and 37°C (86°F and 98.6°F). This range corresponds to the human body temperature, where S. aureus commonly colonizes the skin and nasal passages.

The other options are incorrect:

• Psychrophile: These bacteria prefer cold environments, typically below 15°C (59°F), and wouldn’t survive the human body temperature favorable for S. aureus.
• Thermophile: Thriving in hot environments above 45°C (113°F), these bacteria wouldn’t tolerate the moderate temperatures at which S. aureus grows.
• Mesophile and psychrophile: While S. aureus is a mesophile, it’s not a psychrophile. It cannot survive and grow in cold environments.

Answer: an increase in number of cells

Bacterial growth, like the growth of most single-celled organisms, primarily refers to an increase in their number. This increase occurs through reproduction, where single cells divide and create new daughter cells. Unlike multicellular organisms that grow primarily by increasing the size of individual cells, bacterial growth focuses on cell number multiplication.

The other options are incorrect:

• Changes in the total population: While this is certainly a consequence of bacterial growth, it’s not the specific definition itself. It merely reflects the outcome of increasing individual cell numbers.
• An increase in the size of an individual organism: This is not how bacteria grow. They don’t enlarge existing cells; they reproduce to create more cells.
• An increase in the mass of an individual organism: Similar to the previous point, bacterial growth doesn’t involve significant size changes in individual cells. The increase in mass primarily reflects the combined mass of the increasing cell population.

Answer: Pour-plate and spread plate

Both pour plate and spread plate techniques involve diluting a bacterial sample and then culturing it on an agar plate. The resulting colonies that grow on the plate represent individual bacterial cells that were present in the original sample. By counting the number of colonies and considering the dilution factor, you can estimate the total number of bacteria in the original sample.

The other options are incorrect:

• Spread-plate: The spread plate method is actually a correct option for quantitative determination of bacterial numbers.
• Streak-plate: The streak plate method is used for isolating pure cultures but is not ideal for quantitative determination of bacterial numbers.
• Pour-plate: The pour plate method is a correct option for quantitative determination of bacterial numbers.

Answer: chitin

While fungi share some similarities with plants in having cell walls, their composition differs significantly. The key structural component of the fungal cell wall is chitin, a complex polysaccharide composed of N-acetylglucosamine units linked by β-1,4 glycosidic bonds. Chitin provides rigidity, shape, and protection to the fungal cell.

The other options are incorrect:

• Peptidoglycan: This polysaccharide-peptide complex forms the cell wall of bacteria, not fungi.
• Cellulose: While some fungi can produce cellulose, it’s not a major component of their cell walls. It’s more commonly found in the cell walls of plants.
• Chitin, cellulose, or hemicellulose: While it’s true that chitin is essential, the other two options are not major components of fungal cell walls. Hemicellulose is more associated with plant cell walls.

Answer: mycotic infection

Cryptococcosis is a disease caused by fungi, specifically the Cryptococcus species. It is a fungal infection, making it a mycotic infection. Cryptococcus neoformans is the main pathogenic species associated with human cryptococcosis, and it commonly affects individuals with compromised immune systems.

The other options are incorrect:

• Viral infection: Cryptococcosis is not caused by a virus. Viruses are much smaller and lack the complex cellular structure of fungi.
• Parasitic infection: This disease is not caused by parasites, which are multicellular organisms that live on or within another organism.
• Bacterial infection: Bacteria are also single-celled organisms, but they lack the unique characteristics of fungi like a cell wall made of chitin and the ability to produce yeasts and hyphae.

Answer: Prototheca

While most algae are beneficial or harmless to humans, Prototheca can cause infections under certain circumstances. These algae are single-celled and belong to the genus Chlorophyceae (green algae). They typically live in soil and water but can opportunistically infect humans with weakened immune systems, particularly those with compromised skin (e.g., dermatitis).

The other options are incorrect:

• Cephaleuros: This genus of green algae typically grows on leaves and other plant surfaces, primarily causing aesthetic damage and rarely affecting humans.
• Acanthopeltis: These are unicellular flagellate algae found in marine and freshwater environments and are not known to cause any human diseases.
• Chlorella: This green alga is often used as a dietary supplement and considered safe for human consumption. While some allergic reactions have been reported, it doesn’t typically cause pathogenic infections.

Answer: holozoic

Protozoa that obtain their food by ingesting other organisms are classified as holozoic. This mode of nutrition involves capturing, engulfing, and digesting other microorganisms, such as bacteria, algae, or even other protozoa.

