Microbiology MCQs with Answer and Explnation | Chapter 10

Answer: Fungi

Mycotoxins are toxic compounds that are produced by certain types of mold (fungi). They can be found in a variety of food and feedstuffs, including grains, nuts, spices, dried fruits, and apples. Mycotoxins can cause a variety of adverse health effects in humans and animals, ranging from acute poisoning to long-term effects such as immune deficiency and cancer.

The other options are incorrect:

• Bacteria do not produce mycotoxins.
• Algae do not produce mycotoxins.
• Protozoans do not produce mycotoxins.

Answer: Polysaccharides

The major constituents in agar are polysaccharides. Agar is a complex carbohydrate derived from cell walls of red and purple algae. It is primarily composed of agarose and agaropectin, which are polysaccharides consisting of repeating units of galactose and sulfate residues.

The other options are incorrect:

• Fats are not a major constituent of agar.
• Amino acids are the building blocks of proteins. They are not a major constituent of agar.
• Polypeptides are chains of amino acids. They are not a major constituent of agar.

Answer: 6.8 – 7.2

The pH range for bacterial growth is typically between 6.8 and 7.2. This range is considered neutral to slightly acidic, which is suitable for the growth of many bacteria. Bacteria can exhibit variations in their pH requirements, and some species may thrive in slightly more acidic or alkaline conditions.

Answer: All Options

All three of these groups of organisms, bacteria, yeasts, and algae, have been proposed as sources of single-cell protein (SCP). SCP is a type of protein that is produced by microorganisms, and it is a potential source of food for humans and animals.

Bacteria are a good source of SCP because they are easy to grow and can be produced in large quantities. Yeasts are also a good source of SCP because they are high in protein and can be grown on a variety of substrates. Algae are a promising source of SCP because they are photosynthetic and can be grown using sunlight and water.

All three of these groups of organisms have their own advantages and disadvantages as sources of SCP. Bacteria are the most cost-effective to produce, but they may have a lower protein content than yeasts or algae. Yeasts have a high protein content and are easy to grow, but they may require more expensive substrates than bacteria. Algae are photosynthetic and can be grown using sunlight and water, but they may be more difficult to harvest and process than bacteria or yeasts.

Answer: Clostridium perfringens

The Nagler reaction detects the presence of lecithinase, an enzyme produced by certain bacteria, including Clostridium perfringens. Lecithinase breaks down lecithin, a phospholipid found in egg yolk. When a culture of bacteria containing lecithinase is streaked onto an egg yolk agar plate and incubated anaerobically, a zone of clearing or opalescence is produced around the colonies. This is due to the breakdown of lecithin by the enzyme lecithinase.

The other options are incorrect:

• Corynebacterium diphtheriae is the causative agent of diphtheria. It does not produce lecithinase and would not give a positive Nagler reaction.
• Clostridium tetani is the causative agent of tetanus. It does not produce lecithinase and would not give a positive Nagler reaction.
• Clostridium botulinum is the causative agent of botulism. It produces a different enzyme, neurotoxin, which is responsible for the symptoms of botulism. The Nagler reaction would not detect neurotoxin.

Answer: All of these

The four major elements required for the formation of cell components are carbon, hydrogen, nitrogen, and oxygen. These elements make up the majority of the organic molecules found in cells, including carbohydrates, lipids, proteins, and nucleic acids.

• Carbon is the most abundant element in cells and forms the backbone of most organic molecules. Carbon atoms can bond to four other atoms, making them versatile building blocks for a wide variety of molecules.
• Hydrogen is the second most abundant element in cells and is found in nearly all organic molecules. Hydrogen atoms are often attached to carbon atoms to form carbon-hydrogen bonds, which are essential for the structure and function of many organic molecules.
• Nitrogen is a major component of amino acids, the building blocks of proteins. It is also found in nucleic acids and some other organic molecules. Nitrogen atoms are often involved in hydrogen bonds, which are weak chemical bonds that help to stabilize the structure of many organic molecules.
• Oxygen is a major component of carbohydrates, lipids, and nucleic acids. It is also found in water, which is essential for all life. Oxygen atoms are often involved in covalent bonds, which are strong chemical bonds that hold atoms together in molecules.

Answer: Lag phase

The first phase of a bacterial growth curve is the lag phase. The lag phase is characterized by a period of slow or no growth as bacteria adapt to their new environment. During this time, bacteria are synthesizing enzymes and proteins necessary for growth and division. The length of the lag phase can vary depending on the species of bacteria and the growth conditions.

