SCIENCE CLASS 8 CHAPTER 2 MICROORGANISM FRIEND AND FOE
SCIENCE CLASS-8
CHAPTER -2
MICROORGANISMS - FRIEND AND FOE
EXERCISES
Question number 1
Answer number 1
Question number 2
Answer number 2
Question number 3
Answer number 3
Question number 4
Answer number 4
Question number 5
Answer number 5
- Bacteria
- Fungi
- Protozoa
- Algae
- Viruses
Question number 6
Answer number 6
Question number 7
Answer number 7
- They are helpful in cleaning up of the environment. The organic waste (vegetable peels, remains of animals, faeces etc. ) are broken down into harmless and useful substances by bacteria.
- In agriculture they are used to increase the soil fertility by fixing nitrogen.
- They are used in the preparation of medicines.
- Microorganisms are useful in making curd and bread. Lactobacillus promotes the formation of curd. It multiplies in the milk and converts it into curd.
- Bacteria are involved in the making cheese, pickle and many other food items.
- Microorganisms are used for the large scale production of alcohol, wine and acetic acid (vinegar)
- Antibiotics are being produced by bacteria and fungi.
- Microorganisms are helpful in producing vaccines which protect from several diseases such as cholera, tuberculosis, small pox and hepatitis.
- Some bacteria and blue green algae are able to fix nitrogen from the atmosphere to enrich soil with nitrogen and increase its fertility.
- Microorganisms helps in cleaning the environment by decomposing dead organic waste of plants and animals to convert them into simple substances.
Answer number 8
Question number 9
What are antibiotics? What precautions must be taken while taking antibiotics?
Answer number 9
Antibiotics hill or stop the growth of the disease causing microorganisms.
IMPORTANT QUESTIONS ANS ANSWER
A. Very Short Answer Questions
Q1. What are microorganisms?
Answer: Microorganisms are tiny living organisms that cannot usually be seen with the naked eye. They can be observed with the help of a microscope.
Q2. Name the major groups of microorganisms.
Answer: The major groups of microorganisms are:
Bacteria
Fungi
Protozoa
Algae
Viruses
Q3. Name two useful microorganisms.
Answer: Lactobacillus and yeast are two useful microorganisms.
Q4. Which microorganism is used to make curd?
Answer: Lactobacillus bacteria are used to convert milk into curd.
Q5. What is fermentation?
Answer: Fermentation is the process in which microorganisms, such as yeast, convert sugar into alcohol or other substances.
Q6. What are antibiotics?
Answer: Antibiotics are medicines that kill or stop the growth of certain disease-causing bacteria. They should be taken only under appropriate medical guidance.
Q7. Name two diseases caused by viruses.
Answer: Polio and influenza are two diseases caused by viruses.
Q8. What are pathogens?
Answer: Microorganisms that cause diseases in humans, animals or plants are called pathogens.
Q9. What is food preservation?
Answer: Food preservation is the process of preventing or slowing down food spoilage so that food remains safe and usable for a longer time.
Q10. What is vaccination?
Answer: Vaccination is the process of giving a vaccine to help the body's immune system develop protection against a particular disease.
B. Short Answer Questions
Q11. How are microorganisms useful to us?
Answer: Microorganisms are useful in many ways:
Lactobacillus helps in making curd.
Yeast is used in baking bread and making alcoholic beverages.
Some microorganisms are used to produce antibiotics.
Decomposer microorganisms break down dead plants and animals.
Some bacteria and blue-green algae help in nitrogen fixation.
Q12. How are microorganisms harmful to us?
Answer: Microorganisms can be harmful in the following ways:
They cause diseases in humans, animals and plants.
They spoil food and make it unfit for consumption.
They cause diseases in crops, reducing agricultural production.
They may contaminate water and spread infections.
Q13. What are communicable diseases? Give two examples.
Answer: Diseases that can spread from an infected person to a healthy person through air, water, food, direct contact or other means are called communicable diseases.
Examples: Tuberculosis and influenza.
Q14. How do microorganisms spread from one person to another?
Answer: Disease-causing microorganisms can spread through:
Air, through droplets released when an infected person coughs or sneezes.
Contaminated food and water.
Direct contact with an infected person.
Infected animals and insect carriers, such as mosquitoes.
Q15. What is the role of yeast in baking bread?
Answer: Yeast breaks down sugar and releases carbon dioxide during fermentation. The gas forms bubbles in the dough, making it rise and giving the bread a soft, spongy texture.
Q16. Why should we not take antibiotics without medical advice?
Answer: Antibiotics should not be taken without medical advice because unnecessary or incorrect use can cause side effects and contribute to antibiotic resistance. Antibiotics work against bacteria, not viruses.
Q17. How does heating help in preserving food?
Answer: Heating kills many microorganisms that cause food spoilage. Proper heating and suitable storage conditions help keep food safe for a longer period.
Q18. What is pasteurisation?
Answer: Pasteurisation is a method of preserving milk by heating it to a suitable temperature for a specified time and then cooling it quickly. This process destroys many harmful microorganisms.
Q19. What is nitrogen fixation?
Answer: Nitrogen fixation is the process of converting atmospheric nitrogen into usable nitrogen compounds. Certain bacteria, such as Rhizobium, help fix nitrogen in the root nodules of leguminous plants.
Q20. Why is nitrogen important for living organisms?
Answer: Nitrogen is essential for making proteins and other important substances needed for growth and survival. Plants absorb nitrogen in the form of usable compounds from the soil.
C. Long Answer Questions
Q21. Explain the different methods of food preservation.
Answer: Food can be preserved using several methods:
Chemical preservatives: Substances such as sodium benzoate and sodium metabisulphite are used in certain foods to prevent spoilage.
