Microorganisms: Friend and Foe

Science Class 8 : Chapter 02

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Quick Revision : Microorganisms: Friend and Foe

  • Microorganisms: Tiny organisms visible only under microscope (bacteria, fungi, protozoa, algae).
  • Viruses: Microscopic entities reproducing only inside host cells (cold, flu, polio).
  • Friendly Microbes: Used in curd, bread, alcohol, medicines, cleaning environment.
  • Lactobacillus: Bacteria converting milk to curd.
  • Yeast: Fungus used in baking and alcohol production through fermentation.
  • Antibiotics: Medicines from microbes killing/delaying growth of disease-causing microbes (Penicillin).
  • Vaccines: Weakened/dead microbes stimulating antibody production (smallpox, polio).
  • Nitrogen Fixation: Bacteria/blue-green algae converting atmospheric nitrogen to usable form.
  • Harmful Microbes: Cause diseases (pathogens), food spoilage, food poisoning.
  • Communicable Diseases: Spread through air, water, food, contact (cholera, chicken pox, TB).
  • Carriers: Organisms transmitting pathogens (housefly, mosquito).
  • Food Preservation: Methods: chemical (salt, sugar, oil), heat/cold treatment, storage/packaging.
  • Pasteurization: Heating milk to 70°C then sudden chilling to kill microbes.
  • Nitrogen Cycle: Natural recycling of nitrogen between atmosphere, soil, plants, animals.
  • Rhizobium: Bacteria in legume root nodules fixing atmospheric nitrogen.

Questions

Chapter Summary : Microorganisms: Friend and Foe

What You Will Learn: This chapter explores the microscopic world of microorganisms - their classification, beneficial uses in food, medicine and environment, harmful effects causing diseases, and methods of food preservation.

Key Concepts: Understanding difference between bacteria, fungi, protozoa, algae and viruses; role of microbes in fermentation, antibiotic production, nitrogen fixation; disease transmission through carriers; and various food preservation techniques.

Exam-Oriented Importance: High-weightage chapter with questions on microbial classification, applications in daily life, disease transmission, and preservation methods.

Practical Applications: Knowledge applicable to hygiene practices, food safety, understanding medicines and vaccines, and environmental conservation.

How This Website Helps: Provides graded MCQs from basic to advanced levels with detailed explanations to strengthen conceptual understanding and prepare for exams.

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