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Practice Class 8 Science Chapter 2 Microorganisms: Friend and Foe MCQ Questions with Answers and Useful Details based on the NCERT syllabus. Revise food preservation, nitrogen cycle, microorganisms in agriculture, medicine, food production, disease prevention, and important chapter concepts.
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Chapter Information
Subject: Science
Class: 8
Chapter: Microorganisms: Friend and Foe
Question Type: Multiple Choice Questions (MCQs)
Practice Set: 15
Difficulty Level: Difficult
Based On: NCERT Syllabus
Introduction
Microorganisms are extremely small organisms that cannot usually be seen with the naked eye. They are present in soil, water, air, food, and living organisms.
Although some microorganisms cause diseases and spoil food, many are highly useful. They are involved in food production, medicine, agriculture, nitrogen fixation, decomposition, and nutrient recycling.
This Practice Set 15 is the final set of the Class 8 Science Chapter 2 series. It provides a comprehensive revision of important concepts from Microorganisms: Friend and Foe, including their beneficial and harmful roles.
What You Will Learn
✔ Useful microorganisms
✔ Harmful microorganisms
✔ Food production
✔ Food preservation
✔ Antibiotics
✔ Vaccines
✔ Nitrogen fixation
✔ Nitrogen cycle
✔ Disease-causing microorganisms
✔ Food spoilage
✔ Disease prevention
✔ Role of microorganisms in nature
Why This Topic Is Important
Microorganisms are closely connected with human life and the environment. They can help produce food and medicines, improve soil fertility, and recycle nutrients. Some can also cause diseases and spoil food.
Understanding their beneficial and harmful effects helps students develop a complete understanding of the chapter and prepares them for conceptual and application-based examination questions.
Exam Relevance
These questions are useful for:
✔ CBSE School Exams
✔ State Board Exams
✔ Unit Tests
✔ Half-Yearly Exams
✔ Annual Exams
✔ NCERT-Based Practice
✔ Science Revision
5 MCQs with Answers and Useful Details
Q1. Which combination correctly represents the beneficial roles of microorganisms?
A) Curd formation, nitrogen fixation, and antibiotic production
B) Food spoilage, disease transmission, and crop damage
C) Only disease transmission
D) Only food spoilage
Answer:
A) Curd formation, nitrogen fixation, and antibiotic production
Useful Detail
Microorganisms have many beneficial applications.
Lactobacillus helps in curd formation, Rhizobium helps in nitrogen fixation, and certain microorganisms are associated with the production of antibiotics.
Thus, microorganisms are not only disease-causing agents; many are essential for food production, agriculture, medicine, and natural processes.
Correct Answer: A) Curd formation, nitrogen fixation, and antibiotic production
Q2. Which statement correctly explains why microorganisms are called both “friend” and “foe”?
A) All microorganisms are harmful.
B) All microorganisms are useful.
C) Some microorganisms are useful to humans, while others cause diseases or spoil food.
D) Microorganisms are useful only in agriculture.
Answer:
C) Some microorganisms are useful to humans, while others cause diseases or spoil food.
Useful Detail
The word “friend” refers to microorganisms that provide useful products or services.
For example:
- Lactobacillus helps make curd.
- Yeast is used in fermentation.
- Rhizobium helps in nitrogen fixation.
- Some microorganisms are involved in antibiotic production.
The word “foe” refers to microorganisms that cause diseases or spoil food.
Therefore, microorganisms can have both beneficial and harmful effects.
Correct Answer: C) Some microorganisms are useful to humans, while others cause diseases or spoil food.
Q3. Which sequence correctly connects a microorganism with its important use?
A) Lactobacillus → curd formation
B) Plasmodium → bread making
C) Rhizobium → malaria
D) Yeast → nitrogen fixation in root nodules
Answer:
A) Lactobacillus → curd formation
Useful Detail
Several microorganisms have specific uses.
Lactobacillus helps convert milk into curd.
Yeast is used in fermentation and bread making.
Rhizobium is associated with nitrogen fixation in leguminous plants.
