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NCERT Solutions for Class 8 Science Chapter 2 Microorganisms Friend and Foe
Edited By Irshad Anwar | Updated on May 09, 2025 08:37 PM IST
NCERT Solutions for Class 8 Science Chapter 2 Microorganisms Friend and Foe: Microorganisms are important in our world, having both positive and negative impacts on humans, plants, and animals. This chapter helps students to learn the different types of microorganisms, their applications in food preparation, medicine, and industry, as well as in disease causation. It also shows ways of preserving food, nitrogen fixation, and the significance of vaccines.
This Story also Contains
- NCERT Solutions PDF for Class 8 Science: Microorganisms, Friend and Foe
- NCERT Solutions for Biology Chapter Microorganisms: Friend and Foe
- Approach to Solve Questions of Class 8 Chapter 2
- Important Topics of Class 8 Science Chapter Microorganisms: Friend and Foe
- Most Important Questions Class 8 Chapter 2
- NCERT Solutions For Class 8th Science
For speedy and effective revision, the questions and answers of this chapter enable students to understand concepts effectively. NCERT Solutions for Class 8 Science for the chapter are created in simple language so as to increase the clarity and understanding. These solutions, as per the current CBSE syllabus, are a helpful tool for students to perform well in exams and can also be downloaded in PDF format for easy study and access at their convenience.
NCERT Solutions PDF for Class 8 Science: Microorganisms, Friend and Foe
Students can download the complete questions with detailed answers in a PDF of this chapter for better learning:
NCERT Solutions for Biology Chapter Microorganisms: Friend and Foe
The detailed answers to all the questions in this chapter are given below:
Q.1. Fill in the blanks
Answer:
(a) Microorganisms can be seen with the help of a Microscope .
(b) Blue-green algae fix Nitrogen directly from the air and enhance the fertility of soil.
(c) Alcohol is produced with the help of Yeast .
(d) Cholera is caused by Bacteria .
Q.2.(a) Tick the correct answer. Yeast is used in the production of (i) sugar
(ii) alcohol
(iii) hydrochloric acid
(iv) oxygen
Answer:(a) Yeast is used in the production of (ii) Alcohol
Q.2(b). Tick the correct answer
The following is an antibiotic
(i) Sodium bicarbonate
(ii) Streptomycin
(iii) Alcohol
(iv) Yeast
Answer:(b) The following is an antibiotic (ii) Streptomycin
Q.2(c). Tick the correct answer
The carrier of malaria-causing protozoan is
(i) female Anopheles mosquito (ii) cockroach
(iii) housefly (iv) butterfly
Answer:(c) The carrier of malaria-causing protozoan is (i) female Anopheles mosquito
Q.2(d). The most common carrier of communicable diseases is
(i) ant (ii) housefly (iii) dragonfly (iv) spider
Answer:(d) The most common carrier of communicable diseases is (ii) the housefly.
Q.2(e). Tick the correct answer
The bread or idli dough rises because of
(i) heat (ii) grinding (iii) growth of yeast cells (iv) kneading
Answer:(e) The bread or idli dough rises because of (iii) the growth of yeast cells.
Q.2(f). Tick the correct answer
The process of conversion of sugar into alcohol is called
(i) nitrogen fixation (ii) moulding (iii) fermentation (iv) infection
Answer:(f) The process of conversion of sugar into alcohol is called (iii) Fermentation
Q. 3. Match the organisms in Column A with their action in Column B
| Microorganism | Function |
|---|---|
| (i) Bacteria | (a) Fixing nitrogen |
| (ii) Rhizobium | (a) Fixing nitrogen |
| (iii) Lactobacillus | (b) Setting of curd |
| (iv) Yeast | (c) Baking of bread |
| (v) A Protozoan | (d) Causing malaria |
| (vi) A Virus | (e) Causing cholera / (f) Causing AIDS / (g) Producing antibodies |
Column A | Column B |
Bacteria | Causing Cholera |
Rhizobium | Fixing nitrogen |
Lactobacillus | Setting of curd |
Yeast | Baking of bread |
A protozoan | Causing malaria |
A virus | Causing AIDS |
Q. 4. Can microorganisms be seen with the naked eye? If not, how can they be seen?
Answer:
No, the microorganisms cannot be seen with the human naked eye because they are too small to be seen. microorganisms can be seen with the help of a scientific instrument called microscope.
Example- fungus on bread.
Q. 5. What are the major groups of microorganisms?
Answer:
The significant groups of microorganisms are as follows:
Bacteria – These are single-celled organisms. Examples include Salmonella typhi, Rhizobia, and Mycobacterium. Bacterial infections like typhoid and tuberculosis (TB) are induced by these microorganisms.
Fungi – They are multicellular organisms that are saprophytes, living on dead and rotting matter. An example is bread mould.
Protozoa – They are single-cell organisms, the majority being parasitic. Protozoa includes Amoeba and Plasmodium. Protozoa cause diseases like dysentery and malaria.
