I85PREP
⌘ K
Tamil Nadu HSE First Year Microbiology study materials
Tamil Nadu HSE First Year Microbiology study resources

Tamil Nadu HSE First Year Microbiology practice questions

One question at a time. Build your Tamil Nadu HSE First Year Microbiology understanding.

First 50 of 200 questions. Each one lists the choices, the correct answer, and an explanation. The checker at the top of this page saves progress in this browser when it is available.

Continue in the practice tool above to load more questions, 50 at a time.

Question 1Introduction to Microbiology and History of Microbiology

In the five-kingdom classification proposed by R. H. Whittaker, the prokaryotic microorganisms were placed in which kingdom?

  1. Monera Correct answer.
  2. Fungi
  3. Plantae
  4. Protista

Explanation

Whittaker's 1969 five-kingdom system separated prokaryotes from eukaryotes by placing all bacteria and cyanobacteria in the kingdom Monera. Protista contained unicellular eukaryotes, while Fungi and Plantae were eukaryotic multicellular groups. Monera is therefore the only kingdom in that scheme built entirely of prokaryotic cells.

Question 2Introduction to Microbiology and History of Microbiology

Which scientist first observed and described microorganisms using a single-lens microscope of his own construction?

  1. Antonie van Leeuwenhoek Correct answer.
  2. Robert Koch
  3. Robert Hooke
  4. Louis Pasteur

Explanation

Antonie van Leeuwenhoek, a Dutch draper, ground his own single-lens microscopes and in the 1670s reported 'animalcules' from pond water, saliva and pepper infusions. His observations are the earliest reliable descriptions of bacteria and protozoa. Hooke observed fungal structures and plant cells, while Pasteur and Koch worked two centuries later.

Question 3Introduction to Microbiology and History of Microbiology

The theory that living organisms arise only from pre-existing living organisms is known as which of the following?

  1. Spontaneous generation
  2. Abiogenesis
  3. Panspermia
  4. Biogenesis Correct answer.

Explanation

Biogenesis states that life comes from life, and it replaced the older doctrine of spontaneous generation after experiments by Redi, Spallanzani, Pasteur and Tyndall. Abiogenesis refers to the origin of life from non-living matter, which is a different concept from the everyday generation of maggots or microbes. Spontaneous generation is the theory that biogenesis displaced, and panspermia proposes that life arrived from space.

Question 4Introduction to Microbiology and History of Microbiology

In the swan-neck flask experiment, Pasteur boiled broth in a flask whose neck was drawn into a long curve open to the air. What did this design demonstrate?

  1. That heat alone cannot sterilize a sealed flask
  2. That boiling destroys all nutrients in broth
  3. That airborne microbes are trapped in the curve and cannot reach the sterile broth Correct answer.
  4. That broth can generate microbes when exposed to oxygen

Explanation

The curved neck admitted air but trapped dust and airborne microorganisms in its bend, so the boiled broth remained clear. When the neck was broken off, microbes entered and the broth spoiled. This showed that putrefaction depends on microbes carried in air, not on air itself, refuting spontaneous generation.

Question 5Introduction to Microbiology and History of Microbiology

Which staining technique uses a single basic dye such as crystal violet or methylene blue and is used mainly to observe cell shape and arrangement?

  1. Endospore staining
  2. Acid-fast staining
  3. Gram staining
  4. Simple staining Correct answer.

Explanation

Simple staining applies one basic dye to a heat-fixed smear, giving uniform colour that reveals morphology and arrangement but not differential properties. Gram and acid-fast staining use multiple reagents to divide bacteria into groups. Endospore staining is a special method using heat and contrasting dyes to reveal spores.

Question 6Introduction to Microbiology and History of Microbiology

In the Gram staining procedure, what is the function of Gram's iodine?

  1. It fixes the smear to the slide.
  2. It acts as a mordant that forms a crystal violet-iodine complex in the cell. Correct answer.
  3. It counterstains Gram-negative cells pink.
  4. It decolourizes Gram-negative cells.