The other options are incorrect:

• The log phase is the phase of exponential growth, where the bacterial population doubles at a constant rate.
• The γ phase is a theoretical phase of growth that is not observed in all bacteria.

Answer: Batch culturing

Batch culturing is a type of microbial growth in a closed system where the initial nutrient supply is limited, and waste products accumulate over time. The growth of microorganisms in a batch culture follows a distinct growth curve, with four distinct phases:

Lag phase: A period of adaptation where microorganisms prepare for growth.

Log phase: Exponential growth phase where microorganisms multiply rapidly, utilizing available nutrients.

Stationary phase: Growth slows or stops as nutrients become depleted, and waste products accumulate.

Death phase: Microorganisms die as nutrients are exhausted and waste products become toxic.

The other options are incorrect:

• Ascus: Asci are specialized sac-like reproductive structures found in some fungi. They contain haploid spores that can undergo meiosis to produce new haploid individuals.
• Fruiting body: A fruiting body is a macroscopic reproductive structure found in some fungi. It contains reproductive structures, such as asci or basidia, that produce spores.
• Sporangiophore: A sporangiophore is a specialized stalk-like structure in some fungi that supports sporangia, which are spore-producing structures.

Answer: obligate aerobes

Obligate aerobes are bacteria that require oxygen for growth. They cannot grow in the absence of oxygen. This is because they use oxygen as the final electron acceptor in their electron transport chain, which is a series of chemical reactions that generates ATP, the energy currency of cells.

The other options are incorrect:

• Thermophilic bacteria are bacteria that grow at high temperatures. They are not necessarily obligate aerobes.
• Microaerophilic bacteria are bacteria that require low levels of oxygen for growth. They are not obligate aerobes.
• Facultative anaerobic bacteria are bacteria that can grow in the presence or absence of oxygen. They are not obligate aerobes.
• Mycobacteria are a genus of bacteria that includes the causative agents of tuberculosis and leprosy. They are obligate aerobes.

Answer: Extent to which water is polluted with organic compounds

Biological Oxygen Demand (BOD) is a measure of the extent to which water is polluted with organic compounds. It is expressed as the amount of dissolved oxygen (DO) needed by aerobic microorganisms to break down organic matter present in a water sample at a specified temperature over a specific time period, typically 5 days at 20°C.

The higher the BOD of a water body, the more organic matter is present, which indicates a higher level of pollution. This is because organic matter provides a source of food for aerobic microorganisms, which consume oxygen as they break it down. As a result, BOD is a useful indicator of the health of a water body and its ability to support aquatic life.

The other options are incorrect:

• Industrial wastes poured into water bodies can increase the BOD of the water, but BOD is not a direct measure of industrial waste.
• Carbon monoxide is not inseparably combined with hemoglobin. It binds to hemoglobin reversibly, reducing its ability to carry oxygen.
• Green plants produce oxygen during photosynthesis, not consume it.

Answer: Chemotrophs

Chemotrophs are organisms that obtain their energy from chemical reactions. This is in contrast to phototrophs, which obtain their energy from light. There are two main types of chemotrophs: chemoorganotrophs and chemolithotrophs. Chemoorganotrophs obtain their energy from the oxidation of organic compounds, such as carbohydrates, lipids, and proteins. Chemolithotrophs obtain their energy from the oxidation of inorganic compounds, such as sulfur, iron, and hydrogen.

The other options are incorrect:

• Phototrophs are organisms that obtain their energy from light.
• Autotrophs are organisms that can synthesize their own food from inorganic compounds.
• Chemolithotrophs are a type of chemotroph that obtains its energy from the oxidation of inorganic compounds.

Answer: B-complex

The most important vitamin for the growth of bacteria is the B-complex vitamin. B-complex vitamins are essential for a variety of bacterial metabolic processes, including energy production, protein synthesis, and DNA replication. Some specific B-complex vitamins that are important for bacterial growth include thiamine (B1), riboflavin (B2), niacin (B3), pantothenic acid (B5), pyridoxine (B6), biotin (B7), folic acid (B9), and cobalamin (B12).