Viruses – They are cell-free microbes which can reproduce only within a host cell. Diseases caused by them include chickenpox and polio.
Algae – Algae can either be single cells or multi cells. Some of them include Spirogyra, Chlamydomonas, and Ulva.
Q6. Name the microorganisms which can fix atmospheric nitrogen in the soil.
Answer:
The microorganism that can fix atmospheric nitrogen in the soil are bacteria such as Rhizobium , and blue-green algae. These converted nitrogenous compounds can be easily used by plants for the plant protein synthesis and other purposes.
Q 7. Write 10 lines on the usefulness of microorganisms in our lives.
Answer :
Microorganisms are useful for us in the following ways-
Microorganisms are used to increase the fertility of the soil by fixing the atmospheric nitrogen with the help of blue-green algae and Rhizobium.
Antibiotics which are obtained from microorganisms are used to control the diseases.
There are some bacteria which can turn nitrogen compounds found in the soil into nitrogen gas which is further released into the environment.
Bacterium Lactobacillus reproduces in milk and promotes the formation of curd.
Microorganisms especially yeast can be used for the industrial production of alcohol, wine and acetic acid (vinegar).
Microbes are used to reduce pollution. example- bacteria and fungi break down the dead bodies and excreta to form inorganic compounds which are absorbed by plants
Q. 8. Write a short paragraph on the harmful effects of microorganisms.
Answer:
The harmful effects of microorganisms are given below-
- Microorganisms cause diseases in humans as well as animals. For example cholera and TB are caused by bacteria in humans.
- In plants also diseases are caused by microorganisms. For example, citrus canker in plants is caused by bacteria and rust of wheat is caused by fungi.
- Food poisoning is also caused by the microorganisms that spoils our food by producing some toxic substances. For example- when the bread is left in under moist condition gets spoilt by fungus.
Q. 9. What are antibiotics? What precautions must be taken while taking antibiotics?
Answer:
These are medicines that either kill or inhibit the growth of disease-causing microorganisms. Many antibiotics are derived from bacteria and fungi. Common examples include streptomycin, tetracycline, and erythromycin, which are widely used to treat infections.
Precautions that must be taken while using antibiotics-
- Antibiotics must be taken only on the prescription of a doctor.
- must finish the course prescribed by the doctor.
- An antibiotic should be taken in the right amount only. Antibiotics taken unnecessarily may kill beneficial bacteria in the body.
Answer:
Those medicines that kill or stop the growth of the disease-causing microorganisms are called antibiotics. Antibiotics are produced from bacteria and fungi.
Precautions to be taken while using antibiotics-
- antibiotics should be taken only on the advice of a qualified doctor.
- must finish the course prescribed by the doctor.
- An antibiotic should be taken in the right amount. antibiotics taken unnecessarily may kill beneficial bacteria in the body.
Approach to Solve Questions of Class 8 Chapter 2
To answer Microorganisms: Friend and Foe questions, simply apply the following steps:
- Know the Basics: Read the chapter thoroughly to know what microorganisms are, their types (bacteria, fungi, protozoa, algae, viruses), and how they function as friends and enemies.
- Key Topics in Focus: Rewrite important points such as food preservation, antibiotics, vaccines, disease caused by microorganisms, and the nitrogen cycle.
- Practice Using Examples: Apply examples such as yeast to ferment bread and alcohol or bacteria such as Rhizobium to fix nitrogen to make your answers lucid.
- Learn Definitions and Diagrams: Recall definitions (e.g., microorganisms, antibiotics) and learn diagrams about habitats and processes of microorganisms.
- Solve NCERT Questions: Do all textbook questions, e.g., fill-in-the-blanks, true/false, and short answers, to be sure.
NCERT Solutions For Class 8th: Subject-wise
Important Topics of Class 8 Science Chapter Microorganisms: Friend and Foe
The key topics covered in Chapter 2 are:
| 2 | Microorganisms: Friend and Foe |
| 2.1 | Microorganisms |
| 2.2 | Where do Microorganisms Live? |
| 2.3 | Microorganisms and Us |
| 2.4 | Harmful Microorganisms |
| 2.5 | Food Preservation |
| 2.6 | Nitrogen Fixation |
| 2.7 | Nitrogen cycle |
- Microorganisms – Microorganisms are small living organisms that cannot be seen without the aid of a microscope. They include bacteria, fungi, protozoa, viruses, and algae and can be found in different kinds of environments.
- Where do Microorganisms Live? – Microorganisms can be found everywhere: in air, water, soil, and extreme habitats such as hot springs and polar regions. Some live within other organisms as parasites.
- Microorganisms and Us – Microorganisms have a critical contribution to make towards food production (curd, bread, alcohol), medicine (antibiotics, vaccines), and agriculture (nitrogen fixation), making them useful to human beings.
