Microorganisms: Friend and Foe — Class 8 MCQs with Answers
Class 8 CBSE Science · Chapter 102
Pre-2026 syllabusThis chapter is from the older NCERT book. See the 2026-27 Class 8 Science chapters →
72 practice questions · 24 Easy · 24 Medium · 24 Hard · Updated
Jump to the 6 solved questions
Practise the most important Class 8 CBSE Science questions from Chapter 102, "Microorganisms: Friend and Foe". You get 6 timed quizzes made from 72 NCERT-based MCQs, with answers and explanations. The questions are split into 24 Easy, 24 Medium and 24 Hard. Warm up on the basics, then move on to the exam-level questions that top scorers in CBSE Board exams get right.
To score well in "Microorganisms: Friend and Foe", focus on clear concepts in physics, chemistry and biology basics. Each MCQ here is timed and uses exam-style marking (+4 correct, −1 wrong, 0 skipped). This helps you stay accurate when time is short, just as real papers need. Every question has a short explanation, so a wrong answer becomes a quick lesson. It is the fastest way to fix gaps before a test.
Use this chapter for focused revision. Start with the Easy set to check your basics on Microorganisms: Friend and Foe, then move to Medium and Hard to practise applying them. Your accuracy, streaks and XP save automatically. This chapter also adds to your overall Class 8 Science mastery score. Try the 6 sample questions below: tap an option to see the answer and a worked explanation. Sign in free to start practising.
Microorganisms: Friend and Foe — important questions & MCQs with answers (Class 8 Science)
6 solved questions from this chapter's difficulty levels, each with its answer and explanation. Tap an option to check yourself.
0 of 6 answered
- Q1 of 6Easy
Which group does yeast belong to?
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Answer: Fungi
Explanation: Yeast is a single-celled fungus, widely used in baking and fermentation.
- Q2 of 6Easy
Which bacterium converts milk into curd?
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Answer: Lactobacillus
Explanation: Lactobacillus multiplies in milk and converts it into curd.
- Q3 of 6Medium
Why are antibiotics ineffective against the common cold?
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Answer: The cold is caused by a virus, while antibiotics act on bacteria
Explanation: Antibiotics target bacterial processes; the common cold is viral, so antibiotics do not work on it.
- Q4 of 6Medium
Blue-green algae (cyanobacteria) benefit farmers by:
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Answer: Fixing atmospheric nitrogen in the soil
Explanation: Cyanobacteria fix atmospheric nitrogen, naturally enriching the soil, especially in paddy fields.
- Q5 of 6Hard
Milk left out in summer curdles by evening, but milk in the fridge does not. The best explanation is:
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Answer: Warmth speeds microbial multiplication; cold slows it
Explanation: Microbes multiply rapidly in warmth and slowly in cold, so refrigerated milk keeps longer.
- Q6 of 6Hard
A vaccinated child does not fall ill on later exposure to polio because the vaccine:
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Answer: Made the body produce antibodies and memory cells against the polio virus
Explanation: Vaccination primes the immune system to make antibodies and memory cells, giving lasting protection.
Microorganisms: Friend and Foe notes: key concepts (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.
Start this chapter free
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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 102 (Microorganisms: Friend and Foe) cover on XamBaaz?+
It has 72 NCERT-based MCQs on "Microorganisms: Friend and Foe": 24 Easy, 24 Medium and 24 Hard. Together they make 6 timed quizzes, and you never get the same set twice. Every question has an instant explanation. They help you prepare 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. One year from the day you pay. You stay in Class 8 till 31 March; on 1 April your account moves up to Class 9 and the rest of your year carries over. No chapter is charged separately.
How should I revise "Microorganisms: Friend and Foe" for the exam?+
Start with the Easy quiz to check your basics, then try Medium and Hard to practise applying them. There are 6 timed quizzes on this chapter, so you can come back for a fresh set instead of one you have seen. Read each explanation, retry the questions you miss, and track your accuracy until it stays high.
Are these "Microorganisms: Friend and Foe" MCQs available with answers?+
Yes. 6 sample questions are on this page with answers: tap an option, or "Show answer", to see the correct option and a step-by-step explanation. Sign in free with Google to start practising, with instant scoring.
Is there negative marking in the "Microorganisms: Friend and Foe" quizzes?+
Yes. The timed quizzes use exam-style marking: +4 for a right answer, −1 for a wrong one and 0 for a skip. MHT-CET and CBSE board papers have no negative marking. Our mocks for those are scored their way.
What are the important questions from Microorganisms: Friend and Foe (Class 8 Science)?+
The questions that matter most test Types of microorganisms, Friendly microbes, Harmful microbes, Disease transmission, Food preservation. This page shows 6 solved important MCQs with answers and explanations. Sign in to practise all 72 questions on the chapter as timed quizzes.
Is there an online quiz for Microorganisms: Friend and Foe?+
Yes — Class 8 Science Microorganisms: Friend and Foe has timed online quizzes at Easy, Medium and Hard levels, with instant scoring and a worked explanation on every question. The first quiz on the chapter is free.
Are there question answers and extra questions for Microorganisms: Friend and Foe (Class 8 Science)?+
Yes. This page has 6 solved questions on Microorganisms: Friend and Foe, each with the correct answer and a short explanation. Sign in to practise all 72 questions on the chapter as timed quizzes.