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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 nitrogen fixation, Rhizobium, nitrogen cycle, soil fertility, symbiotic relationships, and the role of microorganisms in nature.
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Chapter Information
Subject: Science
Class: 8
Chapter: Microorganisms: Friend and Foe
Question Type: Multiple Choice Questions (MCQs)
Practice Set: 12
Difficulty Level: Difficult
Based On: NCERT Syllabus
Introduction
Microorganisms play an important role not only in food production and medicine but also in maintaining the balance of nutrients in nature.
One of their most important ecological roles is related to the nitrogen cycle. Nitrogen is essential for the growth of plants, but most plants cannot directly use atmospheric nitrogen.
Certain bacteria, particularly Rhizobium, help convert atmospheric nitrogen into forms that plants can use. Other microorganisms also participate in the decomposition of organic matter and help return nutrients to the environment.
This Practice Set 12 focuses on nitrogen fixation, Rhizobium, the nitrogen cycle, soil fertility, and the ecological importance of microorganisms.
What You Will Learn
✔ Nitrogen fixation
✔ Rhizobium bacteria
✔ Leguminous plants
✔ Root nodules
✔ Nitrogen cycle
✔ Soil fertility
✔ Symbiotic relationship
✔ Role of microorganisms in nature
✔ Atmospheric nitrogen
✔ Nutrient recycling
Why This Topic Is Important
Nitrogen is an essential nutrient required by plants for making proteins and other important substances. Although the atmosphere contains a large amount of nitrogen, plants cannot directly use atmospheric nitrogen in this form.
Microorganisms help make nitrogen available to plants through nitrogen fixation and other processes involved in the nitrogen cycle.
Understanding this topic helps students connect microorganisms with agriculture, soil fertility, plant growth, and environmental balance.
5 MCQs with Answers and Useful Details
Q1. Which bacterium is commonly associated with nitrogen fixation in the root nodules of leguminous plants?
A) Rhizobium
B) Lactobacillus
C) Plasmodium
D) Yeast
Answer:
A) Rhizobium
Useful Detail
Rhizobium is a nitrogen-fixing bacterium commonly found in the root nodules of leguminous plants such as pea, gram, and beans.
It converts atmospheric nitrogen into forms that contribute to the nitrogen nutrition of plants.
The association between Rhizobium and leguminous plants is an example of a symbiotic relationship, in which both partners benefit.
Correct Answer: A) Rhizobium
Q2. Where is Rhizobium commonly found in leguminous plants?
A) Inside flowers
B) In root nodules
C) On the surface of fruits
D) Inside leaves only
Answer:
B) In root nodules
Useful Detail
Rhizobium bacteria live in special structures called root nodules on the roots of leguminous plants.
The bacteria obtain food and shelter from the plant, while the plant benefits from the nitrogen-fixing activity of the bacteria.
This relationship is beneficial to both the microorganism and the plant.
Correct Answer: B) In root nodules
Q3. Why are leguminous plants useful for maintaining soil fertility?
A) They remove all nitrogen from the soil.
B) Their association with nitrogen-fixing bacteria can increase the availability of nitrogen compounds in the soil.
C) They prevent microorganisms from growing.
D) They convert nitrogen into oxygen.
Answer:
B) Their association with nitrogen-fixing bacteria can increase the availability of nitrogen compounds in the soil.
Useful Detail
Leguminous plants such as peas, beans, and gram have root nodules containing Rhizobium bacteria.
These bacteria fix atmospheric nitrogen and help make nitrogen available in forms useful to plants.
Therefore, growing leguminous crops can contribute to maintaining or improving soil fertility and is an important agricultural practice.
Correct Answer: B) Their association with nitrogen-fixing bacteria can increase the availability of nitrogen compounds in the soil.
Q4. Which process helps return nitrogen to the atmosphere as part of the nitrogen cycle?
A) Denitrification
B) Photosynthesis
C) Digestion
D) Transpiration
Answer:
A) Denitrification
Useful Detail
The nitrogen cycle involves several processes through which nitrogen moves between the atmosphere, soil, plants, animals, and microorganisms.
During denitrification, certain bacteria convert nitrates into nitrogen gas, which is released back into the atmosphere.
This helps maintain the balance of nitrogen in nature.
Correct Answer: A) Denitrification
Q5. Which statement best describes the role of microorganisms in the nitrogen cycle?
A) They have no role in nitrogen movement.
B) They help convert nitrogen between different forms and make it available to living organisms.
C) They remove all nitrogen from the atmosphere permanently.
D) They only cause diseases in plants.
Answer:
B) They help convert nitrogen between different forms and make it available to living organisms.
Useful Detail
Microorganisms are essential participants in the nitrogen cycle.
Different microorganisms carry out processes such as nitrogen fixation, decomposition, nitrification, and denitrification.
Through these activities, nitrogen is continuously recycled between the atmosphere, soil, plants, animals, and microorganisms.
Correct Answer: B) They help convert nitrogen between different forms and make it available to living organisms.
Important Formulas & Concepts
Science Chapter 2 does not contain mathematical formulas. Important scientific concepts are given below.
1. Nitrogen Fixation
The conversion of atmospheric nitrogen into forms that can be utilised by plants is called nitrogen fixation.
2. Rhizobium
Rhizobium is a nitrogen-fixing bacterium commonly associated with the root nodules of leguminous plants.
3. Root Nodules
Root nodules are specialised structures on the roots of many leguminous plants that contain nitrogen-fixing bacteria.
4. Leguminous Plants
Plants such as peas, beans, and gram belong to the legume group and commonly form associations with Rhizobium.