Explanation

Iodine is applied after crystal violet and acts as a mordant, combining with the dye to form a large crystal violet-iodine complex trapped in the thick peptidoglycan of Gram-positive cells. Alcohol then decolourizes Gram-negative cells, and safranin counterstains them. Fixing the smear is a separate step done by heat or methanol before staining.

Question 7Introduction to Microbiology and History of Microbiology

A bacterium is stained and appears as a chain of spherical cells. Which morphological description is correct?

  1. Diplobacilli
  2. Staphylococci
  3. Sarcinae
  4. Streptococci Correct answer.

Explanation

Spherical cells are cocci, and a chain arrangement is described by the prefix strepto-, so a chain of cocci is streptococci. Staphylococci form grape-like clusters, and sarcinae are cubical packets of eight cocci. Diplobacilli are paired rod-shaped cells, not spheres.

Question 8Introduction to Microbiology and History of Microbiology

Which structure enables certain bacteria to survive heat, desiccation and radiation for long periods and is produced intracellularly?

  1. Endospore Correct answer.
  2. Pili
  3. Flagellum
  4. Capsule

Explanation

Endospores are highly resistant dormant structures formed inside the bacterial cell, typically by Bacillus and Clostridium species, when nutrients become limiting. They contain dipicolinic acid and calcium salts and have a dehydrated core, which explains their resistance. Capsules, flagella and pili serve attachment, motility and genetic exchange rather than long-term survival.

Question 9Introduction to Microbiology and History of Microbiology

Which of the following correctly pairs a bacterial appendage with its function?

  1. Flagella - transfer of DNA during conjugation
  2. Fimbriae - formation of resistant spores
  3. Pili - motility in liquid media
  4. Capsule - protection against phagocytosis Correct answer.

Explanation

The capsule is a polysaccharide or polypeptide layer outside the cell wall that resists phagocytosis and aids adherence. Flagella, not pili, provide motility, while pili mediate conjugation and attachment. Fimbriae are short attachment structures and have no role in spore formation.

Question 10Introduction to Microbiology and History of Microbiology

Which scientist established a set of criteria linking a specific microorganism to a specific disease, using pure cultures?

  1. Joseph Lister
  2. Robert Koch Correct answer.
  3. Edward Jenner
  4. Alexander Fleming

Explanation

Robert Koch developed criteria, now called Koch's postulates, requiring that a suspected pathogen be isolated in pure culture from a diseased host and reproduce the disease when inoculated into a healthy host. Lister introduced antiseptic surgery, Fleming discovered penicillin, and Jenner pioneered smallpox vaccination.

Question 11Introduction to Microbiology and History of Microbiology

Which postulate is part of Koch's criteria for proving that a microbe causes a disease?

  1. The microbe must be visible in unstained living tissue.
  2. The microbe must be killed before inoculation.
  3. The microbe must be isolated from the diseased host and grown in pure culture. Correct answer.
  4. The microbe must be present in healthy hosts as well.

Explanation

One of Koch's postulates requires that the organism be isolated from the diseased host and maintained in pure culture. Another requires that the pure culture reproduce the disease in a healthy susceptible host. Finding the organism in healthy hosts would weaken the causal claim, and viability is essential for reproducing disease.

Question 12Introduction to Microbiology and History of Microbiology

Which observation by Alexander Fleming led to the discovery of penicillin?

  1. Boiled broth remained clear in a swan-neck flask.
  2. A bacterium transferred DNA to another bacterium through a pilus.
  3. A mould colony on a plate inhibited the growth of surrounding Staphylococcus bacteria. Correct answer.
  4. A virus-infected bacterium lysed rapidly.

Explanation

Fleming noticed that a contaminating Penicillium mould produced a zone in which staphylococci failed to grow, indicating an antibacterial substance. This observation underlies the antibiotic era that followed with Florey and Chain. Conjugation, swan-neck flasks and bacteriophage lysis are associated with other discoveries.

