MicroBiology MCQs with Answer and Explanations | Chapter 70

Answer: Sabouraud’s medium

Sabouraud’s medium is a specifically formulated culture medium designed to promote the growth of fungi. It contains a rich source of carbohydrates (like dextrose) that fungi readily utilize for energy, along with other essential nutrients for fungal development.

The other options are incorrect:

• Nutrient agar: This is a general-purpose medium suitable for growing a wide variety of bacteria but might not provide the optimal nutrients or pH for fungal growth.
• Nutrient broth: Similar to nutrient agar, this is a general-purpose liquid medium for bacteria and may not be ideal for the specific needs of most fungi.
• Minimal agar medium: This type of medium is designed to be very basic, containing only the essential nutrients required for microbial growth. While some fungi might grow on minimal agar, Sabouraud’s medium offers a richer and more favorable environment for most fungal species.

Answer: All of these

D. pneumoniae (Streptococcus pneumoniae) is a versatile bacterium that can be cultivated on a variety of media depending on the specific needs of the test. Here’s a breakdown of the options and their suitability for D. pneumoniae:

• Glucose broth: This simple broth provides a basic environment with a readily available carbon source (glucose) for D. pneumoniae growth. It’s useful for initial culturing or enrichment before further identification.
• Serum broth: This broth is enriched with animal serum, providing additional nutrients that can enhance the growth of D. pneumoniae. It’s particularly helpful for fastidious (needing specific conditions) strains.
• Agar and blood agar: D. pneumoniae can be grown on solid media like agar plates. Blood agar provides additional nutrients from red blood cells and allows for the observation of hemolytic properties (blood cell lysis) of D. pneumoniae, which can be a helpful identification clue.

Answer: None of these

Streptococcus pneumoniae is typically identified through various laboratory methods, including microscopic examination of clinical specimens (e.g., sputum, blood), culture of these specimens on appropriate media, and biochemical tests. Animal inoculation is not a common method for the identification of S. pneumoniae and is not routinely used due to ethical concerns and the availability of other diagnostic techniques.

The other options are incorrect:

• Microscopic exam: While microscopic examination of clinical specimens can provide preliminary information about the presence of S. pneumoniae (e.g., Gram stain morphology), it is not sufficient for definitive identification.
• Culture of sputum/blood: Culturing clinical specimens such as sputum or blood on appropriate media can facilitate the growth and isolation of S. pneumoniae. However, culture alone may not provide definitive identification and usually requires additional tests.
• Animal inoculation: Animal inoculation involves the introduction of clinical specimens into laboratory animals to observe disease symptoms.

Answer: Moller’s staining

Moller’s staining method is used for differential staining of bacterial spores. It involves staining the bacterial cells with malachite green, which selectively stains the spores, followed by counterstaining with safranin or basic fuchsin to stain the vegetative cells.

The other options are incorrect:

• Albert’s staining: There is no widely recognized staining method known as “Albert’s staining” specifically related to the staining of bacterial spores.
• Lugol’s staining: Lugol’s iodine solution is commonly used as a mordant in Gram staining to enhance the crystal violet-iodine complex formation. It is not specifically related to the staining of bacterial spores.
• Indian ink preparation: Indian ink preparation is not a staining method for bacterial spores. It is used for negative staining techniques, such as the negative staining of capsules, but it is not related to spore staining.

Answer: All of these

Electron microscopy (EM) is a powerful tool that allows scientists to visualize the ultrastructure of bacterial spores in great detail. By utilizing EM, researchers can identify and differentiate the various components of a bacterial spore, including:

• Core: This central region contains the bacterial DNA and ribosomes, essential for germination and spore revival.
• Spore cortex: This layer surrounds the core and is composed of peptidoglycan, providing structural support and contributing to the spore’s resistance.
• Capsule (Exosporium): While not present in all bacterial spores, some species have an external capsule made of protein or polysaccharides. It can offer additional protection against harsh environments.

Answer: Salmonella typhi

Wilson and Blair bismuth sulphite medium is a selective culture medium used for the isolation and differentiation of Salmonella species, particularly Salmonella typhi, the causative agent of typhoid fever. This medium contains bismuth sulphite and other selective agents that inhibit the growth of most bacteria while allowing for the growth of Salmonella species.

