Class 8 Science — Chapter 2: Microorganisms: Friend and Foe
72 practice questions · 24 Easy · 24 Medium · 24 Hard
Practise Class 8 Science Chapter 2, "Microorganisms: Friend and Foe", with 72 NCERT-aligned multiple-choice questions. The set is split into 24 Easy, 24 Medium and 24 Hard questions, so you can warm up on the fundamentals and then push into the exam-level problems that separate top scorers in CBSE Board exams.
"Microorganisms: Friend and Foe" is one of the chapters where concept clarity across physics, chemistry and biology basics really pays off. Each MCQ on this chapter is timed and uses exam-grade marking (+2 correct, −1 wrong, 0 skipped), training the same accuracy-under-pressure that real papers demand. Every question carries a short explanation, so a wrong answer becomes a quick lesson rather than a dead end — the fastest way to close gaps before a test.
Use this chapter as targeted revision: attempt the Easy set first to confirm your basics on Microorganisms: Friend and Foe, then move to Medium and Hard to test application and problem-solving. Your accuracy, streaks and XP save automatically, and the chapter feeds into your overall Class 8 Science mastery score. A few sample questions are shown below; sign in free to practise all 72.
Key concepts: Microorganisms: Friend and Foe (Class 8 Science)
This chapter covers microorganisms — their types, their helpful and harmful roles, and food preservation.
- Types of microorganisms
- Bacteria, fungi, protozoa, algae and viruses; viruses reproduce only inside a host.
- Friendly microbes
- Used in making curd, bread and alcohol, in medicines (antibiotics), and in nitrogen fixation by Rhizobium.
- Harmful microbes
- Cause diseases in humans (e.g. TB), animals and plants, and spoil food.
- Disease transmission
- Communicable diseases spread through air, water, food and carriers like the mosquito and housefly.
- Food preservation
- Salting, sugaring, heating, refrigeration and chemical preservatives stop microbial growth.
💡 Exam tips for Microorganisms: Friend and Foe
- Rhizobium bacteria in legume roots fix atmospheric nitrogen — a key nitrogen-cycle fact.
- Antibiotics kill bacteria/fungi but do NOT work against viral diseases like the common cold.
Sample questions
Which bacterium converts milk into curd?
Lactobacillus multiplies in milk and converts it into curd.
Why are antibiotics ineffective against the common cold?
Antibiotics target bacterial processes; the common cold is viral, so antibiotics do not work on it.
Milk left out in summer curdles by evening, but milk in the fridge does not. The best explanation is:
Microbes multiply rapidly in warmth and slowly in cold, so refrigerated milk keeps longer.
Microorganisms: Friend and Foe — FAQs
What are the key concepts in Class 8 Science Microorganisms: Friend and Foe?+
This chapter covers microorganisms — their types, their helpful and harmful roles, and food preservation. Key ideas include Types of microorganisms, Friendly microbes, Harmful microbes, Disease transmission, Food preservation.
What does Class 8 Science Chapter 2 (Microorganisms: Friend and Foe) cover on XamBaaz?+
It covers 72 NCERT-aligned MCQs on "Microorganisms: Friend and Foe" — 24 Easy, 24 Medium and 24 Hard — each with a timed quiz and an instant explanation, suitable for CBSE Board exams.
Are these "Microorganisms: Friend and Foe" questions free to practise?+
Yes — sign in with Google to practise "Microorganisms: Friend and Foe" free. Full unlimited access is ₹999/year (limited-time launch price), with no per-chapter charges.
How should I revise "Microorganisms: Friend and Foe" for the exam?+
Start with the Easy quiz to confirm your fundamentals, then attempt Medium and Hard for application-level practice. Review each explanation, retry the questions you miss, and track your accuracy on this chapter until it is consistently high.
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