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Q1. Why does a cut or wound often get covered with a band-aid?
A band-aid covers a wound to create a protective barrier that prevents harmful microorganisms (bacteria, fungi) from entering the body through the cut. This reduces the risk of infection. While it may also help stop bleeding, its primary purpose in daily use is to protect the wound from germs until it heals.
Q2. Why do we get a foul smell from a garbage dump?
The foul smell from garbage is caused by the decomposition of organic waste by microorganisms like bacteria and fungi. These microbes break down proteins and other organic matter, releasing gases like ammonia, hydrogen sulphide, and methane, which have a strong, unpleasant odour.
Q3. Why does dough increase in volume when kept for some time?
When yeast is added to dough and left for some time, it ferments the sugars present. During fermentation, yeast produces carbon dioxide gas. This gas gets trapped in the dough, making it rise and increase in volume, which makes the final product (bread, idli, dosa) soft and fluffy.
Q4. What is the white cottony layer that appears on moist leather shoes?
The white cottony layer that grows on moist leather shoes is a fungus (mould). Fungi thrive in warm, moist, and dark conditions. They feed on organic matter in leather and produce fuzzy growth. To prevent this, shoes should be kept dry and well-ventilated.
Q5. Why are we advised to drink boiled water during the rainy season?
During the rainy season, water sources often get contaminated with pathogens (bacteria, viruses, protozoa). Boiling water kills most of these harmful microorganisms, making it safe to drink. This is a simple and effective method of purifying water and preventing water-borne diseases like cholera and typhoid.
Q6. Why do pickles, jams, and murabba not spoil for months?
Pickles, jams, and murabba contain high amounts of salt or sugar. These create a hypertonic environment that draws water out of microbial cells, preventing their growth. Without moisture, microorganisms cannot survive, so these foods do not spoil easily.
Q7. Why does a mother tell a child to wash hands with soap before eating?
Washing hands with soap removes dirt, dust, and harmful microorganisms that may have been picked up from surfaces, objects, or other people. This prevents germs from entering the body through food and reduces the risk of foodborne illnesses and infections.
Q8. What is the reason behind the sour taste of curd?
Lactobacillus bacteria convert milk sugar (lactose) into lactic acid. This acid gives curd its sour taste and also causes the milk proteins to coagulate. Lactic acid also helps preserve the curd and is beneficial for digestion.
Q9. Why do we see a greenish layer on stagnant water in ponds?
Stagnant water often develops a greenish layer due to the rapid growth of algae. Algae are photosynthetic microorganisms that thrive in sunlight and nutrient-rich water. This growth is called an algal bloom and can reduce oxygen levels in water, harming aquatic life.
Q10. What causes the ‘holes’ in swiss cheese?
The holes in Swiss cheese are caused by carbon dioxide gas produced by specific bacteria during fermentation. These bacteria release carbon dioxide, which forms bubbles in the cheese, creating the characteristic holes. This is a natural part of the cheesemaking process.
Q11. Why are onions and potatoes often stored in a cool, dry place?
Storing onions and potatoes in a cool, dry place prevents the growth of fungi and bacteria that cause rotting. Moisture and warmth promote microbial growth, which leads to spoilage. Cool, dry conditions slow down microbial activity and extend the shelf life of these vegetables.
Q12. Why is a person with a cold advised to use a handkerchief while sneezing?
Sneezing releases droplets containing the virus into the air. Using a handkerchief or tissue catches these droplets and prevents them from spreading to others. This is a simple but effective way to reduce the transmission of airborne infections like the common cold.
Q13. Why does idli and dosa batter rise when kept overnight?
Idli and dosa batter rises because of fermentation by natural bacteria and yeast present in the batter. They produce carbon dioxide gas, which gets trapped and causes the batter to increase in volume. This fermentation also gives the batter a slightly sour taste and makes the final product soft and fluffy.
Q14. What is the black powder that appears on mustard leaves?
The black powder on mustard leaves is a fungal disease commonly known as black spot or rust. It is caused by fungi that infect the leaves and produce dark, powdery spores. This disease reduces the plant’s health and crop yield.
Q15. Why is it recommended to finish a full course of antibiotics prescribed by a doctor?
Completing the full course of antibiotics ensures that all harmful bacteria are eliminated. Stopping early may leave some bacteria alive, which can multiply and develop resistance. This can make the infection harder to treat in the future and contribute to the problem of antibiotic resistance.
Q16. Why does wet laundry start smelling if left in a bucket for 2-3 days?
Wet laundry provides moisture and nutrients for microorganisms like bacteria and mould to grow. These microbes break down organic matter on the clothes and produce waste products that cause a bad smell. This can be avoided by drying clothes promptly.
Q17. Why are dried fish and dry fruits less likely to spoil than fresh ones?
Microorganisms need moisture to grow. Dried fish and dry fruits have very low water content, which prevents microbial growth. This is why dehydration is an effective method of preservation. Without water, microbes cannot survive or multiply.