The other options are incorrect:

• Shigella dysenteriae: While Wilson and Blair medium can sometimes support the growth of some Shigella species, it’s not the primary target and may not be as selective for them compared to Salmonella.
• Vibrio cholerae: This bacterium has different growth requirements and wouldn’t be effectively isolated or differentiated using Wilson and Blair medium.
• E. coli: Escherichia coli, especially lactose-fermenting strains, are generally inhibited by the ingredients in Wilson and Blair medium.

Answer: Ammonifiaction bacteria

Putrefaction bacteria initiate the decomposition process by breaking down complex organic matter, including proteins. Ammonification bacteria then take over and convert the resulting amino acids and other nitrogenous compounds from putrefaction into ammonia (NH₄⁺). This conversion is a crucial step in the nitrogen cycle.

The other options are incorrect:

• Putrefaction bacteria: As mentioned earlier, these bacteria break down complex organic matter but don’t typically convert it directly to ammonia. They prepare the substrate for ammonification bacteria.
• Nitrification bacteria: These bacteria come after ammonification in the nitrogen cycle. They convert ammonia (NH₄⁺) into nitrites (NO₂⁻) and nitrates (NO₃⁻).
• Denitrifying bacteria: These bacteria play a later role in the nitrogen cycle. They convert nitrates (NO₃⁻) back into atmospheric nitrogen (N₂) in a process called denitrification.

Answer: Claveceps

Ergot disease is a fungal infection that primarily affects cereal grains, especially rye. It is caused by the fungus Claviceps purpurea. This fungus infects developing kernels, replacing them with dark, hard structures called sclerotia. These sclerotia contain toxic alkaloids that can cause ergotism, a serious illness in humans and animals who consume them.

The other options are incorrect:

• Puccinia: This is a genus of fungi that cause rust diseases in plants. While Puccinia species can infect cereal crops like wheat and barley, they are not responsible for ergot disease.
• Rhizopus: This is a genus of molds that can cause spoilage in fruits and vegetables. It is not typically associated with ergot disease in grains.
• Penicillium: This is a genus of fungi that includes some species known for producing penicillin antibiotics. Penicillium species are not known to cause ergot disease.

Answer: Growth Factors

Vitamins are essential for bacteria in small amounts as growth factors. They are not directly used for energy production, carbon skeletons, or electron donation. Instead, vitamins participate in various enzymatic reactions and metabolic pathways crucial for bacterial growth and reproduction.

The other options are incorrect:

• Sources of energy: Bacteria acquire energy from various sources like carbohydrates, proteins, or fats. Vitamins are not broken down for energy but act as cofactors in energy-producing processes.
• Sources of carbon: Bacteria utilize carbon sources like glucose to build their cellular components. Vitamins don’t provide the building blocks for bacterial structures.
• Sources of electron donors: Electron donors are molecules used in bacterial respiration to generate energy. While some vitamins might be involved in these pathways, their primary role is not as electron donors themselves.

Answer: Na+

Among the options provided, Na+ (sodium ion) is not typically utilized as an electron donor in biological systems. Instead, it is commonly involved in osmotic regulation and maintaining cellular ion balance. In biological systems, electron donors are usually reduced compounds such as organic molecules or inorganic substances like hydrogen sulfide (H2S).

Incorrect Options:

• Mg+2 (Magnesium ion): Magnesium ions are essential cofactors in many enzymatic reactions and are involved in stabilizing nucleic acids and ATP, but they are not typically used as electron donors.
• Ca+2 (Calcium ion): Calcium ions play important roles in cellular signaling, muscle contraction, and structural support but are not typically used as electron donors.
• Mn+2 (Manganese ion): Manganese ions are involved in various enzymatic reactions as cofactors, particularly in redox reactions, but they are not typically used as electron donors.

Answer: Capsule

In pneumococcus (Streptococcus pneumoniae), the capsule is the virulence factor responsible for its pathogenicity. The capsule helps the bacterium evade the host immune system by inhibiting phagocytosis, thereby increasing its ability to cause infection.

The other options are incorrect:

• Cell wall: While the cell wall of pneumococcus is important for maintaining cell structure and integrity, it is not considered a virulence factor in the context of pathogenicity.
• Mesosomes: Mesosomes are membrane structures found in some bacterial cells, but they are not specific virulence factors associated with pneumococcus.
• Endotoxins: Endotoxins are lipopolysaccharides found in the outer membrane of Gram-negative bacteria, whereas pneumococcus is a Gram-positive bacterium. Endotoxins are not directly associated with pneumococcal pathogenicity.

