NCERT Solutions|Microorganisms - Friend and Foe NCERT Solutions of Class 8 Science

1. Fill in the blanks:

a. Microorganisms can be seen with the help of a ______.

Ans: Microscope

b. Blue-Green Algae fix ______ directly from the air to enhance the fertility of the soil.

Ans: Nitrogen

c. Alcohol is produced with the help of _________.

Ans: Yeast

d. Cholera is caused by _________.

Ans: Bacteria

2. Tick the correct answer:

a. Yeast is used in the production of

i. Sugar

ii. Alcohol 

iii. Hydrochloric acid 

iv. Oxygen

Ans: (ii) Alcohol.

Yeast is used in the production of alcohol, which converts sugar into ethanol and carbon dioxide. 

b. Which of the following is an antibiotic?

i. Sodium bicarbonate

ii. Streptomycin

iii. Alcohol

iv. Yeast 

Ans: (ii) Streptomycin

Streptomycin is an antibiotic, sodium bicarbonate is an antacid, alcohol is a drug, and yeast is a fungus.

c. The carrier of Malaria-causing protozoan is

i. Female Anopheles mosquito

ii. cockroach

iii.  Housefly

iv. Butterfly 

Ans: (i) Female Anopheles mosquito

Female Anopheles mosquito carries Malaria-causing protozoan which causes Malaria in humans.

d. The most common carrier of communicable diseases is

i. Ant

ii. Housefly 

iii. Dragonfly

iv. Spider 

Ans: (ii) Housefly

Ant, dragonflies, and spiders do not carry any diseases.

e. The bread or idli dough rises because of

i. Heat

ii. Grinding

iii. Growth of yeast cells 

iv. Kneading 

Ans: (iii) Growth of yeast cells 

The yeast cells are microorganisms that grow, respire, and release carbon dioxide, which is responsible for raising the bread or idli dough.

f. The process of conversion of sugar into alcohol is called

i. Nitrogen fixation

ii. Moulding

iii. Fermentation

iv. Infection 

Ans: (iii) Fermentation 

The fermentation process involves the conversion of sugar into alcohol.

3. Match the organisms in column I with their action in column II.

Ans: 

1. Bacteria is a microorganism that causes a disease called cholera.

2. Rhizobium is a bacteria that is useful in the fixation of atmospheric nitrogen in the soil.

3. Lactobacillus produces lactic acid by converting sugar that coagulates and partially digest the milk protein and giving rise to curd.

4. The yeast cells are microorganisms that grow, respire and release carbon dioxide, which is responsible for raising and baking bread.

5. A protozoan is a microorganism carried by female anopheles mosquitoes which causes malaria.

6. A virus named HIV causes AIDS

4. Can microorganisms be seen with the naked eye? If not, how can they be seen?

Ans: No, microorganisms cannot be seen with the naked eye as they are minute organisms. But microorganisms can be seen through a microscope. 

5. What are the major groups of microorganisms?

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

1. Bacteria

1. It is a single-celled organism.

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

3. It causes diseases like cholera and tuberculosis.

2. Fungi

1. Fungi are mostly multicellular organisms that cause several diseases.

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

3. Protozoa

1. Protozoa can either be unicellular or multicellular.

2. Amoeba and Plasmodium are examples of protozoa.

3. They are harmful to humans as well as other organisms.

4. Virus

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

2. It can affect plants as well as animals or humans. 

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

5. Algae

1. They are the only microorganisms that are multicellular and have photosynthetic pigments.

2. They are also known as precursors of plants.

3. Spirogyra and Chlamydomonas are some examples of algae.

6. Name the microorganisms which can fix atmospheric nitrogen in the soil.

Ans: The microorganisms that can fix atmospheric nitrogen in the soil are bacteria. Rhizobium is one such bacteria. They help in making it to nitrogenous compounds that can be taken up by the plants.

These nitrogenous compounds are then used by the plants to make proteins and other important compounds. Rhizobacteria and Blue-green algae are examples of bacteria that have the capacity to fix nitrogen. 