The other options are incorrect:

• Vitamin A is not essential for bacterial growth. It is a fat-soluble vitamin that is important for human vision, immune function, and cell growth.
• Vitamin D is also not essential for bacterial growth. It is a fat-soluble vitamin that is important for human bone health and calcium absorption.
• Vitamin C is an antioxidant that can be beneficial for bacterial growth in some cases. However, it is not essential for most bacteria.

Answer: Log

The rapid bacterial growth phase is known as the Log phase. During this phase, the number of bacteria doubles at a constant rate, and the population can increase by a factor of 1000 or more within a few hours. This is because bacteria are dividing rapidly and producing new cells at a very fast rate.

The other options are incorrect:

• The Lag phase is the phase of growth where bacteria are adapting to their new environment. They are not dividing at their fastest rate in this phase.
• The Lack phase is not a phase of bacterial growth.

Answer: Nitrobacter

Nitrites are oxidized to nitrates by a microorganism called Nitrobacter. Nitrobacter is a genus of aerobic bacteria that are responsible for the second step of nitrification, the conversion of nitrite to nitrate. This process is essential for the nitrogen cycle, as it helps to convert nitrogen into a form that can be used by plants.

The other options are incorrect:

• Nitrosomonas is a genus of aerobic bacteria that are responsible for the first step of nitrification, the conversion of ammonia to nitrite.
• Nitrosococcus is a genus of bacteria that are similar to Nitrosomonas, but they are less common.
• Azotobacter is a genus of aerobic bacteria that are able to fix nitrogen from the air. They are not involved in nitrification.

Answer: Stationary phase

Mycotoxins are formed during the stationary phase. This phase of bacterial growth is characterized by a slowdown or cessation of growth as nutrients become depleted and waste products accumulate. During this phase, some species of fungi begin to produce mycotoxins, which are toxic secondary metabolites. Mycotoxins are produced as a defense mechanism to protect the fungi from other organisms or to compete for resources.

The other options are incorrect:

• The lag phase is the phase of growth where bacteria are adapting to their new environment. They are not producing mycotoxins in this phase.
• The log phase is the phase of exponential growth where bacteria are dividing rapidly. They are not producing mycotoxins in this phase.
• The death phase is the phase of growth where bacteria are dying. They are not producing mycotoxins in this phase.

Answer: Log phase

The stage of growth where cells are active and synthesizing new protoplasm is called the log phase. This phase is characterized by exponential growth, where the population of cells doubles at a constant rate. During this phase, cells are dividing rapidly and producing new cellular components, such as proteins, nucleic acids, and lipids. The log phase is typically followed by the stationary phase, where growth slows or stops as nutrients become depleted and waste products accumulate.

The other options are incorrect:

• The lag phase is the phase of growth where cells are adapting to their new environment. They are not dividing at their fastest rate in this phase.
• The stationary phase is the phase of growth where the population of cells reaches a plateau. Cells are not dividing at their fastest rate in this phase.

Answer: None of these

Antagonism typically refers to a situation where the effect of one substance or organism opposes or counteracts the effect of another. In the context given, “None of these” would be the most accurate answer, as antagonism is not specifically associated with the lag phase, log phase, or plasmids in the options provided. The term may be more relevant in the context of interactions between microbes or the effects of substances, rather than specific phases of microbial growth or genetic elements like plasmids.

Answer: Citrus canker

The correct answer is Citrus canker. Citrus canker is a bacterial disease of citrus trees that is caused by a different type of bacteria, Xanthomonas citri subsp. citri. Mycoplasma are not known to cause diseases in citrus trees.

The other three options are all diseases that are caused by Mycoplasma:

• Pneumonia in human beings can be caused by Mycoplasma pneumoniae, which is a type of bacteria that can cause respiratory infections.
• Little leaf of Brinjal is a disease of brinjal (eggplant) that is caused by Mycoplasma brinjali.
• Dwarf disease of Mulberry is a disease of mulberry trees that is caused by Mycoplasma mori.

Answer: Plasmid

Multiple antibiotic resistance is mediated by plasmids. Plasmids are small, circular pieces of DNA that can be transferred between bacteria. They often carry genes that confer resistance to antibiotics, and this is how bacteria can become resistant to multiple antibiotics.

The other options are incorrect:

• An episome is a general term for any extrachromosomal DNA element, including plasmids. However, the term “episome” is not as commonly used as “plasmid” when referring to antibiotic resistance.
• A colplasmid is a type of plasmid that is specifically involved in colicinogeny, which is the ability to produce and release colicins, which are antibacterial toxins. Colplasmids are not as common as plasmids that confer antibiotic resistance.