Answer: Aquaspirillum Magnetotacticum

Aquaspirillum Magnetotacticum is a type of magnetotactic bacteria. These bacteria have special organelles called magnetosomes containing magnetic crystals that allow them to align and move in response to the Earth’s magnetic field. This helps them navigate towards optimal oxygen concentrations for their survival.

The other options are incorrect:

• Spirochets: Spirochetes are a group of spiral-shaped bacteria, but they do not typically exhibit magnetotaxis.
• Treponema: Treponema is a genus of spirochete bacteria, including species such as Treponema pallidum, which causes syphilis. Treponema species are not known for magnetotaxis.
• None of these is incorrect because Aquaspirillum Magnetotacticum is a real bacterium with magnetotaxis ability.

Answer: Clostridium perfringens

The Nagler reaction is a specific test used to identify Clostridium perfringens. This test detects the presence of an enzyme called lecithinase (also known as alpha-toxin) produced by C. perfringens. When C. perfringens is cultured on a medium containing egg yolk (which has lecithin), the lecithinase breaks down the lecithin, creating a zone of opacity or a precipitate around the colonies.

The other options are incorrect:

• Corynebacterium diphtheriae: This bacterium produces a different toxin called diphtheria toxin. Diagnosis of C. diphtheriae involves other tests like culture on special media and toxin detection methods.
• Clostridium tetani: Tetanus caused by C. tetani is associated with a different toxin called tetanospasmin. Diagnosis involves clinical symptoms and sometimes culture tests, but not the Nagler reaction.
• Clostridium botulinum: Botulism caused by C. botulinum involves the production of botulinum toxin. Diagnosis relies on detecting the toxin in patient samples or culture isolates, not the Nagler reaction.

Answer: Both first and second

• Mycoplasma: These are the smallest free-living organisms and lack a cell wall entirely. Their cell membrane is their only rigid structure.
• L-forms: These are bacterial cells that have lost most or all of their cell wall due to mutations, exposure to antibiotics, or other factors. They can revert to their original form under certain conditions.

The other options are incorrect:

• Bacteria: Most bacteria have a cell wall made of peptidoglycan, which provides rigidity and shape. This is essential for their survival and distinguishes them from Mycoplasma and L-forms.

Answer: Citrus canker

Mycoplasma are a type of bacteria that lack a cell wall. This characteristic makes them difficult to treat with antibiotics and allows them to invade plant and animal cells. Citrus canker, however, is caused by a different type of bacteria called Xanthomonas axonopodis. This bacteria has a cell wall and is susceptible to antibiotics.

The other options are incorrect:

• Pneumonia in human beings: Mycoplasma pneumoniae can cause a type of pneumonia often referred to as “walking pneumonia” because symptoms are milder than typical bacterial pneumonia.
• Little leaf of Brinjal (eggplant): This disease is caused by phytoplasma, which are similar to mycoplasma but specifically infect plants.
• Dwarf disease of Mulberry: Mycoplasma infection is a known cause of dwarfism in mulberry trees.

Answer: Fungi

Mycotoxins are toxic secondary metabolites produced by certain fungi under specific environmental conditions. These toxins can contaminate various agricultural products such as grains, nuts, and fruits, posing health risks to humans and animals if ingested.

The other options are incorrect:

• Bacteria: Bacteria are single-celled prokaryotic organisms and do not produce mycotoxins.
• Algae: Algae are eukaryotic organisms that typically live in water or moist environments. They do not produce mycotoxins.
• Protozoans: Protozoans are single-celled eukaryotic organisms, some of which can cause diseases. However, they do not produce mycotoxins.

Answer: B Vitamin

Yeast extract is concentrated from inactivated yeast cells. Yeast is a rich source of B vitamins, including thiamine (B1), riboflavin (B2), niacin (B3), pantothenic acid (B5), pyridoxine (B6), biotin (B7), and folic acid (B9). However, it does not contain vitamin B12.

The other options are incorrect:

• A Vitamin: Vitamin A is typically found in animal sources like liver, eggs, and dairy or plant sources with beta-carotene that our bodies convert to vitamin A. Yeast extract doesn’t contain significant amounts of vitamin A.
• Proteins: While yeast extract does contain some protein, it’s not the most outstanding characteristic. Other sources, like meat, legumes, and dairy, are generally better protein sources.
• Carbohydrates: Yeast itself consumes carbohydrates during fermentation. While there may be some residual carbohydrates in yeast extract, it’s not a significant source.

