CBSE Class 8 Science Chapter 2: Microorganisms - Friend and Foe NCERT Solutions

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NCERT Solutions PDF Class 8 PDF

CBSE Class 8 Science, Chapter 2, "Microorganisms - Friend and Foe," introduces students to the fascinating world of tiny living things. This chapter explores how microorganisms, like bacteria and fungi, can be both helpful and harmful. We learn about their beneficial roles in making curd, bread, and even in processes like nitrogen fixation, which enriches the soil. On the other hand, the chapter also discusses how some microorganisms act as pathogens, causing diseases such as cholera, typhoid, and malaria. Understanding these microscopic organisms is crucial, and the chapter covers topics like common diseases, how they spread, and ways to prevent them. It also touches upon the importance of antibiotics and the use of microscopes to study these invisible life forms. These NCERT Solutions offer clear explanations to help students grasp these concepts effectively for their studies.

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Quick info

BoardCBSE
ClassClass 8
SubjectScience
Session2026
LanguageEnglish
TypeNCERT Solutions
ChapterChapter 2

Chapter summary

Chapter 2 of the CBSE Class 8 Science textbook focuses on "Microorganisms - Friend and Foe." This NCERT Solutions set covers key concepts such as the types of microorganisms (bacteria, fungi, protozoa, algae, viruses), their habitats, and their dual nature – beneficial and harmful. It explains important processes like fermentation and nitrogen fixation, discusses diseases caused by pathogens, and introduces the role of antibiotics. The solutions aim to provide a clear understanding of how these microscopic organisms interact with our environment and daily lives.

Learning outcomes

  • Understand the definition and types of microorganisms.
  • Identify the role of microorganisms in food production and industrial processes.
  • Explain the process of fermentation and nitrogen fixation.
  • Recognize microorganisms that cause diseases and their modes of transmission.
  • Learn about the function of antibiotics and vaccines.
  • Understand how to observe microorganisms using a microscope.

Topics covered

Paper topics

  • Microorganisms
  • Types of Microorganisms (Bacteria, Fungi, Protozoa, Algae, Viruses)
  • Microorganisms and Us
  • Beneficial Microorganisms
  • Harmful Microorganisms
  • Diseases Caused by Microorganisms
  • Food Preservation
  • Fermentation
  • Nitrogen Fixation
  • Antibiotics
  • Vaccines
  • Microscope

Important topics

  • Role of Microorganisms (Friend and Foe)
  • Diseases and their Causative Agents
  • Fermentation Process
  • Nitrogen Fixation
  • Antibiotics and Vaccines

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Questions and Solutions

Question 1

Fill in the blanks:
  1. Microorganisms can be seen with the help of a ______.

(b) Blue green algae fix _____ directly from air to enhance fertility of soil.

(c) Alcohol is produced with the help of _____.

  1. Cholera is caused by _____.
Solution:
  1. Microorganisms can be seen with the help of a microscope. These instruments magnify tiny objects, making them visible to the human eye.

(b) Blue green algae fix nitrogen directly from air to enhance fertility of soil. This process is known as nitrogen fixation.

(c) Alcohol is produced with the help of microorganisms, specifically yeast, through a process called fermentation.

  1. Cholera is caused by bacteria. It is a bacterial infection that affects the intestines.

Question 2

Tick the correct answer:
  1. Yeast is used in the production of
    1. sugar
    2. alcohol
    3. hydrochloric acid
    4. oxygen
  2. The following is an antibiotic
    1. Sodium bicarbonate
    2. Streptomycin
    3. Alcohol
    4. Yeast
  3. Carrier of malaria-causing protozoan is
    1. female Anopheles mosquito
    2. cockroach
    3. housefly
    4. butterfly
  4. The most common carrier of communicable diseases is
    1. ant
    2. housefly
    3. dragonfly
    4. spider
  5. The bread or idli dough rises because of
    1. heat
    2. grinding
    3. growth of yeast cells
    4. kneading
  6. The process of conversion of sugar into alcohol is called
    1. nitrogen fixation
    2. fermentation
Solution:
  1. Yeast is used in the production of alcohol. Yeast performs fermentation, converting sugars into alcohol.
  2. Streptomycin is an antibiotic. Antibiotics are used to kill or inhibit the growth of bacteria.
  3. The carrier of malaria-causing protozoan is the female Anopheles mosquito. This mosquito transmits the Plasmodium parasite when it bites an infected person and then bites a healthy person.
  4. The most common carrier of communicable diseases is the housefly. Houseflies land on garbage and animal excreta, picking up germs, which they then transfer to food.
  5. The bread or idli dough rises because of the growth of yeast cells. Yeast produces carbon dioxide gas during fermentation, which causes the dough to expand and rise.
  6. The process of conversion of sugar into alcohol is called fermentation. This is a metabolic process carried out by microorganisms like yeast.