Answer: Both Mycoplasma and L-forms

Mycoplasma are a group of bacteria that lack a cell wall completely. This makes them resistant to antibiotics that target the cell wall, such as penicillin. L-forms are bacteria that have lost their cell wall but retain some of their cell membrane. They are also resistant to penicillin but are more susceptible to other antibiotics.

The other options are incorrect:

• Bacteria are a kingdom of organisms that are characterized by their prokaryotic cells, which lack a nucleus and other membrane-bound organelles. All bacteria have a cell wall, although some species have a very thin or atypical cell wall.

Answer: Ellner medium

Ellner medium is a specialized medium that is used to induce sporulation in Clostridium perfringens, which is the scientific name for Clostridium welchii. This medium contains a combination of nutrients that are essential for spore formation, including meat extract, peptone, and agar. It also contains a reducing agent, such as sodium thioglycolate, which helps to create an anaerobic environment that is favorable for sporulation.

The other options are incorrect:

• Wilson-Blair medium is a selective medium that is used to culture Bacillus cereus, a facultative anaerobe. It is not suitable for sporulation of Clostridium perfringens.
• MacConkey medium is a selective and differential medium that is used to culture Gram-negative bacteria. It is not suitable for sporulation of Clostridium perfringens.
• Thayer-Martin medium is a selective medium that is used to culture Neisseria gonorrhoeae, a Gram-negative bacterium. It is not suitable for sporulation of Clostridium perfringens.

Answer: Molybdenum

Molybdenum is a mineral element that plays an essential role in biological nitrogen fixation. It is a component of the enzyme nitrogenase, which is responsible for converting atmospheric nitrogen (N2) into ammonia (NH3). Ammonia is a form of nitrogen that can be used by plants and other organisms.

The other options are incorrect:

• Copper is a mineral element that is involved in a number of biological processes, including energy production and oxygen transport. However, it is not directly involved in biological nitrogen fixation.
• Magnesium is a mineral element that is involved in a number of biological processes, including muscle contraction and nerve function. However, it is not directly involved in biological nitrogen fixation.
• Zinc is a mineral element that is involved in a number of biological processes, including wound healing and immune function. However, it is not directly involved in biological nitrogen fixation.

Answer: Robertson’s cooked meat medium

Robertson’s cooked meat medium is an anaerobic medium that is used to culture obligate anaerobes, which are bacteria that cannot survive in the presence of oxygen. The medium contains meat extract, peptone, and agar, and it is boiled before use to remove oxygen.

The other options are incorrect:

• Wilson Blair medium is a selective medium that is used to culture Bacillus cereus, a facultative anaerobe.
• MacConkey broth is a selective medium that is used to culture Gram-negative bacteria.
• EMB agar is a selective and differential medium that is used to culture enterobacteriaceae.

Answer: Succinic dehydrogenase by malonic acid

Competitive inhibition is a type of enzyme inhibition in which a molecule structurally similar to the enzyme’s substrate binds to the enzyme’s active site and prevents the substrate from binding. This results in a decrease in the rate of the enzyme-catalyzed reaction.

In the case of succinic dehydrogenase and malonic acid, malonic acid is an analog of succinate, the normal substrate for the enzyme. Malonic acid binds to the active site of succinic dehydrogenase with a higher affinity than succinate, effectively blocking the enzyme from binding to its substrate. This results in a decrease in the rate of the reaction that succinic dehydrogenase catalyzes, which is the conversion of succinate to fumarate.

The other options are incorrect:

• Cytochrome oxidase is a component of the electron transport chain, and cyanide binds to the enzyme and prevents it from transferring electrons. This is an example of non-competitive inhibition, not competitive inhibition.
• Hexokinase is an enzyme that catalyzes the first step of glycolysis, the conversion of glucose to glucose-6-phosphate. Glucose-6-phosphate is a product of the enzyme-catalyzed reaction, and it does not inhibit hexokinase. This is not an example of enzyme inhibition.
• Carbonic anhydrase is an enzyme that catalyzes the reversible reaction between carbon dioxide and carbonic acid. Carbon dioxide is a substrate for the enzyme, and it does not inhibit carbonic anhydrase. This is not an example of enzyme inhibition.