Answer: Robertson’s cooked meat medium

Robertson’s cooked meat medium is a type of anaerobic culture medium used for the cultivation and isolation of anaerobic bacteria. It contains finely minced meat in a semisolid agar medium, creating an oxygen-deprived environment suitable for the growth of anaerobic organisms.

The other options are incorrect:

• Wilson Blair Medium: Wilson Blair medium is actually an example of an enrichment medium used for the isolation of Campylobacter species, which are microaerophilic bacteria that require reduced oxygen levels for growth, rather than strict anaerobic conditions.
• MacConkey Broth: MacConkey broth is a selective and differential medium used for the cultivation of Gram-negative bacteria, particularly Enterobacteriaceae. It is not an anaerobic medium.
• EMB Agar: Eosin methylene blue (EMB) agar is a selective and differential medium used for the isolation and differentiation of Gram-negative enteric bacteria, primarily Escherichia coli and other coliforms. It is not designed for anaerobic growth.

Answer: All the these

Single-cell protein (SCP) refers to protein produced from microorganisms. All three options – bacteria, yeasts, and algae – can be cultivated and harvested as sources of SCP.

• Bacteria: Certain bacteria species can be grown rapidly and efficiently on various substrates, making them a promising source of SCP.
• Yeasts: Baker’s yeast (Saccharomyces cerevisiae) is a classic example of SCP production. Yeasts can be grown on sugars and starches.
• Algae: Some algae species have very high protein content and can be cultivated in large-scale systems. They can also be a source of essential nutrients.

Answer: Nitrobacter

Nitrobacter is a genus of bacteria that plays a crucial role in the second step of the nitrification process. Nitrification is the conversion of ammonia into nitrate, a more usable form of nitrogen for plants. Nitrobacter specifically oxidizes nitrites (NO2-) into nitrates (NO3-).

The other options are incorrect:

• Nitrosomonas: Nitrosomonas is another genus of bacteria involved in nitrification, but it performs the first step. It oxidizes ammonia (NH4+) into nitrites (NO2-).
• Nitrosococcus: Nitrosococcus is an older name sometimes used for certain species within the Nitrosomonas genus. So, the function is still related to the first step of nitrification, oxidizing ammonia to nitrite.
• Azatobacter: Azatobacter is a genus of free-living nitrogen-fixing bacteria. While they play a role in the nitrogen cycle, they are not involved in nitrification.

Answer: Polysaccharides

Agar is a gelatinous substance derived from red algae. The major constituents of agar are complex sugars called polysaccharides. These polysaccharides, specifically agarose and agaropectin, are responsible for the gelling properties of agar.

The other options are incorrect:

• Fats: Agar does not contain significant amounts of fats.
• Amino Acids: Amino acids are the building blocks of proteins. While there may be trace amounts of amino acids present as impurities, they are not a major constituent of agar.
• Polypeptides: Polypeptides are chains of amino acids linked together. Similar to amino acids, polypeptides are not a major component of agar.

Answer: Plasmid

Plasmids are extrachromosomal genetic elements found in bacteria that can carry genes encoding resistance to multiple antibiotics. These plasmids can be transferred between bacteria through horizontal gene transfer mechanisms such as conjugation, transformation, or transduction, leading to the spread of antibiotic resistance among bacterial populations.

The other options are incorrect:

• Episome: An episome is a genetic element that can exist either as a plasmid or integrated into the bacterial chromosome. While some episomes may carry antibiotic resistance genes, the term “episome” does not specifically refer to the mediation of multiple antibiotic resistance.
• Colplasmid: “Colplasmid” is not a recognized term in microbiology. It seems to be a combination of “col” possibly referring to colicin (a bacteriocin produced by some strains of Escherichia coli) and “plasmid.” However, it is not a commonly used term for describing antibiotic resistance mediation.
• Both second and third: This option combines “Plasmid” and “Colplasmid,” which is not accurate. The correct term for the mediation of multiple antibiotic resistance is solely “Plasmid.”

Answer: None of these

Antagonism refers to an interaction between organisms where one organism harms or suppresses the growth of another. The growth phases (Lag, Log, Stationary, Death) describe the population dynamics of microorganisms in a culture, not interactions between them.

