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📘 Study MCQs
Q1. which of these is a disease-causing microorganism in plants?
• rhizobium
• lactobacillus
• virus causing yellow vein mosaic of bhindi
• yeast
Answer: virus causing yellow vein mosaic of bhindi
many plant diseases are caused by microorganisms. yellow vein mosaic of bhindi (okra) is a common viral disease.
Q2. what is the process of converting atmospheric nitrogen into usable nitrogen compounds called?
• nitrogen cycle
• nitrogen fixation
• pasteurization
• fermentation
Answer: nitrogen fixation
nitrogen fixation is the conversion of atmospheric nitrogen (n2) into ammonia or related nitrogenous compounds in the soil.
Q3. what is the name of the natural process that recycles nitrogen in various forms between the atmosphere, soil, plants, and animals?
• water cycle
• carbon cycle
• nitrogen cycle
• oxygen cycle
Answer: nitrogen cycle
the nitrogen cycle describes how nitrogen moves through the living and non-living parts of the environment.
Q4. which of these is an example of algae?
• mushroom
• amoeba
• spirogyra
• rhizobium
Answer: spirogyra
spirogyra is a common green alga found in ponds, recognized by its spiral-shaped chloroplasts.
Q5. what are the proteins produced by the body’s immune system to fight pathogens called?
• antigens
• antibiotics
• antibodies
• antiseptics
Answer: antibodies
antibodies are specialized proteins that recognize and help destroy specific pathogens like bacteria and viruses.
Q6. which microorganism is used in the fermentation process to make bread and alcohol?
• lactobacillus
• rhizobium
• yeast
• penicillium
Answer: yeast
yeast (a fungus) ferments sugars, producing carbon dioxide (for bread) and alcohol (for beverages).
Q7. what do we call the bacteria commonly found in curd and beneficial for digestion?
• rhizobium
• lactobacillus
• streptococcus
• acetobacter
Answer: lactobacillus
lactobacillus bacteria convert lactose in milk to lactic acid, making curd. they are also probiotics.
Q8. what is the general term for an organism that carries a disease-causing microbe without getting sick itself?
• host
• pathogen
• vector or carrier
• decomposer
Answer: vector or carrier
a carrier, like a mosquito or housefly, transmits pathogens from an infected host to a healthy one.
Q9. diseases that can spread from one person to another are called?
• deficiency diseases
• non-communicable diseases
• communicable diseases
• genetic diseases
Answer: communicable diseases
communicable or infectious diseases are caused by pathogens and can be transmitted directly or indirectly.
Q10. which process involves the conversion of sugar into alcohol or acids by microorganisms?
• nitrogen fixation
• pasteurization
• fermentation
• preservation
Answer: fermentation
fermentation is a metabolic process where microbes like yeast or bacteria break down sugars in the absence of oxygen.
Q11. ringworm in humans is caused by which type of microorganism?
• bacteria
• virus
• fungus
• protozoa
Answer: fungus
ringworm is a common skin infection caused by a fungus, not a worm.
Q12. what do we call a living organism that is visible only under a microscope?
• insect
• microorganism
• mammal
• reptile
Answer: microorganism
microorganisms, or microbes, are microscopic organisms like bacteria, viruses, fungi, and protozoa.
Q13. which bacteria live in the root nodules of leguminous plants and fix atmospheric nitrogen?
• lactobacillus
• rhizobium
• e. coli
• salmonella
Answer: rhizobium
rhizobium bacteria form a symbiotic relationship with plants like peas and beans, fixing nitrogen in root nodules.
Q14. what is the process of heating milk to a high temperature to kill harmful bacteria called?
• fermentation
• pasteurization
• nitrogen fixation
• preservation
Answer: pasteurization
pasteurization, named after louis pasteur, involves heating milk to about 70°c for 15-30 seconds to kill pathogens.
Q15. what is the term for a disease-causing microorganism?
• antibody
• antibiotic
• pathogen
• carrier
Answer: pathogen
pathogens are harmful microorganisms that cause diseases in their host (plants, animals, or humans).
Q16. which method involves treating food to prevent spoilage by microorganisms?
• fermentation
• pasteurization
• preservation
• all of the above
Answer: all of the above
all these are methods of food preservation. they inhibit or kill microbes to extend the shelf life of food.
