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By rohit.pandey1
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Updated on 1 Sep 2025, 17:59 IST
NCERT Solutions for Class 8 Science Chapter 2 – Microorganisms: Friend and Foe are prepared to help students clearly understand the role of microorganisms in our daily life. This chapter introduces the five main groups of microorganisms—bacteria, fungi, protozoa, algae, and viruses—and explains how they can be both useful and harmful. Students learn about the importance of microbes in food production (curd, bread, alcohol), medicine (antibiotics, vaccines), agriculture (nitrogen fixation), and waste management, as well as their role in causing diseases and food spoilage.
These step-by-step NCERT solutions provide accurate answers to all textbook questions, strictly following the CBSE guidelines, making them ideal for revision and exam preparation. Students can also download the free PDF of Class 8 Science Chapter 2 solutions to practice questions and answers anytime, ensuring strong preparation for school tests and final examinations.
The NCERT Class 8 Science Chapter 2 PDF for Microorganisms: Friend and Foe is available here for free download. These solutions are carefully prepared by subject experts to give clear, accurate, and step-by-step answers to all textbook exercises. With this PDF, students can revise the entire chapter quickly, solve homework questions, and prepare effectively for exams without needing bulky textbooks.
By downloading the Class 8 Science Chapter 2 NCERT Solutions PDF, you will:
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With this free NCERT solutions PDF, students can study anytime, anywhere, and build strong conceptual knowledge for higher classes.
The chapter Microorganisms: Friend and Foe introduces students to the fascinating world of microbes and explains how these tiny living organisms affect our lives in both positive and negative ways. The NCERT Class 8 Science Chapter 2 solutions help learners understand the types of microorganisms, their habitats, beneficial uses, harmful effects, food preservation methods, and the nitrogen cycle.
Microorganisms, or microbes, are very small living organisms that cannot be seen with the naked eye and require a microscope to be observed. They belong to five main groups:
Understanding the groups of microorganisms is the foundation of this chapter.
Microorganisms live in diverse habitats:
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Classification can be done based on:
This helps students understand why microorganisms are present almost everywhere and how they adapt to different conditions.
Not all microorganisms are harmful. Many play a crucial role in our daily life:
These points show why microbes are called friends of humans.
Some microorganisms act as foes because they cause harm to humans, animals, and plants:
These harmful microorganisms are known as pathogens.
To prevent food spoilage by microorganisms, different methods of preservation are used:
These preservation techniques ensure safe food storage and longer shelf life.
Microorganisms also play an important role in the nitrogen cycle, which maintains the balance of nitrogen in nature.
The nitrogen cycle ensures that plants get essential nutrients and the balance of nitrogen is maintained in air, soil, and living beings.
Here are the complete NCERT solutions Class 8 Science Chapter 2 questions and answers for Microorganisms: Friend and Foe. These solutions are written in a clear, step-by-step manner to help students revise and prepare for exams confidently.
| Column A | Column B |
| (i) Rhizobium | (a) Malaria |
| (ii) Plasmodium | (b) Antibiotic |
| (iii) Penicillium | (c) Nitrogen fixation |
| (iv) Yeast | (d) Alcohol production |
Answer:
Microorganisms are very tiny living organisms, but they are extremely important in our daily lives. Even though we cannot see them without a microscope, they play a big role in food, medicine, agriculture, and the environment.
In food production, bacteria like Lactobacillus convert milk into curd. This bacterium also improves the taste and makes the curd healthy for digestion. Yeast, which is a type of fungus, is used in baking bread, cakes, and buns. It produces carbon dioxide, which makes the dough soft and spongy. Yeast is also used in making alcohol, wine, and beer through a process called fermentation.
In the field of medicine, microorganisms are used to produce antibiotics. For example, the fungus Penicillium gives us penicillin, which is used to treat bacterial infections. Microbes are also used in making vaccines like the polio vaccine, which protect us from dangerous diseases.
In agriculture, some bacteria such as Rhizobium fix atmospheric nitrogen into the soil, which helps plants to grow better without using too many chemical fertilisers.