The other options are incorrect:

• Lag phase: This is the initial adaptation period when bacteria are adjusting to the growth environment. There is no specific interaction with other organisms here.
• Plasmids: Plasmids are extrachromosomal DNA elements that can carry various genes, including those for antibiotic resistance. While plasmids can be involved in competition between bacteria, antagonism is a broader concept.
• Log phase: This is the exponential growth phase where bacteria are actively reproducing. Antagonism can occur during this phase, but it’s not exclusive to it.

Answer: Lag phase

The lag phase is the first phase of a growth curve. During this phase, bacteria are adjusting to their new environment and preparing for cell division. They are not actively growing in number yet, but they are synthesizing enzymes and other molecules needed for replication.

The other options are incorrect:

• Log phase: The log phase, also called the exponential phase, comes after the lag phase. This is when bacteria are actively reproducing and their population is increasing exponentially.
• ? phase: There isn’t a standard term for a “mystery phase” in a growth curve. The four well-defined phases are lag, log, stationary, and death.
• Both a and b: While the lag phase precedes the log phase, they are distinct phases, not a combined one.

Answer: Batch culturing

Batch culturing is a closed system where all the nutrients are provided at the beginning, and there’s no addition or removal of substances during the culturing process. As the culture grows, nutrients become depleted, and waste products accumulate, eventually limiting further growth.

The other options are incorrect:

• Ascus: Ascus is a sac-like structure in fungi that contains spores for sexual reproduction. It’s not a culturing method.
• Fruiting body: This is the visible reproductive structure of a fungus, like a mushroom. It’s not a culturing method either.
• Sporangiosphore: This is a specialized structure in some fungi that bears spores for asexual reproduction. It’s also not a culturing method.

Answer: Log phase

The log phase, also called the exponential phase, is the stage of growth where cells are most active and rapidly dividing. They are synthesizing new protoplasm (cellular material) to support this rapid growth.

The other options are incorrect:

• Lag phase: During the lag phase, cells are adjusting to their new environment and preparing for growth. While some synthesis might occur, it’s not the defining characteristic of this stage.
• Stationary phase: The stationary phase is reached when the growth of the cell population plateaus due to limitations like nutrient depletion or waste product accumulation. Cell division slows down or stops altogether.
• All of these: While all these phases involve some level of cellular activity, the log phase is specifically characterized by the most active growth and protoplasm synthesis.

Answer: Molybdenum

Molybdenum is a micronutrient that plays a crucial role in biological nitrogen fixation. It is a component of nitrogenase, a key enzyme complex responsible for converting atmospheric nitrogen (N2) into ammonia (NH3), a usable form of nitrogen for plants and many other organisms.

The other options are incorrect:

• Copper: Copper is an essential element for many cellular processes, but it’s not directly involved in nitrogen fixation.
• Magnesium: Magnesium is another essential element involved in various cellular functions, including photosynthesis and enzyme activity. However, it’s not specific to nitrogen fixation.
• Zinc: Zinc is also an essential element with diverse roles in cellular processes, but it’s not directly involved in nitrogen fixation.

Answer: log

The log phase, also called the exponential phase, is characterized by rapid bacterial growth. During this phase, the bacterial population increases exponentially as cells divide at a constant rate.

The other options are incorrect:

• Lag: The lag phase is the initial adaptation period when bacteria are adjusting to the new environment. Growth isn’t rapid during this phase.
• Lack: “Lack” doesn’t refer to a specific growth phase. It simply means absence or deficiency.
• None of these: While the other options aren’t correct, there is a defined growth phase associated with rapid bacterial growth.

Answer: Ellner medium

Ellner medium is a specifically formulated enrichment broth used to promote spore formation in Clostridium species, including Clostridium welchii (also known as Clostridioides difficile). It provides specific nutrients and anaerobic conditions that trigger sporulation.

The other options are incorrect:

• Wilson-Blair medium: This medium is designed for detecting anaerobic bacteria and doesn’t specifically promote spore formation.
• MacConkey medium: This is a differential and selective medium used to differentiate lactose-fermenting from lactose-non-fermenting bacteria. It’s not suitable for inducing spore formation.
• Thayee-Martin medium: This is a selective and differential medium used to isolate and identify Salmonella and Shigella species. It’s not for promoting spore formation in Clostridium.

