Microbes in Human Welfare — Practice Questions with Answers

Q1.

Which microorganism is responsible for the conversion of milk into curd?

• A Saccharomyces cerevisiae
• B Lactobacillus
• C Aspergillus niger
• D Penicillium notatum

Q2.

Which organism is used for fermentation in bread making?

• A Lactobacillus
• B Aspergillus niger
• C Saccharomyces cerevisiae
• D Rhizobium

Q3.

Penicillin, the first antibiotic, was discovered from which fungus?

• A Aspergillus niger
• B Trichoderma polysporum
• C Penicillium notatum
• D Monascus purpureus

Q4.

Which bacterium is used as a biocontrol agent against caterpillars and other insect pests?

• A Rhizobium, a nitrogen-fixing root bacterium
• B Bacillus thuringiensis
• C Azotobacter, a free-living nitrogen fixer
• D Pseudomonas, a common soil bacterium

Q5.

Rhizobium bacteria fix nitrogen in symbiotic association with which type of plants?

• A Paddy plants
• B Legumes
• C Wheat plants
• D Ferns

Q6.

Which step of sewage treatment involves the use of aerobic microorganisms?

• A Primary treatment
• B Tertiary treatment
• C Secondary treatment
• D Chlorination

Q7.

BOD stands for which of the following?

• A Biological Oxygen Demand
• B Biochemical Oxygen Deficiency
• C Bacterial Oxygen Demand
• D Biological Oxidation Depth

Q8.

Which cyanobacterium forms a symbiotic association with the water fern Azolla?

• A Nostoc
• B Anabaena
• C Spirulina
• D Oscillatoria

Q9.

Citric acid is commercially produced using which microorganism?

• A Lactobacillus
• B Saccharomyces
• C Aspergillus niger
• D Streptococcus

Q10.

Which gas is the major component of biogas produced in sludge digesters?

• A Carbon dioxide
• B Hydrogen sulfide
• C Methane
• D Nitrogen

Q11.

Mycorrhiza is a symbiotic association between fungi and which part of a plant?

• A Leaves
• B Roots
• C Stems
• D Flowers

Q12.

Which microorganism produces the immunosuppressant drug cyclosporin A?

• A Monascus purpureus
• B Aspergillus niger
• C Trichoderma polysporum
• D Penicillium chrysogenum

Q13.

What is the primary treatment of sewage mainly concerned with?

• A Biological degradation of organic matter using activated sludge
• B Removal of suspended solids by settling and screening
• C Chlorination of treated water before final discharge
• D Addition of coagulant chemicals to settle out solids

Q14.

Azotobacter is a bacterium that fixes nitrogen in which manner?

• A Symbiotically in root nodules
• B Freely in the soil
• C In partnership with legumes
• D Inside leaf cells

Q15.

Which microorganism is used as a biofertilizer to provide phosphorus to plants?

• A Rhizobium
• B Glomus
• C Azotobacter
• D Anabaena

Q16.

The enzyme streptokinase used as a clot buster is produced by which organism?

• A Streptococcus
• B Aspergillus
• C Penicillium
• D Lactobacillus

Q17.

Statins, which lower blood cholesterol, are produced by which microorganism?

• A Trichoderma polysporum
• B Aspergillus niger
• C Monascus purpureus
• D Penicillium notatum

Q18.

Which type of microorganism belongs to the genus Nucleopolyhedrovirus used in biocontrol?

• A Bacterium
• B Fungus
• C Baculovirus
• D Protozoan

Q19.

Lactic acid fermentation is carried out by which microorganism?

• A Aspergillus niger
• B Saccharomyces cerevisiae
• C Lactobacillus
• D Rhizobium

Q20.

Which organism is used to produce toddy, a traditional fermented drink?

• A Lactobacillus
• B Saccharomyces cerevisiae
• C Aspergillus niger
• D Nostoc

Q21.

The cry proteins (delta endotoxins) of Bacillus thuringiensis are stored in the bacterium as which structure?

• A Flagella, used for bacterial motility
• B Plasmids, small circular DNA molecules
• C Spores and crystals
• D Capsules, the protective outer layer

Q22.

In sewage treatment, the term floc refers to which structure?

• A A free-floating cluster of photosynthetic algal cells
• B Masses of bacteria held together by fungal filaments
• C A perforated filter bed used in the primary settling tank
• D Activated sludge specifically recycled from secondary settling tanks

Q23.

Which enzyme produced by microorganisms is widely used in detergent formulations to remove oil stains?