Plasmodium is a disease-causing protozoan responsible for malaria.
Remembering these microorganism-use or microorganism-disease pairs is important for examinations.
Correct Answer: A) Lactobacillus → curd formation
Q4. Which statement best explains how microorganisms contribute to the balance of nutrients in nature?
A) They stop all decomposition.
B) They help decompose organic matter and participate in nutrient cycles.
C) They permanently remove nutrients from ecosystems.
D) They prevent nitrogen from entering plants.
Answer:
B) They help decompose organic matter and participate in nutrient cycles.
Useful Detail
Microorganisms play an important role as decomposers.
They break down dead plants, animals, and other organic matter, releasing nutrients back into the environment.
Microorganisms also participate in processes such as the nitrogen cycle, helping move nitrogen between different forms and organisms.
Thus, microorganisms contribute significantly to maintaining ecological balance.
Correct Answer: B) They help decompose organic matter and participate in nutrient cycles.
Q5. Which statement is the most appropriate conclusion about microorganisms?
A) Microorganisms should always be destroyed.
B) Microorganisms are useful only for making food.
C) Microorganisms can be beneficial or harmful depending on the organism and its activity.
D) Microorganisms have no importance in nature.
Answer:
C) Microorganisms can be beneficial or harmful depending on the organism and its activity.
Useful Detail
Microorganisms have extremely diverse roles.
Some are useful in food production, medicine, agriculture, decomposition, and nutrient cycling. Others cause diseases in humans, animals, and plants or spoil food.
Therefore, microorganisms cannot simply be classified as good or bad as a whole. Their effect depends on the particular microorganism and its interaction with living organisms and the environment.
Correct Answer: C) Microorganisms can be beneficial or harmful depending on the organism and its activity.
Important Formulas & Concepts
Science Chapter 2 does not contain mathematical formulas. Important scientific concepts are given below.
1. Microorganisms
Very small organisms that generally require a microscope for observation.
2. Bacteria
Microorganisms that include both useful and harmful species.
3. Fungi
A group of organisms that includes yeast and many other forms.
4. Protozoa
Mostly unicellular microorganisms such as Amoeba and Plasmodium.
5. Algae
Photosynthetic organisms, including some microscopic forms.
6. Viruses
Very small infectious agents that generally reproduce inside living host cells.
7. Fermentation
A process in which microorganisms such as yeast convert sugars into products such as alcohol and carbon dioxide.
8. Nitrogen Fixation
A process that converts atmospheric nitrogen into forms that can contribute to plant nutrition.
9. Food Preservation
Methods used to prevent or slow down the growth of microorganisms in food.
10. Antibiotics
Medicines used to treat certain bacterial infections.
11. Vaccination
An important method of preventing specific infectious diseases by stimulating an immune response.
12. Decomposition
The breakdown of dead organic matter by decomposers, including microorganisms.
Related Practice Questions
Q1. Why are microorganisms called both friends and foes?
Q2. How does yeast help in bread making?
Q3. How does Rhizobium benefit leguminous plants?
Q4. Why is food preservation important?
Q5. What role do microorganisms play in decomposition?
Mini Quiz Challenge
Try answering these questions within 60 seconds.
Q1. Which microorganism helps in curd formation?
A) Lactobacillus
B) Plasmodium
C) Virus
D) Amoeba
Q2. Which microorganism is useful in bread making?
A) Yeast
B) Rhizobium
C) Plasmodium
D) Lactobacillus
Q3. Which microorganism helps in nitrogen fixation?
A) Rhizobium
B) Amoeba
C) Yeast
D) Plasmodium
Q4. Which microorganism causes malaria?
A) Plasmodium
B) Rhizobium
C) Lactobacillus
D) Yeast
Q5. Microorganisms that break down dead organic matter are important as:
A) Decomposers
B) Producers only
C) Predators only
D) Consumers of sunlight
Exam Tips
✔ Learn the major groups of microorganisms and their examples.
✔ Remember Lactobacillus → curd.