Answer: 6.8 – 7.2

The majority of bacteria are neutrophils, meaning they prefer a near-neutral environment for optimal growth. This range of 6.8 – 7.2 falls within the neutral range (pH 7) and provides the most favorable conditions for most bacterial functions like enzyme activity and nutrient transport.

The other options are incorrect:

• 5.6 – 8.2: While this range encompasses the preferred neutral range, some bacteria may not tolerate the entire spectrum.
• 3.0 – 6.0: This range is acidic and suitable for acidophilic bacteria, which can survive and grow in acidic environments. However, most bacteria wouldn’t thrive in this range.
• 8.0 – 14.0: This range is alkaline and suitable for alkalophilic bacteria. Most bacteria wouldn’t grow well in such an alkaline environment.

Answer: Cobalt

Cobalt is an essential trace element required by some bacteria for the synthesis of vitamin B12 (cobalamin), which is crucial for various metabolic processes, including DNA synthesis and energy metabolism. While cobalt is required in trace amounts, its presence is necessary for the growth and viability of certain bacterial species.

The other options are incorrect:

• Calcium: Calcium is a mineral ion that plays various roles in bacterial physiology, including cell wall stability and signaling processes. However, it is not typically required in trace amounts for bacterial growth and is not considered an essential trace element.
• Magnesium: Magnesium is an essential mineral ion required by all living organisms, including bacteria, for various biochemical processes. It is involved in stabilizing ribosomes, enzyme activation, and nucleic acid structure. However, it is not typically considered an ion required in trace amounts for bacterial growth.
• Sodium: Sodium is an important cation involved in maintaining osmotic balance and membrane potential in bacteria. While sodium is necessary for some bacterial species, particularly those that inhabit high-salt environments, it is not typically required in trace amounts for bacterial growth.

Answer: B-complex

B-complex vitamins are essential for bacterial growth and metabolism. These vitamins play crucial roles as coenzymes in various biochemical reactions, including energy metabolism, nucleic acid synthesis, and amino acid metabolism. Bacteria often require B-complex vitamins for their growth and survival, as they cannot synthesize these vitamins de novo.

The other options are incorrect:

• Vitamin A: Vitamin A is primarily important for vision in animals and not essential for bacterial growth.
• Vitamin D: Vitamin D is essential for calcium absorption in animals and not required by bacteria.
• Vitamin C: Vitamin C is an antioxidant important for some animals but not essential for most bacteria.

Answer: Concentration of growth factor have a linear relationship with the growth of the organism

Microbiological assays involve quantifying the concentration of a growth factor, such as a nutrient or a growth-promoting substance, by measuring its effect on the growth of a microorganism. The principle is based on the assumption that the concentration of the growth factor directly influences the growth of the organism in a linear manner. By determining the relationship between the concentration of the growth factor and the growth response of the organism, the concentration of the growth factor can be accurately determined.

The other options are incorrect:

• At certain range the concentration of growth factor will bear a linear relationship to the amount of nutrients added: This statement doesn’t directly connect growth factor concentration to organism growth. It refers to the growth factor itself potentially being affected by nutrient levels, which might indirectly impact the organism’s growth.
• Both a and b: While there might be some connection between growth factor concentration and nutrient addition, the core principle focuses on the organism’s growth response to the growth factor itself.
• None of the above: The core principle described is valid within the context of microbiological assays using limiting growth factors.

Answer: Chemotrophs

Chemotrophs are organisms that obtain their energy from breaking down chemical compounds. This category includes a wide variety of bacteria, as many use organic or inorganic chemicals for energy.

The other options are incorrect:

• Phototrophs: These organisms use light as their energy source, like plants and some bacteria that perform photosynthesis.
• Autotrophs: While some chemotrophs can be autotrophs, meaning they can synthesize their own organic molecules, the category itself isn’t specific to the energy source. Autotrophs can be phototrophs (using light) or chemotrophs (using chemical compounds).
• Chemolithotroph: This is a specific type of chemotroph that gets its energy from oxidizing inorganic compounds. While some bacteria fall into this category, it’s not all-encompassing for chemotrophs that can also utilize organic compounds.

Answer: Carbon

Carbon is the backbone of most biological molecules, including carbohydrates, proteins, lipids, and nucleic acids. Its unique ability to form strong covalent bonds with itself and other elements allows for the complex structures found in living cells.