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

Microbiological assays are quantitative methods used to determine the concentration of specific substances, such as growth factors or nutrients, in a sample. The principle is based on the assumption that there is a linear relationship between the concentration of the growth factor and the growth response of the microorganism being tested. By measuring the growth response, researchers can infer the concentration of the substance being assayed. This allows for the precise determination of the quantity of a particular factor in a given sample.

Answer: B Vitamin

east extract is a concentrated form of yeast that has been broken down into its individual components. This process removes the cell walls of the yeast, making it easier for the body to absorb the nutrients. Yeast extract is a rich source of B vitamins, including:

Thiamin (B1)
Riboflavin (B2)
Niacin (B3)
Pantothenic acid (B5)
Pyridoxine (B6)
Biotin (B7)
Folic acid (B9)
Cobalamin (B12)
Yeast extract also contains a small amount of protein, carbohydrates, and minerals. It is a versatile ingredient that can be used in a variety of food and beverages.

The other options are incorrect:

• Yeast extract is not a good source of vitamin A, vitamin C, or vitamin D.
• Yeast extract is a good source of protein, but it is not as good a source of protein as meat, poultry, fish, eggs, or legumes.
• Yeast extract is a good source of carbohydrates, but it is not as good a source of carbohydrates as grains, fruits, or vegetables.

Answer: Factor R

Drug resistance in bacteria is mainly determined by R plasmids. R plasmids are small circular pieces of DNA that can be transferred between bacteria. They carry genes that confer resistance to antibiotics. When a bacterium acquires an R plasmid, it becomes resistant to the antibiotics that the plasmid encodes resistance to.

The other options are incorrect:

• F plasmids are small circular pieces of DNA that can be transferred between bacteria. They carry genes that are involved in conjugation, which is the process by which bacteria exchange genetic material. F plasmids do not typically carry genes that confer resistance to antibiotics.
• Col plasmids are small circular pieces of DNA that can be transferred between bacteria. They carry genes that are involved in colicinogeny, which is the production of bacteriocins, which are toxins that can kill other bacteria. Col plasmids do not typically carry genes that confer resistance to antibiotics.
• Lysogenic viruses are viruses that can integrate their DNA into the genome of a bacterium. They do not typically carry genes that confer resistance to antibiotics.

Answer: Sulphur

Sulphur is a crucial element for the synthesis of amino acids cysteine, cystine, and methionine. The sulphur atom in these amino acids plays a vital role in their structure and function.

Cysteine contains a sulfhydryl group (-SH), which is essential for its biological activity. The sulfhydryl group can participate in disulfide bonds, which are important for protein folding and stability. Cysteine is also a precursor for other sulfur-containing compounds, such as glutathione and taurine.

The other options are incorrect:

• Oxygen is a crucial element for the synthesis of many amino acids, but it is not specifically required for cysteine, cystine, and methionine.
• Nitrogen is a crucial element for the synthesis of all amino acids, including cysteine, cystine, and methionine.

Answer: Apo enzyme

The protein moiety of an enzyme is known as an apoenzyme. An apoenzyme is an inactive form of an enzyme that lacks its cofactor or prosthetic group. A cofactor is a non-protein molecule that is required for the catalytic activity of an enzyme. A prosthetic group is a tightly bound cofactor that is essential for the structure and function of an enzyme.

When an apoenzyme binds to its cofactor or prosthetic group, it becomes an active enzyme, or holoenzyme. The holoenzyme is the form of the enzyme that is capable of carrying out its catalytic activity.

The other options are incorrect:

• Holoenzyme is the complete, active form of an enzyme, consisting of an apoenzyme and its cofactor or prosthetic group.
• Coenzyme is a non-protein molecule that is required for the catalytic activity of an enzyme.
• Enzyme is a protein that catalyzes a biochemical reaction.

Answer: Cobalt

The ion that is required in trace amounts for the growth of bacteria is Cobalt. It is essential for the activity of several enzymes involved in bacterial metabolism, including vitamin B12 synthesis, anaerobic respiration, and nitrogen fixation. Cobalt deficiency can lead to a variety of problems in bacteria, including impaired growth, reduced virulence, and increased antibiotic susceptibility.

The other options are incorrect:

• Calcium is a major macronutrient that is required in large amounts for bacterial growth. It is essential for cell wall synthesis, protein stability, and enzyme activity.
• Magnesium is another major macronutrient that is required in large amounts for bacterial growth. It is essential for ribosome function, DNA replication, and enzyme activity.
• Sodium is an essential ion that is required in small amounts for bacterial growth. It is important for maintaining osmotic balance and for the transport of nutrients into and out of cells.