7. Write 10 lines on the usefulness of microorganisms in our lives.

Ans: Usefulness of microorganisms:

1. Microorganisms such as rhizobium bacteria are used to increase soil fertility by fixing atmospheric nitrogen.

2. They are also useful in preparing many medicines and antibiotics.

3. Yeast is a microorganism that is used at home to make batter for fermented food. 

4. Various fungi are the ones responsible for decaying the waste in nature, they obtain nutrients from the dead and decompose the waste.

5. They are used in making wine, bread, pickles, and other food products.

6. Lactobacillus bacteria are mainly used at homes to make curd from milk.

7. Certain microbes are also used in the biological treatment of sewage and industrial effluent.

8. Some microorganisms are taken as probiotics which provide health benefits.

9. Bacteria are also involved in making cheese.

10.  Acetobacter acetic is used for producing acetic acid from alcohol.

8. Write a short paragraph on the harms caused by microorganisms.

Ans: The harms caused by microorganisms are enlisted below:

1. They can cause diseases in humans. Some diseases caused by bacteria are tuberculosis, cholera, typhoid, etc.

2. There are viruses that can affect the cattle by causing foot and mouth disease.

3. Microorganisms tend to reduce the productivity of the plants like wheat, rice, apple, sugarcane, etc.

4. When microorganisms are present in our body, they can harm the body cells by producing harmful substances.

5. There are microbes that can spoil food as well as other materials.

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

Ans: Antibiotics are the drugs or medicines that are taken to kill disease-causing microorganisms. They are produced from microorganisms. There are different types of antibiotics that are used to protect against each type of microorganisms like bacteria, fungus, and other organisms and kill them. Some examples of antibiotics are Penicillin, Tetracycline, Streptomycin, and so on.

The precautions to be taken while taking antibiotics are listed below:

1. They should be taken under the supervision of a qualified doctor.

2. The prescribed course of antibiotics should be taken completely for good results.

3. Taking the correct dosage of antibiotics is important. Any dose higher than or less than the prescribed dosage can harm the body.

Benefits of NCERT Solutions Class 8 Science Chapter 2

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• Highly accurate solutions that have been prepared by a team of subject specialists.

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These benefits will ensure that students are able to grow and become better learners.

Preparation Tips for Class 8 Science

Mentioned below are some of the preparation tips which can help students to perform better in the upcoming examination.

• Always practise as many questions as possible. Science is a subject that requires a lot of practice, and solving questions is one of the best ways to do it.

• Make sure to solve the examples. Students often overlook the solved and unsolved examples of the chapter but solving them ensures a better understanding of the concept.

• Make sure to use flowcharts and diagrams for understanding the concept.

• Revise the previously learnt concept at regular intervals.

• Always solve previous year's questions before the examination to get an idea of the format and weightage of the questions.

• Make a note of the key formula and phrases. This would greatly help in last-minute revision.

Chapter-wise NCERT Solutions for Class 8 Science

• Chapter 1 - Crop Production and Management

• Chapter 3 - Synthetic Fibres and Plastics

• Chapter 4 - Materials: Metals and Non-Metals

• Chapter 5 - Coal and Petroleum

• Chapter 6 - Combustion and Flame

• Chapter 7 - Conservation of Plants and Animals

• Chapter 8 - Cell - Structure and Functions

• Chapter 9 - Reproduction in Animals

• Chapter 10 - Reaching The Age of Adolescence

• Chapter 11 - Force and Pressure

• Chapter 12 - Friction

• Chapter 13 - Sound

• Chapter 14 - Chemical Effects of Electric Current

• Chapter 15 - Some Natural Phenomena

• Chapter 16 - Light

• Chapter 17 - Stars and The Solar System

• Chapter 18 - Pollution of Air and Water

This was the complete discussion on Microorganisms: Friend and Foe NCERT Solutions of Class 8 Science. We have learnt some of the key points and the important topics covered in the chapter along with the benefits of practising the NCERT Solutions. We highly recommend students download the NCERT solutions pdf and practise each and every question of the pdf. Solving these questions will definitely help students develop a better understanding of the concept, thus helping them perform better in the upcoming examinations.