5. Symbiotic Relationship
A close relationship between two different organisms in which both benefit is called a symbiotic relationship.
6. Nitrogen Cycle
The nitrogen cycle describes the continuous movement and transformation of nitrogen through the atmosphere, soil, plants, animals, and microorganisms.
7. Denitrification
Denitrification is a microbial process in which nitrogen compounds such as nitrates are converted into nitrogen gas.
8. Soil Fertility
Soil fertility refers to the ability of soil to provide essential nutrients and suitable conditions for plant growth.
9. Nutrient Recycling
Microorganisms help recycle nutrients by breaking down dead plants and animals and returning nutrients to the environment.
10. Ecological Role
Microorganisms are important decomposers and participate in several natural cycles, helping maintain environmental balance.
Related Practice Questions
Q1. What is nitrogen fixation?
Q2. What is the role of Rhizobium?
Q3. Why are root nodules important?
Q4. What is the nitrogen cycle?
Q5. How do microorganisms help maintain soil fertility?
Mini Quiz Challenge
Try answering these questions within 60 seconds.
Q1. Rhizobium is mainly associated with:
A) Root nodules
B) Flowers
C) Fruits
D) Seeds only
Q2. Which plants commonly form associations with Rhizobium?
A) Leguminous plants
B) Mosses only
C) Ferns only
D) Algae only
Q3. Nitrogen is important for plants because it is needed to make:
A) Proteins
B) Glass
C) Plastic
D) Metals
Q4. Which process returns nitrogen gas to the atmosphere?
A) Denitrification
B) Photosynthesis
C) Respiration
D) Transpiration
Q5. Microorganisms are important in the nitrogen cycle because they:
A) Transform nitrogen compounds
B) Stop all plant growth
C) Remove all oxygen
D) Prevent decomposition
Exam Tips
✔ Remember Rhizobium → root nodules → leguminous plants.
✔ Learn examples of leguminous plants such as pea, gram, and beans.
✔ Understand the meaning of nitrogen fixation.
✔ Remember that atmospheric nitrogen cannot be directly used by most plants.
✔ Revise the importance of nitrogen for plant growth.
✔ Learn the basic idea of the nitrogen cycle.
✔ Remember denitrification as a process that returns nitrogen gas to the atmosphere.
✔ Understand the connection between Rhizobium and soil fertility.
✔ Do not confuse nitrogen fixation with denitrification.
✔ Revise the role of microorganisms in nutrient recycling.
Quick Revision Notes
✔ Rhizobium: Nitrogen-fixing bacterium.
✔ Root Nodules: Structures on legume roots where Rhizobium commonly lives.
✔ Leguminous Plants: Include pea, gram, and beans.
✔ Nitrogen Fixation: Makes atmospheric nitrogen available in usable forms.
✔ Nitrogen: Essential for plant growth and protein formation.
✔ Symbiosis: Both the plant and Rhizobium benefit from their association.
✔ Nitrogen Cycle: Movement and transformation of nitrogen in nature.
✔ Denitrification: Returns nitrogen gas to the atmosphere.
✔ Soil Fertility: Can be improved or maintained through nitrogen-fixing associations.
✔ Microorganisms: Important participants in nutrient recycling and natural cycles.
Common Mistakes Students Make
❌ Thinking Rhizobium is a fungus.
❌ Forgetting that Rhizobium lives in root nodules.
❌ Thinking all plants can directly use atmospheric nitrogen.
❌ Confusing nitrogen fixation with denitrification.
❌ Thinking leguminous plants reduce soil fertility.
❌ Forgetting examples of leguminous plants.
❌ Assuming microorganisms are useful only in food production.
❌ Ignoring the role of microorganisms in natural nutrient cycles.
Key Takeaways
✔ Microorganisms play important roles in nature.
✔ Rhizobium is associated with the roots of leguminous plants.
✔ Root nodules provide a suitable environment for Rhizobium.
✔ Rhizobium helps in nitrogen fixation.
✔ Nitrogen is essential for plant growth and protein formation.
✔ Nitrogen fixation contributes to soil fertility.
✔ Microorganisms participate in the nitrogen cycle.
✔ Denitrification helps return nitrogen gas to the atmosphere.
✔ Microorganisms help recycle nutrients in ecosystems.
FAQs
Q. What is Rhizobium?
Answer:
Rhizobium is a nitrogen-fixing bacterium commonly found in the root nodules of leguminous plants.
Q. What are root nodules?
Answer:
Root nodules are specialised structures on the roots of many leguminous plants that contain nitrogen-fixing bacteria such as Rhizobium.
Q. What is nitrogen fixation?
Answer:
Nitrogen fixation is the conversion of atmospheric nitrogen into forms that can contribute to the nitrogen nutrition of plants.
Q. Why are leguminous plants useful for soil fertility?
Answer:
Their association with nitrogen-fixing bacteria such as Rhizobium can increase the availability of nitrogen compounds and help maintain soil fertility.
Q. What is the nitrogen cycle?
Answer:
The nitrogen cycle is the continuous movement and transformation of nitrogen between the atmosphere, soil, plants, animals, and microorganisms.
Conclusion
Class 8 Science Chapter 2 – Microorganisms: Friend and Foe focuses on the important ecological role of microorganisms in the nitrogen cycle.
Students revised Rhizobium, root nodules, leguminous plants, nitrogen fixation, soil fertility, symbiotic relationships, denitrification, and nutrient recycling.
These concepts demonstrate that microorganisms are not only useful in food production and medicine but are also essential for maintaining nutrient cycles and environmental balance.
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