Answer: Carbon

The major element required in the synthesis of cell components is carbon. Carbon atoms form the backbone of most organic molecules in cells, including carbohydrates, lipids, proteins, and nucleic acids. Carbon atoms can bond to four other atoms, making them versatile building blocks for a wide variety of molecules.

The other options are also important elements for cell synthesis, but they are not as abundant as carbon.

• Nitrogen is a major component of amino acids, the building blocks of proteins. It is also found in nucleic acids and some other organic molecules.
• Sulfur is found in amino acids, some vitamins, and other organic molecules. It is also important for the structure of proteins.
• Oxygen is a major component of carbohydrates, lipids, and nucleic acids. It is also found in water, which is essential for all life.

Answer: Pyruvate

Glycolysis is a metabolic pathway that breaks down glucose into pyruvate. This process occurs in all cells, including plant and animal cells. Under aerobic conditions, pyruvate can enter the mitochondria and be further metabolized through the citric acid cycle and oxidative phosphorylation to produce energy in the form of ATP.

Lactate is a product of glycolysis that is only produced under anaerobic conditions, such as when there is not enough oxygen available. Lactate is produced from pyruvate by the enzyme lactate dehydrogenase. This process helps to regenerate NAD+, which is a necessary cofactor for glycolysis.

Answer: All of the above

Sulphur is a versatile element that can be utilized by bacteria in a variety of forms. Bacteria can obtain sulphur from organic compounds, inorganic compounds, and elemental compounds.

• Organic compounds containing sulphur include amino acids, such as cysteine and methionine, and vitamins, such as biotin and thiamine. Bacteria can break down these compounds to release sulphur, which they can then use for their own metabolic processes.
• Inorganic compounds containing sulphur include hydrogen sulfide (H2S), thiosulfate (S2O3(2-)), and sulfate (SO4(2-)). Bacteria can oxidize these compounds to release sulphur, which they can then use for their own metabolic processes.
• Elemental sulphur is the pure, uncombined form of sulphur. Bacteria can oxidize elemental sulphur to release sulphur, which they can then use for their own metabolic processes.

Answer: All the above

Phosphorus is an essential component of nucleotides, nucleic acids, phospholipids, and teichoic acids. These molecules play important roles in various biological processes within cells.

• Nucleotides: Phosphorus is a key component of the phosphate backbone of nucleotides, the building blocks of nucleic acids like DNA and RNA.
• Nucleic acids: Phosphorus is crucial for the structure and function of DNA and RNA, which store and transmit genetic information.
• Phospholipids: Phosphorus forms the polar head group of phospholipids, which are essential components of cell membranes. They provide structural integrity and regulate the passage of substances across the membrane.
• Teichoic acids: Phosphorus is present in teichoic acids, complex molecules found in the cell walls of certain bacteria. They contribute to bacterial structure, adherence to surfaces, and protection against antimicrobial agents.

Answer: Both Zn+2, Cu+2, Mn+2 and MO6+, Ni2+, B3+ and CO2+

Trace elements are essential for many biochemical reactions in bacteria, but they are required in very small amounts. Therefore, they are also known as microminerals or micronutrients.

The list of trace elements required by bacteria can vary depending on the specific species, but some of the most common trace elements include:

• Zinc (Zn+2): Zinc is essential for the activity of many enzymes, including those involved in DNA replication, protein synthesis, and energy production.
• Copper (Cu+2): Copper is essential for the activity of enzymes involved in iron metabolism, electron transport, and antioxidant defense.
• Manganese (Mn+2): Manganese is essential for the activity of enzymes involved in photosynthesis, nitrogen fixation, and carbohydrate metabolism.
• Molybdenum (MO6+): Molybdenum is essential for the activity of enzymes involved in nitrogen fixation and sulfur metabolism.
• Nickel (Ni2+): Nickel is essential for the activity of enzymes involved in hydrogen metabolism and urea synthesis.
• Boron (B3+): Boron is essential for the activity of enzymes involved in cell wall synthesis and membrane function.
• Cobalt (CO2+): Cobalt is essential for the activity of enzymes involved in vitamin B12 synthesis and nitrogen fixation.