Question 13Introduction to Microbiology and History of Microbiology

A student isolates an organism that grows on a medium lacking a nitrogen source but readily fixes atmospheric nitrogen in aerobic conditions. Which genus best fits this description?

  1. Nitrosomonas
  2. Clostridium
  3. Azotobacter Correct answer.
  4. Escherichia

Explanation

Azotobacter is a free-living aerobic soil bacterium that fixes atmospheric nitrogen and can therefore grow without combined nitrogen. Nitrosomonas is a nitrifying chemolithotroph that oxidizes ammonia rather than fixing nitrogen. Clostridium fixes nitrogen only under anaerobic conditions, and Escherichia is not a nitrogen fixer.

Question 14Introduction to Microbiology and History of Microbiology

Which group of microorganisms is characterized by the absence of a cell wall and the ability to grow on media containing penicillin?

  1. Mycoplasma Correct answer.
  2. Actinomycetes
  3. Cyanobacteria
  4. Rickettsia

Explanation

Mycoplasma lacks a peptidoglycan cell wall, so it is intrinsically resistant to penicillin and other cell-wall-active antibiotics. Colonies show a fried-egg appearance on agar, and the cells are pleomorphic. Actinomycetes and cyanobacteria have cell walls, and Rickettsia has a cell wall and is an obligate intracellular parasite.

Question 15Introduction to Microbiology and History of Microbiology

Which of the following is a distinguishing feature of archaea compared with bacteria?

  1. Presence of a membrane-bound nucleus
  2. Absence of ribosomes
  3. Presence of ether-linked branched-chain lipids in the membrane Correct answer.
  4. Presence of peptidoglycan in the cell wall

Explanation

Archaeal membranes contain ether-linked isoprenoid lipids rather than the ester-linked fatty acids of bacteria and eukaryotes. Their cell walls also lack peptidoglycan, although some have pseudopeptidoglycan. Archaea have ribosomes and are prokaryotic, so they lack a membrane-bound nucleus.

Question 16Introduction to Microbiology and History of Microbiology

Which statement about viruses is correct?

  1. They contain either DNA or RNA as genetic material but not both. Correct answer.
  2. They are cellular organisms with a plasma membrane and ribosomes.
  3. They generate ATP through their own mitochondria.
  4. They reproduce by binary fission inside host cells.

Explanation

Viruses are acellular particles containing a nucleic acid genome, either DNA or RNA but not both, enclosed in a protein capsid. They lack ribosomes and mitochondria and cannot generate energy independently. They replicate by assembling components within a host cell rather than by binary fission.

Question 17Introduction to Microbiology and History of Microbiology

Which scientist demonstrated that the causative agent of tobacco mosaic disease is smaller than a bacterium and passes through filters that retain bacteria?

  1. Dmitri Ivanovsky Correct answer.
  2. Sergei Winogradsky
  3. Ferdinand Cohn
  4. Martinus Beijerinck

Explanation

Dmitri Ivanovsky showed in 1892 that sap from infected tobacco plants remained infectious after passing through a filter that retained bacteria. Beijerinck later described the agent as a 'contagium vivum fluidum' and is credited with the concept of a virus. Cohn and Winogradsky made major contributions to bacterial taxonomy and soil microbiology.

Question 18Introduction to Microbiology and History of Microbiology

A soil sample is enriched in a medium containing only inorganic salts and ammonium as the energy source. Which organism is most likely to be favoured?

  1. Nitrosomonas Correct answer.
  2. Staphylococcus aureus
  3. Escherichia coli
  4. Saccharomyces cerevisiae

Explanation

Nitrosomonas is a chemolithoautotroph that obtains energy by oxidizing ammonium to nitrite and uses carbon dioxide as its carbon source. The other options are heterotrophs requiring organic carbon and energy sources. Such an enrichment therefore selects for nitrifying bacteria.