Question 3

Match the organisms in Column I with their action in Column II.

Column I

  1. Bacteria
  2. Rhizobium
  3. Lactobacillus
  4. Yeast
  5. A protozoan
  6. A Virus

(g) Producing antibodies

Column II

(Note: Column II options are not explicitly provided in the source text, but common associations are used for the answer.)

Solution:

Here is the matching of organisms from Column I with their typical actions:

  1. Bacteria - Can cause diseases (like cholera) or be beneficial (like nitrogen fixation).
  2. Rhizobium - Fixes atmospheric nitrogen in the root nodules of leguminous plants.
  3. Lactobacillus - Converts milk into curd.
  4. Yeast - Used in fermentation to produce alcohol and bread.
  5. A protozoan - Can cause diseases like malaria (e.g., Plasmodium).
  6. A Virus - Causes diseases like common cold, flu, and COVID-19.
  7. (g) Producing antibodies is primarily a function of the immune system (like lymphocytes), not a direct action of these listed microorganisms themselves, though some microorganisms trigger antibody production.

Question 4

Can microorganisms be seen with the naked eye? If not, how can they be seen?
Solution:

No, microorganisms cannot be seen with the naked eye because they are extremely small, often microscopic in size. To observe them, we need to use a microscope. A microscope is an instrument that magnifies very small objects, allowing us to see their structure and details clearly.

Common mistakes

  • Confusing beneficial and harmful roles of microorganisms.
  • Incorrectly identifying the causative agent of specific diseases.
  • Misunderstanding the process of fermentation.
  • Not recognizing the importance of antibiotics.

Revision tips

  • Focus on the dual role of microorganisms – friend and foe.
  • Memorize the specific microorganisms responsible for common diseases.
  • Understand the scientific terms like fermentation and nitrogen fixation.
  • Review the examples of beneficial microorganisms and their uses.

Practice MCQs

Q1. Which microorganism is used in the production of alcohol?

Q2. Which of the following is a common carrier of communicable diseases?

Q3. The process of conversion of sugar into alcohol is known as:

Q4. Which microorganism is responsible for causing cholera?

Q5. What is used to see microorganisms that cannot be seen with the naked eye?

Frequently asked questions

What are microorganisms and where are they found?

Microorganisms are tiny living organisms, such as bacteria, fungi, protozoa, algae, and viruses, that are too small to be seen with the naked eye. They are found almost everywhere, including in the air, water, soil, and inside the bodies of plants and animals.

How do microorganisms help in increasing soil fertility?

Certain microorganisms, like blue-green algae and bacteria (e.g., Rhizobium), fix atmospheric nitrogen into a usable form, which enhances the fertility of the soil.

What is fermentation and which microorganism is commonly used for it?

Fermentation is the process where microorganisms, typically yeast, convert sugars into alcohol and carbon dioxide. Yeast is widely used in the production of bread, alcohol, and other food products through fermentation.

Can you name some diseases caused by microorganisms?

Yes, diseases like cholera (caused by bacteria), malaria (caused by protozoa), common cold and flu (caused by viruses), and ringworm (caused by fungi) are caused by different types of microorganisms.

What are antibiotics and how do they work?

Antibiotics are medicines that kill or inhibit the growth of harmful bacteria. They are produced by certain microorganisms and are used to treat bacterial infections.

Why are microorganisms called 'friend and foe'?

Microorganisms are called 'friends' because many are beneficial, aiding in processes like digestion, food production (fermentation), and nutrient cycling. They are called 'foes' because some can cause serious diseases in humans, animals, and plants.

Important links

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