The other options are incorrect:

• Parasitic: While some protozoa are indeed parasitic, relying on a host organism for survival, not all protozoa that eat other organisms are parasitic. Some live freely in the environment and prey on other microorganisms independently.
• Mutualistic: Mutualistic relationships involve two organisms living together with a mutually beneficial interaction. While some protozoa engage in mutualistic partnerships with other organisms, those that eat other organisms wouldn’t fall under this category.
• Saprophytic: Saprophytic organisms obtain their nutrients from dead and decaying organic matter. Protozoa that actively prey on other organisms wouldn’t be considered saprophytic.

Answer: Multiple fission

Plasmodium, the parasite responsible for malaria, exhibits a complex life cycle that alternates between a female Anopheles mosquito and a vertebrate host (typically humans). During its asexual replication phase within the vertebrate host’s red blood cells, Plasmodium reproduces mainly through multiple fission.

The other options are incorrect:

• Regeneration: Plasmodium doesn’t regenerate lost body parts or reconstruct itself from fragments.
• Budding: While some unicellular organisms like yeast reproduce by budding, this mode isn’t observed in Plasmodium.
• Binary fission: Binary fission involves dividing into two identical daughter cells. While Plasmodium might undergo a few initial binary fissions after entering the red blood cell, it primarily utilizes multiple fission for further multiplication.

Answer: prophage

When viral DNA becomes associated with the bacterial chromosome, it enters a dormant state and integrates itself into the host’s DNA. This integrated viral DNA is called a prophage. The prophage doesn’t actively replicate or produce new viruses, but it gets replicated along with the bacterial chromosome as the cell divides. Under certain conditions, the prophage can become active and initiate the viral replication cycle, leading to cell lysis and release of new viruses.

The other options are incorrect:

• Plasmid: Plasmids are small, circular pieces of DNA that exist independently of the bacterial chromosome. They can carry additional genes and replicate on their own, but they are not viral DNA integrated into the chromosome.
• Plaque: A plaque is a clear zone of dead bacteria on a culture plate caused by infection with a bacteriophage (virus that infects bacteria). It’s not a specific structure of the viral DNA itself.
• Gene: A gene is a unit of inheritance that carries the instructions for a specific protein. While the prophage contains genes, it’s not just a single gene but rather a whole segment of viral DNA integrated into the chromosome.

Answer: Jenner

Edward Jenner is widely recognized as the father of vaccination. In 1796, he developed the first successful vaccine against smallpox, a deadly and highly contagious disease. His groundbreaking work involved inoculating a young boy with cowpox, a milder related virus, which provided immunity to the much more severe smallpox. This discovery revolutionized public health and paved the way for the development of numerous vaccines for other diseases, saving countless lives worldwide.

The other options are incorrect:

• Watson: James Watson, along with Francis Crick, made a significant contribution to science by discovering the structure of DNA in 1953. While DNA plays a crucial role in understanding how vaccines work, their discovery did not directly invent vaccination.
• Crick: Similar to Watson, Francis Crick was part of the duo that unveiled the structure of DNA in 1953. While their work is foundational to modern biology and genetics, it wasn’t directly connected to the invention of vaccination.
• Pasteur: Louis Pasteur was a renowned microbiologist and immunologist who made groundbreaking discoveries in vaccines for rabies, anthrax, and other diseases. However, he wasn’t the first to invent the concept of vaccination, although his later contributions significantly advanced the field.

Answer: Measles

The measles vaccine, developed in the 1960s, is now produced using modern continuous cell lines, which are essentially immortalized versions of animal or human cells grown in tissue culture. This means the virus can be grown in large quantities without relying on animal hosts, ensuring consistent quality and safety.

The other options are incorrect:

• Smallpox: The smallpox vaccine was historically grown in the skin of cows using a technique called scarification. However, since smallpox was declared eradicated in 1980, vaccine production has ceased.
• Rabies: The rabies vaccine, developed by Louis Pasteur in the 1880s, originally used rabbit nerve tissue for virus growth. However, modern rabies vaccines primarily use continuous cell lines for production.
• Mumps: The mumps vaccine, available since the 1960s, utilizes chick embryo fibroblasts for virus propagation. While not tissue culture in the strictest sense, it involves growing the virus in chicken embryos rather than using live animals.