Question 19Introduction to Microbiology and History of Microbiology

Which contribution is correctly attributed to Sergei Winogradsky?

  1. Development of the Gram staining procedure
  2. Discovery of penicillin
  3. Demonstration of chemolithotrophy in sulfur-oxidizing bacteria Correct answer.
  4. Formulation of the five-kingdom classification

Explanation

Winogradsky established the concept of chemolithotrophy by showing that Beggiatoa and other sulfur bacteria obtain energy from oxidizing inorganic sulfur compounds. He also described nitrogen-fixing Clostridium and developed the Winogradsky column. Gram staining, penicillin and the five-kingdom system belong to other scientists.

Question 20Introduction to Microbiology and History of Microbiology

Which statement best explains why Koch's postulates cannot be applied strictly to all pathogens today?

  1. Some pathogens cannot be cultured in vitro or lack a suitable animal host. Correct answer.
  2. Pure culture techniques have been abandoned.
  3. Antibiotics prevent the growth of all pathogens in culture.
  4. All pathogens are obligate intracellular parasites.

Explanation

Koch's postulates assume that the organism can be grown in pure culture and introduced into a susceptible host. Some pathogens, such as certain viruses and obligate intracellular bacteria, cannot be cultured alone or lack an animal model, so the postulates must be modified. Pure culture remains a standard technique, and antibiotic resistance varies among organisms.

Question 21Microbial Cell Structure and Morphology (Bacteria, Fungi, Viruses, Algae, Protozoa)

In the cell wall of most Gram-positive bacteria, the peptidoglycan layer is characteristically:

  1. Absent, leaving only a plasma membrane
  2. Thin and overlaid by an outer membrane
  3. Composed mainly of cellulose microfibrils
  4. Thick and extensively cross-linked Correct answer.

Explanation

Gram-positive walls contain a thick peptidoglycan sacculus with extensive peptide cross-links, which retains crystal violet during Gram staining. Gram-negative walls are thin and covered by an outer membrane, and cellulose is a plant cell wall polymer, not a bacterial one.

Question 22Microbial Cell Structure and Morphology (Bacteria, Fungi, Viruses, Algae, Protozoa)

A bacterium is placed in a hypotonic solution. Which structure prevents the cell from bursting as water enters?

  1. The flagellum
  2. The nucleoid
  3. The cell wall Correct answer.
  4. The capsule

Explanation

The rigid peptidoglycan wall resists the turgor pressure generated when water enters a cell in a hypotonic medium. Without a wall, as in protoplasts, the cell lyses. The capsule, flagellum and nucleoid do not provide mechanical strength against osmotic swelling.

Question 23Microbial Cell Structure and Morphology (Bacteria, Fungi, Viruses, Algae, Protozoa)

Which feature is characteristic of the archaeal cytoplasmic membrane?

  1. Unbranched fatty acids linked to glycerol by ester bonds
  2. Branched isoprenoid chains linked to glycerol by ether bonds Correct answer.
  3. A bilayer made solely of peptidoglycan
  4. A complete absence of any lipid bilayer

Explanation

Archaeal membranes contain branched isoprenoid hydrocarbon chains attached to glycerol by ether linkages, which resist heat and acid. Bacterial and eukaryotic membranes use unbranched fatty acids joined by ester bonds.

Question 24Microbial Cell Structure and Morphology (Bacteria, Fungi, Viruses, Algae, Protozoa)

The lipopolysaccharide of the Gram-negative outer membrane is medically important mainly because it:

  1. Functions as endotoxin and induces fever Correct answer.
  2. Stores phosphate reserves for the cell
  3. Serves as the main locomotor organelle
  4. Acts as the primary site of ATP synthesis

Explanation

Lipid A of lipopolysaccharide is an endotoxin that triggers fever, inflammation and septic shock in the host. ATP synthesis occurs on the plasma membrane, motility depends on flagella, and phosphate is stored in metachromatic granules.

