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Microorganisms: Friend and Foe — Revision Notes

Gujarat Board · Class 8 · Science

Microorganisms: Friend and Foe revision notes for Gujarat Board Class 8 Science: 4 topics in quick points. Includes What are Microorganisms?, Friendly.

44 questions5 concepts

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Key Topics to Revise

1

What are Microorganisms?

  • Microorganisms (microbes) are living organisms too small to be seen with the unaided (naked) eye.
  • Some microbes like bread mould can be seen with a magnifying glass, but most need a microscope.
  • They are classified into four major groups: Bacteria, Fungi, Protozoa, and some Algae.
2

Friendly Microorganisms — Beneficial Uses

  • Lactobacillus bacteria convert milk into curd by multiplying in warm milk — this is why a spoonful of curd (starter) is added to warm milk.
  • Yeast is used in baking — it produces CO2 during respiration, which makes dough rise and gives bread, cakes, and pastries a soft, spongy texture.
  • Yeast is used for commercial production of alcohol and wine through the process of fermentation.
3

Harmful Microorganisms — Diseases and Food Spoilage

  • Microorganisms that cause diseases are called pathogens.
  • Diseases that spread from an infected person to a healthy person are called communicable diseases.
  • Pathogens can spread through air (sneezing, coughing), water, food, direct physical contact, and through carriers (animals/insects that carry the microbe).
4

Food Preservation

  • Food spoilage is caused by microorganisms — spoiled food has a bad smell, bad taste, and changed colour.
  • The goal of food preservation is to prevent microbial growth in food.
  • Chemical method: Common salt, edible oils, vinegar (acetic acid), sodium benzoate, and sodium metabisulphite are used as preservatives.

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Full Notes

Key Concepts

Microorganisms are living creatures so smallMicroorganisms are grouped into four mainMicroorganisms are incredibly adaptable and liveBacteria like Lactobacillus convert milk intoAntibiotics are medicines produced from bacteria

Frequently Asked Questions

What are the important topics in Microorganisms: Friend and Foe for Gujarat Board Class 8 Science?
Key topics in Microorganisms: Friend and Foe include What are Microorganisms?, Friendly Microorganisms — Beneficial Uses, Harmful Microorganisms — Diseases and Food Spoilage, Food Preservation. Study these first, then practise questions on each for Class 8 exams.
How should I revise Microorganisms: Friend and Foe for Class 8 exams?
Learn the core ideas first, then work through the 44 practice questions on Microorganisms: Friend and Foe. Revise definitions regularly and use flashcards for quick recall before the exam.

Sources & Official References

Content is aligned to the official syllabus. Refer to the board website for the latest curriculum.

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All Gujarat Board Class 8 Science Revision Notes

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