Salting: Salt is used to preserve foods such as pickles and fish.
Sugaring: High concentrations of sugar help preserve jams and jellies.
Oil and vinegar: Oil and vinegar help prevent the growth of microorganisms in some pickles.
Heating and cooling: Pasteurisation, refrigeration and freezing help control microorganisms.
Proper storage: Airtight containers and dry storage help protect food from moisture and contamination.
Q22. Explain the importance of microorganisms in making curd, bread and alcohol.
Answer:
Curd: Lactobacillus bacteria convert milk sugar into lactic acid, which helps form curd.
Bread: Yeast produces carbon dioxide during fermentation, causing the dough to rise.
Alcohol: Yeast converts sugar into alcohol and carbon dioxide under suitable conditions.
Q23. How can we prevent the spread of communicable diseases?
Answer: Communicable diseases can be prevented by following these practices:
Wash hands regularly with soap and water.
Drink clean and safe water.
Eat properly cooked and hygienically prepared food.
Cover the mouth and nose while coughing or sneezing.
Keep surroundings clean and prevent mosquito breeding.
Take recommended vaccinations.
Avoid close contact with people when they are contagious.
Q24. Explain the role of microorganisms in the nitrogen cycle.
Answer: The nitrogen cycle is the continuous movement of nitrogen between the atmosphere, soil and living organisms.
Nitrogen fixation: Certain bacteria convert atmospheric nitrogen into usable nitrogen compounds.
Absorption by plants: Plants absorb nitrogen compounds from the soil and use them to make proteins.
Transfer to animals: Animals obtain nitrogen by eating plants or other animals.
Decomposition: Microorganisms break down dead organisms and waste, returning nitrogen compounds to the soil.
Return to the atmosphere: Certain bacteria convert nitrogen compounds back into atmospheric nitrogen.
Thus, microorganisms help maintain the balance of nitrogen in nature.
Q25. Differentiate between useful and harmful microorganisms.
Answer:
Useful microorganisms | Harmful microorganisms |
|---|---|
Help in making curd and bread. | Cause diseases in humans and animals. |
Produce certain antibiotics. | Spoil food and contaminate water. |
Decompose dead organisms. | Cause diseases in crops. |
Help in nitrogen fixation. | May reduce agricultural production. |
D. Fill in the Blanks
Microorganisms can usually be seen with the help of a microscope.
Lactobacillus helps in converting milk into curd.
Yeast is used in the production of bread.
Disease-causing microorganisms are called pathogens.
The process of converting atmospheric nitrogen into usable compounds is called nitrogen fixation.
Rhizobium bacteria are found in the root nodules of leguminous plants.
The process of preserving milk by heating and rapid cooling is called pasteurisation.
Salt and sugar are used in certain methods of food preservation.
E. True or False
All microorganisms are harmful to humans. — False
Yeast is used in baking bread. — True
Antibiotics can cure every viral disease. — False
Some bacteria help in nitrogen fixation. — True
Refrigeration can slow down the growth of many microorganisms. — True
Microorganisms help decompose dead plants and animals. — True
Food should be kept uncovered in dirty surroundings. — False
Vaccination helps protect against certain infectious diseases. — True
F. Important NCERT Exercise-Based Questions
Q26. What are the major groups of microorganisms?
Answer: The major groups are bacteria, fungi, protozoa, algae and viruses.
Q27. Write the names of two diseases caused by bacteria.
Answer: Cholera and typhoid.
Q28. Write the names of two diseases caused by protozoa.
Answer: Malaria and amoebic dysentery.
Q29. Name two diseases caused by microorganisms in plants.
Answer: Citrus canker and rust of wheat.
Q30. What is the difference between bacteria and viruses?
Answer: Bacteria are single-celled living organisms that can perform many life processes independently. Viruses are much smaller and can reproduce only inside the living cells of a host.
Q31. Why should we keep cooked food covered?
Answer: Cooked food should be kept covered to protect it from dust, insects and contamination by microorganisms.
Q32. Why are leguminous plants useful for maintaining soil fertility?
Answer: Leguminous plants have root nodules containing nitrogen-fixing bacteria such as Rhizobium. These bacteria help convert atmospheric nitrogen into usable nitrogen compounds, improving soil fertility.
Q33. What is the role of decomposers in the environment?
Answer: Decomposer microorganisms break down dead plants, animals and organic waste into simpler substances. This recycles nutrients and returns them to the environment.
Q34. Why does food spoil when left in warm and moist conditions?
Answer: Warm and moist conditions often encourage microorganisms to grow and multiply rapidly. They break down food substances, causing changes in smell, taste, colour and texture.
Q35. What precautions should be taken while storing food?
Answer:
Store food in clean, covered containers.
Refrigerate perishable food promptly.
Keep dry foods away from moisture.
Use clean utensils.
Check expiry dates and discard food that shows signs of spoilage.
Quick Revision: Important Terms
Term | Meaning |
|---|---|
Microorganisms | Tiny organisms usually seen with a microscope |
Pathogens | Disease-causing microorganisms |
Fermentation | A process in which microorganisms convert substances such as sugar into other products |
Antibiotics | Medicines used against certain bacterial infections |
Vaccination | Giving a vaccine to help develop protection against a disease |
Pasteurisation | Controlled heating and rapid cooling used to reduce harmful microorganisms in milk |
Nitrogen fixation | Conversion of atmospheric nitrogen into usable compounds |
Food preservation | Methods used to prevent or slow down food spoilage |
Crop Production And Management
Microorganisms - Friend And Foe
Synthetic Fibre And Plastic
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