Question 25Microbial Cell Structure and Morphology (Bacteria, Fungi, Viruses, Algae, Protozoa)

Bacterial ribosomes are described as 70S and consist of:

  1. A single 70S particle with no subunits
  2. A 60S and a 40S subunit
  3. A 50S and a 30S subunit Correct answer.
  4. A 40S and a 30S subunit

Explanation

The 70S bacterial ribosome is formed from a large 50S subunit and a small 30S subunit. Eukaryotic cytoplasmic ribosomes are 80S, made of 60S and 40S subunits, and all ribosomes are assembled from subunits.

Question 26Microbial Cell Structure and Morphology (Bacteria, Fungi, Viruses, Algae, Protozoa)

Endospores of Bacillus species are best described as:

  1. Highly resistant dormant structures formed inside the cell Correct answer.
  2. A means of sexual reproduction in bacteria
  3. Storage granules of poly-beta-hydroxybutyrate
  4. Motile swimming cells produced under starvation

Explanation

Endospores are dormant, dehydrated, calcium dipicolinate-rich structures formed within the bacterial cell and are highly resistant to heat and chemicals. Bacteria do not reproduce sexually, and endospores are non-motile and not storage granules.

Question 27Microbial Cell Structure and Morphology (Bacteria, Fungi, Viruses, Algae, Protozoa)

A monotrichous bacterium such as Vibrio cholerae possesses:

  1. Two flagella, one at each pole
  2. A tuft of flagella at one pole
  3. Flagella distributed over the entire surface
  4. A single flagellum at one pole Correct answer.

Explanation

Monotrichous means a single polar flagellum, as seen in Vibrio cholerae. A polar tuft is lophotrichous, flagella all over the surface are peritrichous, and one flagellum at each end is amphitrichous.

Question 28Microbial Cell Structure and Morphology (Bacteria, Fungi, Viruses, Algae, Protozoa)

Pili that mediate the transfer of plasmid DNA between conjugating bacteria are called:

  1. Cilia
  2. Axial filaments
  3. Fimbriae
  4. Sex pili Correct answer.

Explanation

Sex pili are longer, fewer appendages that form a conjugation tube for plasmid transfer between bacteria. Fimbriae are shorter and numerous and mediate adhesion, cilia are eukaryotic organelles, and axial filaments occur in spirochaetes.

Question 29Microbial Cell Structure and Morphology (Bacteria, Fungi, Viruses, Algae, Protozoa)

A bacterial culture is treated with lysozyme, which hydrolyses peptidoglycan. In a Gram-positive organism the immediate result in a suitable medium is:

  1. Formation of a protoplast Correct answer.
  2. Formation of a capsule
  3. Formation of a spheroplast
  4. Formation of an endospore

Explanation

Removing the thick wall of a Gram-positive cell leaves a protoplast, bounded only by the plasma membrane. In Gram-negative bacteria the outer membrane persists, so removal of peptidoglycan yields a spheroplast. Endospores and capsules are not products of wall digestion.

Question 30Microbial Cell Structure and Morphology (Bacteria, Fungi, Viruses, Algae, Protozoa)

The cell wall of most true fungi consists mainly of:

  1. Peptidoglycan
  2. Chitin Correct answer.
  3. Silica
  4. Cellulose

Explanation

Fungal walls are built chiefly of chitin, a polymer of N-acetylglucosamine, together with glucans and glycoproteins. Peptidoglycan is bacterial, cellulose dominates plant and some algal walls, and silica occurs in diatom frustules.

Question 31Microbial Cell Structure and Morphology (Bacteria, Fungi, Viruses, Algae, Protozoa)

Coenocytic hyphae are distinguished by:

  1. Cross-walls dividing each hypha into uninucleate compartments
  2. A single nucleus per hypha without septa
  3. Absence of cross-walls, so nuclei share a common cytoplasm Correct answer.
  4. Chains of yeast cells joined end to end

Explanation

Coenocytic hyphae lack regular septa, producing a continuous multinucleate cytoplasm, as in Mucor and Rhizopus. Septate hyphae, by contrast, are divided by cross-walls into compartments.