The other options are incorrect:

• Nitrogen: While crucial for amino acids (protein building blocks), nitrogen makes up a smaller portion compared to carbon in cell components.
• Sulphur: Found in some amino acids and plays a role in protein structure and function, but its overall presence is less abundant than carbon.
• Oxygen: Essential for cellular respiration and a component of many molecules like water, but it’s not the major building block for cell structures.

Answer: All of these

Cells require a combination of elements for building their components.

• Nitrogen: Crucial for amino acids, the building blocks of proteins.
• Oxygen: A component of many molecules like carbohydrates, proteins, and nucleic acids (DNA and RNA).
• Sulphur: Found in some amino acids and plays a role in protein structure and function.

Answer: Na+

While some bacteria can benefit from sodium (Na+), most bacteria don’t require it for essential functions. They can maintain their internal ion balance with other mechanisms.

The other options are incorrect:

• Mg2+: Magnesium is a crucial element for many cellular processes, including ribosome structure, enzyme function, and DNA stabilization. Most bacteria require Mg2+.
• Ca2+: Calcium can be important for some bacteria in cell wall structure, signaling, and regulation. While not universally required, it’s beneficial for many.
• Fe+2: Iron is essential for many enzymatic reactions, especially those involved in respiration and electron transport. Most bacteria require Fe2+ in some form.

Answer: Lactobacillus spp.

Lactobacillus spp. are a group of beneficial bacteria found in the gut that play a crucial role in vitamin K production. Vitamin K is essential for blood clotting and bone health.

The other options are incorrect:

• Bacillus anthracis: This bacterium is a pathogen responsible for anthrax, a serious illness. It does not require vitamin K.
• Bacteroides melaninogenicus: This is another gut bacterium, but it does not synthesize vitamin K.pen_spark

Answer: Psychrophiles

Psychrophiles are bacteria that thrive in cold environments with optimal growth temperatures around 15°C or lower. They can still grow at 0°C, although at a slower rate.

The other options are incorrect:

• Facultative psychrophiles: This term doesn’t exist in standard bacterial classification. Bacteria are either psychrophiles (cold-loving) or not. Some bacteria may tolerate a wider temperature range, but wouldn’t be classified as “facultative” in this context.
• Average psychrophiles: There’s no specific category for “average” psychrophiles. Psychrophiles have a range of optimal temperatures within the cold spectrum.
• Mesophiles: Mesophiles are bacteria that prefer moderate temperatures, typically between 20°C and 45°C. While some mesophiles might survive at 0°C, they wouldn’t be able to grow at that temperature.

Answer: Growth

Growth refers to the overall increase in a cell’s size and mass due to the production of new cellular components. This includes replication of DNA, organelles, and other cellular machinery.

The other options are incorrect:

• Reproduction: Reproduction involves the creation of new daughter cells from a parent cell. Growth is a necessary precursor to reproduction, but it’s a distinct process.
• Binary fission: Binary fission is a specific type of cell division that results in two daughter cells. While it’s a key part of the reproductive process, it doesn’t encompass the broader concept of growth that can occur without immediate cell division.
• None of these: While the other options are specific processes related to growth, overall cellular growth is a fundamental concept in biology.

Answer: Binary fission

Binary fission is the most prevalent mode of cell division in bacteria. It involves a single parent cell replicating its DNA and then dividing into two genetically identical daughter cells.

The other options are incorrect:

• Transverse binary fission: This is a more specific term that falls under binary fission. It describes when the division plane is perpendicular to the long axis of the cell, creating roughly equal-sized daughter cells. Most bacteria undergo transverse binary fission, but it’s not always necessary to specify this direction.
• Longitudinal binary fission: This is another specific type of binary fission where the division plane runs along the long axis of the cell, resulting in elongated daughter cells. This is uncommon in most bacteria.
• None of these: All the options are related to bacterial cell division, but binary fission is the most widely used method.

Answer: 20 min.

The duplication time for bacteria varies significantly depending on the specific species and its growth conditions. While 20 minutes is a commonly cited example, some bacteria can reproduce much faster (as little as 4 minutes) while others take longer (up to 20 minutes or more).

The other options are incorrect:

• 30 min.: This option suggests a longer doubling time than what is typically observed in bacteria under favorable conditions. A doubling time of 30 minutes is relatively slow compared to the rapid growth rates characteristic of many bacterial species.
• 10 min.: A doubling time of 10 minutes is much shorter than what is typically observed in bacteria. While some bacteria may have shorter doubling times under specific conditions, a doubling time of 10 minutes is uncommon and would indicate extremely rapid growth.
• 25 min.: A doubling time of 25 minutes is slightly longer than the typical doubling time observed in many bacterial species under optimal conditions.

