Chapter 2: Microorganisms – Friend and Foe
1. Introduction
• Microorganisms (Microbes) are tiny living organisms that are not visible to the naked eye.
• Seen under a microscope.
• Types: Bacteria, Fungi, Protozoa, Algae, and Viruses.
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2. Types of Microorganisms
1. Bacteria – Single-celled, found everywhere, helpful in digestion, nitrogen fixation, etc.
2. Fungi – Grow on dead and decaying matter (e.g., bread mould).
3. Protozoa – Cause diseases (e.g., Amoeba, Plasmodium).
4. Algae – Green, contain chlorophyll (e.g., Chlamydomonas).
5. Viruses – Not considered true living organisms. Can reproduce only inside host cells.
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3. Where Microorganisms Live
• In soil, water, air, inside our bodies, and even in extreme conditions like hot springs or ice-cold mountains.
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4. Microorganisms: Friend
a. In Food
• Lactobacillus (bacteria) turns milk into curd.
• Yeast used in baking and alcohol production (fermentation).
b. In Medicine
• Microbes produce antibiotics (e.g., Penicillin by fungus Penicillium).
• Vaccines made using dead/weakened microbes (e.g., Polio vaccine).
c. In Agriculture
• Rhizobium bacteria fix nitrogen in soil (in legume roots).
• Increases soil fertility.
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5. Microorganisms: Foe
a. Disease-Causing Microbes (Pathogens)
• Cause diseases in humans, animals, and plants.
|
Disease |
Microbe Type |
Spread by |
Example |
|
Tuberculosis |
Bacteria |
Air |
Cough/Sneeze |
|
Malaria |
Protozoa |
Mosquito (Vector) |
Female Anopheles |
|
Chickenpox |
Virus |
Contact |
Touch |
|
Cholera |
Bacteria |
Water/Food |
Contaminated items |
b. Food Spoilage
• Microbes grow on food, making it spoiled and poisonous.
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6. Food Preservation Methods
1. Chemical preservatives – Salts, oils, sodium benzoate.
2. Refrigeration – Slows down microbial growth.
3. Heating & Pasteurization – Kills microbes (e.g., milk).
4. Drying – Removes moisture.
5. Vacuum packing – Removes air to stop microbe growth.
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7. Nitrogen Cycle
• Nitrogen is essential for plants and animals.
• Nitrogen-fixing bacteria (like Rhizobium) convert atmospheric nitrogen to usable forms.
• Decomposers release nitrogen back into the soil.
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Important Definitions
• Pathogens: Disease-causing microorganisms.
• Antibiotics: Medicines that kill or stop the growth of bacteria.
• Fermentation: Process by which yeast converts sugar into alcohol and CO₂.
• Pasteurization: Heating milk at 70°C for 15–30 seconds to kill harmful microbes.
Short Questions for Practice
1. Name any two useful microorganisms.
2. What is fermentation?
3. How do vaccines work?
4. Mention two methods of food preservation.
5. What role do nitrogen-fixing bacteria play?