Question 32Microbial Cell Structure and Morphology (Bacteria, Fungi, Viruses, Algae, Protozoa)

In the classification of fungi by sexual spore type, a fungus producing zygospores belongs to which group?

  1. Basidiomycetes
  2. Zygomycetes Correct answer.
  3. Deuteromycetes
  4. Ascomycetes

Explanation

Zygomycetes are characterised by thick-walled zygospores formed by fusion of gametangia, as in Rhizopus. Ascomycetes form ascospores, basidiomycetes form basidiospores, and deuteromycetes lack known sexual stages.

Question 33Microbial Cell Structure and Morphology (Bacteria, Fungi, Viruses, Algae, Protozoa)

A yeast cell reproduces asexually by forming a small outgrowth that enlarges and separates. This process is:

  1. Fragmentation
  2. Binary fission
  3. Conidiation
  4. Budding Correct answer.

Explanation

Budding is the pinching off of a new daughter cell from the parent yeast, leaving a bud scar. Binary fission divides the cell into two equal cells, conidiation forms asexual spores on specialised hyphae, and fragmentation splits mycelium.

Question 34Microbial Cell Structure and Morphology (Bacteria, Fungi, Viruses, Algae, Protozoa)

Which statement correctly distinguishes a virus from a bacterium?

  1. A virus possesses a cell wall made of chitin
  2. A virus reproduces independently by binary fission on nutrient agar
  3. A virus has no cellular organisation and is an obligate intracellular parasite Correct answer.
  4. A virus contains both DNA and RNA in the same particle

Explanation

Viruses are acellular, consisting of nucleic acid enclosed in a protein capsid, and multiply only inside a living host cell. Bacteria are cellular, have walls and ribosomes, and can grow on laboratory media.

Question 35Microbial Cell Structure and Morphology (Bacteria, Fungi, Viruses, Algae, Protozoa)

A bacteriophage with an icosahedral head, a hollow tail and tail fibres is typical of which morphological group?

  1. Helical viruses
  2. Enveloped viruses
  3. Icosahedral viruses
  4. Complex viruses Correct answer.

Explanation

Viruses combining head, tail and tail fibres, such as T4 phage, are classified as complex because their symmetry is neither purely helical nor purely icosahedral. Helical and icosahedral viruses lack the tail assembly, and enveloped viruses carry a lipid envelope.

Question 36Microbial Cell Structure and Morphology (Bacteria, Fungi, Viruses, Algae, Protozoa)

The enzyme reverse transcriptase, found in retroviruses such as HIV, catalyses the synthesis of:

  1. Protein from an mRNA template
  2. DNA from an RNA template Correct answer.
  3. RNA from a DNA template
  4. ATP from ADP and phosphate

Explanation

Reverse transcriptase copies the viral RNA genome into complementary DNA, which then integrates into the host genome. RNA synthesis from DNA is carried out by RNA polymerase, protein synthesis by ribosomes, and ATP formation by ATP synthase.

Question 37Microbial Cell Structure and Morphology (Bacteria, Fungi, Viruses, Algae, Protozoa)

During the lysogenic cycle of a temperate phage, the viral DNA:

  1. Remains free in the periplasm as a plasmid
  2. Is immediately replicated and the host is lysed
  3. Is degraded by host restriction enzymes
  4. Integrates into the host chromosome as a prophage Correct answer.

Explanation

In lysogeny the phage genome integrates into the bacterial chromosome as a prophage and is replicated along with it, without killing the host. Immediate replication with lysis describes the lytic cycle.

