Lactobacillus is NOT harmful — this statement is FALSE. Lactobacillus is a beneficial (useful) bacterium. It is a lactic acid bacterium that converts milk into curd (yogurt). It is also a part of the normal human gut flora and helps in digestion. Lactobacillus is used as a probiotic to maintain gut health. This is covered in NCERT Class 8 Science (Microorganisms).
Lactobacillus is NOT harmful — it is beneficial bacteria (statement: FALSE).
Lactobacillus converts milk to curd by fermentation (lactose → lactic acid).
It is found in curd, yogurt, fermented foods, and the human gut.
Used as a probiotic to maintain gut health and prevent intestinal infections.
NCERT Class 8 Science Chapter 2 — Microorganisms: Friend and Foe.
Lactic acid produced by Lactobacillus preserves food and inhibits harmful bacteria.
Statement: Lactobacillus is harmful — FALSE
Lactobacillus is beneficial (useful) bacteria, NOT harmful.
What is Lactobacillus? • A genus of gram-positive, rod-shaped bacteria • Belongs to lactic acid bacteria (LAB) group • Converts lactose (milk sugar) → lactic acid (fermentation) • Lactic acid curdles milk → forms curd (dahi) • Found in: curd, yogurt, fermented foods, human digestive tract
Why is Lactobacillus Beneficial?
Curd Formation: • Lactobacillus causes milk to ferment → curd/yogurt • When a small amount of curd (starter) is added to warm milk, Lactobacillus multiplies and sets the curd • Temperature required: ~40–45°C
Gut Health (Probiotic): • Part of normal gut flora • Produces lactic acid → creates acidic environment → inhibits harmful bacteria • Helps prevent diarrhoea and intestinal infections
Food Preservation: • Used in fermented foods: pickles, sauerkraut, kimchi, cheese • Lactic acid acts as a natural preservative
Digestion: • Helps break down food in the intestine • Produces vitamins (e.g., B vitamins)
Harmful Bacteria (for comparison):
| Bacteria | Disease |
|---|---|
| Mycobacterium tuberculosis | Tuberculosis |
| Vibrio cholerae | Cholera |
| Salmonella typhi | Typhoid |
| Clostridium tetani | Tetanus |
Lactobacillus is NOT in the above list — it is beneficial.
NCERT Class 8 Science — Chapter 2: Microorganisms: Friend and Foe Key line: 'Lactobacillus promotes the formation of curd. It is also found in our stomach.'
FALSE. Lactobacillus is NOT harmful — it is a beneficial bacterium. It converts milk into curd through fermentation (lactose → lactic acid). It is part of normal human gut flora, acts as a probiotic, aids digestion, and helps preserve fermented foods. NCERT Class 8 Science (Chapter 2) classifies Lactobacillus as a 'friendly microorganism.'
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