Important Questions Class 8 Science Chapter 2

Important Questions Class 8 Science Chapter 2 – Microorganisms: Friend and Foe

Class 8 Science is a foundation subject that students study before they proceed to secondary level education. In the following syllabus, the second chapter is based on microorganisms. Those living organisms we cannot see with our naked eyes are known as microorganisms or microbes. Here, students will get to learn whether microorganisms are our friends or enemies. By the chapter’s name, you can easily figure out that this chapter will discuss the microorganisms that help us and those microbes that cause diseases. It is not a very critical chapter to study, but a lot of information and new concepts are introduced to understand and remember. 

To make learning easier for the Class 8 students, the experts of Extramarks have developed Class 8 Science Chapter 2 notes to follow. In these notes, you can find an excellent explanation of all the chapters in simpler language. These question-answer solutions will help you understand the new side of the world of microorganisms. You can use these step-wise solutions as revision notes and store them on your preferred smart devices for access. Our chapter and revision notes can be perfectly used to recapitulate the chapter before an exam.

After studying these important questions Class 8 Science Chapter 2, students will be able to understand the concept of microorganisms, their habitats, various classes of microorganisms such as fungi, bacteria, protozoans and viruses, the mode of their reproduction, harmful microorganisms, pathogens, soil microorganisms, different uses of microorganisms, nitrogen fixation by bacteria. The important questions Class 8 Science Chapter 2 provided here are very helpful for students to self-clarify all their doubts in the chapter easily and interestingly.

Extramarks is one of the most trusted websites used extensively by students from class 1 to class 12 all over India. Extramarks provides the most comprehensive and reliable study and practice resources,  such as NCERT solutions, CBSE revision notes, NCERT books, CBSE sample papers, etc., developed carefully by our experienced Science faculty to help students get an in-depth and clear understanding of all the concepts mentioned in every chapter.

A full list of Chapter 2 Class 8 Science important questions, CBSE extra questions, CBSE past year question papers, and other such study materials will help you get acquainted with examination question patterns and also pick up on time management skills. Students are advised to thoroughly practise these Class 8 Chapter 2 important questions for their exam preparation. With the help of important questions Class 8 Science Chapter 2 study materials, students will be able to score well.

To access important questions in Class 8 Science Chapter 2 and other study materials, register on the Extramarks website now.

Get Access to CBSE Class 8 Science Important Questions 2022-23 with Chapter-Wise Solutions

You can also find CBSE Class 8 Science Chapter-by-Chapter Important Questions here:

CBSE Class 8 Science Important Questions
Sr No. Chapters Chapters Name
1 Chapter 1 Crop Production and Management
2 Chapter 2 Microorganisms : Friend and Foe
3 Chapter 3 Synthetic Fibres and Plastics
4 Chapter 4 Materials : Metals and NonMetals
5 Chapter 5 Coal and Petroleum
6 Chapter 6 Combustion and Flame
7 Chapter 7 Conservation of Plants and Animals
8 Chapter 8 Cell Structure and Functions
9 Chapter 9 Reproduction in Animals
10 Chapter 10 Reaching The Age of Adolescence
11 Chapter 11 Force and Pressure
12 Chapter 12 Friction
13 Chapter 13 Sound
14 Chapter 14 Chemical Effects of Electric Current
15 Chapter 15 Some Natural Phenomena
16 Chapter 16 Light
17 Chapter 17 Stars and The Solar System
18 Chapter 18 Pollution of Air and Water

Important Questions Class 8 Science Chapter 2 – With Solutions

The Science experts at Extramarks have compiled an entire list of Important Questions with the help of different resources. Students can obtain good scores in their examinations when they choose the right study material that is accurate to learn and comprehend. Students of Class 8 find it difficult to understand the new concepts covered in this chapter. Doubts during class hours can be solved by clarifying with their teachers or using reference material per their needs. So choosing the right study material requires a lot of understanding of the current CBSE syllabus. The important questions in Class 8 Science Chapter 2 cover most of the topics presently prescribed in the NCERT textbook. Students can register on the Extramarks website and access the complete list of solutions to chapter-wise questions.

Mentioned below is a set of a few important questions in Class 8 Science Chapter 2 compiled by the Extramarks team:


Question 1. Pathogenic microorganisms present in host cells are killed by ____.

  • antibiotics
  • antibodies
  • vaccines
  • pain killers

Answer 1: The correct option is A- Antibiotics.


