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

Very Short Answer Questions

1. Which one of the following is caused by bacteria?

1. Cold 

2. Polio

3. Chicken pox 

4. Tuberculosis

Ans: (A) Cold

2. Which one of the following is an antibiotic?

1. Streptomycin 

2. Tetracycline

3. Erythromycin 

4. All of these

Ans: (D) All of these

3. Bread mould is an example of ……...

1. Bacteria 

2. Fungi

3. Virus 

4. Algae

Ans: (B) Fungi

4. Disease causing microorganisms are called ……….

1. Antibodies 

2. Vaccines

3. Pathogens

4. Carriers

Ans: (C) Pathogens

5. ……….. is a bacterial disease in human and cattle

1. Anthrax 

2. Foot and mouth

3. Rust 

4. Citrus canker

Ans: (A) Anthrax

6. The temperature at which milk is heated in order to preserve is ……..

1. $70{}^\circ $ 

2. $110{}^\circ $

3. $45{}^\circ $

4. $250{}^\circ $

Ans: (A) $70{}^\circ $

7. Air contains …….. of nitrogen.

1. $65\%$ 

2. $78\%$

3. $95\%$

4. $80\%$

Ans: (B) $78\%$

Very Short Answer Questions

1. Name the five groups of microorganisms.

Ans: Five groups of microorganisms are bacteria, fungi, protozoa, algae and virus.

2. Name any two serious diseases caused by virus.

Ans: Polio and chickenpox are caused by viruses.

3. Name any two diseases caused by protozoa.

Ans: Dysentery and malaria are caused by protozoa.

4. Name any two domestic uses of microorganisms.

Ans: Two domestic uses of microorganisms are as follows:

• Setting of curd, 

• Fermentation of idlis.

5. Which bacteria promotes the formation of curd?

Ans: Lactobacillus promotes the formation of curd.

6. Name the bacteria used in making bread, pastries and cakes.

Ans: Yeast is used in making bread, pastries and cakes.

7. Name the commercial use of yeast.

Ans: Yeast is used in the production of alcohol and wine.

8. Name the scientist who discovered penicillin.

Ans: Alexander Fleming discovered penicillin.

9. Name any two communicable diseases.

Ans: Cholera and common cold.

10. Name any two carriers of diseases.

Ans: Two common carriers of diseases are mosquitoes and houseflies.

11. Name any two food preservatives.

Ans: Two food preservatives are sugar and vinegar.

12. Name the nitrogen fixation bacteria.

Ans: Rhizobium is the nitrogen fixation bacteria.

13. Who discovered pasteurisation?

Ans: Louis Pasteur.

14. Why milk is boiled before storage and consuming?

Ans: Milk is boiled to prevent spoilage due to development of microorganisms.

Short Answer Questions

1. What are microorganisms?

Ans: Extremely small living organisms that cannot be seen by naked eye are called microorganisms. They may be unicellular or single-celled or multicellular.

2. Define virus.

Ans: Viruses are tiny transferable agents that act as non-living outside host cells and act living inside host cells and show reproduction. Viruses can affect all kinds of organisms including animals, plants and bacteria.

3. Why are viruses different from other microorganisms?

Ans: Viruses are also tiny but are different from other microorganisms as they show reproduction. They reproduce inside the host cell which may be a bacterium, plant or animal.

4. Where are microorganisms found?

Ans: Microorganisms are found in all kinds of environments, ranging from ice cold climate to hot springs; and deserts to marshy lands. They are also found inside the bodies of animals and humans. Some microorganisms grow on other organisms while others exist freely.

5. How do microorganisms help in agriculture?

Ans: Microorganisms increase the soil fertility by combining the air, nitrogenous compounds and minerals. Bacteria like Rhizobium and blue green algae are microorganisms which can fix atmospheric nitrogen in the soil and increase soil fertility, which helps in agriculture.

6. What is fermentation?

Ans: Fermentation is the process in which conversion of sugar into alcohol takes place through the action of enzymes.

7. Why is yeast used in the baking industry for making bread, cakes and pastries?

Ans: Yeast reproduces quickly and produces carbon dioxide during respiration. Yeast makes breads, cakes and pastries soft and spongy. This is the basis of using yeast in the baking industry.

8. What are antibodies?

Ans: An antibody is a protein released by the body's immune system in response to the microbes carrying diseases in our body. Antibody provides the strength to fight against the disease-causing microbe. Antibodies protect our body against infectious diseases. 

9. What are communicable diseases?

Ans: Infectious diseases that can spread from an infected person to a healthy person through mediums like air, water, food or physical contact are known as communicable diseases. Examples of communicable diseases are cholera, common cold, chicken pox and tuberculosis.

10. Name the modes of transmission of communicable disease.

Ans: The modes of transmission of communicable diseases can be direct and indirect. In direct transmission diseases can be spread by direct contact, by droplet infection, sharing infected needles, syringes and razors, infected blood transfusion. In indirect transmission diseases can be spread by infected food, water or air, through carriers like the housefly, mosquitoes, and rats or through dirty hands.

11. Write any four ways in which spread of communicable diseases can be prevented.

Ans: Communicable diseases can be prevented by using following ways:

• Always keep food covered and do not eat exposed food.

• Avoid breeding of mosquitoes by keeping the surroundings dry.

• Always cover your mouth while sneezing and coughing.

• Wash your hands before and after meals.

12. Why are some microorganisms considered as harmful?

Ans: Some species of bacteria, viruses cause diseases in human beings, plants and animals. Some bacteria cause tuberculosis and typhoid, some kinds of virus cause common cold and influenza. Some microorganisms also cause decomposition of food and clothing. Thus this kind of microorganisms are considered as harmful.

