📌 How to Use
First read the questions carefully using the Read section. Use the Details button to understand concepts clearly. After completing reading, click Practice Quiz to test yourself.
📘 Study MCQs
Q1. why does a wet kitchen sponge start to smell bad after a few days?
• because it absorbs food smells
• because bacteria and mould grow in the damp, organic material
• because the plastic is breaking down
• because it dries out
Answer: because bacteria and mould grow in the damp, organic material
the sponge provides a damp, warm environment with food particles. microbes decompose these particles, producing foul-smelling waste gases.
Q2. you see a potted plant with yellowing leaves and stunted growth. what could be a natural way to help it, using friendly microbes?
• water it with sugar water
• re-pot it with soil from near the roots of a pea or bean plant
• spray it with soapy water
• put it in the dark
Answer: re-pot it with soil from near the roots of a pea or bean plant
pea/bean plants have nitrogen-fixing rhizobium bacteria in their root nodules. soil from there is rich in natural nitrogen, a key nutrient for plant growth.
Q3. after a family picnic, several people have stomach cramps and diarrhea. what is the most likely cause?
• they ate too much
• the food was contaminated with harmful bacteria like e. coli or salmonella
• they were in the sun too long
• they drank cold water
Answer: the food was contaminated with harmful bacteria like e. coli or salmonella
symptoms of food poisoning appear when harmful bacteria or their toxins from improperly stored or prepared food are ingested.
Q4. a jar of tomato sauce you opened last week now has bubbles and a sour smell. what happened?
• it has fermented
• it has evaporated
• the jar is leaking
• the color has just changed
Answer: it has fermented
yeast or bacteria from the air have entered the jar. they are fermenting the sugars in the sauce, producing gas (bubbles) and acids (sour smell).
Q5. why are cuts and scrapes cleaned with an antiseptic like dettol?
• to make them hurt less
• to kill any harmful microbes that could cause an infection
• to make them heal faster magically
• to stain the skin
Answer: to kill any harmful microbes that could cause an infection
antiseptics are chemicals that kill or inhibit pathogens on living tissue, preventing them from entering the body through the wound.
Q6. your grandmother puts a silver coin in a jar of pickles. why might she do this?
• for good luck
• silver has antimicrobial properties that can help prevent spoilage
• to add a metallic taste
• to make it look valuable
Answer: silver has antimicrobial properties that can help prevent spoilage
silver ions can disrupt the cellular processes of bacteria and fungi, acting as a traditional preservative.
Q7. why does a compost heap in the garden feel warm inside?
• the sun heats it up
• microbes are actively decomposing the organic matter, releasing heat
• someone put hot coals in it
• it is always warm outside
Answer: microbes are actively decomposing the organic matter, releasing heat
the metabolic activity of millions of decomposer bacteria and fungi breaking down waste generates significant heat.
Q8. you forget to put the milk back in the fridge overnight. in the morning, it tastes sour but isn’t chunky. is it safe to use?
• yes, it’s just sour milk
• no, it is spoiled and could contain harmful bacteria
• yes, you can make cheese from it
• no, but you can boil it to make it safe
Answer: no, it is spoiled and could contain harmful bacteria
sour taste is from lactic acid bacteria, which are generally harmless. however, other harmful bacteria could have also grown during the night. it’s safest to discard it.
Q9. during the rainy season, leather shoes often get a white, powdery coating. what is it and how can you prevent it?
• it’s salt from sweat; wash shoes more often
• it’s a fungal growth; keep shoes in a dry, well-ventilated place
• it’s dried soap; rinse shoes better
• it’s pollen; avoid going outside
Answer: it’s a fungal growth; keep shoes in a dry, well-ventilated place
the white powder is mould. fungi thrive in damp, warm, dark conditions. keeping shoes dry and airy removes the conditions they need to grow.
Q10. a neighbour is diagnosed with tuberculosis (tb). what should they do to protect others?
• continue daily life as normal
• wear a mask when outside and cover their mouth while coughing
• go to crowded places to build immunity in others
• nothing, tb is not contagious
Answer: wear a mask when outside and cover their mouth while coughing
tb spreads through airborne droplets. wearing a mask and practicing cough hygiene (into elbow/tissue) drastically reduces the chance of spreading the bacteria to others.
Q11. you are camping and only have river water. how can you make it safe to drink?
