'The Invisible Living World: Beyond Our Naked Eye' — Practice

Question 1

Name the microorganism used in making curd.

Accepted Answer

✦ Answer: Lactobacillus — a bacterium that converts lactose (milk sugar) into lactic acid, which curdles milk.

Question 2

Name the disease caused by Plasmodium and its vector.

Accepted Answer

✦ Answer: Malaria. Vector: female Anopheles mosquito (it bites and transfers Plasmodium from infected to uninfected people).

Question 3

Describe three beneficial uses of microorganisms with examples.

Accepted Answer

Step 1 — In food production.
  Lactobacillus converts milk to curd. Yeast makes bread rise (produces CO₂). Other fermentation: cheese, idli, dosa, beer, wine, vinegar.

Step 2 — In medicine.
  Antibiotics from Penicillium (penicillin) and other moulds kill harmful bacteria. Vaccines (weakened microbes) train our immune system. Modern medicine could not exist without microbes.

Step 3 — In agriculture / environment.
  Rhizobium in root nodules of legumes fixes nitrogen from air, fertilising soil naturally. Decomposers (bacteria, fungi) break down dead matter, recycling nutrients. Without them, dead organisms would pile up.

✦ Answer: Three beneficial uses: (1) FOOD: Lactobacillus for curd, yeast for bread; (2) MEDICINE: Penicillin (antibiotic from Penicillium), vaccines; (3) AGRICULTURE: Rhizobium fixes nitrogen, decomposers recycle nutrients.

Question 4

How can communicable diseases be prevented?

Accepted Answer

Step 1 — Personal hygiene.
  Wash hands with soap and water frequently (especially before eating, after toilet). Brush teeth. Bathe daily. Cover mouth when coughing/sneezing.

Step 2 — Safe food and water.
  Drink boiled or filtered water. Eat freshly cooked food. Avoid street food in unhygienic areas. Wash fruits and vegetables.

Step 3 — Clean environment.
  Don't allow water stagnation (mosquito breeding). Dispose garbage properly. Maintain sanitation in homes and public places.

Step 4 — Vaccination.
  Take all recommended vaccines (polio, measles, hepatitis B, COVID-19, etc.). Universal Immunisation Programme in India provides many free.

Step 5 — Avoid exposure.
  Stay away from sick people. Use masks during outbreaks. Use mosquito nets and repellents.

Step 6 — Healthy lifestyle.
  Eat balanced diet. Exercise. Adequate sleep. All boost immunity.

✦ Answer: Prevention requires (1) personal hygiene (handwashing), (2) safe food/water, (3) clean environment, (4) vaccination, (5) avoiding exposure to sick people, (6) healthy lifestyle to boost immunity. COVID-19 taught the world the importance of these practices.

Question 5

Explain food preservation methods with the scientific principle behind each.

Accepted Answer

Step 1 — Refrigeration / Freezing.
  Principle: Microbes need warmth to grow rapidly. Low temperatures (5°C refrigerator; −18°C freezer) slow or stop microbial growth.

Step 2 — Boiling / Cooking.
  Principle: Heat denatures (destroys) proteins in microbes, killing them. Boiling at 100°C kills most pathogens. Pressure cooking at 121°C kills even bacterial spores.

Step 3 — Pasteurisation.
  Principle: Quick heating (60-70°C for milk) destroys harmful microbes without ruining nutrition. Invented by Louis Pasteur. Used for milk, juice.

Step 4 — Salt / Sugar preservation.
  Principle: High salt/sugar concentration pulls water OUT of microbes by osmosis. Microbes shrivel and die. Used in pickles, jams, dried meat, honey.

Step 5 — Oil and vinegar.
  Principle: Oil creates an air barrier (microbes need oxygen). Vinegar is acidic — most microbes can't survive low pH.

Step 6 — Drying.
  Principle: Microbes need water. Removing water (sun-drying, freeze-drying) prevents growth. Used for grains, fruits, fish, herbs.

Step 7 — Smoking.
  Principle: Smoke contains antimicrobial chemicals (formaldehyde) and dries the food. Used for fish, meat, cheese.

Step 8 — Canning.
  Principle: Boil food in airtight container — kills microbes and prevents new ones entering. Long shelf life.

Step 9 — Vacuum packing.
  Principle: Removes oxygen — anaerobic microbes are slowed; aerobic microbes can't grow.

Step 10 — Chemical preservatives.
  Principle: Specific chemicals (sodium benzoate, sodium nitrite, potassium sorbate) inhibit microbial growth. Used in processed foods, jams, juices.

Step 11 — Conclusion.
  Understanding food preservation IS understanding microbial biology. India's traditional methods (pickling, drying, sun-curing) align with modern science.

✦ Answer: Food preservation methods all work by REMOVING WHAT MICROBES NEED (water, warmth, food) or by KILLING them directly. Common methods: refrigeration (cold slows growth), boiling (heat kills), salt/sugar (osmosis), oil (no air), drying (no water), pasteurisation (gentle heat), canning, vacuum packing, chemical preservatives. India's traditional pickles, jams, dried foods all use these principles.

Practice — 'The Invisible Living World: Beyond Our Naked Eye'

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