Answer: Geometric progression

Bacterial populations, under ideal conditions, typically exhibit geometric progression in their growth. This means the population size doubles with each generation cycle. For example, if you start with 10 bacteria, after one generation you might have 20, then 40, then 80, and so on.

The other options are incorrect:

• Multiplication: While multiplication is involved in bacterial growth, it doesn’t capture the exponential nature of their population increase.
• Doubling: Doubling is accurate for each generation, but geometric progression highlights the continuous exponential growth pattern.
• None of these: All the options are related to bacterial population increase, but geometric progression best describes the specific pattern observed.

Answer: Log phase

The Log phase, also known as the exponential phase, is the stage of bacterial growth characterized by rapid and exponential increase in cell number. During this phase, cells are metabolically active and are synthesizing new cellular components, such as proteins, nucleic acids, lipids, and carbohydrates.

The other options are incorrect:

• Lag phase: In the lag phase, bacteria are adjusting to a new environment and primarily focus on synthesizing essential molecules to prepare for division. Cell growth might occur, but not active cell division.
• Stationary phase: The stationary phase occurs when essential nutrients become depleted or waste products accumulate, limiting further growth. While some metabolic activity continues, cell division slows down or stops.
• None of these: All the options are stages in bacterial growth, but the log phase best represents the period of active cell division and new protoplasm synthesis.

Answer: Log phase

The log phase, also known as the exponential phase, is the period in the bacterial growth curve where bacteria experience the most rapid and exponential increase in their population. During this phase, cells are actively dividing and reproducing at the fastest rate.

The other options are incorrect:

• Lag phase: This is the initial adaptation period where bacteria adjust to a new environment. Growth is slow or absent.
• Stationary phase: This phase signifies a plateau in growth as resources become limited and the number of dividing cells equals the number dying.
• Decline phase: This final phase is marked by a decrease in the bacterial population due to depletion of nutrients and accumulation of waste products.

Answer: Exponential phase

The log phase, also known as the exponential phase, is characterized by rapid and exponential bacterial growth. Cells are actively dividing and maximizing their population.

The other options are incorrect:

• Death phase: This final phase in the growth curve signifies a decrease in the bacterial population due to a lack of resources and waste buildup.
• Lag phase: This initial adjustment period precedes the log phase. Bacteria are not actively reproducing during this time.

Answer: Generation time

Generation time refers to the average time it takes for a single bacterial cell to divide and produce two daughter cells. It directly reflects the growth rate of the bacteria under specific conditions.

The other options are incorrect:

• Growth rate: This term describes the speed at which a bacterial population increases over time. It can be expressed as the number of generations per hour, but it’s a broader concept encompassing generation time.
• Sigmoid curve: This is the graphical representation of the bacterial growth cycle, including all phases (lag, log, stationary, and decline). It doesn’t represent a specific time unit.
• None of these: While the other options are related to bacterial growth, generation time directly reflects the number of generations occurring per hour.

Answer: 4

The bacterial growth curve is typically divided into four distinct phases:

1. Lag phase: Initial adjustment period, slow or no growth.
2. Log phase (exponential phase): Rapid and exponential population increase.
3. Stationary phase: Plateau phase, growth stops due to resource limitations.
4. Decline phase: Decrease in population due to nutrient depletion and waste buildup.

The other options are incorrect:

• 3: The bacterial growth curve has four distinct phases, not three.
• 2: There are more than two distinct phases in the bacterial growth curve.
• 5: While there could be variations depending on specific conditions, the standard bacterial growth curve is typically described by four phases.

Answer: Stationary phase

The stationary phase is characterized by a stable population size. In this phase, the rate of cell division (reproduction) slows down and equals the rate of cell death. This occurs because essential nutrients become depleted, waste products accumulate, and the environment becomes less favorable for growth.

The other options are incorrect:

• Decline phase: During the decline phase, the death rate exceeds the reproduction rate, leading to a decrease in the overall population.
• Lag phase: This initial adaptation period has minimal cell division, with the reproduction rate being lower than the death rate (though death rate might be very low as well).
• Log phase: This phase is characterized by rapid exponential growth, with the reproduction rate significantly exceeding the death rate.