• A Streptokinase
• B Pectinase
• C Lipase
• D Amylase

Q24.

What does a higher BOD value in a water sample indicate?

• A The water is unusually clean and contains abundant dissolved oxygen
• B Greater level of organic pollution requiring more oxygen
• C The presence of dissolved heavy metals such as lead and mercury
• D An unusually low level of bacterial metabolic activity in the sample

Q25.

Which free-living nitrogen-fixing bacterium is closely associated with the rhizosphere of grasses and cereals?

• A Rhizobium
• B Nostoc
• C Azospirillum
• D Anabaena

Q26.

Cyclosporin A is used primarily for which medical purpose?

• A As an antibiotic against bacterial infections
• B To lower blood cholesterol levels
• C To prevent organ rejection after transplants
• D As a clot-dissolving agent

Q27.

Which microorganism acts as a biocontrol agent against plant pathogens by competing for nutrients and space?

• A Bacillus thuringiensis
• B Trichoderma
• C Pseudomonas
• D Azotobacter

Q28.

In the production of cheese, the characteristic large holes in Swiss cheese are made by which organism?

• A Penicillium roqueforti
• B Propionibacterium shermanii
• C Lactobacillus helveticus
• D Streptococcus thermophilus

Q29.

Roquefort cheese gets its characteristic flavour from which microorganism?

• A Lactobacillus
• B Saccharomyces cerevisiae
• C Penicillium roqueforti
• D Aspergillus niger

Q30.

Biogas produced in sewage sludge digesters consists of which combination of gases?

• A Methane and oxygen
• B Methane, CO2, and H2S
• C Hydrogen and nitrogen
• D Carbon monoxide and methane

Q31.

Pectinases and proteases produced by microbes are used in which industrial application?

• A Production of antibiotics
• B Clarification of fruit juices
• C Sewage treatment
• D Nitrogen fixation

Q32.

Which species of Pseudomonas is used as a bioherbicide against the weed Phalaris minor?

• A Pseudomonas fluorescens
• B Pseudomonas putida
• C Pseudomonas aeruginosa
• D Pseudomonas syringae

Q33.

Mycorrhizal fungi of the genus Glomus provide which benefit besides phosphorus absorption?

• A Direct atmospheric nitrogen fixation within the root cortex
• B Resistance to root pathogens and tolerance to salinity
• C Production of plant growth hormones as their sole additional benefit
• D Conversion of soil urea into ammonia for plant uptake

Q34.

Which cyanobacterium is found free-living in paddy fields and fixes atmospheric nitrogen?

• A Anabaena and Nostoc
• B Spirulina mainly
• C Chlorella mainly
• D Oscillatoria mainly

Q35.

The activated sludge produced during secondary sewage treatment is used for what purpose?

• A Directly applied as fertilizer without any further treatment steps
• B Pumped into anaerobic sludge digesters to produce biogas
• C Discharged directly into nearby rivers and streams
• D Used to make biochar through pyrolysis treatment

Q36.

Which property makes baculoviruses especially suitable as biocontrol agents?

• A They are broad-spectrum agents capable of killing nearly all insect pests
• B They are species-specific and do not harm non-target organisms
• C They remain heat-stable and persist for years within soil reservoirs
• D They produce potent chemical toxins that diffuse through plant tissue

Q37.

The process by which sewage effluent is released into water bodies after treatment is regulated by measuring which parameter?

• A Mainly pH levels measured before discharge
• B BOD reduction to acceptable levels
• C Chlorine concentration measured before discharge
• D Turbidity alone measured before discharge

Q38.

Streptokinase is classified as which type of enzyme based on its function?

• A A lipase enzyme that breaks down dietary fats into fatty acids
• B Thrombolytic enzyme that dissolves blood clots
• C A protease enzyme commonly incorporated into laundry detergents
• D An amylase enzyme that hydrolyzes starch into simple sugars

Q39.

Which component of Bacillus thuringiensis is responsible for its insecticidal activity?

• A Flagellar proteins used for bacterial movement
• B Cry proteins encoded by cry genes
• C Capsular polysaccharides forming a protective layer
• D Endospore coat proteins protecting the dormant spore

Q40.

Which type of treatment in sewage management is associated with the term effluent?

• A The raw, untreated sewage entering the treatment plant initially
• B The liquid that passes out after primary and secondary treatment
• C The settled sludge collected from the bottom of the settling tanks
• D Biogas collected from the anaerobic sludge digesters

Q41.

Biofertilizers differ from chemical fertilizers in what fundamental way?