In the environment, microorganisms help by decomposing dead plants and animals into simpler substances. This recycling of nutrients keeps the soil fertile and the environment clean.
Thus, microorganisms are called our friends because they help us in preparing food, producing medicines, maintaining soil fertility, and cleaning the environment. Without them, life would be very difficult.
Although microorganisms are very useful to us, some of them can also be harmful. These harmful microorganisms are known as pathogens, as they cause diseases in humans, animals, and plants, and also spoil food.
In humans, microorganisms can spread many diseases. For example, Vibrio cholerae causes cholera, Plasmodium (a protozoan) causes malaria, and viruses like the polio virus and influenza virus cause serious illnesses. These diseases are sometimes communicable and can spread from one person to another through air, water, food, or insects.
In animals, microorganisms also cause diseases. Anthrax is a dangerous disease caused by bacteria that affects cattle and even humans. Another disease is foot-and-mouth disease, which spreads in cows and buffaloes, reducing milk production.
In plants, harmful microbes can destroy crops. Wheat rust, caused by a fungus, damages wheat crops. Citrus canker affects orange and lemon trees, while yellow vein mosaic virus damages bhindi (ladyfinger) plants. These plant diseases reduce the farmer’s yield and cause economic loss.
Microorganisms also cause food spoilage. When food is kept open, bacteria and fungi grow on it. This makes the food smell bad and sometimes release toxins that are harmful for health. For example, fungus growing on bread makes it green and poisonous.
Because of these harmful effects, microorganisms are sometimes called our foes. They can spread diseases, destroy crops, and spoil food. Therefore, we must always follow good hygiene, use food preservation methods, and take preventive measures to stay safe from them.
Answer (Approx. 250 words):
The atmosphere has almost 78% nitrogen, but this nitrogen cannot be used directly by plants. Plants need nitrogen in the form of nitrates or nitrites to grow properly. This is where microorganisms, especially Rhizobium bacteria, play an important role in the nitrogen cycle.
Rhizobium is a nitrogen-fixing bacterium that lives in the root nodules of leguminous plants like pea, gram, beans, and groundnut. This bacterium has a symbiotic relationship with these plants. The plants provide shelter and food to Rhizobium, and in return, the bacterium converts atmospheric nitrogen into nitrogen compounds such as nitrates and nitrites, which plants can absorb from the soil. This process is called nitrogen fixation.
After plants and animals die, decomposer microorganisms like bacteria and fungi break down their bodies and release nitrogen back into the soil. Some bacteria also convert these compounds back into nitrogen gas, which goes into the atmosphere. This is called denitrification.
Thus, microorganisms play a major role in maintaining the nitrogen cycle in nature. This cycle ensures that nitrogen is constantly moving between the atmosphere, soil, and living beings. It helps maintain soil fertility and supports healthy crop production.
The role of Rhizobium is very important because it reduces the need for chemical fertilisers and makes farming more sustainable. Farmers who grow leguminous crops naturally enrich the soil with nitrogen, which benefits the next crops as well.
Practicing important questions and class 8 science worksheets for Microorganisms: Friend and Foe helps students strengthen their preparation for exams. Below are selected exam-oriented questions that cover very short, short, and long answer types as per the CBSE exam pattern. A free worksheet on Microorganisms: Friend and Foe with answers is also provided for download.
Practicing these important questions for Class 8 Science Chapter 2 ensures that students are exam-ready and can write structured answers confidently.
To make learning easier and more effective, we have curated extra study materials along with the NCERT Solutions for Class 8 Science Chapter 2 – Microorganisms: Friend and Foe. These resources will help students with quick revision, concept clarity, and exam preparation.
| S.No. | Study Material Links for Chapter 2: Microorganisms Friend and Foe |
| 1. | Class 8 Microorganisms: Friend and Foe Important Questions |
| 2. | Class 8 Microorganisms: Friend and Foe Revision Notes |
| 3. | Class 8 Microorganisms: Friend and Foe Exemplar Solutions |
| S. No | Important Resources for Class 8 Science |
| 1. | Class 8 Science Revision Notes |
| 2. | Class 8 Science NCERT Solutions |
| 3. | Class 8 Important Questions |
| 4. | Class 8 Science Sample Paper |
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The five groups of microorganisms are bacteria, fungi, protozoa, algae, and viruses. Each group has useful as well as harmful members. For example, Lactobacillus (bacteria) helps in curd formation, while Plasmodium (protozoa) causes malaria.
