Microorganisms: Friend and Foe
Overview
Even those invisible to the naked eye are running the world — bacteria, virus, fungi, protozoa. These microorganisms are our friends (curd, medicine) as well as our enemies (disease). Let us look at both their faces.
Typed Notes
Microorganisms — 4 families
(1) Bacteria — rod (bacilli), round (cocci), spiral (spirilla) — the smallest; (2) Viruses — neither bacteria nor a cell — live only inside a host cell: polio, chickenpox, flu, HIV; (3) Fungi — mould (green-black on bread), mushroom, yeast; (4) Protozoa — single cell, found in water: amoeba-like — Plasmodium (malaria), Entamoeba (dysentery). All are visible only through a microscope — that is why they are called 'micro'. Found everywhere: water, soil, air, the body — some useful, some harmful.
The friendly face
(1) Curd — Lactobacillus bacteria added to milk — makes it sour; (2) Bread-idli-dosa — yeast: eats sugar — releases CO2 — dough rises; (3) Fermentation — discovered by Louis Pasteur — the basis of wine, bread, and cheese; (4) Antibiotic — medicine made from bacteria and fungi (streptomycin, tetracycline) — kills germs, saves humans; (5) Vaccine — weakened or dead microbe — gives the body advance practice — immunity: polio, TB (BCG), smallpox (eradicated from the world), chickenpox; (6) Nitrogen fixation — Rhizobium (legume roots) and cyanobacteria — enrich the soil with nutrients; (7) Environment — break down biodegradable waste into compost; cheese, idli batter are also gifts of microbes.
The harmful face — diseases
Microbes also cause disease: Human — cholera (bacteria, contaminated water), TB (bacteria, through coughing), chickenpox (virus), polio (virus), AIDS (HIV virus), malaria (protozoa — female Anopheles mosquito), dengue (virus — female Aedes mosquito), rabies (dog bite). Plants — citrus canker (on lemon), wheat rust. Animals — anthrax (bacteria, animals). Food poisoning — spoiled food (Staphylococcus, Salmonella) — diarrhoea and vomiting. Prevention: cleanliness, clean water, mosquito net-vaccine-boiling.
Methods of food preservation
Microbes need food — stop them: (1) Heat — boiling/steam (kills germs); (2) Cold — fridge (slows growth), freezer (freezes — stops growth); (3) Drying — dehydration (dried vegetables, fish) — water removed — microbe cannot grow; (4) Salt-sugar — pickle-preserve — draws out water — microbe starves; (5) Oil-vinegar — top layer in pickle — blocks air and germs; (6) Vacuum packing — air removed — microbe cannot survive; (7) Pasteurization — milk heated to 70°C for 15-30 seconds, then quickly cooled (by Pasteur) — microbes killed, nutrients preserved.
Key Concepts
Revision ke liye ek nazar — exam se pehle yahi padhna hai.
- 01Microorganisms: bacteria (cholera, TB), viruses (polio, chickenpox), fungi (mould — bread), protozoa (malaria, dysentery). Unicellular — visible only through a microscope.
- 02Useful: curd (Lactobacillus), bread-idli (yeast — CO2), antibiotic (streptomycin, tetracycline), vaccine (polio, TB, smallpox), nitrogen fixation (Rhizobium, cyanobacteria), environment cleaning (biodegradable waste), cheese-idli-dosa batter.
- 03Harmful: diseases — human (cholera, TB, malaria, dengue, chickenpox, AIDS-HIV), plants (citrus canker), animals (anthrax); food poisoning (spoiled food).
- 04Malaria — protozoa (Plasmodium) — female Anopheles mosquito; Dengue — virus — female Aedes mosquito.
- 05Food preservation: heat-cold (boiling, fridge-freezer), drying (dehydration), salt-sugar (pickle-preserve), oil-vinegar, vacuum packing, pasteurization (milk — Pasteur).
Questions & Solutions
Pehle khud try karo — phir solution kholo. Yahi tariqa topper banata hai.
What are the 4 families of microorganisms? Give one example each.
Which microbe is responsible for setting curd?
How does a vaccine protect us? Give the example of polio.
Which mosquito spreads malaria and which spreads dengue?
What is pasteurization?
Why does pickle not spoil in salt and oil?
Microbes belong to 4 families: bacteria-virus-fungi-protozoa. Friends: curd (Lactobacillus), bread (yeast), antibiotic-vaccine, nitrogen fixation, compost. Enemies: cholera-TB (bacteria), polio (virus), malaria (protozoa — Anopheles), dengue (Aedes). Prevention: cleanliness + vaccine. Preservation: heat-cold-drying-salt-oil-vacuum-pasteurization.
Chapter-end quiz
4 MCQsOption tap karo — turant pata chalega sahi ya galat, explanation ke saath.
Q1.Which microbe is responsible for setting curd?
Q2.Which mosquito spreads malaria?
Q3.What is the function of a vaccine?
Q4.Heating milk to 70°C and then cooling it quickly is called?
Mark karo — dashboard par progress dikhega.