• strain it through a cloth
• boil it vigorously for at least one minute
• add sugar to it
• let it sit in the sun
Answer: boil it vigorously for at least one minute
boiling is the most reliable method to kill disease-causing bacteria, viruses, and protozoa that may be present in untreated water.
Q12. why do bakers keep a small piece of dough from today’s batch to use in tomorrow’s bread?
• to save money on flour
• that piece acts as a sourdough starter, containing natural yeast and bacteria for fermentation
• for good luck
• to test if the oven is hot
Answer: that piece acts as a sourdough starter, containing natural yeast and bacteria for fermentation
the saved dough contains a stable culture of wild yeast and lactobacillus. adding it to the new batch kick-starts fermentation and adds flavor.
Q13. a child has a high fever and a rash of small, fluid-filled blisters. what should the parent do to prevent siblings from getting sick?
• let the children play together to get it over with
• keep the sick child isolated and ensure others are vaccinated against chickenpox
• share the child’s toys to spread immunity
• give antibiotics to all children
Answer: keep the sick child isolated and ensure others are vaccinated against chickenpox
the symptoms suggest chickenpox, a highly contagious viral disease. isolation prevents direct contact, and vaccination provides immunity to those not yet infected.
Q14. your homemade wine tastes like vinegar instead of alcohol. what went wrong?
• you didn’t add enough sugar
• air got in, allowing acetobacter bacteria to convert alcohol to acetic acid
• you used the wrong grapes
• it wasn’t kept in a dark place
Answer: air got in, allowing acetobacter bacteria to convert alcohol to acetic acid
wine turns to vinegar when acetobacter bacteria, which require oxygen, are present. they ferment the ethanol (alcohol) into acetic acid.
Q15. why are babies given several rounds of vaccinations (like 3 doses of DTP)?
• the first doses didn’t work
• to build stronger and longer-lasting immunity gradually
• doctors make more money this way
• babies forget the first dose
Answer: to build stronger and longer-lasting immunity gradually
multiple doses, called booster shots, help the immune system produce a high level of memory cells and antibodies, ensuring robust and lasting protection.
Q16. you see green, fuzzy mould on an orange. can you eat the rest of the orange if you cut off the mouldy part?
• yes, the rest is fine
• no, the mould’s threads and toxins have likely spread through the soft fruit
• yes, but only if you cook it
• no, all citrus fruits are poisonous with mould
Answer: no, the mould’s threads and toxins have likely spread through the soft, moist fruit
in soft, high-moisture foods, mould can penetrate deeply. it’s safer to discard the entire fruit.
Q17. a farmer plants a field with wheat year after year, and the yield keeps decreasing. what natural method can restore the soil?
• water the field more
• plant a crop like peas or lentils (legumes) for one season
• spray more pesticides
• plant more wheat
Answer: plant a crop like peas or lentils (legumes) for one season
leguminous plants host nitrogen-fixing bacteria. planting them adds natural nitrogen fertilizer to the soil, replenishing what the wheat crops depleted.
Q18. why is there often a sign saying “Employees Must Wash Hands” in restaurant bathrooms?
• to make the bathroom look official
• to remind employees to maintain personal hygiene and prevent spreading germs to food
• because soap is expensive
• it’s just a law
Answer: to remind employees to maintain personal hygiene and prevent spreading germs to food
handwashing is one of the most effective ways to prevent food handlers from transferring pathogens from their hands to the food customers eat.
Q19. you accidentally step on a rusty nail. why is a tetanus vaccine booster important in this situation?
• rust causes instant poisoning
• the bacterium clostridium tetani, found in soil and rust, can enter through the deep wound
• the nail has germs from the factory
• to prevent the nail from causing infection
Answer: the bacterium clostridium tetani, found in soil and rust, can enter through the deep wound
tetanus bacteria thrive in low-oxygen environments like deep puncture wounds. a booster shot ensures the body has enough antibodies to fight the infection.
Q20. why does buttermilk or lassi last longer outside in summer than fresh milk?
• it is served cold
• it is already fermented and acidic, which inhibits the growth of many spoilage bacteria
• it has less fat
• it is always kept in a clay pot
Answer: it is already fermented and acidic, which inhibits the growth of many spoilage bacteria
the lactic acid produced during fermentation lowers the pH, creating an environment where many harmful microbes cannot easily grow.