Q18. Why are mosquitoes more common around stagnant water?
Mosquitoes breed in stagnant water. Female mosquitoes lay their eggs on the surface of standing water. The larvae develop in water, so stagnant water provides an ideal breeding ground. This is why mosquito-borne diseases are more common in areas with poor drainage and standing water.
Q19. Why does a rust-like reddish powder appear on wheat plants?
The reddish-brown powder on wheat plants is a fungal disease called rust, caused by Puccinia fungi. It appears as rusty pustules on leaves and stems and can reduce crop yield significantly. It is a common plant disease spread by wind and moisture.
Q20. What is the common reason for stomach upset or food poisoning after eating food from a street vendor?
Street food can sometimes be exposed to dust, flies, or unsanitary handling, leading to contamination by harmful bacteria like Salmonella or E. coli. These bacteria can cause stomach upset, diarrhoea, and food poisoning. Proper hygiene and fresh preparation can reduce this risk.
Q21. Why does a doctor clean a wound with a brown-colored liquid (antiseptic) before giving an injection?
Antiseptics like iodine or Dettol are applied to the skin to kill microorganisms present on the surface. This prevents them from being pushed into the body during an injection, reducing the risk of infection. It is a standard hygiene practice in healthcare.
Q22. Why does a gardener sometimes grow pea or bean plants in a field?
Pea and bean plants belong to the legume family. They have Rhizobium bacteria in their root nodules that fix atmospheric nitrogen into the soil. This increases soil fertility, reducing the need for chemical fertilisers. This practice is often used in crop rotation.
Q23. Why does the surface of an old loaf of bread become fuzzy and blackish-green?
The fuzzy blackish-green growth on old bread is mould, a type of fungus. Mould grows on moist, carbohydrate-rich food when kept in warm conditions. It produces spores that appear as fuzzy patches. Eating mouldy bread can be harmful, so it should be discarded.
Q24. Why are vaccination camps organized for children?
Vaccination camps are organized to immunize children against serious infectious diseases like polio, measles, and TB. Vaccines help the body develop immunity without causing the disease, providing long-term protection and helping control disease outbreaks.
Q25. Why does adding a little old curd to warm milk help in setting new curd?
Old curd contains live Lactobacillus bacteria that act as a starter culture. When added to warm milk, these bacteria multiply and ferment the milk sugar, producing lactic acid, which sets the milk into curd. This is how curd is traditionally made.
Q26. Why are dry neem leaves put in containers storing grains?
Neem leaves have natural antimicrobial and insect-repelling properties. When placed in grain storage containers, they help protect the grains from insects and microorganisms, reducing spoilage and loss. This is an age-old traditional method of preservation.
Q27. What causes the ‘fizz’ or bubbles in soft drinks?
The fizz in soft drinks is caused by carbon dioxide gas dissolved under pressure. When the bottle is opened, pressure is released, and the gas escapes as bubbles, creating the characteristic fizz. This process is also used in fermentation for some beverages.
Q28. Why does a vaccinated person not get a disease even if exposed to the germs?
Vaccines stimulate the immune system to produce antibodies and memory cells against a specific pathogen. If the vaccinated person is later exposed to that pathogen, the immune system responds quickly and effectively, preventing the disease. The body already has the “readymade” fighters to destroy the germs.
Q29. Why does a farmer sometimes plough the stubble (leftover plant parts) into the soil after harvest?
Ploughing plant stubble into the soil allows microorganisms to decompose it. This process returns nutrients to the soil and converts the organic matter into natural manure, improving soil fertility and reducing the need for chemical fertilisers. It is an eco-friendly agricultural practice.
Q30. Why do we sometimes see a slippery green layer on steps of a public bathroom?
The slippery green layer on damp surfaces like bathroom steps is algae. Algae grow in moist, shady conditions and form a slimy film. They can make the surface slippery and dangerous. Regular cleaning and drying help prevent their growth.
Q31. Why does a mother insist on covering cooked food?
Covering cooked food protects it from dust, flies, and other insects that can carry disease-causing microorganisms. This is a simple but important step to prevent contamination and foodborne illnesses, especially in warm weather.
Q32. Why does vinegar act as a good preservative for pickles?
Vinegar contains acetic acid, which creates an acidic environment. Most microorganisms cannot survive in highly acidic conditions, so vinegar acts as an effective preservative. It is used in many pickling processes to prevent spoilage and add flavour.
Q33. Why does a cut apple turn brown after some time?
When an apple is cut, its cells are exposed to oxygen in the air. Enzymes in the apple react with oxygen (oxidation), and microorganisms may also begin to grow, causing the fruit to turn brown. This is a common natural process and not spoilage, but it reduces freshness.
Q34. Why are pulses (dal) and grains often sun-dried before storage?
Sun-drying reduces the moisture content of pulses and grains. Since microorganisms need moisture to grow, drying them prevents fungal and bacterial growth during storage. This is a traditional and effective method of preservation.
