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

Reviewed by · Updated on

NCERT Solutions PDF Class 8 PDF

CBSE Class 8 Science, Chapter 2: Microorganisms: Friend and Foe, delves into the fascinating world of tiny organisms that significantly impact our lives. This chapter explores the diverse roles of microorganisms, highlighting how they can be both beneficial and harmful. We learn about their uses in processes like fermentation, essential for making bread and alcohol, and their crucial role in nitrogen fixation, vital for plant growth. Conversely, the chapter also addresses how certain microorganisms act as pathogens, causing diseases like malaria and cholera, and discusses methods to prevent their spread. Understanding these microbes, including the function of antibiotics and the importance of hygiene, is key to appreciating their dual nature and preparing effectively for exams.

Home

Quick info

BoardCBSE
ClassClass 8
SubjectScience
Session2026
LanguageEnglish
TypeNCERT Solutions
ChapterChapter 2: Microorganisms: Friend and Foe

Chapter summary

Chapter 2 of the CBSE Class 8 Science curriculum focuses on Microorganisms: Friend and Foe. This NCERT Solutions set provides clear explanations for exercises covering the identification of microorganisms using microscopes, their beneficial roles in processes like fermentation and nitrogen fixation, and their harmful effects as pathogens causing diseases. It also discusses disease carriers, antibiotics, and the importance of hygiene. The solutions aim to build a strong foundation in microbiology for Class 8 students.

Learning outcomes

  • Understand that microorganisms are tiny and require a microscope for observation.
  • Identify different types of microorganisms like bacteria, protozoa, fungi, and viruses.
  • Explain the beneficial roles of microorganisms in processes like fermentation and nitrogen fixation.
  • Recognize microorganisms as causative agents of diseases and identify their carriers.
  • Describe the function of antibiotics and the importance of vaccination.
  • Differentiate between beneficial and harmful microorganisms.

Topics covered

Paper topics

  • Microorganisms
  • Types of Microorganisms (Bacteria, Virus, Protozoa, Fungi)
  • Microscope
  • Beneficial Microorganisms
  • Harmful Microorganisms
  • Diseases caused by Microorganisms
  • Disease Carriers
  • Antibiotics
  • Vaccination
  • Fermentation
  • Nitrogen Fixation
  • Lactobacillus

Important topics

  • Identification and types of microorganisms
  • Beneficial roles of microorganisms (fermentation, nitrogen fixation)
  • Harmful effects and diseases caused by microorganisms
  • Disease carriers and prevention
  • Antibiotics and their function

PDF preview

Read page by page below. PDF is streamed from the official NCERT website — no download button on this page.

Loading document …
Page of
Loading page …

Questions and Solutions

Question 1

Fill in the blanks:
  1. Microorganisms can be seen with the help of a ______.
  2. Blue green algae fix _____ directly from air to enhance fertility of soil.
  3. Alcohol is produced with the help of _____.
  4. Cholera is caused by _____.
Solution:

Here are the completed sentences:

  1. Microorganisms can be seen with the help of a microscope. These organisms are too small to be observed with the naked eye, requiring magnification.
  2. Blue green algae fix nitrogen directly from the air to enhance the fertility of the soil. This process is known as biological nitrogen fixation.
  3. Alcohol is produced with the help of microorganisms, specifically yeast, through the process of fermentation.
  4. Cholera is caused by bacteria. This 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:

Here are the correct answers:

  1. Yeast is used in the production of alcohol. Yeast undergoes fermentation to produce 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.
  4. The most common carrier of communicable diseases is the housefly. Houseflies spread germs by landing on food after visiting garbage or feces.
  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.
  6. The process of conversion of sugar into alcohol is called fermentation. This process is carried out by 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

Column II

(g) Producing antibodies

Solution:

Here is the correct matching of organisms with their actions:

  1. Bacteria - Can cause diseases (like cholera) or be beneficial (like in nitrogen fixation).
  2. Rhizobium - Fixes atmospheric nitrogen in the root nodules of leguminous plants, enriching the soil.
  3. Lactobacillus - Converts milk into curd by producing lactic acid.
  4. Yeast - Used in fermentation to produce alcohol and in baking to make bread rise.
  5. A protozoan - Such as Plasmodium, can cause diseases like malaria.
  6. A Virus - Can cause diseases like common cold, influenza, and polio.

Note: The option '(g) Producing antibodies' is typically associated with the immune system (like lymphocytes) in response to pathogens, not directly with the listed microorganisms themselves as their primary action.

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. They are extremely small, often referred to as microbes, and require magnification to be observed. They can be seen clearly with the help of a microscope, which magnifies these tiny organisms, allowing us to study their structure and behavior.

Common mistakes

  • Confusing the roles of different microorganisms (e.g., bacteria vs. viruses).
  • Not understanding the process of fermentation or nitrogen fixation.
  • Inability to identify common disease carriers.
  • Misunderstanding the purpose and use of antibiotics.

Revision tips

  • Focus on understanding the specific roles of different microorganisms mentioned.
  • Memorize the examples of beneficial and harmful microbes and the diseases they cause.
  • Pay attention to the processes like fermentation and nitrogen fixation.
  • Review the list of disease carriers and the diseases they transmit.
  • Understand the importance of hygiene and preventive measures against microbial diseases.

Practice MCQs

Q1. Which instrument is essential to observe microorganisms?

Q2. Which microorganism is primarily used in the production of alcohol?

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

Q4. Which of the following is a common carrier of malaria?

Q5. Lactobacillus is a type of bacteria beneficial for:

Q6. Which of these is an antibiotic?

Frequently asked questions

What are microorganisms and how are they observed?

Microorganisms are very small living organisms that cannot be seen with the naked eye. They can only be observed using a microscope.

What is fermentation and which microorganism is involved?

Fermentation is the process where microorganisms, like yeast, convert sugars into alcohol and carbon dioxide. It is used in making bread and alcohol.

How do microorganisms help in increasing soil fertility?

Certain microorganisms, such as blue-green algae and Rhizobium bacteria, fix nitrogen directly from the air into the soil, enhancing its fertility.

What are antibiotics and how do they work?

Antibiotics are medicines that kill or stop the growth of harmful bacteria. They do not work against viruses.

What is the role of Lactobacillus?

Lactobacillus is a beneficial bacterium that helps in the curdling of milk, converting lactose into lactic acid.

Which mosquito carries the malaria-causing protozoan?

The female Anopheles mosquito is the carrier of the malaria-causing protozoan.

Important links

Content reviewed by the NCERT Help team. Editorial Team and update policy

NCERT Solutions PDF PDF on NCERT Help. URL unchanged for search indexing.