Q21. a flood has contaminated the local water supply. what is the most important health message from authorities?
• drink only bottled or boiled water
• take vitamins
• stay indoors
• eat more protein
Answer: drink only bottled or boiled water
floodwater mixes with sewage and dirt, carrying a high load of pathogens. boiling or treating water is critical to prevent outbreaks of cholera, typhoid, etc.
Q22. why does a doctor prescribe different antibiotics for a sore throat and for tuberculosis?
• to make more money
• different antibiotics are effective against different types of bacteria
• patients prefer different colors
• one is for virus, one for bacteria
Answer: different antibiotics are effective against different types of bacteria
antibiotics are specific. the bacteria causing a strep throat (streptococcus) is different from the one causing TB (mycobacterium). Each requires a specific antibiotic.
Q23. you are making lemon pickle. why do you use a lot of salt and lemon juice?
• only for taste
• salt and acid (from lemon) create an environment where spoilage microbes cannot grow
• to make it heavy
• to change the color
Answer: salt and acid (from lemon) create an environment where spoilage microbes cannot grow
high salt concentration draws water out of microbes, and the acidic environment is hostile to most bacteria. this combination preserves the pickle.
Q24. your friend has a bad cold. should you share their water bottle?
• yes, if you are good friends
• no, because viruses from their mouth can transfer to the bottle and then to you
• yes, colds are not contagious
• no, because the water will taste bad
Answer: no, because viruses from their mouth can transfer to the bottle and then to you
the cold virus can be present in saliva. sharing utensils or bottles is a direct way for the virus to spread from an infected person to a healthy one.
Q25. why does a gardener sometimes mix dry leaves and vegetable peels into the soil instead of throwing them away?
• to fill up space
• microbes in the soil will decompose them into nutrient-rich compost
• to attract earthworms
• to keep the soil warm
Answer: microbes in the soil will decompose them into nutrient-rich compost
this is a form of composting. decomposer microbes break down the organic waste, recycling its nutrients back into the soil to feed plants.
Q26. you see a mosquito breeding in a water-filled old tire in your yard. why is it important to empty the tire?
• mosquitoes are annoying
• to prevent mosquitoes from breeding and potentially spreading diseases like malaria or dengue
• the water smells bad
• the tire might rust
Answer: to prevent mosquitoes from breeding and potentially spreading diseases like malaria or dengue
mosquitoes lay eggs in stagnant water. eliminating these breeding sites is a key public health measure to control mosquito-borne diseases.
Q27. why does a deep cut that is not cleaned properly sometimes ooze pus?
• it is healing
• it is a sign of infection; pus contains dead white blood cells and bacteria
• the body is making extra blood
• it is sweating
Answer: it is a sign of infection; pus contains dead white blood cells and bacteria
pus forms when the immune system fights an infection at the site. it is a mixture of dead bacteria, white blood cells, and tissue debris.
Q28. why is it important to get a flu vaccine every year, but the measles vaccine only once or twice in childhood?
• the flu vaccine is weaker
• the flu virus changes (mutates) rapidly, so last year’s vaccine may not work this year
• people forget they had measles vaccine
• measles is less serious
Answer: the flu virus changes (mutates) rapidly, so last year’s vaccine may not work this year
influenza viruses evolve quickly. new strains emerge each season, requiring an updated vaccine. the measles virus is stable, so immunity from childhood vaccination lasts for decades.
Q29. you are preserving green chilies by sun-drying them. how does this method work?
• the sun cooks them
• sunlight kills germs and removal of moisture prevents microbial growth
• the sun changes their color
• it makes them spicier
Answer: sunlight kills germs and removal of moisture prevents microbial growth
UV rays have a germicidal effect. More importantly, drying removes the water that microbes need to grow, preserving the chilies.
Q30. a person with a persistent cough for over 3 weeks and weight loss is advised to get a sputum test. what disease is being suspected?
• common cold
• tuberculosis (TB)
• asthma
• allergy
Answer: tuberculosis (TB)
a persistent cough (sometimes with blood), fever, night sweats, and weight loss are classic symptoms of pulmonary tuberculosis.
Q31. why does a layer of oil on top of pickles help in preservation?
• it adds flavor
• oil is nutritious
• it forms an airtight seal that prevents oxygen from reaching the pickles
• it makes them look shiny
Answer: it forms an airtight seal that prevents oxygen from reaching the pickles
many spoilage-causing microbes need oxygen to grow. The oil layer acts as a barrier, creating anaerobic conditions that inhibit their growth.