Q35. What is the white layer sometimes seen on the surface of salty pickles or very salty fish?
The white layer on salty pickles or fish is often salt crystals. When salt dissolves in the brine and the water evaporates, salt can crystallize on the surface. This is normal and does not indicate spoilage. It may also be due to kahm yeast, but in most cases, it is salt.
Q36. Why does a jar of honey last for years without spoiling?
Honey lasts for years because it has low water content (which prevents microbial growth), is acidic, and contains natural preservatives like hydrogen peroxide. Keeping it sealed also prevents moisture and contaminants from entering. This combination makes honey one of the best natural preservatives.
Q37. Why do we feel body ache and fever during a viral infection like flu?
Fever and body ache during viral infections are caused by the body’s immune response. The immune system releases chemicals called pyrogens and cytokines that raise body temperature and cause muscle aches. This helps fight the infection and speeds up recovery.
Q38. Why does a deep puncture wound from a rusty nail risk causing tetanus?
Tetanus is caused by the bacterium Clostridium tetani, which is commonly found in soil, dust, and on rusty objects. A deep wound from a rusty nail can introduce this bacterium into the body, where it produces a toxin affecting the nervous system. Vaccination (tetanus shot) prevents this disease.
Q39. Why do we add baking soda (eno) or yeast while making cakes?
Baking soda (or yeast) releases carbon dioxide gas when heated or mixed with acidic ingredients. This gas forms bubbles in the batter, which expand during baking, making the cake rise and become light, soft, and fluffy. This is the leavening action of these agents.
Q40. Why does a person with tuberculosis often cough for a long time?
Tuberculosis (TB) is caused by Mycobacterium tuberculosis, which mainly infects the lungs. The bacteria cause inflammation, cavities, and damage in lung tissue, leading to a persistent cough, chest pain, and coughing up blood. This is why TB patients often have a long-lasting cough.
Q41. Why should we avoid storing cooked food in copper or brass containers?
Copper and brass can react with acidic or salty foods, forming toxic compounds that are harmful to health. These metals can leach into the food and cause food poisoning. It is safer to use stainless steel, glass, or food-grade plastic for storing cooked food.
Q42. Why does buttermilk feel cooling in summer and also help in digestion?
Buttermilk contains Lactobacillus bacteria, which promote healthy gut flora and aid digestion. It also has a cooling effect on the body and is often recommended during summer to maintain hydration and improve digestive health. Its probiotic nature makes it beneficial.
Q43. What causes the spongy, bad-smelling patches on citrus fruits like oranges?
Spongy, bad-smelling patches on citrus fruits are caused by fungal infections, often due to species like Penicillium. These fungi invade the fruit through small wounds and cause decay, producing spores and a foul smell. Proper storage and handling can reduce this spoilage.
Q44. Why are children given deworming medicine periodically?
Children are at higher risk of intestinal worm infections due to poor hygiene and exposure to contaminated soil or food. Deworming medication kills these parasites, improving nutrition, growth, and overall health. It is a common public health practice in many schools.
Q45. Why does a person often get a recurring infection if they have a weak immune system?
A weak immune system cannot produce enough antibodies or immune cells to fight off pathogens effectively. This makes the person vulnerable to recurring infections, as the body cannot remember or quickly respond to the same germs. Conditions like HIV or malnutrition can weaken immunity.
Q46. Why do we add oil to the surface of pickles?
Adding oil to pickles creates an airtight layer on the surface. This prevents oxygen from reaching the pickle and inhibits the growth of aerobic microbes that require oxygen to survive. It also prevents the pickle from being exposed to air and developing mould.
Q47. Why does a compost pit in the garden not smell bad if managed properly?
In a properly managed compost pit, aerobic microorganisms break down organic matter in the presence of oxygen. This process produces fewer foul-smelling gases like methane and hydrogen sulphide, unlike anaerobic decomposition. Regular turning and aeration keep the compost healthy and less odorous.
Q48. Why does a small piece of raw mango make the whole jar of pickles safe from spoilage?
Raw mango contains natural antimicrobial compounds that help prevent the growth of microorganisms in pickles. It also adds to the sourness, which creates an acidic environment unfavourable for spoilage organisms. This is why pickles made with raw mango last longer.
Q49. Why does a vaccine sometimes cause mild fever or pain at the injection site?
Mild fever or pain at the injection site after vaccination is a normal immune response. The body is recognizing the antigens in the vaccine and mounting a defence, which may cause temporary inflammation and fever. This shows that the vaccine is working and immunity is developing.
Q50. Why does water from an old tank or cooler sometimes cause itching or ear infection?
Stagnant water in old tanks or coolers can become contaminated with bacteria or amoebae like Pseudomonas or Acanthamoeba. These microorganisms can cause skin itching or ear infections when the water comes into contact with the body. Regular cleaning and disinfecting of water storage systems are essential to prevent this.