Antibiotics are those substances that may inhibit or kill the growth of different microbes. Antibiotics are antimicrobial drugs from other organisms (such as moulds, fungus and some soil bacteria) to combat harmful microorganisms. The consumption of these antibiotics kills the microorganisms causing infection in host bodies. The definition of a pathogenic organism is the organism capable of causing disease in its host. A human pathogen has the capability of causing illness in humans. Common examples of various pathogenic organisms include specific strains of bacteria like Salmonella, Listeria and E. coli, and other viruses such as Cryptosporidium. An antibiotic is a chemical substance that inhibits the growth of these harmful bacteria. They hinder the bacteria’s reproductive cycle inside the host’s body.


Question 2. How do vaccines work?

Answer 2:

Vaccines are treatments that improve your immunity to a certain disease. Vaccines contain dead or weakened but alive microorganisms of a particular disease. When a vaccine containing dead or alive microorganisms is introduced into a healthy body, orally (by mouth) or by injection, that person’s body triggers an immune response. The immune system of the person, in turn, responds by producing some substances called antibodies in its blood to protect against the pathogens introduced. These antibodies kill the ‘live’ disease-causing microorganisms present in the vaccine. Some of the antibodies remain in the person’s blood for a very long time and fight against the same microorganism and kill them if they enter the body naturally later. So, due to antibodies in the blood, a person remains protected from that disease. With a vaccine, the immune system can safely learn to recognize them as hostile invaders, produce antibodies, and remember them for the future.

Thus, a vaccine develops immunity from a disease.


Question 3. Write a paragraph on the harms caused by microorganisms.

Answer 3:

Microorganisms are causative agents in many infectious diseases. Therefore, microbes are termed pathogens. Microorganisms are very minute organisms that are invisible to the human eye. Microorganisms are so tiny that they can be seen only under a microscope. These include many organisms such as bacteria, viruses, fungi, algae, protozoa, etc. Some microbes prove beneficial; however, most microorganisms can be very harmful to us. They cause many diseases in humans, plants and animals that prove to be fatal.

Harmful effects of microorganisms are:

  • Some microorganisms are pathogens which cause diseases to humans, animals and plants.
  • Bacteria and fungi cause food spoilage and make them unfit for eating. Consumption of such food causes food poisoning. 
  • Human diseases like the common cold, tuberculosis, measles, chicken pox, polio, cholera, typhoid, hepatitis B, malaria, etc., are caused by microorganisms. 
  • Some serious diseases like anthrax are also caused in animals by microbes. 
  • Microbes also cause diseases in plants like blights in potatoes, sugarcanes, oranges etc. Some viruses can affect cattle by causing foot and mouth disease. 
  • They are also responsible for reducing crop yield, causing loss to farmers.
  • Microbes also spoil clothing and leather products. They reduce the lifespan and the quality of the product.


Question 4. What are the major groups of microorganisms?

Answer 4:

Microorganisms are very minute organisms that are invisible to the human eye. Microorganisms are so minute that they can only be seen under the microscope. Microorganisms include bacteria, fungi, archaea or protists. Microorganisms differ in size and structure, habitat, metabolism, and many other characteristics. Most bacteria are harmless or helpful, but some are pathogens, causing disease in humans and other animals.

There are five major groups of microorganisms. They are enlisted as

  • Bacteria:

It is a single-celled organism.

They can be spiral, rod-shaped, spherical-shaped, or comma-shaped.

It causes diseases like cholera, tetanus and tuberculosis.

  • Fungi:

Fungi are usually multicellular organisms that cause several diseases.

Symptoms depend on the area affected

The moulds formed on bread are a specific type of fungi.

  • Protozoa:

Protozoa can either be multicellular or unicellular.

Amoeba and Plasmodium are a few examples of protozoa.

They can be harmful to humans as well as different other organisms.

  • Virus:

Viruses are disease-causing microorganisms that can only divide inside a host organism/cell. 

They remain inactive outside the cell.

It can affect plants, animals as well as humans. 

HIV in humans and TMV virus occurring in plants are some examples of viruses.

  • Algae:

These are the only microorganisms that are multicellular. 

Algae have photosynthetic pigments.

They are also known as precursors of plants.

Spirogyra and Chlamydomonas are some examples of algae.


Question 5. The bread or idli dough rises because of ______.