Microorganisms are tiny living organisms that cannot be seen with the naked eye. They can be observed only under a microscope. They are present in soil, water, air, and even inside our bodies.
Beneficial microorganisms are used in food production (curd, bread, alcohol), medicine (antibiotics, vaccines), agriculture (Rhizobium fixes nitrogen), and environmental cleaning (decomposing waste). These functions make them valuable “friends” of humans.
Harmful microorganisms are called pathogens. They cause diseases in humans (cholera, polio, malaria), animals (anthrax, foot-and-mouth disease), and plants (wheat rust, citrus canker). They also spoil food by growing on it and releasing toxins.
Fermentation is the process in which yeast converts sugar into alcohol and carbon dioxide. It is used in baking bread, brewing beer, and making wine. This is one of the important NCERT solutions Class 8 Science chapter 2 questions and answers.
Pasteurisation is the process of heating milk to a high temperature and then cooling it quickly. It kills harmful microbes while keeping milk fresh for longer. This method, discovered by Louis Pasteur, ensures safe consumption.
Rhizobium is a nitrogen-fixing bacterium found in the root nodules of leguminous plants. It converts atmospheric nitrogen into forms usable by plants. This improves soil fertility and reduces the need for chemical fertilisers.
The nitrogen cycle is the circulation of nitrogen between atmosphere, soil, and living beings. Microorganisms like Rhizobium fix nitrogen, decomposers return it to soil, and denitrifying bacteria release nitrogen back into the air. It balances nature’s nitrogen supply.
Microorganisms grow on food and produce toxins that make it stale, smelly, and unfit to eat. Common examples are fungus on bread and bacteria on cooked food. Refrigeration, drying, and preservatives help prevent spoilage.
Communicable diseases are infections caused by harmful microorganisms that spread from one person to another through air, water, food, or contact. Examples include cholera, tuberculosis, influenza, and malaria.
Antibiotics are medicines made from microorganisms that kill or stop the growth of bacteria. Example: penicillin. They should only be taken under medical supervision, and the full prescribed dose must be completed to prevent antibiotic resistance.
Viruses cannot reproduce or survive on their own. They need a host cell to multiply. Outside a host, viruses behave like non-living particles, which is why they are not classified as fully living organisms.
Carriers or vectors are organisms that spread pathogens. Examples include mosquitoes (spread malaria, dengue) and houseflies (spread cholera, typhoid). They transmit microbes from one host to another.
Penicillin was discovered by Alexander Fleming in 1928. It is the world’s first antibiotic, produced from a fungus. It is significant because it saved millions of lives by curing bacterial infections.
Decomposition is the breakdown of dead plants and animals into simpler substances by bacteria and fungi. It recycles nutrients back to the soil and maintains balance in the ecosystem.
Antibiotics should only be taken when prescribed by a doctor. One must complete the full course and never overuse them. Misuse can lead to antibiotic resistance and reduced effectiveness in future treatments.
Food can be preserved using heat, refrigeration, salting, sugaring, vinegar, oil, drying, and pasteurisation. These methods stop or slow down the growth of harmful microorganisms.
Vaccines are made from weakened or dead microbes. They train the immune system to produce antibodies, which protect the body against future infections of the same disease. Example: polio vaccine.
Microorganisms are used at home to make curd, idli batter, bread, and pickles. They also help in composting kitchen waste into manure, showing their importance in daily life.
Students should revise NCERT solutions Class 8 Science chapter 2 questions and answers, practice worksheets, solve exemplar problems, and learn diagrams like the nitrogen cycle. Writing definitions and short notes regularly helps in scoring well.