✔ Remember Yeast → fermentation and bread making.
✔ Remember Rhizobium → nitrogen fixation.
✔ Remember Plasmodium → malaria.
✔ Revise important food preservation methods.
✔ Understand the difference between antibiotics and vaccines.
✔ Learn the basic nitrogen cycle.
✔ Remember the role of microorganisms as decomposers.
✔ Always distinguish between beneficial and harmful microorganisms.
✔ Focus on microorganism–use and microorganism–disease relationships.
Quick Revision Notes
✔ Lactobacillus: Helps make curd.
✔ Yeast: Used in fermentation and bread making.
✔ Rhizobium: Helps in nitrogen fixation.
✔ Plasmodium: Causes malaria.
✔ Antibiotics: Used against certain bacterial infections.
✔ Vaccines: Help prevent specific infectious diseases.
✔ Food Preservation: Helps prevent or delay microbial spoilage.
✔ Decomposers: Microorganisms break down dead organic matter.
✔ Nitrogen Cycle: Microorganisms participate in several nitrogen transformations.
✔ Microorganisms: Can be both beneficial and harmful.
Common Mistakes Students Make
❌ Thinking every microorganism causes disease.
❌ Thinking all bacteria are harmful.
❌ Confusing yeast with bacteria.
❌ Confusing Rhizobium with Lactobacillus.
❌ Thinking antibiotics can treat viral infections.
❌ Forgetting the role of microorganisms in decomposition.
❌ Confusing Plasmodium with a bacterium.
❌ Thinking food preservation makes food permanently safe under every condition.
❌ Forgetting that microorganisms participate in nutrient cycles.
Key Takeaways
✔ Microorganisms are present almost everywhere.
✔ Some microorganisms are useful to humans and the environment.
✔ Some microorganisms cause diseases and food spoilage.
✔ Lactobacillus is useful in curd formation.
✔ Yeast is useful in fermentation and bread making.
✔ Rhizobium helps in nitrogen fixation.
✔ Plasmodium causes malaria.
✔ Microorganisms participate in decomposition and nutrient recycling.
✔ Antibiotics and vaccines have different roles.
✔ Understanding both beneficial and harmful microorganisms is the central idea of this chapter.
FAQs
Q. Why are microorganisms called both friend and foe?
Answer:
Microorganisms are called both friend and foe because some are useful in food production, agriculture, medicine, and decomposition, while others cause diseases or spoil food.
Q. Which microorganism is used to make curd?
Answer:
Lactobacillus is used to convert milk into curd.
Q. What is the role of yeast?
Answer:
Yeast is a fungus used in fermentation and bread making. It converts sugars into alcohol and carbon dioxide during fermentation.
Q. What is the role of Rhizobium?
Answer:
Rhizobium lives in the root nodules of many leguminous plants and helps in nitrogen fixation.
Q. Why are microorganisms important in nature?
Answer:
Microorganisms help decompose dead organic matter and participate in nutrient cycles such as the nitrogen cycle, helping maintain ecological balance.
Conclusion
Class 8 Science Chapter 2 – Microorganisms: Friend and Foe is the final practice set of this chapter series.
This set provides a comprehensive revision of the chapter’s major concepts, including useful and harmful microorganisms, curd formation, fermentation, nitrogen fixation, antibiotics, vaccines, decomposition, food preservation, disease-causing microorganisms, and nutrient cycling.
Related links
- Class 8 English Chapter 3 Wisdom Paves the Way part-2
- Class 8 Maths Chapter 5– Number Play part-5
- Class 8 Science Chapter 2 Microorganisms Friend and Foe part-13
- Class 8 English Chapter 3 Wisdom Paves the Way part-1
- Class 8 Maths Chapter 5 – Number Play part-4
- Class 8 History Chapter 2 From Trade to Territory part-10
- Class 8 English Chapter 2 A Concrete Example part-10
- Class 8 Science Chapter 2 Microorganisms Friend and Foe part-12
- Class 8 Maths Chapter 5 – Number Play part-3
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