Answer: UV light

UV (ultraviolet) light can inhibit DNA replication by causing damage to the DNA molecule. UV light induces the formation of thymine dimers, where adjacent thymine bases on the same DNA strand become covalently bonded. This thymine dimer formation disrupts the normal DNA structure and function, including the ability to undergo replication.

The other options are incorrect:

• x-rays: X-rays can cause damage to DNA, but their mechanism of action is different from UV light. X-rays primarily cause ionization of atoms, leading to the formation of free radicals that can damage DNA.
• gamma rays: Similar to x-rays, gamma rays can cause damage to DNA through ionization. Gamma rays have high energy and can penetrate deeply into tissues, causing damage to cellular structures.
• cathode rays: Cathode rays are streams of electrons, and while they can cause ionization and damage to biological molecules, their impact on DNA replication is not as significant as that of UV light.

Answer: Syphilis

Syphilis was the first disease for which a chemotherapeutic agent, specifically Salvarsan (arsphenamine), was used. Salvarsan, developed by Paul Ehrlich in 1909, was an arsenic-based compound that proved effective against Treponema pallidum, the bacterium responsible for syphilis.

The other options are incorrect:

• Smallpox: Smallpox was not the first disease for which a chemotherapeutic agent was used. The development of Salvarsan for syphilis predates the use of antiviral drugs against smallpox.
• AIDS: Acquired Immunodeficiency Syndrome (AIDS) is caused by the human immunodeficiency virus (HIV). The first chemotherapeutic agents used for HIV/AIDS were developed later than Salvarsan, making AIDS an incorrect choice for the first disease treated with such agents.
• Malaria: While antimalarial drugs have been crucial in the treatment of malaria, the development of Salvarsan for syphilis predates the development of antimalarials. Malaria is not the first disease for which a chemotherapeutic agent was used.

Answer: spherical

When bacterial cells are grown in a medium exposed to high osmotic pressure, they undergo a change in shape from rod-shaped to spherical. This phenomenon is known as coccus conversion or osmotic lysis. The increased osmotic pressure causes the cell to take on a more spherical or coccus shape.

The other options are incorrect:

• Elongated: While some studies suggest slight elongations in specific species under very high osmotic pressure, the predominant shape change is towards sphericity due to the need to preserve cell wall integrity.
• Rod-shaped: The initial shape is rod-shaped, but under high osmotic pressure, this shape changes due to plasmolysis and cell wall bulging.
• Irregular: While the sphericity might not be perfectly round, the overall shape becomes more spherical under high osmotic pressure, not truly irregular.

Answer: Gram-positive organisms

Tyrocidines are cyclic decapeptide antibiotics produced by the bacterium Bacillus brevis. They are more effective against Gram-positive organisms. Tyrocidines disrupt bacterial cell membranes, leading to lysis, and are particularly effective against bacteria with a Gram-positive cell wall structure.

The other options are incorrect:

• Gram-negative organisms: Tyrocidines are less effective against Gram-negative organisms. The outer membrane of Gram-negative bacteria provides a barrier that makes them more resistant to these peptides.
• Spirochetes: While tyrocidines may have some antimicrobial activity against certain bacteria, they are not specifically known for being effective against spirochetes.
• Mycoplasmas: Tyrocidines are not particularly known for their effectiveness against Mycoplasmas. Mycoplasmas lack a cell wall, and their susceptibility to antibiotics can vary.

Answer: Biological assay

The most accurate method for microbial assay of antibiotics is the biological assay. This method evaluates the potency of antibiotics by measuring their ability to inhibit the growth of a specific microorganism. The response of the microorganism to the antibiotic is observed, and the concentration of the antibiotic that produces a specified effect is determined.

The other options are incorrect:

• Chemical and biological assay: While chemical assays can provide information about the chemical composition of antibiotics, the most accurate determination of their potency is achieved through biological assays that involve testing against specific microorganisms.
• Chemical assay: Chemical assays focus on the chemical properties and composition of the antibiotic but may not accurately reflect their biological activity or potency against microorganisms.
• Physical assay: Physical assays typically measure physical properties of substances, and they are not the most suitable method for assessing the antimicrobial potency of antibiotics. Biological assays are more specific for this purpose.

Answer: Nitrospina gracilis

Nitrospina gracilis is not an ammonia-oxidizing bacteria. It belongs to the genus Nitrospina and is a nitrite-oxidizing bacteria (NOB). Unlike ammonia-oxidizing bacteria (AOB) that convert ammonia (NH3) to nitrite (NO2-), Nitrospina gracilis oxidizes nitrite to nitrate (NO3-).

