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

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NCERT Solutions PDF Class 8 PDF

This comprehensive set of NCERT Solutions for CBSE Class 8 Science Exemplar, Chapter 2, focuses on 'Microorganisms: Friend and Foe'. It covers key concepts related to various microorganisms like bacteria, viruses, fungi, and protozoa, explaining their roles as both beneficial and harmful agents. The solutions detail how certain microorganisms cause diseases, the function of antibiotics and vaccines, and the symbiotic relationships found in nature, such as in lichens. It also touches upon the use of microorganisms in food production, like the fermentation process by yeast in bread making. These solutions are designed to help students understand the fundamental principles of microbiology and prepare effectively for their examinations by providing clear explanations and accurate answers to all questions.

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BoardCBSE
ClassClass 8
SubjectScience Exemplar
Session2026
LanguageEnglish
TypeNCERT Solutions
ChapterChapter 2

Chapter summary

Chapter 2 of the CBSE Class 8 Science Exemplar, 'Microorganisms: Friend and Foe', delves into the world of microscopic organisms. This NCERT Solutions set provides detailed answers to multiple-choice questions covering the characteristics of viruses, common viral and bacterial diseases, the action of antibiotics, symbiotic relationships like lichens, and the role of yeast in fermentation. It clarifies how microorganisms impact our lives, both positively and negatively, aiding students in grasping essential biological concepts.

Learning outcomes

  • Understand the unique reproductive nature of viruses.
  • Identify diseases caused by specific microorganisms (viruses, bacteria, protozoa).
  • Differentiate between antibiotics, antibodies, and vaccines.
  • Explain the symbiotic relationship between algae and fungi in lichens.
  • Describe the process of fermentation by yeast in bread making.
  • Recognize microorganisms that cause diseases and their modes of transmission.

Topics covered

Paper topics

  • Microorganisms
  • Bacteria
  • Viruses
  • Fungi
  • Protozoa
  • Diseases caused by microorganisms
  • Antibiotics
  • Vaccines
  • Symbiotic relationships (Lichens)
  • Fermentation (Yeast)
  • Microorganisms in food preparation
  • Beneficial and harmful microorganisms

Important topics

  • Characteristics and reproduction of viruses
  • Identification of diseases and their causative agents
  • Function and difference between antibiotics, antibodies, and vaccines
  • Role of yeast in fermentation
  • Symbiotic associations in lichens

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Questions and Solutions

Multiple Choice Questions

1. Which of the following reproduces only inside a host cell?
  1. Bacteria
  2. Virus
  3. Amoeba
  4. Fungus.
Solution: The correct option is (b) Virus.

Viruses are unique microorganisms that cannot reproduce on their own. They require a living host cell to replicate. Outside the host, they remain inert. Bacteria, amoeba, and fungi are capable of independent reproduction.

2. A disease in human beings caused by a virus is _____.
  1. typhoid
  2. influenza
  3. dysentry
  4. cholera
Solution: The correct option is (b) influenza.

Influenza is a viral respiratory illness. Typhoid and cholera are caused by bacteria (Salmonella Typhi and Vibrio cholerae, respectively). Dysentery can be caused by protozoa like Amoeba or bacteria.

3. Pathogenic micro-organisms present in host cells are killed by medicines called
  1. pain killer
  2. antibodies
  3. antibiotics
  4. vaccines
Solution: The correct option is (c) antibiotics.

Antibiotics are a class of drugs that kill or inhibit the growth of bacteria. Pain killers relieve pain but do not fight infection. Antibodies are produced by the immune system to fight pathogens. Vaccines provide immunity against specific diseases.

4. The two micro-organisms which live in symbiotic association in lichens are
  1. fungus and protozoa
  2. alga and bacteria
  3. bacteria and protozoa
  4. alga and fungus
Solution: The correct option is (d) alga and fungus.

Lichens are formed by a mutualistic symbiotic relationship between an alga (or cyanobacterium) and a fungus. The alga provides food through photosynthesis, and the fungus provides structure, protection, and absorbs water and minerals.

5. The gas released during the preparation of bread is
  1. oxygen
  2. carbon dioxide
  3. nitrogen
  4. sulphur dioxide
Solution: The correct option is (b) carbon dioxide.

Yeast, a type of fungus, is used in bread making. It undergoes fermentation, breaking down sugars in the dough into ethanol and carbon dioxide. The carbon dioxide gas gets trapped in the dough, causing it to rise and become fluffy.

6. The disease caused by a protozoan and spread by an insect is ______.
  1. dengue
  2. malaria
  3. polio
  4. measles
Solution: The correct option is (b) malaria.

Malaria is caused by protozoa of the genus Plasmodium. It is transmitted to humans through the bite of infected female Anopheles mosquitoes, which act as insect vectors.

Common mistakes

  • Confusing the causes of different bacterial and viral diseases.
  • Misunderstanding the specific functions of antibiotics, antibodies, and vaccines.
  • Incorrectly identifying the microorganisms involved in symbiotic relationships or fermentation.

Revision tips

  • Focus on the specific characteristics that distinguish viruses from other microorganisms.
  • Create flashcards for diseases, their causative agents, and modes of transmission.
  • Review the explanations for antibiotics and vaccines to understand their distinct roles.
  • Pay attention to the examples of beneficial microorganisms, like yeast and those in lichens.

Practice MCQs

Q1. Which of the following microorganisms is known to reproduce exclusively within the cells of a host organism?

Q2. Influenza is a common human illness caused by which type of microorganism?

Q3. Medicines that are effective in killing or inhibiting the growth of pathogenic microorganisms within the host are called:

Q4. Lichens are a classic example of a symbiotic relationship between which two types of microorganisms?

Q5. The gas released during the fermentation process by yeast, which causes dough to rise and bread to become fluffy, is:

Q6. Malaria is a disease transmitted by an insect vector and caused by which type of microorganism?

Frequently asked questions

What is the main characteristic of viruses that distinguishes them from other microorganisms?

Viruses can only reproduce inside a host cell, making them obligate intracellular parasites. They are inactive outside a host.

Can antibiotics be used to treat viral infections like the common cold?

No, antibiotics are effective against bacteria, not viruses. They do not work for viral infections.

What is the role of yeast in making bread?

Yeast produces carbon dioxide gas through fermentation. This gas causes the dough to rise, making the bread fluffy.

What are lichens and what microorganisms form them?

Lichens are a symbiotic association between an alga (or cyanobacterium) and a fungus. They live together, each providing benefits to the other.

Which microorganism causes malaria, and how is it spread?

Malaria is caused by protozoa of the genus Plasmodium and is spread through the bite of infected female Anopheles mosquitoes.

How do vaccines help protect us from diseases?

Vaccines introduce a weakened or inactive form of a pathogen (or its components) into the body, stimulating the immune system to develop immunity without causing the disease.

Important links

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