Q17. amoeba is an example of which group of microorganisms?
• bacteria
• fungi
• protozoa
• algae
Answer: protozoa
amoeba is a single-celled, animal-like protist belonging to the group protozoa.
Q18. what is the name of the bacterial vaccine that prevents tuberculosis?
• opv
• mmr
• bcg
• dtp
Answer: bcg
the bcg vaccine is made from a weakened strain of mycobacterium bovis and provides immunity against tuberculosis.
Q19. which microorganism is considered non-living outside a host cell and causes diseases like the common cold?
• bacteria
• fungus
• virus
• protozoa
Answer: virus
viruses are unique. they show characteristics of life only inside a living host cell, where they reproduce.
Q20. what have you learnt about the size of microorganisms?
• they are giant organisms
• they are too small to be seen with the unaided eye
• they are all the same size
• they are visible as small dots
Answer: they are too small to be seen with the unaided eye
microorganisms are microscopic. we need instruments like microscopes to see them.
Q21. where can microorganisms live?
• only in water
• only in warm places
• in all kinds of environments (cold, hot, deserts, marshy lands)
• only inside human bodies
Answer: in all kinds of environments (cold, hot, deserts, marshy lands)
microbes are found everywhere due to their ability to adapt—from ice caps to hot springs.
Q22. microorganisms are found in:
• air only
• air, water, and bodies of plants and animals
• only in spoiled food
• only in soil
Answer: air, water, and bodies of plants and animals
microbes are ubiquitous. they are present in air, water, soil, and inside or on the bodies of all living organisms.
Q23. microorganisms can be:
• only unicellular
• only multicellular
• both unicellular and multicellular
• neither unicellular nor multicellular
Answer: both unicellular and multicellular
bacteria and protozoa are unicellular. fungi and algae can be unicellular (yeast) or multicellular (mushroom, spirogyra).
Q24. which groups are included under microorganisms?
• only bacteria and viruses
• bacteria, fungi, protozoa, and some algae
• only fungi and algae
• only pathogenic bacteria
Answer: bacteria, fungi, protozoa, and some algae
the major groups of microbes are bacteria, fungi, protozoa, and some algae. viruses are also considered but are different.
Q25. how are viruses different from other microorganisms?
• they can reproduce on their own
• they reproduce only inside the host organism’s cell
• they are the largest microbes
• they make their own food
Answer: they reproduce only inside the host organism’s cell
viruses are obligate parasites. they lack cellular machinery and can replicate only by taking over a host cell (bacterial, plant, or animal).
Q26. some microorganisms are useful for the commercial production of:
• plastics
• medicines and alcohol
• metals
• fuels only
Answer: medicines and alcohol
microbes are used industrially—fungi for antibiotics (penicillin) and yeast for alcohol (ethanol) production.
Q27. which protozoan causes serious diseases like dysentery and malaria?
• entamoeba (causes amoebic dysentery) and plasmodium (causes malaria)
• rhizobium and lactobacillus
• penicillium and aspergillus
• yeast and algae
Answer: entamoeba (causes amoebic dysentery) and plasmodium (causes malaria)
entamoeba histolytica causes amoebic dysentery. plasmodium, transmitted by mosquitoes, causes malaria.
Q28. what can cause food poisoning?
• some microorganisms growing on our food
• adding salt to food
• keeping food in the fridge
• cooking food
Answer: some microorganisms growing on our food
bacteria like salmonella and staphylococcus can grow on food and produce toxins, leading to food poisoning.
Q29. where do nitrogen-fixing microorganisms reside in leguminous plants?
• in the leaves
• in the flowers
• in the root nodules
• in the stem
Answer: in the root nodules
bacteria like rhizobium live in the root nodules of plants like peas, grams, and beans, where they fix atmospheric nitrogen.
Q30. what is the role of these bacteria in root nodules?
• they cause disease
• they fix nitrogen from air into soil, increasing fertility
• they absorb water
• they help in pollination
Answer: they fix nitrogen from air into soil, increasing fertility
they convert atmospheric nitrogen into ammonia, a form plants can use, thus enriching the soil naturally.