13. How is food poisoning caused?

Ans: Food poisoning is caused due to the eating of contaminated food. Some microorganisms like bacteria, viruses grow on our food and produce toxic substances. These make the food toxic and consuming that food causes serious illness and even death.

14. How do we preserve cooked food at home?

Ans: We preserve cooked food at home by adding some preservatives. We can add salt, sugar and edible oil in cooked food. To preserve meat and fish, raw mango, tamarind and amla, common salt has been used. Sugar is added to jams, jellies and squashes to preserve them. Vegetables, fruits, and pickles are preserved by adding oil and vinegar.

15. Explain preservation by sugar.

Ans: Sugar maintains the moisture content in food which prevents the growth of bacteria. Sugar is used in jams and jellies to preserve the color, flavor and texture.

16. What is pasteurization?

Ans: In the pasteurization process milk is heated at about $70{}^\circ $ for 15 to 30 seconds and cooled suddenly. By pasteurization the growth of microbes is prevented. 

17. What are preservatives? State their importance?

Ans: Preservatives are natural or synthetic substances that are used to prevent the growth of microorganisms. Common salt, vinegar, oil and sugar used as preservatives to prevent the growth of microorganisms. Preservatives are important to prevent food from spoilage. Sodium benzoate and sodium metabisulphite are common preservatives.

Long Answer Questions

1. What are antibiotics? What precautions must be taken while taking antibiotics?

Ans: Antibiotics are medicines which kill or stop the growth of microorganisms in our body. These are very effective to prevent the effects of microorganisms. Antibiotics are made from bacteria and fungi. Antibiotics are used to treat various human and animal diseases as they target bacteria and viruses. Examples of common antibiotics are streptomycin, tetracycline, erythromycin etc.

Precautions to be taken while taking antibiotics:

• Antibiotics should be taken only by the advice of a qualified doctor.

• Antibiotics should only be taken when needed and in an adequate amount.  Otherwise, they can be harmful and become less effective in future.

2. What is nitrogen cycle? Draw a neat labelled diagram.

Ans: The organic process by which nitrogen is converted between its various chemical forms is the process of nitrogen cycle. Our atmosphere contains 78% nitrogen gas. Nitrogen is one among the essential constituents of all living organisms as a part of proteins, chlorophyll, nucleic acids and vitamins. The atmospheric nitrogen can't be taken directly from plants and animals. Some bacteria and blue chlorophytes present within the soil fix nitrogen from the atmosphere and convert it into compounds of nitrogen. Once nitrogen is converted into these usable compounds, it can be used by plants from the soil through their roots. Nitrogen is then used for the synthesis of plant proteins and other compounds. Animals feeding on plants get these proteins and other nitrogen compounds. When plants and animals die, bacteria and fungi present within the soil convert the nitrogenous wastes into nitrogenous compounds to be employed by plants again. Certain other bacteria convert some parts of them to nitrogen gas which matches back to the atmosphere. As a result, the share of nitrogen within the atmosphere remains more or less constant.

A labelled diagram of nitrogen cycle is as follows:

Nitrogen Cycle

3. Write any ten uses of microorganisms.

Ans: Ten uses of microorganisms are as follows:

• Microorganisms help in the preparation of curd, bread, cake etc.

• They are used in the production of alcohol on a huge scale.

• Yeast is used to make vinegar.

• Microbes are used to reduce pollution.

• They act as cleaning agents and decay the waste products into compost.

• They decompose the plant and animal dead bodies and reduce the waste.

• They increase soil fertility by fixing nitrogen in the atmosphere.

• Some microbes are used in production of medicines like antibiotics and vaccines.

• They are used as preservatives for food items.

• They help in various metabolic activities in our body.

4. Write short notes on increasing soil fertility by the action of microorganisms.

Ans: Microorganisms increase the soil fertility by combining the air, nitrogenous compounds and minerals. Bacteria like Rhizobium and blue green algae are microorganisms which can convert atmospheric nitrogen into nitrates and fix it in the soil and increase soil fertility. These microorganisms are generally called biological nitrogen fixers. Rhizobium is nitrogen fixing bacteria that live in the root nodules of leguminous plants, such as beans and peas, with which it has a symbiotic relationship. Sometimes nitrogen gets stable through the action of lightning.

5 Important Topics of Class 8 Science Chapter 2 You Shouldn’t Miss!

Benefits of Class 8 Chapter 2 Science Important Questions

• Clarification of Key Concepts: Important questions help students understand key ideas about microorganisms and what roles they play.

• Enhanced Critical Thinking: Engaging with these questions encourages careful thinking about how microorganisms affect health and the environment.

• Improved Retention of Information: Answering questions helps students remember important facts about microorganisms better.

• Better Exam Preparation: Practising important questions gives students a clear idea of what to expect in their exams, helping them do better.

• Real-World Application: The questions connect classroom learning to real-life issues, showing how microorganisms are relevant in different areas.

• Development of Research Skills: Important questions encourage students to explore beyond their textbooks, helping them become more curious and knowledgeable.

• Increased Confidence: Regular practice makes students feel more confident in their knowledge, preparing them well for tests and discussions.

Conclusion

Bacteria have been on Earth long before humans. These tiny organisms can survive in extreme environments, such as hot mud pots, icy waterways, and places with high levels of chemicals like sulfuric acid and caustic soda.

You can download and add questions and answers about microorganisms to your study materials in a PDF format. Focus on the answers to learn how to use them effectively. Fill in the spaces with these questions and answers to check how ready you are. Make sure to practise and prepare well before your exam.

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