Microorganisms: Friend and Foe – Short Answer Type Questions
Class 8
Science
Chapter 2
Microorganisms: Friend and Foe — 50 Short Answer Questions (Topic-wise)
CBSE Class 8 Science – Chapter Wise Study Materials Based on NCERT
CBSE Board Examinations — Chapter Presentation (Systematic):
- Focus: types, roles, habitats, control measures and practical activities related to microorganisms.
- Question Style: Short Answer Type (2–4 lines) for conceptual clarity and exam practice.
Topic 1: Basics & Types of Microorganisms (Q1–Q8)
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Q1: What are microorganisms?
A1: Microorganisms are tiny living organisms, such as bacteria, fungi, viruses, protozoa and some algae, that are usually visible only under a microscope.
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Q2: How are bacteria different from viruses?
A2: Bacteria are single-celled living organisms (cells) that can grow and reproduce independently; viruses are non-cellular particles that require a host cell to reproduce.
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Q3: Give two examples of useful fungi.
A3: Yeast used in bread-making and Penicillium used to produce the antibiotic penicillin.
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Q4: What is a protozoan? Provide one example.
A4: Protozoa are single-celled eukaryotes that often live in water; an example is Amoeba.
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Q5: Define 'pathogen'.
A5: A pathogen is a microorganism (bacterium, virus, fungus or protozoan) that can cause disease in plants, animals or humans.
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Q6: What are algae and why are they important?
A6: Algae are simple photosynthetic organisms (some microscopic) that produce oxygen and serve as the base of aquatic food chains.
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Q7: Describe how bacteria reproduce.
A7: Most bacteria reproduce asexually by binary fission, where one cell divides into two identical daughter cells.
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Q8: Why are viruses considered obligate parasites?
A8: Because viruses can replicate only inside living host cells and depend entirely on host machinery for reproduction.
Topic 2: Habitats & Growth Requirements (Q9–Q16)
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Q9: Name three places where microbes are commonly found.
A9: Soil, water (fresh and marine), and inside the bodies of plants and animals.
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Q10: List two factors that affect microbial growth.
A10: Temperature and moisture; pH and nutrient availability also influence growth.
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Q11: What conditions favour fungal growth on food?
A11: Warmth, moisture and organic material favour fungal (mould) growth on food items like bread and fruits.
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Q12: Can microbes live in extreme environments? Give an example.
A12: Yes — extremophiles live in harsh places, e.g. thermophilic bacteria in hot springs.
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Q13: Why is oxygen important for some microbes?
A13: Aerobic microbes need oxygen for respiration to release energy; anaerobic microbes grow in absence of oxygen.
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Q14: How does refrigeration slow microbial growth?
A14: Lower temperatures slow down microbial metabolism and reproduction, delaying spoilage.
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Q15: What is normal flora?
A15: Normal flora are harmless or beneficial microbes that normally live on or in the human body, e.g. gut bacteria.
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Q16: How does moisture influence microbial contamination of food?
A16: High moisture promotes microbial growth, increasing the chance of spoilage and contamination.
Topic 3: Beneficial Microorganisms (Q17–Q28)
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Q17: How does yeast help in bread-making?
A17: Yeast ferments sugars producing CO₂ which makes the dough rise and gives bread its texture.
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Q18: Name two foods produced using microbial fermentation.
A18: Curd and cheese (bacterial fermentation), and idli/dosa batter (yeast/lactic fermentation).
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Q19: What role do Rhizobium bacteria play in agriculture?
A19: Rhizobium fix atmospheric nitrogen in legume root nodules, enriching soil nitrogen for plant use.
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Q20: How are microbes used in medicine?
A20: Microbes produce antibiotics, vaccines and enzymes; recombinant microbes produce medicines like insulin.
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Q21: Explain bioremediation in one line.
A21: Bioremediation uses microbes to clean environmental pollutants, such as oil spills or contaminated soils.
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Q22: How do microbes help in waste management?
A22: Microbes decompose organic waste in composting and sewage treatment, recycling nutrients.
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Q23: Name one microbe used in yogurt production.
A23: Lactobacillus species and Streptococcus thermophilus are used to make yogurt/curd.
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Q24: Why are microbes important in the food industry?
