Microorganisms: Friend and Foe — Practice Quiz

To prevent the growth of harmful microbes in milk

Step 1: Raw milk contains various microorganisms, some of which can cause diseases in humans. Step 2: Louis Pasteur developed the process of pasteurisation to make milk safe for consumption without changing its nutritional properties. Step 3: Heating milk to about 70°C kills harmful microbes, and sudden chilling prevents the surviving ones from multiplying. Step 4: Pasteurised milk can be consumed without boiling because it is already free from harmful microbes. The process does NOT increase nutrition, change taste, or make curd — it simply makes milk safe by killing microbes.

Chicken pox

Step 1: It is important to know which type of microorganism causes which disease. Step 2: Chicken pox is caused by a virus — specifically the Varicella-zoster virus. It spreads through air and direct contact. Step 3: Tuberculosis (TB) is caused by bacteria (Mycobacterium tuberculosis); Typhoid is caused by bacteria (Salmonella typhi); Malaria is caused by a protozoan (Plasmodium). Step 4: Viruses are different from other microorganisms — they can only reproduce inside the cells of a host organism. Other viral diseases include polio, measles, influenza, and hepatitis A.

They fix atmospheric nitrogen into usable compounds, increasing soil fertility

Step 1: The atmosphere contains about 78% nitrogen, but most plants cannot use this nitrogen directly from the air. Step 2: Rhizobium bacteria live in root nodules of leguminous plants (like peas, beans, lentils) in a symbiotic relationship — both organisms benefit. Step 3: These bacteria fix atmospheric nitrogen (N₂) by converting it into nitrogen compounds that plants can absorb through their roots. Step 4: This increases soil fertility because more nitrogen compounds become available in the soil. This is why farmers rotate crops and grow leguminous plants — to naturally enrich the soil with

Placing food in direct sunlight for a long time

Step 1: Food preservation methods work by preventing or slowing down the growth of microorganisms. Step 2: Salt and sugar reduce moisture in food, which inhibits bacterial growth. Refrigeration uses low temperatures to slow microbial activity. Airtight sealed packets prevent microbes from entering the food. Step 3: Placing food in direct sunlight for a long time does NOT reliably preserve food — in fact, warm and moist conditions promote faster microbial growth and spoilage. Step 4: While drying food (removing moisture) in sunlight can preserve some foods like papad or fish, simply leaving foo