• A Biofertilizers contain synthetic nitrogen compounds manufactured industrially
• B Biofertilizers use living microorganisms to enrich soil nutrients naturally
• C Biofertilizers act considerably faster than conventional chemical fertilizers
• D Biofertilizers are effective exclusively within tropical soil conditions

Q42.

The cry proteins of Bacillus thuringiensis become active toxins only after being ingested by an insect. What activates them in the insect gut?

• A Acidic pH of the insect gut directly dissolves the protective protein crystals over time
• B Alkaline pH of the insect gut along with gut proteases dissolve the crystals
• C Insect digestive enzymes acting at a neutral gut pH alone, independent of pH level
• D High temperature within the insect gut directly denatures the protective outer coat

Q43.

In the Anabaena-Azolla symbiosis used in paddy fields, what is the specific role of each partner?

• A Azolla fixes atmospheric N2 directly while Anabaena supplies it with photosynthates instead
• B Anabaena fixes N2 providing it to Azolla which provides carbon through photosynthesis
• C Both Azolla and Anabaena independently fix nitrogen on their own without cooperating at all
• D Azolla supplies dissolved soil minerals while Anabaena instead supplies water uptake support

Q44.

Statins produced by Monascus purpureus lower cholesterol by which specific mechanism?

• A Increasing hepatic bile acid production specifically to eliminate excess circulating cholesterol
• B Competitively inhibiting HMG-CoA reductase, a key enzyme in cholesterol biosynthesis
• C Blocking intestinal absorption of dietary cholesterol directly from ingested food sources
• D Enhancing LDL receptor expression mainly within liver cell membranes specifically

Q45.

During secondary sewage treatment, what is the significance of reducing BOD before discharge?

• A To prevent offensive odors mainly, with little concern for aquatic oxygen levels overall
• B High BOD effluent would consume oxygen in receiving water bodies, causing death of aquatic life
• C To make the discharged water colorless mainly for aesthetic purposes and appearance
• D To eliminate most pathogenic microorganisms present in the treated wastewater stream

Q46.

Penicillium chrysogenum is now preferred over Penicillium notatum for industrial penicillin production. What is the main reason?

• A P. chrysogenum produces a noticeably different type of penicillin compound entirely
• B P. chrysogenum produces significantly higher yields of penicillin
• C P. chrysogenum is considerably easier to identify under standard laboratory conditions
• D P. notatum was found to be mildly toxic to humans under certain conditions

Q47.

Which characteristic of mycorrhizal associations with Glomus makes them more efficient than plant roots alone at absorbing phosphorus?

• A Mycorrhizal fungi produce phosphatase enzymes mainly, with little other contribution
• B The extraradical hyphae vastly increase the absorptive surface area beyond the root hair zone
• C Mycorrhizal fungi convert organic phosphorus to plant-available forms mainly, rarely otherwise
• D Glomus secretes phosphorus-mobilizing acids mainly in alkaline soils, rarely in acidic ones

Q48.

The sludge digester in sewage treatment operates under anaerobic conditions. Which group of microorganisms is primarily responsible for methane production?

• A Aerobic heterotrophs
• B Sulfate-reducing bacteria
• C Methanogenic archaea
• D Lactic acid bacteria

Q49.

Baculoviruses used in biocontrol have a narrow host range. This property is advantageous because it means they are what?

• A Highly effective against essentially all agricultural pest species simultaneously and equally
• B Safe for use in integrated pest management without harming beneficial insects, birds, and mammals
• C Able to persist for considerably longer periods within the surrounding environment overall
• D Capable of being manufactured more cheaply than synthetic chemical pesticides generally

Q50.

In the context of biocontrol, Trichoderma species act against plant pathogens through which combination of mechanisms?

• A Mainly through the production of antibiotic compounds released continuously into the surrounding soil environment
• B Through mycoparasitism, antibiosis, competition for nutrients and space, and induced systemic resistance
• C Mainly by outcompeting pathogens for available physical space within the surrounding soil matrix
• D Through secretion of broad-spectrum toxins that indiscriminately kill all other soil microbes present nearby

Q51.

Why are microbes considered essential for the efficient operation of biogas plants that use agricultural waste?

• A Microbes mainly provide passive structural support within the digester tank, with little biochemical contribution in most cases under typical conditions
• B Anaerobic microbes including bacteria and archaea hydrolyze, ferment, and ultimately convert organic waste to methane through a multi-stage process
• C Microbes present in the digester produce mainly carbon dioxide gas, with little methane generated at any stage according to standard textbooks
• D Mainly generally aerobic microbes are utilized throughout the entire biogas production process inside the digester in general practice as frequently described

Q52.