Q31. which organisms, present in soil, can fix atmospheric nitrogen?
• some bacteria and blue-green algae
• only earthworms
• only fungi
• only viruses
Answer: some bacteria and blue-green algae
besides rhizobium, free-living soil bacteria (azotobacter) and blue-green algae (nostoc) also fix atmospheric nitrogen.
Q32. what is the role of decomposer microorganisms?
• they cause diseases
• they decompose organic waste and dead plants/animals into simple substances
• they fix nitrogen
• they make food
Answer: they decompose organic waste and dead plants/animals into simple substances
decomposers like bacteria and fungi break down dead matter, recycling nutrients and cleaning the environment.
Q33. what do certain bacteria do to nitrogen compounds in the soil?
• convert them into oxygen
• convert them into nitrogen gas released to the atmosphere
• convert them into gold
• store them forever
Answer: convert them into nitrogen gas released to the atmosphere
this process is called denitrification. bacteria like pseudomonas convert nitrates in soil back to nitrogen gas, completing the nitrogen cycle.
Q34. which plant disease is caused by a fungus?
• citrus canker (bacterial)
• yellow vein mosaic of bhindi (viral)
• rust of wheat (fungal)
• all of the above
Answer: rust of wheat (fungal)
wheat rust is a widespread fungal disease that appears as reddish-brown pustules on stems and leaves.
Q35. in the nitrogen cycle, plants absorb nitrogen from the soil in the form of:
• nitrogen gas (n2)
• ammonia (nh3)
• nitrates and nitrites
• proteins
Answer: nitrates and nitrites
plants cannot use atmospheric nitrogen directly. they absorb simple nitrogen compounds like nitrates through their roots.
Q36. which of these is not a part of the nitrogen cycle?
• nitrogen fixation
• photosynthesis
• nitrification
• denitrification
Answer: photosynthesis
photosynthesis is part of the carbon cycle. nitrogen fixation, nitrification, and denitrification are key steps in the nitrogen cycle.
Q37. algae are important because they:
• cause many human diseases
• are used as food and produce oxygen through photosynthesis
• fix nitrogen in root nodules
• are used to make antibiotics
Answer: are used as food and produce oxygen through photosynthesis
many algae are edible (like seaweed). as autotrophs, they produce a significant amount of earth’s oxygen.
Q38. antibodies are produced by:
• pathogens
• our body’s white blood cells
• vaccines
• antibiotics
Answer: our body’s white blood cells
when a pathogen enters, specific white blood cells (lymphocytes) produce antibodies that target that pathogen.
Q39. fermentation by yeast is used in making:
• cheese and yogurt
• bread and beer
• pickles and vinegar
• compost
Answer: bread and beer
yeast fermentation produces co2 for bread rising and ethanol for alcoholic beverages like beer.
Q40. the process of preservation by adding salt or sugar works by:
• adding flavor
• killing all microbes instantly
• creating a hypertonic condition that draws water out of microbial cells
• providing nutrients to microbes
Answer: creating a hypertonic condition that draws water out of microbial cells
high salt or sugar concentration causes osmosis, dehydrating and killing microbes or inhibiting their growth.
Q41. which of these is a communicable disease?
• diabetes
• heart disease
• influenza (flu)
• cancer
Answer: influenza (flu)
influenza is caused by a virus and spreads from person to person through the air, making it communicable.
Q42. a mosquito carrying malaria parasites is an example of a:
• host
• pathogen
• carrier or vector
• decomposer
Answer: carrier or vector
the female anopheles mosquito is the vector that transmits the malaria parasite (plasmodium) between humans.
Q43. penicillin, an antibiotic, is obtained from:
• a bacterium
• a fungus (penicillium)
• a virus
• a protozoan
Answer: a fungus (penicillium)
alexander fleming discovered penicillin from the mould penicillium notatum.
Q44. the virus that causes polio primarily affects the:
• digestive system
• nervous system
• respiratory system
• circulatory system
Answer: nervous system
the poliovirus attacks the nervous system, which can lead to paralysis.
Q45. which microorganism helps in the formation of curd?
• yeast
• lactobacillus
• rhizobium
• acetobacter
Answer: lactobacillus
lactobacillus bacteria convert the lactose in milk to lactic acid, causing the milk to coagulate and form curd.