  • heat
  • grinding
  • growth of yeast cells
  • kneading

Answer 5: The correct option is C- growth of yeast cells


Yeast can be utilised as a leavening agent in bread and idli making. The yeast consumes the sugar in the dough and burps carbon dioxide gas and ethanol. This gas is trapped inside the bread dough due to gluten present in it, thus making the dough rise. The alcohol also gets evaporated in the baking process. While bread-making, the dough is left in a warm place. During fermentation, carbon dioxide gas is produced and gets trapped in tiny pockets of air within the dough. This makes the dough rise. If you let the dough rise for too long, the finished bread’s taste and texture suffer. Due to different yeast cell development, the dough of bread or idli rises. If there is lots of food present around to take advantage of the food, the yeast cells reproduce in great numbers. They normally develop a tiny bud from one edge of themselves when they reproduce. Then a small nucleus is placed and pinched off to make a smaller new yeast cell. The leavening agent or yeast converts sugars in the dough to carbon dioxide and derives energy from this reaction. Due to this, yeast cells grow, and the dough also expands. Hence, the bread and idli develop a soft and spongy texture. 


Question 6. Explain the nitrogen cycle.

Answer 6:

The nitrogen cycle is the continuous process of exchanging nitrogen between organisms and the environment. Nitrogen is an essential nutrient needed to make amino acids and other important organic compounds. Still, most organisms cannot use free nitrogen, which is abundant as a gas in the atmosphere. This is a biogeochemical process through which nitrogen is converted into many forms, consecutively passing from the atmosphere to the soil to the organism and back into the atmosphere. Nitrogen is an important plant nutrient. However, plants and animals cannot directly use the plentiful nitrogen in the atmosphere. Nitrogen nitrification, nitrogen fixation, decay, and putrefying are among the mechanisms that pass from the ambience to the soil to the organism and then return to the atmosphere. Nitrogen gas exists in both organic as well as inorganic forms. 

Organic nitrogen primarily exists in living organisms, and it gets passed through the food chain by consuming other living organisms. 

While the inorganic forms of nitrogen are present in abundance in our atmosphere. This inorganic form of nitrogen is available for plants through symbiotic bacteria, which converts the inert nitrogen into a more usable form – such as nitrates and nitrites. Nitrogen will undergo a wide range of transformations to maintain a good ecosystem balance. This process extends to diverse biomes. The marine nitrogen cycle is known to be one of the most intricate biogeochemical cycles.

The nitrogen cycle is about the movement of nitrogen occurring between various elements on Earth (like air, soil, living organisms etc.). The amount of the element nitrogen in the atmosphere remains constant.

  • The atmosphere contains approximately 78% nitrogen.
  • Atmospheric nitrogen gets fixed into the soil.
  • N2 fixing microbes facilitate the conversion of atmospheric N2 into nitrogen compounds like NH3.
  • The plants utilise nitrogen from soil through their roots.
  • Animals utilise nitrogen, feeding on plants.
  • When plants & animals die, nitrogenous wastes are returned to the soil.
  • Decomposers convert some parts to nitrogen compounds to be used by plants.
  • Denitrifying bacteria convert into atmospheric N2.


Question 7. What are antibiotics? What precautions must be taken while taking antibiotics?

Answer 7:

Antibiotics are medicines produced by certain microorganisms which kill or stop the growth of microorganisms in our body. These are very effective in preventing the effects of microorganisms. Antibiotics are made from bacteria and fungi. Antibiotics treat various human and animal diseases as they target bacteria and viruses. They have significantly enhanced our ability to treat severe diseases like plague, whooping cough, and leprosy. Examples of general antibiotics are streptomycin, tetracycline, erythromycin etc.

Precautions to be taken while taking antibiotics:

  • Antibiotics should only be taken under the guidance of a skilled physician.
  • Antibiotics must only be taken when needed and in an adequate amount. Otherwise, they may be harmful and will become less effective in future.
  • The antibiotic course should be finished according to the doctor’s instructions.
  • Antibiotics must be administered in the correct dosage and at the appropriate time.
  • Antibiotics that are given in the wrong dose become useless.
  • Excessive medication usage might also harm the beneficial bacteria in our bodies.

Read more about Science Class 8 Chapter 2 important questions on Extramarks.



Question 8. Write ten lines on the usefulness of microorganisms in our lives.

Answer 8:

Microorganisms are very minute organisms that are invisible to the naked eye. However, these microbes are vital to plants and the environment. Here are some uses of microorganisms in our daily life.