The heterocysts found in cyanobacteria like Anabaena are specialized cells for what purpose, and why are they necessary?

• A Heterocysts are specialized photosynthetic cells that primarily function to generate extra oxygen for the surrounding filament
• B Heterocysts are nitrogen-fixing cells with thick walls that exclude O2, protecting the oxygen-sensitive nitrogenase enzyme
• C Heterocysts store starch reserves specifically to sustain the cyanobacterial organism through periods of drought stress
• D Heterocysts secrete specific growth-regulating hormones that control the overall growth rate of the cyanobacterial filament

Q53.

The immunosuppressive action of cyclosporin A involves inhibiting which cellular pathway in T lymphocytes?

• A The mTOR signaling pathway that governs T-cell growth and proliferation
• B The calcineurin-NFAT pathway, preventing cytokine gene transcription
• C The JAK-STAT pathway responsible for interferon-mediated signaling
• D The NF-kB pathway that mediates the broader inflammatory response

Q54.

In food fermentation, what is the precise role of lactic acid produced by Lactobacillus during curd formation?

• A Lactic acid adds extra nutritional protein content directly to the finished curd product in most textbook accounts
• B Lactic acid lowers pH, causing casein proteins to denature and coagulate, forming the gel structure of curd
• C Lactic acid acts mainly as a preservative by killing most contaminating bacteria present during normal conditions
• D Lactic acid contributes a distinct sweetness to the final curd product over time as generally observed

Q55.

What distinguishes the mode of action of streptokinase from other fibrinolytic agents in clinical use?

• A Streptokinase cleaves fibrin strands directly and immediately, rarely involving plasminogen in the process in typical laboratory settings
• B Streptokinase forms a complex with plasminogen, inducing a conformational change that activates it to plasmin, which then lyses fibrin clots
• C Streptokinase is clinically effective mainly on blood clots that are less than roughly one hour old under usual circumstances according to most researchers
• D Streptokinase inhibits thrombin activity directly mainly to prevent the formation of new blood clots in the majority of cases studied as widely reported

Q56.

In the context of biofertilizers, what is the term for the process by which Rhizobium infects legume roots and how do the plant and bacterium mutually signal each other?

• A Infection occurs entirely at random throughout the root system, without any specific chemical signaling exchanged between the two partners at all
• B Nod factors produced by Rhizobium in response to flavonoids secreted by the legume root trigger root hair curling and infection thread formation
• C The legume root itself produces antibiotic compounds specifically designed to attract Rhizobium bacteria from the surrounding soil
• D Rhizobium bacteria mechanically penetrate root cells directly, without using any form of chemical signaling whatsoever between the partners

Q57.

Aspergillus niger produces citric acid through which metabolic pathway and under what culture conditions?

• A Through the glyoxylate cycle under aerobic, high-sugar, low-pH conditions
• B Through fermentation under anaerobic conditions at neutral pH
• C Through beta-oxidation of fatty acids under aerobic conditions
• D Through the pentose phosphate pathway under nitrogen-rich conditions

Q58.

The genus Nucleopolyhedrovirus infects insects through which route, and what happens to infected cells?

• A Through direct penetration of the insect skin surface, causing rapid and explosive lysis of host cells over time in standard practice under most conditions encountered
• B Through ingestion of contaminated plant material, with the virus replicating in the nucleus forming polyhedral inclusion bodies that cause liquefaction of the insect
• C Through entry via the respiratory tract of the insect, leading to progressive damage of the central nervous system over time as frequently observed in practice
• D Through transovarial infection of the developing egg, causing mainly relatively minor developmental defects in many documented cases according to conventional understanding

Q59.

What is the key difference between the nitrogen fixation by Azotobacter and Rhizobium in terms of oxygen sensitivity and their respective solutions?

• A Both of these soil bacteria are sometimes thought to rely on a largely identical molecular mechanism to shield their nitrogenase enzyme from oxygen damage in routine practice overall in most cases
• B Azotobacter uses high respiration rates and an alginate capsule to maintain low internal O2, while Rhizobium relies on leghaemoglobin (plant-produced) in nodules to buffer O2 supply to bacteroids
• C Mainly Rhizobium shows meaningful sensitivity to oxygen, while Azotobacter requires little protective mechanism by comparison under typical conditions according to standard textbooks in general practice
• D Azotobacter instead relies specifically on specialized heterocysts, while Rhizobium relies mainly on the outer nodule cortex layer for protection as frequently described in most textbook accounts