Microbes in Household Products – NCERT Key Points (NEET/CBSE)

MICROBES IN HUMAN WELFARE CLASS 12 BIOLOGY TOPIC 2

1. Curd Formation

  • Microbe involved: Lactobacillus and other Lactic Acid Bacteria (LAB).
  • LAB convert milk into curd.
  • They produce lactic acid, which:
    • Coagulates (curdles) milk proteins.
    • Partially digests milk proteins.
  • A small amount of curd is used as a starter (inoculum).
  • Starter contains millions of LAB.
  • At suitable temperature, LAB multiply rapidly and convert milk into curd.
  • LAB increase the nutritional value of curd by increasing Vitamin B₁₂.
  • LAB in the human intestine help prevent the growth of disease-causing microbes (probiotics).

2. Idli and Dosa Batter

  • Batter is fermented by bacteria (mainly LAB).
  • Fermentation produces CO₂ gas.
  • CO₂ makes the batter soft, fluffy, and puffed up.
  • Metabolic pathway involved: Fermentation (Anaerobic respiration).
  • The bacteria usually come from:
    • Previous fermented batter (starter)
    • Rice and urad dal surfaces
    • Surrounding environment

3. Bread Making

  • Microbe used: Baker’s yeast (Saccharomyces cerevisiae).
  • Yeast ferments sugars and produces:
    • CO₂
    • Ethanol
  • CO₂ causes the dough to rise and become soft.

4. Traditional Fermented Foods and Drinks

  • Toddy
    • Traditional drink of southern India.
    • Produced by fermenting palm sap.
  • Microbes are also used to ferment:
    • Fish
    • Soybean
    • Bamboo shoots

5. Cheese Production

  • Cheese is one of the oldest fermented foods.
  • Different microbes produce different:
    • Texture
    • Flavour
    • Taste

(a) Swiss Cheese

  • Microbe: Propionibacterium sharmanii
  • Produces large amounts of CO₂.
  • CO₂ forms the large holes (eyes) in Swiss cheese.

(b) Roquefort Cheese

  • Ripened using a specific fungus.
  • The fungus gives the cheese its characteristic flavour.

NEET Important Microbes Table

ProductMicroorganismImportant Function
CurdLactobacillus (LAB)Converts milk into curd; increases Vitamin B₁₂
Idli/DosaLactic Acid BacteriaFermentation; CO₂ makes batter fluffy
BreadSaccharomyces cerevisiaeCO₂ makes dough rise
ToddyYeastFerments palm sap
Swiss CheesePropionibacterium sharmaniiProduces holes by CO₂
Roquefort CheeseSpecific fungusDevelops characteristic flavour

NEET One-Liners

  • LAB = Lactic Acid Bacteria.
  • Lactobacillus converts milk into curd.
  • LAB increase Vitamin B₁₂ content in curd.
  • LAB suppress harmful microbes in the gut (probiotic effect).
  • Baker’s yeast = Saccharomyces cerevisiae.
  • CO₂ causes bread dough and idli batter to rise.
  • Swiss cheese holes are due to Propionibacterium sharmanii.
  • Roquefort cheese is ripened by a specific fungus.
  • Toddy is prepared by fermentation of palm sap.

🎯 NCERT Facts Frequently Asked in NEET

  • Starter used in curd making: Inoculum containing millions of LAB.
  • Gas responsible for puffing of idli/dosa batter: CO₂.
  • Metabolic pathway: Fermentation (anaerobic respiration).
  • Vitamin increased in curd: Vitamin B₁₂.

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