Harmful
Spoilage, pathogens, hygiene practices.
Harmful
Harmful Microbes
What you'll learn
- Some microbes cause food spoilage, food poisoning, and disease — called pathogens at intro level.
- Hygiene: hand washing, clean water, covered food, refrigeration.
- Difference between spoilt food (visible mould) and invisible harmful bacteria.
- NCERT Looking Around 5, Chapter 4 (Mangoes Round the Year) and Chapter 8 (A Treat for Mosquitoes).
Key concepts
Level 1 — Harmful effects
Verbal: Harmful microbes multiply on food in warm, moist conditions — produce toxins or bad smell.
Symbolic: Pathogen + host → illness or spoilage.
| Problem | Cause (intro) | Prevention |
|---|---|---|
| Food spoilage | Bacteria, mould on bread | Refrigerate; eat fresh |
| Stomach upset | Contaminated food/water | Boil water; clean hands |
| Tooth decay | Bacteria + sugar on teeth | Brush twice, limit sweets |
| Mould on bread | Fungi | Store dry, sealed |
NCERT link: Ch 4 — why mangoes rot; preservation methods.
Level 2 — Hygiene practices
Verbal: Wash hands before eating and after toilet; ORS for diarrhoea dehydration (Ch 8 link).
Real-life: Street food risk if hygiene poor; school toilet soap use; cover drinking water in summer.
| Practice | When |
|---|---|
| Hand wash with soap | Before meals, after play, after toilet |
| Cook food thoroughly | Especially meat, eggs |
| Use clean utensils | Mid-day meal kitchens |
Worked example
Bread has green patches. Safe to scrape and eat?
Step 1 — Mould threads spread invisibly inside bread.
Step 2 — Scraping surface does not remove all toxins/spores.
Answer: Discard the bread — not safe.
Why refrigerate leftover dal in summer?
Step 1 — Warm temperature speeds bacterial growth.
Step 2 — Cooling slows microbes → food stays safe longer.
Answer: Slows harmful microbial multiplication.
Common mistakes
| Mistake | Why it happens | Fix |
|---|---|---|
| Smell OK = safe always | Some toxins odourless | When in doubt, throw out |
| Cold kills all microbes instantly | Fridge slows, not sterilises | Cook/reheat properly; don't keep forever |
| All bacteria on hands bad | Normal flora exists | Wash before food — reduce harmful load |
| Antiseptic on food | Wrong product use | Antiseptic for skin, not food surfaces |
Quick check
- Name two harmful effects of microbes.
- When must you wash hands with soap?
- Why does milk spoil faster outside fridge?
- Stretch: List three ways mid-day meal kitchen keeps food safe.
Revision tip: Poster at home: "Before eat — soap, water, 20 seconds scrub" — practise the steps.
Open the Practice tab for graded questions on Harmful Microbes.
Key Takeaways (TL;DR)
- What you'll learn
- Key concepts
- Worked example
- Common mistakes
Master this topic with Drishti OS
Get unlimited mock tests, AI-powered mentorship, and complete video courses when you join.
Start Free Practice