Q46. blue-green algae are now classified as:
• cyanobacteria
• protozoa
• fungi
• viruses
Answer: cyanobacteria
blue-green algae are photosynthetic bacteria called cyanobacteria. they can fix atmospheric nitrogen.
Q47. in the nitrogen cycle, the conversion of ammonia to nitrites and nitrates is called:
• nitrogen fixation
• nitrification
• denitrification
• assimilation
Answer: nitrification
nitrification is done by nitrifying bacteria (like nitrobacter). they convert ammonia into nitrites and then into nitrates.
Q48. vaccines work by:
• killing the pathogen directly
• stimulating the body to produce antibodies
• weakening the immune system
• providing nutrients to fight disease
Answer: stimulating the body to produce antibodies
vaccines contain antigens that trigger an immune response, leading to the production of memory cells and antibodies for future protection.
Q49. which of these is a method of food preservation that uses low temperature?
• salting
• canning
• refrigeration
• smoking
Answer: refrigeration
refrigeration or freezing slows down the metabolic activity of microorganisms, delaying food spoilage.
Q50. microorganisms that thrive in extreme environments like hot springs are called:
• pathogens
• extremophiles
• decomposers
• carriers
Answer: extremophiles
extremophiles are microorganisms that live in conditions of extreme temperature, acidity, salinity, etc.
Q51. the causative agent of citrus canker in plants is a:
• fungus
• bacterium
• virus
• nematode
Answer: bacterium
citrus canker is a plant disease caused by the bacterium xanthomonas axonopodis.
Q52. which step in the nitrogen cycle is performed by rhizobium bacteria?
• denitrification
• nitrogen fixation
• nitrification
• ammonification
Answer: nitrogen fixation
rhizobium performs biological nitrogen fixation, converting atmospheric nitrogen into ammonia within root nodules.
Q53. antibodies are specific, meaning:
• one type fights all diseases
• they are produced only at night
• each type fights a specific antigen/pathogen
• they are not useful
Answer: each type fights a specific antigen/pathogen
antibodies are highly specific. an antibody against the measles virus will not work against the chickenpox virus.
Q54. the process where bacteria convert dead organic matter into ammonia is called:
• nitrogen fixation
• nitrification
• ammonification
• denitrification
Answer: ammonification
during decomposition, decomposer bacteria convert organic nitrogen from dead plants and animals into ammonia.
Q55. a person who has recovered from measles will not get it again because their body now has:
• antibiotics against measles
• memory cells that produce specific antibodies quickly
• weakened measles viruses
• no immunity
Answer: memory cells that produce specific antibodies quickly
after the first infection, the immune system retains memory cells. upon re-exposure, these cells trigger a rapid production of antibodies, preventing illness.
Q56. which of these is a free-living nitrogen-fixing bacterium in soil?
• rhizobium
• azotobacter
• lactobacillus
• salmonella
Answer: azotobacter
azotobacter is a free-living (non-symbiotic) bacterium in soil that fixes atmospheric nitrogen.
Q57. malaria is caused by a protozoan, but it is spread by:
• contaminated water
• a vector (mosquito)
• airborne droplets
• direct contact
Answer: a vector (mosquito)
the plasmodium parasite requires a female anopheles mosquito as a vector to move from an infected person to a healthy one.
Q58. the ‘active immunity’ provided by a vaccine is:
• temporary
• permanent or long-lasting
• not effective
• only for plants
Answer: permanent or long-lasting
vaccines typically provide long-term, sometimes lifelong, immunity by training the body’s own immune system.
Q59. which gas makes up about 78% of the atmosphere but is unusable by most organisms in that form?
• oxygen
• carbon dioxide
• nitrogen
• hydrogen
Answer: nitrogen
atmospheric nitrogen (n2) is inert. it must be “fixed” into compounds like ammonia or nitrates for use by plants and animals.
Q60. what is the primary reason for adding yeast to bread dough?
• for flavor
• to produce carbon dioxide gas for rising
• to add color
• to kill bacteria
Answer: to produce carbon dioxide gas for rising
yeast ferments sugars in the dough, producing carbon dioxide gas. the gas gets trapped, causing the dough to rise and become fluffy.