Q32. why should you not take antibiotics prescribed for someone else’s infection?
• they might be the wrong color
• the antibiotic may not be effective against your specific infection, and misuse promotes antibiotic resistance
• they are too expensive
• sharing is not caring for medicine
Answer: the antibiotic may not be effective against your specific infection, and misuse promotes antibiotic resistance
antibiotics are specific. Taking the wrong one wastes the medicine and encourages bacteria to develop resistance, making future infections harder to treat.
Q33. you are canning beans at home. why is it crucial to use a pressure canner and not just boil the jars?
• it’s faster
• to kill heat-resistant spores of bacteria like clostridium botulinum that can survive boiling
• boiling breaks the jars
• pressure makes the beans softer
Answer: to kill heat-resistant spores of bacteria like clostridium botulinum that can survive boiling
Low-acid foods like beans require temperatures above 100°C (achieved in a pressure canner) to destroy botulism spores, which can produce a deadly toxin in sealed, oxygen-free jars.
Q34. why does a small cut heal faster than a large, deep wound?
• small cuts are less painful
• the body can quickly seal a small cut from microbes and begin repair; a large wound is more exposed and prone to serious infection
• small cuts don’t bleed
• white blood cells ignore small cuts
Answer: the body can quickly seal a small cut from microbes and begin repair; a large wound is more exposed and prone to serious infection
A large, deep wound provides a bigger entry point for pathogens and damages more tissue, requiring a much more complex and longer immune response and healing process.
Q35. you are making yogurt, but it turns out runny and sour. what likely happened?
• you used too much milk
• the milk was too hot when you added the starter, killing the bacteria
• you didn’t add sugar
• you stirred it while it was setting
Answer: the milk was too hot when you added the starter, killing the bacteria
If the milk is above ~45°C when the culture (starter) is added, it can kill the lactobacillus bacteria, preventing proper setting and leading to a sour, liquid result.
Q36. during a cholera outbreak, why is rehydration with ORS (oral rehydration solution) more important than antibiotics for most patients?
• antibiotics don’t work on cholera
• the immediate danger is death from severe dehydration and loss of electrolytes, which ORS corrects
• ORS is cheaper
• cholera is a virus
Answer: the immediate danger is death from severe dehydration and loss of electrolytes, which ORS corrects
Cholera causes profuse watery diarrhea. Rapid fluid and electrolyte replacement with ORS is lifesaving. Antibiotics reduce severity but are secondary to rehydration.
Q37. why is it important to cover food items in a market?
• to keep them warm
• to prevent dust and flies (which carry germs) from contaminating them
• to make them look neat
• so people don’t touch them
Answer: to prevent dust and flies (which carry germs) from contaminating them
Flies land on garbage and sewage, picking up pathogens on their legs. Dust also carries microbes. Covering food provides a physical barrier against these carriers.
Q38. you have a fever and the doctor says it’s a viral infection. why might they not prescribe antibiotics?
• antibiotics are out of stock
• antibiotics only work against bacteria, not viruses
• viruses are too strong
• you need a stronger medicine
Answer: antibiotics only work against bacteria, not viruses
Antibiotics target specific structures or processes in bacterial cells. Viruses are not cells and have completely different machinery, so antibiotics are ineffective against them.
Q39. a field has been used for cattle grazing for years. why is the soil particularly fertile?
• cattle till the soil with their hooves
• cattle dung and urine are decomposed by microbes, enriching the soil with nutrients
• cattle eat the weeds
• cattle attract earthworms
Answer: cattle dung and urine are decomposed by microbes, enriching the soil with nutrients
Animal waste is organic matter. Soil microbes decompose it into humus and simple nutrients like nitrates and phosphates, which are excellent natural fertilizers.
Q40. you are storing wheat grains in a metal bin. why do you put some dried neem leaves in it?
• for a nice smell
• neem leaves have insect-repelling and anti-fungal properties
• to take up extra space
• to absorb moisture
Answer: neem leaves have insect-repelling and anti-fungal properties
Neem contains compounds that are natural pesticides and fungicides. This traditional method helps protect stored grains from insect pests and fungal growth (like aflatoxins).