- Harmful Microorganisms – Certain microorganisms cause illnesses in human beings, animals, and plants. They also deteriorate food and pollute water, resulting in diseases such as cholera, tuberculosis, and malaria.
- Preservation of Food – Different processes such as refrigeration, salting, drying, pasteurization, and the addition of preservatives prevent food from getting spoiled due to microorganisms.
- Nitrogen Fixation – Some bacteria (such as Rhizobium) assist in fixing atmospheric nitrogen into forms that can be utilised by plants, enriching soil and supporting plant growth.
- Nitrogen Cycle – Nitrogen cycle regulates balance within the ecosystem by circulating nitrogen in the atmosphere, soil, plants, and animals, providing an uninterrupted supply for all living things.
Also, check the NCERT Books and the NCERT Syllabus here
Most Important Questions Class 8 Chapter 2
Some questions from Microorganisms: Friend and Foe are given below:
Which of the following is NOT a characteristic of viruses?
(a) They can reproduce only inside living cells
(b) They are visible under a light microscope
(c) They contain genetic material
(d) They can cause diseases
Explanation: Viruses are extremely small and cannot be seen under a light microscope; they require an electron microscope to be seen. They reproduce only inside living cells and contain genetic material, either DNA or RNA.
Hence, the correct answer is option (b).
Which microorganism is used in the production of curd?
(a) Yeast
(b) Lactobacillus
(c) Penicillium
(d) Amoeba
Explanation: Lactobacillus is a beneficial bacterium that ferments milk sugar (lactose) into lactic acid, turning milk into curd.
Hence, the correct answer is option (b).
Antibiotics are effective against:
(a) Viruses only
(b) Bacteria only
(c) Both viruses and bacteria
(d) Fungi only
Explanation: Antibiotics kill or inhibit bacteria, but are ineffective against viruses because viruses live inside host cells and have different structures.
Hence, the correct answer is option (b).
Which of the following microorganisms helps in the decomposition of dead plants and animals?
(a) Algae
(b) Fungi
(c) Protozoa
(d) Viruses
Explanation: Fungi secrete enzymes that break down dead organic matter, recycling nutrients back into the ecosystem.
Hence, the correct answer is option (b).
The process by which yeast helps in making bread rise is called:
(a) Fermentation
(b) Photosynthesis
(c) Respiration
(d) Decomposition
Explanation: Yeast ferments sugars in the dough, producing carbon dioxide gas that makes the bread rise.
Hence, the correct answer is option (a).
NCERT Solutions For Class 8th Science
Below are the chapter-wise solutions:
Frequently Asked Questions (FAQs)
1. What are microorganisms?
Microorganisms are tiny living organisms that cannot be seen with the naked eye. They can only be observed under a microscope. These include bacteria, viruses, fungi, protozoa, and some algae.
2. Name the major groups of microorganisms.
Bacteria
Viruses
Fungi
Protozoa
Algae
3. Where do microorganisms live?
Microorganisms are found everywhere — in air, water, soil, food, and inside the bodies of plants, animals, and humans. Some live in extreme conditions like hot springs, salty lakes, and deep oceans.
4. How do microorganisms affect our lives?
Beneficial: Used in food production (yogurt, bread), medicine (antibiotics, vaccines), agriculture (nitrogen fixation), and cleaning the environment (decomposers).
Harmful: Cause diseases in humans, animals, and plants; spoil food and contaminate water.
5. Name two diseases caused by:
Bacteria: Tuberculosis, Typhoid
Viruses: Influenza, COVID-19
6. What are antibiotics? Give examples.
Antibiotics are medicines that kill or stop the growth of harmful bacteria.
Examples: Penicillin, Streptomycin, Amoxicillin
7. How do microorganisms help in the production of antibiotics?
Certain fungi and bacteria (like Penicillium and Streptomyces) produce substances that inhibit or kill other bacteria. These substances are extracted and purified to make antibiotics.
8. What are the uses of microorganisms in agriculture?
Improve soil fertility (e.g., nitrogen-fixing bacteria)
Decompose organic waste into compost
Act as biofertilizers and biopesticides
9. How do microorganisms help in nitrogen fixation?
Some bacteria (like Rhizobium) live in the root nodules of legume plants and convert atmospheric nitrogen into a form plants can use, enriching the soil.
10. What are pathogens? How do they spread?
Pathogens are disease-causing microorganisms.
They spread through:
Air (sneezing, coughing)
Water (contaminated)
Food (spoiled/uncooked)
Direct contact or insect bites
11. What is food preservation? Name some common methods.
Food preservation prevents spoilage by stopping the growth of microorganisms.
Common methods:
Refrigeration
Drying
Canning
Pickling
Pasteurization
Adding salt or sugar
12. What is pasteurization? Who discovered it?
Pasteurization is the process of heating a liquid (like milk) to kill harmful microbes without affecting its quality.
Discovered by Louis Pasteur
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