SEBA Class 8 Science Chapter 2 Micro-Organisms: Friend and Foe

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SEBA Class 8 Science Chapter 2 Micro-Organisms: Friend and Foe

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Also, you can read the NCERT book online in these sections Solutions by Expert Teachers as per Central Board of Secondary Education (CBSE) Book guidelines. SEBA Class 8 General Science Textual Solutions in English are part of All Subject Solutions. Here we have given Class 8 Science Textbook Question Answer, SEBA Class 8 Science English Medium Textbook Solutions for All Chapters, You can practice these here.

Micro-Organisms: Friend and Foe

Chapter: 2

PART – I

EXERCISE

1. Fill in the blanks.

(a) Micro-organisms can be seen with the help of a__________.

Ans: Micro-organisms can be seen with the help of a microscope.

(b) Blue green algae fix_______ directly from air to enhance fertility of soil.

Ans: Blue green algae fix nitrogen directly from air to enhance fertility of soil.

(c) Alcohol is produced with the help of _______.

Ans: Alcohol is produced with the help of Yeast.

(d) Cholera is caused by_______.

Ans: Cholera is caused by bacteria.

2. Tick the correct answer.

(a) Yeast is used in the production of-

Sugar / alcohol / hydrochloric acid / oxygen.

Ans: Alcohol.

(b) The following is an antibiotic – 

Sodium bicarbonate / Streptomycin / Alcohol / Yeast.

Ans: Streptomycin.

(c) Canier of malaria-causing protozoan is –

Female Anopheles mosquito / cockroach/housefly / butterfly.

Ans: Female Anopheles mosquito.

(d) The most common earner of communicable diseases is- 

Ant/ housefly /dragonfly / spider.

Ans: Housefly.

(e) The bread or idli dough rises because of –

Heat / grinding / growth of yeast cells / kneading.

Ans: Growth of yeast cells.

(f) The process of conversion of sugar into alcohol is called –

Nitrogen fixation / moulding / fermentation / infection.

Ans: Fermentation.

3. Match the organisms in Column A with their action in Column B.

Ans: 

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

Ans: No, micro-organisms cannot be seen with the naked eye because they are extremely small in size. To observe them, we use a microscope, which magnifies their structure, making them visible. A microscope has lenses that enlarge the image of micro-organisms, allowing us to study their shape, size, and structure.

5. What are the major groups of micro-organisms?

Ans: Micro-organisms are tiny living organisms that cannot be seen with the naked eye. They are classified into five major groups based on their structure and functions. bacteria, archaea, protozoa, algae, fungi, viruses, and multicellular animal parasites ( helminths ). Each type has a characteristic cellular composition, morphology, mean of locomotion, and reproduction.

6. Name the micro-organisms which can fix atmospheric nitrogen in the soil.

Ans: Micro-organisms that can fix atmospheric nitrogen in the soil are essential for maintaining soil fertility and promoting plant growth. One of the most well-known nitrogen-fixing bacteria is Rhizobium, which forms a symbiotic relationship with the root nodules of leguminous plants, converting atmospheric nitrogen into a usable form. Free-living bacteria such as Azotobacter also play a significant role in nitrogen fixation in the soil. Additionally, cyanobacteria like Anabaena and Nostoc are capable of fixing atmospheric nitrogen, often forming symbiotic associations with plants. Another important group includes Frankia, which forms symbiotic relationships with non-leguminous plants, such as those from the genus Alnus. In anaerobic conditions, Clostridium bacteria also contribute to nitrogen fixation. These micro-organisms enhance soil health by increasing the nitrogen content, making it available for plant absorption and utilization.

7. Write 10 lines on the usefulness of micro-organisms in our lives.

Ans: (i) Decomposition: Micro-organisms help decompose organic matter, recycling nutrients back into the ecosystem.

(ii) Nitrogen Fixation: Bacteria like Rhizobium fix atmospheric nitrogen into a usable form for plants, enhancing soil fertility.

(iii) Food Production: Yeast is used in baking bread, and bacteria are used in fermenting milk to make curd and cheese.

(iv) Medical Uses: Micro-organisms like Penicillium produce antibiotics that treat bacterial infections.

(v) Biodegradation: They break down waste materials in sewage treatment plants.

(vi) Agriculture: Biofertilizers containing bacteria improve soil quality and crop yield.

(vii) Industrial Production: Microbes are used to produce alcohol, vinegar, and organic acids.

(viii) Vaccine Production: Weakened or killed micro-organisms are used to make vaccines that protect against diseases.

(ix) Biogas Production: Anaerobic bacteria break down organic waste to produce biogas, a renewable energy source.

(x) Genetic Engineering: Bacteria like E. coli are used in producing insulin and other useful proteins.

8. Write a short paragraph on the harms caused by micro-organisms.

Ans: Micro-organisms, while beneficial in many ways, can also cause significant harm to humans, animals, and plants. Some bacteria, viruses, fungi, and protozoa are pathogenic and can lead to diseases such as tuberculosis, influenza, ringworm, and malaria. These harmful micro-organisms can spread through air, water, food, or direct contact, causing infections that may range from mild to life-threatening. They can also spoil food, making it unsafe for consumption, and damage crops, leading to agricultural losses. Additionally, some bacteria produce toxins that can contaminate food and water, posing health risks. Therefore, managing harmful micro-organisms through hygiene, vaccination, and proper food handling is crucial.

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

Ans: Antibiotics are medicines derived from microorganisms that kill or inhibit the growth of bacteria. Certain fungi and bacteria produce common antibiotics, such as penicillin and tetracycline.

When taking antibiotics, always follow the doctor’s prescription and complete the full course to prevent resistance. Avoid self-medication and do not share antibiotics with others. Inform your doctor about any allergies beforehand. Follow dietary guidelines, as some antibiotics interact with certain foods, and avoid alcohol as it may reduce effectiveness. Take antibiotics with water to aid absorption and monitor for side effects like rashes or nausea. Maintaining hygiene during treatment helps prevent reinfection. These precautions ensure effective and safe use of antibiotics.

Parimol

Hi! my Name is Parimal Roy. I have completed my Bachelor’s degree in Philosophy (B.A.) from Silapathar General College. Currently, I am working as an HR Manager at Dev Library. It is a website that provides study materials for students from Class 3 to 12, including SCERT and NCERT notes. It also offers resources for BA, B.Com, B.Sc, and Computer Science, along with postgraduate notes. Besides study materials, the website has novels, eBooks, health and finance articles, biographies, quotes, and more.