Q41. why does a person who has recovered from measles not get the disease again?
• they avoid sick people
• their body has produced memory cells that provide lifelong immunity
• the measles virus disappears from the world
• they take special vitamins
Answer: their body has produced memory cells that provide lifelong immunity
After the first infection, the immune system retains memory B-cells and T-cells specific to the measles virus. If exposed again, these cells mount a rapid, effective defense, preventing illness.
Q42. why is it risky to eat raw or undercooked eggs?
• they taste bad
• they can contain salmonella bacteria on the shell or inside the egg
• they have less protein
• they are difficult to digest
Answer: they can contain salmonella bacteria on the shell or inside the egg
Poultry can carry Salmonella bacteria, which can contaminate eggs. Proper cooking kills these bacteria, reducing the risk of food poisoning.
Q43. in a village, people use a common pond for bathing, washing clothes, and drinking water. what health problem is likely common?
• obesity
• water-borne diseases like diarrhea, cholera, and typhoid
• heart disease
• vitamin deficiency
Answer: water-borne diseases like diarrhea, cholera, and typhoid
Using the same water source for sanitation and drinking leads to fecal contamination, which spreads pathogens that cause gastrointestinal diseases.
Q44. why does a doctor clean your arm with an alcohol swab before giving an injection?
• to cool the skin
• to make the needle slide in easily
• to kill microbes on the skin’s surface and prevent them from being pushed into the body by the needle
• to mark the spot
Answer: to kill microbes on the skin’s surface and prevent them from being pushed into the body by the needle
The alcohol acts as an antiseptic, disinfecting the skin to minimize the risk of introducing bacteria from the skin surface into the underlying tissue or bloodstream.
Q45. your stored potatoes have started to shrivel and sprout. what does this tell you about the storage conditions?
• they were too cold
• the place was likely too warm and humid, promoting growth
• they needed more sunlight
• they were packed too tightly
Answer: the place was likely too warm and humid, promoting growth
Potatoes are living tubers. Warm, moist conditions signal them to break dormancy, using stored water and nutrients to sprout, causing them to shrivel.
Q46. a beekeeper never needs to preserve honey. why does natural honey not spoil?
• bees add a special chemical
• it has very low water content and natural antimicrobial substances
• it is always kept in the fridge by bees
• it is sealed in wax
Answer: it has very low water content and natural antimicrobial substances
Honey’s high sugar concentration draws water out of microbial cells (osmosis), and it contains hydrogen peroxide and other compounds that inhibit microbial growth.
Q47. after playing in the park, a child has a ring-shaped, itchy rash on their skin. what is it and how did they get it?
• allergy to grass; from touching grass
• ringworm (a fungal infection); likely from contact with soil or an infected animal
• mosquito bite; from a mosquito
• eczema; from dry skin
Answer: ringworm (a fungal infection); likely from contact with soil or an infected animal
Ringworm is a common fungal skin infection. The fungi live in soil and on the skin of animals. It spreads through direct contact with these sources or an infected person.
Q48. why is it important for a person with hepatitis B to not donate blood?
• they have weak blood
• the hepatitis B virus can be transmitted through contaminated blood to the recipient
• their blood is too thick
• donating blood will make them sicker
Answer: the hepatitis B virus can be transmitted through contaminated blood to the recipient
Hepatitis B is a blood-borne virus. Screening blood donors and not accepting blood from infected individuals is crucial to prevent transmission through transfusions.
Q49. you clean a fish tank and the water becomes cloudy a day later. what is happening?
• the fish are dirty
• a bacterial bloom is occurring as microbes multiply to decompose waste in the water
• the filter is broken
• algae are growing
Answer: a bacterial bloom is occurring as microbes multiply to decompose waste in the water
Disturbing the tank stirs up organic matter. Heterotrophic bacteria rapidly multiply to decompose this matter, causing a temporary cloudy appearance.
Q50. you have leftover cooked rice. what is the safest way to store it for later to avoid food poisoning?
• leave it in the pot on the stove
• let it cool to room temperature, then cover and refrigerate
• put it directly into the fridge while hot
• leave it uncovered on the counter
Answer: let it cool to room temperature, then cover and refrigerate
Letting it cool first prevents raising the fridge’s internal temperature. Refrigerating within 2 hours prevents the growth of Bacillus cereus spores, which can cause food poisoning if rice is left at room temperature.