The other options are incorrect:

• Nitrosococcus oceanus: This bacterium belongs to the genus Nitrosococcus and is indeed an ammonia-oxidizing bacteria. It plays a crucial role in the marine nitrogen cycle by converting ammonia into nitrite.
• Nitrosomonas europaea: Similar to Nitrosococcus oceanus, this bacterium belongs to the genus Nitrosomonas and is an ammonia-oxidizing bacteria commonly found in soil and water environments.
• Nitrosovibrio tenuis: This bacterium belongs to the genus Nitrosovibrio and falls under the category of ammonia-oxidizing bacteria. It is known for its ability to tolerate low oxygen conditions.

Answer: cellulase

Cellulase is the enzyme responsible for degrading cellulose, a complex polysaccharide composed of glucose units linked by β-1,4-glycosidic bonds. Cellulase breaks down these bonds, releasing smaller units of sugar, including cellobiose, which consists of two glucose molecules linked by a β-1,4-glycosidic bond.

The other options are incorrect:

• Cellulose dehydrogenase: This enzyme oxidizes the C1 and C6 hydroxyl groups of cellulose, but it doesn’t break down the glycosidic bonds. It plays a role in modifying cellulose for further degradation by other enzymes.
• Hexokinase: This enzyme phosphorylates glucose, converting it into glucose-6-phosphate. While it plays a role in glucose metabolism, it doesn’t target cellulose or cellobiose.
• Beta-glucosidase: This enzyme specifically breaks down β-1,4-glycosidic bonds in cellobiose, releasing two glucose molecules. However, it doesn’t directly degrade cellulose itself.

Answer: Desulfotomaculum sp.

Desulfotomaculum species are bacteria belonging to the group of sulfate-reducing bacteria (SRB). They play a crucial role in the global sulfur cycle by using sulfates (SO4²⁻) as electron acceptors during their anaerobic respiration. During this process, they reduce sulfates to hydrogen sulfide (H2S).

The other options are incorrect:

• Thiobacillus thiooxidans: This bacterium belongs to the group of sulfur-oxidizing bacteria. Contrary to Desulfotomaculum, they oxidize sulfur compounds like hydrogen sulfide or thiosulfate to sulfates, not the other way around.
• Rhodospirillum: These bacteria are photosynthetic and utilize light energy for their metabolism. While some species can use hydrogen sulfide as an electron donor, they don’t reduce sulfates to hydrogen sulfide.
• Photosynthetic sulfur bacteria: This broad term encompasses various groups of bacteria that use light and sulfur compounds for their energy source. However, not all of them specifically reduce sulfates to hydrogen sulfide. Some use other sulfur compounds like thiosulfate or elemental sulfur.

Answer: below 1 percent

Microorganisms from lakes and rivers are typically adapted to freshwater environments. Therefore, they can generally grow at salt concentrations below 1 percent. These organisms are considered to be freshwater microorganisms and may face challenges in environments with higher salt concentrations.

The other options are incorrect:

• above 1 percent: Microorganisms from lakes and rivers are not well-adapted to high salt concentrations, so growth above 1 percent salt concentration may inhibit their growth.
• 2.5 to 4 percent: This range of salt concentration is higher than what is typically found in freshwater environments, and microorganisms from lakes and rivers may struggle to grow under such conditions.
• 5 percent: A salt concentration of 5 percent is considered relatively high, and microorganisms from freshwater environments would likely face significant challenges or inhibition of growth at this level.

Answer: appendaged bacteria

 These bacteria, like Hyphomicrobium and Magnetococcus, have unique appendages or stalks that allow them to attach to surfaces and scavenge for nutrients more efficiently in resource-limited environments. These appendages can also increase their surface area for nutrient uptake.

The other options are incorrect:

• Viruses: Viruses are not organisms and don’t have their own metabolism. They rely on host cells for survival and reproduction, so they would be less likely to thrive in areas with scarce resources.
• Coliforms: These bacteria are indicators of fecal contamination and typically prefer richer environments with organic matter. While some coliforms may be present in estuaries, their abundance would likely be lower in nutrient-poor regions.
• Fecal streptococci: Similar to coliforms, these bacteria also thrive in environments with organic matter and are associated with fecal pollution. Their presence would be less likely in nutrient-poor estuarine regions.