A24: They ferment, preserve and add flavours/textures to foods and produce enzymes for processing.
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Q25: What is recombinant DNA technology (brief)?
A25: It inserts useful genes into microbes to produce medicines or enzymes, e.g., human insulin from bacteria.
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Q26: Give one example where microbes improve soil fertility.
A26: Nitrogen-fixing bacteria in legume roots enhance soil nitrogen content for subsequent crops.
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Q27: How do microbes contribute to oxygen production?
A27: Photosynthetic algae and cyanobacteria produce oxygen during photosynthesis, supporting aquatic ecosystems.
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Q28: What advantage does microbial fermentation offer in food preservation?
A28: Fermentation lowers pH or produces preservatives (like alcohol), slowing spoilage and extending shelf life.
Topic 4: Harmful Microorganisms & Diseases (Q29–Q38)
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Q29: Name two human diseases caused by bacteria.
A29: Tuberculosis and cholera are bacterial diseases.
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Q30: Give two examples of viral diseases.
A30: Influenza and common cold (caused by different viruses).
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Q31: How can contaminated water spread disease?
A31: Drinking or using contaminated water can introduce pathogens causing diseases like cholera and dysentery.
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Q32: What is food poisoning?
A32: Illness caused by eating food contaminated with pathogenic microbes or their toxins.
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Q33: Mention one plant disease caused by microbes.
A33: Late blight of potato caused by a fungus-like organism (Phytophthora).
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Q34: What is a carrier or vector in disease transmission?
A34: An organism (like a mosquito) that transmits pathogens between hosts without being affected itself.
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Q35: Why can't antibiotics treat viral infections?
A35: Antibiotics target bacterial structures/processes and are ineffective against viruses which replicate inside host cells.
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Q36: What simple hygienic practice reduces spread of microbes?
A36: Regular handwashing with soap and clean water reduces transmission of pathogens.
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Q37: How does vaccination help control infectious diseases?
A37: Vaccines stimulate the immune system to recognise and fight specific pathogens, preventing disease.
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Q38: What symptom commonly indicates bacterial infection?
A38: Fever with localized signs (e.g., pus, inflammation) often suggests bacterial infection.
Topic 5: Controlling Microorganisms (Q39–Q44)
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Q39: What is sterilisation and where is it used?
A39: Sterilisation kills all microbes and spores, used for surgical instruments and laboratory equipment.
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Q40: Explain pasteurisation briefly.
A40: Pasteurisation is mild heating (e.g., milk) to kill most pathogens while preserving taste and nutrients.
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Q41: Give an example of an antiseptic.
A41: Iodine solution or alcohol used to clean wounds.
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Q42: How does boiling water make it safer?
A42: Boiling kills many disease-causing microbes, making water safer to drink.
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Q43: Why is proper storage important for food safety?
A43: Drying and cool storage slow microbial growth and prevent spoilage and foodborne illness.
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Q44: What is the role of disinfectants?
A44: Disinfectants reduce microbes on surfaces, helping prevent spread of infections (not for use on skin).
Topic 6: Practical Activities & Revision (Q45–Q50)
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Q45: Outline a simple experiment to show yeast fermentation.
A45: Mix yeast, sugar and warm water in a bottle, fit a balloon on the mouth and observe balloon inflation from CO₂ production.
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Q46: How to make curd at home (brief steps)?
A46: Boil milk, cool to lukewarm, add a spoon of curd as starter and keep covered in a warm place until set.
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Q47: What safety precautions are needed during microbe practicals?
A47: Work under supervision, avoid tasting, use gloves if needed and sterilise/ dispose materials safely.
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Q48: Give a quick tip to revise this chapter effectively.
A48: Make a two-column chart: 'Microbe type — one use — one disease' and memorise key examples.
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Q49: What is the difference between disinfectant and antiseptic (short)?
A49: Disinfectants are for inanimate surfaces; antiseptics are milder and safe for skin use.
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Q50: Why is vaccination considered a preventive measure?
A50: Vaccination prepares the immune system to recognise and fight a pathogen, preventing disease on exposure.
Note: These Short Answer Questions with Answers are organised topic-wise and strictly follow the NCERT syllabus, making them ideal for CBSE Class 8 board exams standard.