Chapter 2: Microorganisms: Friend and Foe
सूक्ष्मजीव: मित्र एवं शत्रु (किण्वन, पेनिसिलिन, टीके एवं नाइट्रोजन चक्र)
Don't Let a 20-Minute Bubbling Delay Cost You CTET Qualification
In offline CTET exams, bubbling 150 bubbles takes 18 to 22 minutes of mechanical time. A single misaligned row can trigger an 8-question domino error. Practice bubble-filling this chapter's solved MCQs inside Mentora's official OMR simulator.
- Four major groups of microorganisms: Bacteria, Fungi, Protozoa, and Algae. Viruses reproduce only inside host cells.
- Lactobacillus: Bacterium that promotes the curdling of milk by multiplying and converting lactose into lactic acid.
- Fermentation: Discovered by Louis Pasteur in 1857. Process of converting sugar into alcohol by yeast with the evolution of carbon dioxide gas (making bread dough rise).
- Penicillin: The first antibiotic, discovered by Alexander Fleming in 1929 from the fungus Penicillium notatum.
- Smallpox Vaccine: Discovered by Edward Jenner in 1798.
- Pasteurization: Heating milk to about 70°C for 15 to 30 seconds and then suddenly chilling it to prevent microbial growth; discovered by Louis Pasteur.
- Biological Nitrogen Fixers: Rhizobium bacteria live in the root nodules of leguminous plants (peas, beans) and fix atmospheric nitrogen into nitrates; Blue-green algae (Cyanobacteria) also fix atmospheric nitrogen.
- Trap: CBSE matches Louis Pasteur with Penicillin. Correct: Louis Pasteur discovered Fermentation (1857) and Pasteurization. Alexander Fleming discovered Penicillin (1929).
- Trap: CBSE matches Edward Jenner with Polio vaccine. Correct: Edward Jenner discovered the Smallpox vaccine (1798).
- Trap: CBSE states antibiotics are effective against viruses. Correct: Antibiotics kill bacteria and fungi; they have ZERO effect on viral infections like common cold and influenza.
NCERT Core Facts: Microbiology Scientists, Commercial Applications & Nitrogen Fixation
Class 8 Chapter 2 is a frequent source of matching-column questions in CTET Paper 2 Science.
1. Historic Discoveries & Scientists Matching Matrix
| Scientist | Year | NCERT Scientific Discovery |
|---|---|---|
| Louis Pasteur | 1857 / 1864 | Discovered Fermentation and developed the method of Pasteurization. |
| Edward Jenner | 1798 | Developed the Smallpox Vaccine (the world's first successful vaccine). |
| Alexander Fleming | 1929 | Discovered the antibiotic Penicillin from the mold Penicillium notatum. |
| Robert Koch | 1876 | Discovered the bacterium Bacillus anthracis which causes Anthrax disease. |
2. Commercial & Agricultural Uses of Microbes
- Curd Production: Lactobacillus converts milk into curd.
- Baking Industry: Yeast reproduces rapidly and produces CO_2 gas during respiration, creating bubbles that make bread, cakes, and idli/dosa batter spongy.
- Nitrogen Fixation: Rhizobium bacteria reside symbiotically in root nodules of leguminous plants (gram, peas, beans) to fix atmospheric nitrogen (N_2) into soluble nitrogenous compounds that fertilize the soil.
Test Your Mastery: Microorganisms: Friend and Foe
Authentic CBSE exam questions tested directly from this NCERT chapter.
Match the scientists with their landmark scientific discoveries: (A) Alexander Fleming - 1. Fermentation (B) Edward Jenner - 2. Smallpox Vaccine (C) Louis Pasteur - 3. Penicillin (D) Robert Koch - 4. Anthrax Bacterium Which combination is correct?
वैज्ञानिकों को उनकी ऐतिहासिक वैज्ञानिक खोजों से सुमेलित कीजिए: (A) अलेक्जेंडर फ्लेमिंग - 1. किण्वन (B) एडवर्ड जेनर - 2. चेचक का टीका (C) लुई पाश्चर - 3. पेनिसिलिन (D) रॉबर्ट कोच - 4. एंथ्रेक्स जीवाणु कौन सा संयोजन सही है?
Which bacterium lives in the root nodules of leguminous plants and fixes atmospheric nitrogen into the soil?
कौन सा जीवाणु दलहनी पौधों की जड़ों की ग्रंथियों में रहता है और वायुमंडलीय नाइट्रोजन को मिट्टी में स्थिर करता है?
Who discovered the process of fermentation?
Louis Pasteur in 1857.
Who discovered Penicillin and from what organism?
Alexander Fleming in 1929 from the fungus Penicillium notatum.
Why do antibiotics not cure the common cold or influenza?
Because common cold and flu are caused by viruses, and antibiotics only work against bacterial and fungal infections.