Answer: Secondary treatment

Secondary wastewater treatment involves the biological degradation of organic matter present in the wastewater. This process primarily relies on the activity of microorganisms, which break down organic compounds into simpler substances like carbon dioxide, water, and ammonia. This decomposition process occurs through aerobic oxidation, meaning oxygen is required for the microorganisms to function.

The other options are incorrect:

• Primary treatment: This stage focuses on the physical removal of suspended solids through sedimentation and skimming. While some organic matter may be removed along with the solids, oxidation is not the primary mechanism of action.
• Final treatment: This stage typically involves disinfection and nutrient removal to further polish the treated wastewater before discharge. Oxidation might play a role in some specific nutrient removal processes, but it’s not the main focus of this stage.
• Advanced treatment: This stage can involve various additional processes depending on the specific needs of the wastewater treatment plant. While some advanced treatments might utilize oxidation for specific purposes (e.g., ozone disinfection), it’s not a defining characteristic of this stage.

Answer: Micrococci

Micrococci, specifically Micrococcus luteus and Micrococcus varians, are the most common microorganisms found in the ducts of cow’s mammary glands and dairy utensils. They are acid-producing and weakly proteolytic, meaning they can break down proteins to some extent. While they are not harmful in small numbers, they can contribute to spoilage of milk and dairy products if their population grows too large.

The other options are incorrect:

• Microbacteria: These bacteria are also found in dairy environments, but they are typically associated with the skin and hair of cows rather than the mammary glands themselves.
• Lactobacilli: These are beneficial bacteria commonly found in fermented dairy products like yogurt and cheese. However, they are not naturally present in the mammary glands in significant numbers.
• Coliforms: These bacteria are indicators of fecal contamination and are generally not found in healthy mammary glands. Their presence would suggest unsanitary conditions and potential health risks.

Answer: Clostridium botulinum

Canned foods undergo a sterilization process involving high heat and pressure. This process effectively eliminates most microorganisms, including the highly dangerous Clostridium botulinum. This bacterium produces a potent neurotoxin, botulinum toxin, which can cause botulism, a potentially fatal foodborne illness. The canning process ensures that any Clostridium botulinum spores present are destroyed, preventing toxin production and protecting consumers.

The other options are incorrect:

• Lactobacillus: These are beneficial bacteria commonly found in fermented foods like yogurt and sauerkraut. They are not harmful and can even contribute to the preservation of certain food products. In fact, some canned foods may even contain Lactobacillus cultures to enhance flavor and texture.
• Mycobacterium tuberculosis: This bacterium causes tuberculosis, a serious respiratory illness. While it can survive in some environments like milk, it is not typically associated with canned foods and is effectively eliminated by the canning process.
• Coxiella burnetii: This bacterium causes Q fever, primarily transmitted through inhalation of contaminated aerosols from animals. It is not typically found in canned foods and is unlikely to be present in significant numbers to pose a threat.

Answer: proteins

When bacteria grow on hydrocarbon wastes from the petroleum industry, they utilize these carbon-rich compounds as their primary energy source. They break down the hydrocarbons through metabolic processes and use the carbon skeletons to build various cellular components, including proteins.

The other options are incorrect:

• Fats: While bacteria can synthesize some fats, especially under certain conditions, the primary emphasis when utilizing hydrocarbons is often on protein production. Hydrocarbons provide a good source of carbon and energy for building proteins, which are essential for bacterial growth and reproduction.
• Vitamins: Bacteria generally synthesize their own vitamins or acquire them from the environment. While some specific vitamins might be produced in certain scenarios, they are not typically the main products of bacterial growth on hydrocarbons.
• Carbohydrates: Similar to vitamins, bacteria can synthesize their own carbohydrates or take them up from the environment. Hydrocarbons don’t readily provide the building blocks for carbohydrate synthesis, so their production is less likely in this context.

Answer: Leuconostoc mesenteroides

Leuconostoc mesenteroides is a gram-positive, lactic acid bacterium (LAB) well-known for its ability to produce dextran, a high-molecular-weight polysaccharide composed of glucose units. Dextran production occurs when L. mesenteroides utilizes sucrose as a carbon source and synthesizes dextran as a storage product. This bacterium is commonly used in the food industry for dextran production and also plays a role in the fermentation of various food products like sauerkraut and kimchi.