Answer: Na+

While sodium (Na+) is an essential ion for many organisms, including bacteria, it is not strictly required for the growth and survival of all bacteria. Some bacteria have adapted to environments with very low sodium levels and can thrive in the absence of this ion.

The other options are incorrect:

• Mg2+ is an essential ion for all bacteria, as it is involved in many critical biological processes, including enzyme activity, protein synthesis, and DNA replication.
• Ca2+ is also an essential ion for many bacteria, as it is involved in cell wall synthesis, membrane function, and enzyme activity.
• Fe2+ is an essential ion for most bacteria, as it is a component of heme, a molecule that is involved in cellular respiration and oxygen transport.

Answer: Co-enzymes

Vitamins function as coenzymes. Coenzymes are non-protein molecules that are required for the activity of enzymes. They act as cofactors, binding to enzymes and helping them to catalyze chemical reactions.

The other options are incorrect:

• Co-melecules is not a scientific term.
• Building blocks of cell is not a specific enough answer. Vitamins are building blocks of cells in the sense that they are required for the synthesis of many cellular components. However, they do not function as structural components of cells.

Answer: Niacin

The vitamin required for Lactobacillus species is niacin. Niacin is a B vitamin that is essential for the activity of several enzymes involved in bacterial metabolism. It is also involved in the synthesis of NADPH, a molecule that is used in many redox reactions.

The other options are also important for some Lactobacillus species, but they are not as essential as niacin.

• Riboflavin is a B vitamin that is involved in the synthesis of FAD, a molecule that is used in many redox reactions.
• Pyridoxine is a B vitamin that is involved in the synthesis of coenzyme A, a molecule that is used in many metabolic reactions.
• Folic acid is a B vitamin that is involved in the synthesis of DNA.

Answer: Cytochrome o

The peculiar cytochrome in bacteria that can react with molecular oxygen is cytochrome o. It is a terminal oxidase in the bacterial respiratory chain and is responsible for the reduction of oxygen to water. Cytochrome o is found in a variety of bacteria, including aerobes, microaerophiles, and facultative anaerobes.

The other options are incorrect:

• Cytochrome b is a cytochrome found in the electron transport chain of mitochondria. It does not react with molecular oxygen.
• Cytochrome c is a cytochrome found in the electron transport chain of mitochondria and bacteria. It does not react with molecular oxygen.
• Cytochrome d is a cytochrome found in the electron transport chain of some bacteria. It does not react with molecular oxygen.

Answer: ssRNA

The genetic material in HIV is single-stranded RNA (ssRNA). This means that the HIV virus contains a single strand of RNA, which is the genetic material that carries the instructions for making the virus.

The other options are incorrect:

• ds DNA (double-stranded DNA) is the genetic material in most organisms, including humans.
• ss DNA (single-stranded DNA) is a type of DNA that is found in some viruses, but not in HIV.
• s RNA (single-stranded RNA) is the genetic material in some viruses, including HIV.

Answer: Eukaryotic RNA

Poly A tail is frequently found in eukaryotic RNA. It is a non-templated addition of adenines at the 3′ end of most eukaryotic mRNA. The poly A tail is important for the stability and translation of mRNA.

The other options are incorrect:

• Histone is a protein that is found in the nucleus of eukaryotic cells. It is not found in RNA.
• Bacterial RNA does not have a poly A tail.
• tRNA (transfer RNA) does not have a poly A tail.

Answer: Tobacco mosaic virus

Tobacco mosaic virus is a plant virus that causes a characteristic mosaic pattern on the leaves of infected plants. It is an RNA virus, meaning that its genetic material is RNA.

The other options are incorrect:

• SV40 is a DNA virus that can cause cancer in animals.
• T4 phage is a DNA virus that infects bacteria.
• Adenovirus is a DNA virus that can cause respiratory infections in humans.

Answer: Genomic library

A genomic library is a collection of DNA fragments that represents the entire genome of an organism. It is created by extracting genomic DNA from an organism, breaking it into fragments of a reasonable size, and then inserting those fragments into a cloning vector. The cloned fragments are then amplified in bacteria, which produces a large number of identical copies of each fragment.

The other options are incorrect:

• Clones are individual copies of a DNA fragment. A genomic library contains many different clones, each representing a different fragment of the genome.
• mRNA is a type of RNA that carries the instructions for making a protein. It is not used to create genomic libraries.