Question 38Microbial Cell Structure and Morphology (Bacteria, Fungi, Viruses, Algae, Protozoa)

Diatoms are easily recognised among algae by their:

  1. Contractile vacuoles used for osmoregulation
  2. Single cup-shaped chloroplast with a pyrenoid
  3. Cell walls of overlapping silica frustules Correct answer.
  4. Cell walls made of chitin and glucan

Explanation

Diatoms (Bacillariophyceae) have cell walls of silica called frustules, consisting of two overlapping halves or valves. Chitin walls are fungal, and contractile vacuoles are protozoan organelles.

Question 39Microbial Cell Structure and Morphology (Bacteria, Fungi, Viruses, Algae, Protozoa)

The reserve food material of brown algae such as Sargassum is chiefly:

  1. Starch
  2. Laminarin and mannitol Correct answer.
  3. Paramylon
  4. Glycogen

Explanation

Brown algae store carbohydrate as laminarin, together with mannitol, and their brown colour comes from fucoxanthin. Starch is the green algal and plant reserve, glycogen is the animal and bacterial reserve, and paramylon occurs in euglenoids.

Question 40Microbial Cell Structure and Morphology (Bacteria, Fungi, Viruses, Algae, Protozoa)

Red algae are distinguished from other algal groups mainly by:

  1. Absence of any photosynthetic pigment
  2. Presence of chlorophyll b as the only pigment
  3. Presence of fucoxanthin as the dominant pigment
  4. Presence of phycoerythrin and phycocyanin Correct answer.

Explanation

Rhodophyceae contain the accessory pigments phycoerythrin and phycocyanin, which mask chlorophyll a and give the red colour. Fucoxanthin dominates brown algae, and no alga lacks photosynthetic pigments.

Question 41Microbial Cell Structure and Morphology (Bacteria, Fungi, Viruses, Algae, Protozoa)

Amoeba proteus captures food by extending pseudopodia around a particle. The process is:

  1. Binary fission
  2. Phagocytosis Correct answer.
  3. Pinocytosis
  4. Exocytosis

Explanation

Phagocytosis is the engulfment of solid particles by pseudopodia, forming a food vacuole, as in Amoeba. Pinocytosis takes in dissolved substances in fluid droplets, exocytosis expels material, and binary fission is reproduction.

Question 42Microbial Cell Structure and Morphology (Bacteria, Fungi, Viruses, Algae, Protozoa)

The contractile vacuole of a freshwater protozoan such as Paramecium functions mainly in:

  1. Sexual reproduction by conjugation
  2. Locomotion through cilia
  3. Osmoregulation by expelling excess water Correct answer.
  4. Digestion of ingested bacteria

Explanation

Freshwater protozoa gain water osmotically, and the contractile vacuole collects and expels it to maintain osmotic balance. Digestion occurs in food vacuoles, cilia provide movement, and conjugation is a nuclear exchange process.

Question 43Microbial Cell Structure and Morphology (Bacteria, Fungi, Viruses, Algae, Protozoa)

The macronucleus of ciliates such as Paramecium is best characterised as:

  1. A diploid nucleus that undergoes meiosis before every division
  2. A polyploid nucleus controlling vegetative cell activities Correct answer.
  3. A small nucleus exchanged during conjugation
  4. An organelle that secretes the pellicle

Explanation

Ciliates are dimorphic for nuclei: the large macronucleus is polyploid and governs vegetative metabolism, while the micronucleus is diploid and takes part in conjugation. The macronucleus does not undergo meiosis at each division.

Question 44Microbial Cell Structure and Morphology (Bacteria, Fungi, Viruses, Algae, Protozoa)

A researcher finds a wall-less prokaryote that grows on artificial media containing sterols and forms small colonies. It is most likely a member of:

  1. Chlamydia
  2. Mycoplasma Correct answer.
  3. Rickettsia
  4. Mycobacterium

Explanation

Mycoplasma lacks a cell wall, requires sterols in the medium and forms very small colonies, and it is the only wall-less bacterium among the options. Chlamydia and Rickettsia are obligate intracellular parasites, and Mycobacterium has a waxy but present wall.