  • Some microorganisms are used as a probiotic (live bacteria and yeasts that are good for the digestive system and maintain the good health of the host). They are called ‘good’ or ‘useful’ bacteria.
  • In pulse plants’ roots, rhizobium fixes nitrogen from the air and supplies nitrogen compounds to the pulse plants. It also helps to make the soil more fertile.
  • Microorganisms are used in winemaking, baking, pickling, and other food-making processes.
  • Alcoholic fermentation by yeast is widely used for the commercial preparation of wine and bread. Yeast makes idli, bhaturas, bread, pastries, and cakes.
  • Microbes are used to reduce pollution. For example, decomposers like bacteria and fungi break down dead bodies and excreta for forming inorganic compounds, which plants can easily absorb.
  • Microbes also play a crucial role in the preparation of medicines. Antibiotics are chemicals produced by microorganisms to kill bacteria. Penicillin is an antibiotic made from penicillium.
  • Bacteria in our intestine help in proper digestion and release vitamin B, absorbed by the intestine. They induce immunity in our bodies.
  • Many vaccines are prepared from microorganisms. These vaccines are usually given to children to protect them from the disease.
  • Certain microbes are used in the biological treatment of sewage and industrial effluents.
  • Lactobacillus is used in dairy industries for the setting of curd and cheese making. Microorganisms carry out the processing and ageing of cheese.


Question 9. What measures can be taken to prevent the spread of communicable diseases?

Answer 9:

Infectious diseases are communicable diseases that can spread from one person to another. Chickenpox, mumps, influenza etc., are a few examples of communicable diseases.

Precautions to prevent the spreading of communicable diseases:

  • Wash your hands often: This is mainly important before and after preparing food, eating, and after the toilet is used.
  • Get vaccinated: Immunisation can have a drastic reduction in your chances of contracting many diseases. Keep the recommended vaccinations up-to-date.
  • Use of antibiotics sensibly: Take antibiotics only when you are prescribed. Unless directed, or unless you are allergic to these antibiotics, take all prescribed doses of your antibiotic, even though you begin to feel better before you have finished the medication.
  • Stay at home if you observe signs and symptoms of an infection: Don’t go to work or class if you’re vomiting, have diarrhoea or are running a fever.
  • Be smart in food preparation: Keep counters, and kitchen surfaces clean when preparing meals. In addition, promptly refrigerate your food leftovers. Never let the cooked foods remain at room temperature for a long period.
  • Practice safer sex: Use condoms. Get tested for various sexually transmitted diseases (STDs), and have your partner get tested— or abstain altogether.
  • Don’t share personal items: Use your toothbrush, comb or razor blade. Avoid sharing drinking glasses or dining utensils.
  • Travel wisely: Avoid going to public places or events when ill.


Benefits of Solving Important Questions Class 8 Science Chapter 2

Science is a broad subject with multiple theories and concepts. All of this makes it difficult for students to understand and remember. Students are encouraged to go through Extramarks question bank of Important Questions Class 8 Science Chapter 2. Students can gather confidence by answering the important questions and going over their provided solutions. The Important Questions Class 8 Science Chapter 2  provides a strong foundation of basic concepts among students. These step-wise solutions will help you to attain perfection on the concepts involved in the chapter ‘Microorganisms: Friend and Foe’. 

Mentioned below are some benefits of solving Important Questions Class 8 Science Chapter 2:

  • These solutions will help students to save time while preparing for their upcoming examination and cover the entire chapter as well as revise crucial concepts covered in the chapter.
  • Important Questions Class 8 Science Chapter 2 covers the majority of concepts of the entire chapter-Introduction to microorganisms, their habitats, classes of microorganisms like bacteria, fungi, protozoans and viruses, mode of their reproduction, use of microorganisms, harmful microorganisms, pathogens, soil microorganisms, nitrogen fixation by bacteria.
  • Students can entirely rely upon these important questions as these solutions are prepared following all the guidelines laid by CBSE.
  • Class 8 Science Chapter 2 important questions are compiled by the experts at Extramarks who have experience in teaching Biology and Science related subjects for several years.

Extramarks provides students from Class 1 to Class 12 with comprehensive learning solutions. Our website has abundant study materials and resources, along with important questions and solutions. Students can easily click on the links given below to get access to important questions Class 8 Science Chapter 2 along with some of these other resources:

FAQs (Frequently Asked Questions)

1. Are the NCERT Class 8 Science Solutions Important?

The Class 8 NCERT Solutions for every subject are important since they will help you understand each concept and topic included in the chapter. In addition, they also support you to ease the process of studying the chapters which will enable you to do well on examinations. By referring to important Questions Class 8 Science Chapter 2 students will be able to better understand the chapter. On the Extramarks website, these important questions are readily accessible.

2. How can students get ready for the Science exam in Class 8?

Science is a theoretical subject that revolves around different concepts and functions of plants and the human body. Students may use the following methods and tips to get ready for the Class 8 Science examination:

  • Read the textbook chapter, each chapter in its whole.
  • Get your respective subject teacher to answer all of your queries.
  • Don’t hesitate to ask your doubts and participate actively during your classes.
  • All the exercises from the textbook are provided at the end of each chapter. Make sure you solve and revise these questions from time to time.
  • Read over each chapter’s solutions at Extramarks.