The other options are incorrect:

• Streptomyces olivaceus: This bacterium belongs to the genus Streptomyces, known for producing various antibiotics and other secondary metabolites. While some Streptomyces species can produce polysaccharides, dextran production is not a characteristic feature of S. olivaceus.
• Bacillus thuringiensis: This bacterium is commonly used as a biopesticide due to its production of insecticidal crystal proteins. It does not have the metabolic pathways or enzymes necessary for dextran synthesis.
• Bacillus polymyxa: Similar to B. thuringiensis, this bacterium also belongs to the genus Bacillus and is known for producing antibiotics and antifungal compounds. It lacks the ability to produce dextran.

Answer: Streptococcus thermophilus

The principal microorganism for yogurt is Streptococcus thermophilus. Along with Lactobacillus bulgaricus, which is not listed as an option, Streptococcus thermophilus is a key bacterial species used in the fermentation of milk to produce yogurt. These bacteria metabolize lactose to produce lactic acid, contributing to the characteristic texture and flavor of yogurt.

The other options are incorrect:

• Leuconostoc citrovorum: Leuconostoc citrovorum is not a principal microorganism for yogurt fermentation. It is not commonly used in yogurt production.
• Streptococcus lactis: While Streptococcus thermophilus is used in yogurt fermentation, Streptococcus lactis is not a typical species used for yogurt production.
• Lactobacillus acidophilus: Lactobacillus acidophilus is a beneficial bacteria that is often used in the production of probiotic foods, but it is not a principal microorganism for the traditional fermentation of yogurt.

Answer: Candida utilis

Candida utilis is a yeast that can be used to produce microbial protein. It is an industrial yeast strain that is commonly employed for the production of single-cell protein (SCP). Single-cell protein refers to the use of microorganisms, such as Candida utilis, as a protein-rich food source for humans and animals.

The other options are incorrect:

• Eremothecium ashbyi: Eremothecium ashbyi is a yeast species, but it is not commonly used for the production of microbial protein.
• Saccharomyces cerevisiae: Saccharomyces cerevisiae is a well-known yeast used in baking and brewing but is not typically employed for large-scale microbial protein production.
• Candida milleri: Candida milleri is a yeast species, but it is not as widely used for microbial protein production as Candida utilis. Candida utilis is more recognized for its application in SCP production.

Answer: intercalating agents

Acridine orange is an intercalating agent, a type of mutagen that inserts itself between the base pairs of DNA, causing errors during replication. These errors can lead to mutations, which are changes in the genetic code.

The other options are incorrect:

• Chemical compounds: While this is technically true, it is a very broad category. Intercalating agents are a specific type of chemical mutagen with a distinct mechanism of action.
• Transposons: These are mobile genetic elements that can move around within the genome, but they don’t directly insert themselves into DNA like intercalating agents.
• Base analogs: These are molecules that resemble natural DNA bases and can be incorporated into the DNA during replication, leading to mispairing and mutations. However, acridine orange does not belong to this category.

Answer: Gram-negative bacteria

Lipopolysaccharide (LPS) is a complex molecule found in the outer membrane of Gram-negative bacteria. It plays a crucial role in maintaining the cell wall structure, protecting the bacterium from environmental stresses, and acting as a virulence factor.

The other options are incorrect:

• Algae: Algae do not have cell walls with a similar structure to bacterial cell walls. Their cell walls are typically composed of cellulose or other polysaccharides, not containing LPS.
• Fungi: Fungi have cell walls composed of chitin, a complex polysaccharide not found in bacteria. They lack the outer membrane structure characteristic of Gram-negative bacteria and therefore do not possess LPS.
• Gram-positive bacteria: These bacteria have a thick cell wall composed primarily of peptidoglycan, a polymer not present in the outer membrane of Gram-negative bacteria. They lack the outer membrane and lipopolysaccharide component.

Answer: ribitol or glycerol residues

Teichoic acids are complex polymers found in the cell walls of Gram-positive bacteria. They are composed of repeating units of either ribitol phosphate or glycerol phosphate, linked together by phosphodiester bonds. Additionally, these units may be further substituted with various carbohydrates, such as glucose or galactose.

The other options are incorrect:

• Glycerol residues: While teichoic acids can contain glycerol residues, their presence is not universal. Some teichoic acids are exclusively composed of ribitol phosphate.
• Ribitol residues: Similar to glycerol, ribitol residues can be present in teichoic acids, but not all types necessarily contain them.
• Glucose residues: While glucose can be attached as a sugar substituent to teichoic acids, it is not a core component of the backbone polymer itself.