Question 45Microbial Nutrition, Growth and Culture Techniques

A bacterial culture is described as oligotrophic. Which nutritional condition does this term indicate?

  1. Growth in a medium containing high salt concentration
  2. Growth requiring a medium supplemented with blood or serum
  3. Growth only in the presence of oxygen at high concentration
  4. Growth in a medium containing very low concentrations of nutrients Correct answer.

Explanation

Oligotrophic organisms are adapted to survive and multiply in environments where the concentration of available nutrients is very low, such as distilled water or deep ocean samples. They usually possess high-affinity uptake systems for scarce substrates. High nutrient formulations are the opposite situation, termed copiotrophic.

Question 46Microbial Nutrition, Growth and Culture Techniques

Which element is required by bacteria in the largest quantity and forms the backbone of all organic molecules?

  1. Molybdenum
  2. Sulphur
  3. Carbon Correct answer.
  4. Cobalt

Explanation

Carbon typically makes up about half the dry weight of a bacterial cell and is the structural framework of proteins, carbohydrates, lipids and nucleic acids. It is therefore required in the greatest amount. Sulphur, molybdenum and cobalt are needed only in small or trace quantities.

Question 47Microbial Nutrition, Growth and Culture Techniques

A bacterium uses hydrogen sulphide as its electron donor and carbon dioxide as its carbon source, with light as energy. How is its nutrition classified?

  1. Photoautotroph Correct answer.
  2. Chemoautotroph
  3. Chemoheterotroph
  4. Photoheterotroph

Explanation

The organism uses light as energy source (photo-) and carbon dioxide as carbon source (auto-), so it is a photoautotroph, like green sulphur bacteria. The electron donor is inorganic, which is consistent with this class. Chemo- prefixes would require an organic or inorganic chemical energy source rather than light.

Question 48Microbial Nutrition, Growth and Culture Techniques

In the context of bacterial nutrition, what does the term 'fastidious' describe?

  1. An organism requiring complex preformed nutrients such as vitamins or amino acids Correct answer.
  2. An organism that grows only in the absence of oxygen
  3. An organism that grows only at elevated temperature
  4. An organism that tolerates very high sugar concentrations

Explanation

A fastidious organism cannot synthesise all its own cell constituents and therefore needs preformed growth factors, amino acids or vitamins supplied in the medium. Blood agar and yeast extract are often added for such organisms. The term refers to nutritional demand, not to temperature, oxygen or sugar tolerance.

Question 49Microbial Nutrition, Growth and Culture Techniques

Which statement correctly distinguishes a selective medium from a differential medium?

  1. Selective media are always liquid, while differential media are always solid
  2. Selective media contain indicators, while differential media contain inhibitors
  3. Selective media are used only for fungi, while differential media are used only for bacteria
  4. Selective media allow growth of particular organisms, while differential media reveal metabolic differences by colony appearance Correct answer.

Explanation

A selective medium includes substances that suppress unwanted organisms so that only the desired group grows, whereas a differential medium contains an indicator that makes colonies of different metabolic types look distinct. MacConkey agar is an example that does both. The two functions are defined by purpose, not by physical state or organism group.

Question 50Microbial Nutrition, Growth and Culture Techniques

Which medium is best described as a defined (synthetic) medium?

  1. Nutrient broth containing peptone and beef extract
  2. A medium whose exact chemical composition and quantities of each ingredient are known Correct answer.
  3. A medium to which blood or serum has been added
  4. A medium containing an undefined mixture of yeast extract and casein hydrolysate

Explanation

A defined or synthetic medium is prepared from pure chemical compounds whose identity and amount are precisely known, such as a glucose–salts medium. Complex ingredients like peptone, beef extract or blood vary in composition and therefore make a medium undefined. Knowing the exact composition allows reproducible control of nutrition in experiments.