Answer: MT gene

Transgenic animals are produced when the growth hormone (GH) gene is fused with the metallothionein (MT) gene. The MT gene is a promoter that is responsible for turning on the GH gene. When these two genes are fused together, the GH gene is expressed at high levels, which leads to the production of excess growth hormone. This excess growth hormone causes the transgenic animals to grow larger than their normal counterparts.

The other options are incorrect:

• The GH gene itself is not sufficient to produce transgenic animals. It must be fused with a promoter, such as the MT gene, in order to be expressed.
• The GH receptor (GRF) is not involved in the production of transgenic animals.
• The FIX gene is not involved in the production of transgenic animals.

Answer: Both Hypoxanthine aminopterin thyminine and Hypoxathing-guaning phosphoribosyl transferase

Hydridoma cells are grown selectively in HAT medium, which contains hypoxanthine, aminopterin, and thymidine. Aminopterin blocks the synthesis of purines, while thymidine provides a source of salvage deoxythymidine. HAT-sensitive cells, which lack the HGPRT enzyme, cannot convert hypoxanthine and guanine to guanine nucleotides, and they are killed by aminopterin. HAT-resistant cells, which have the HGPRT enzyme, can convert hypoxanthine and guanine to guanine nucleotides, and they survive in HAT medium.

Therefore, HAT medium is used to select for hydridoma cells, which are HAT-resistant. These cells are then grown in HGPRT medium, which contains hypoxanthine and guanine, but does not contain aminopterin. In HGPRT medium, HAT-resistant cells can continue to grow and produce monoclonal antibodies.

Answer: Restriction endonuclease and ligase

Exonucleases and polymerases are also used in genetic engineering, but they are not as commonly used as restriction endonucleases and ligases. I hope this helps!

• Restriction endonucleases are enzymes that cut DNA at specific sequences. They are used to cut DNA into fragments that can be inserted into a vector.
• Ligases are enzymes that join DNA fragments together. They are used to seal the nicks in the DNA that are created by restriction endonucleases.
• Exonucleases are enzymes that remove nucleotides from the ends of DNA molecules. They are used to trim DNA fragments to a specific length.
• Polymerases are enzymes that synthesize DNA. They are used to amplify DNA fragments

Answer: Plasma cells and myeloma cells

Hybridomas are produced by fusing plasma cells with myeloma cells. Plasma cells are B lymphocytes that produce antibodies, while myeloma cells are cancer cells that are immortal. When these two cells are fused, the hybridoma cell produces antibodies that are specific to the antigen that the plasma cell was originally exposed to.

The other options are incorrect:

• Plasma cells and plasmids cannot be fused together. Plasmids are small, circular pieces of DNA that can be used to transfer genes between bacteria.
• Myeloma cells and plasmids cannot be fused together.
• Plasma cells and bacterial cells cannot be fused together.

Answer: Genetic finger printing

The technique involved in comparing the DNA components of two samples is known as genetic fingerprinting. It is a molecular biological technique used to identify individuals based on their unique DNA patterns. Genetic fingerprinting is also used in paternity testing, forensic investigations, and other areas where it is necessary to identify or distinguish between individuals.

The other options are incorrect:

• Monoclonal antibody techniques are used to produce large quantities of identical antibodies.
• Recombinant DNA technology is used to create new DNA molecules by combining DNA from two different sources.
• Polymerase chain reaction (PCR) is a technique used to amplify DNA fragments.

Answer: They are self replicating within the bacterial cell

Plasmids are ideal vectors for gene cloning because they are self-replicating within the bacterial cell. This means that when a gene is inserted into a plasmid, the plasmid will replicate along with the bacterial DNA, producing many copies of the gene. This makes it easy to amplify the gene and produce large quantities of it.

The other options are incorrect:

• Plasmids can be multiplied by culturing, but this is not as efficient as replicating them within a bacterial cell.
• Plasmids can be multiplied in the laboratory using enzymes, but this is more complex and time-consuming than replicating them within a bacterial cell.
• Plasmids cannot replicate freely outside the bacterial cell.

Answer: 44

Humans normally have 46 chromosomes in their cells, and these include 22 pairs of autosomes (non-sex chromosomes) and one pair of sex chromosomes. In a kidney cell, the number of autosomes would still be 22 pairs, so there would be 44 autosomes in total. The sex chromosomes (X and Y) determine the individual’s sex and are not considered autosomes.