Lakhmir Singh Solutions For Class 8 Science Chapter 2 Microorganisms: Friends and Foe

How can a microorganism be a friend as well as a foe? The answer to this question is given in this chapter. Microorganisms play a vital role in maintaining ecological balance. They reside within and outside us. Some of them are visible to us and some are not. This chapter tells us how friendly these microorganisms are to us. Why are they important and some microorganisms are not vital is also mentioned in this lesson.

We get to know that the different cycles like the nitrogen cycle, oxygen cycle, and carbon cycle are mainly done by these microorganisms. We will also learn about the harmful effects of these microbes. How these microbes enter our body, how these cause disease and how they are communicable are also described in this chapter. In the end, we also learn that microbes are our friends as well as our enemies.

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Access Lakhmir Singh Science Class 8 Solutions For Chapter 2 Microorganisms: Friends and Foe

Very Short Answer Type Questions

1. Name the instrument (or device) which is needed to see the micro-organisms.

The instrument (or device) which is needed to see the micro-organisms is a microscope.

2. What is the name of micro-organisms which reproduce only inside the living cells of other organisms?

The micro-organisms which reproduce only inside the living cells of other organisms are viruses.

3. What are the major groups of microorganisms?

The five major groups of microorganisms are

  • Bacteria
  • Viruses
  • Protozoa
  • Fungi
  • Algae

4. Name any two human diseases caused by bacteria.

The two human diseases caused by bacteria are Cholera and typhoid.

5. Name any two human diseases caused by viruses.

The two human diseases caused by virus bacteria are Corona and influenza.

6. Name any two human diseases caused by protozoa.

The two human diseases caused by protozoa are dysentery and malaria.

7. Name any two human diseases caused by fungi.

The two human diseases caused by fungi are diseases athlete’s food and ringworm

8. Which micro-organism is utilized in making curd from milk?

Lactobacillus bacteria are utilized in making curd from milk.

9. Name the -micro-organism which is used for the large scale production of alcohol.

The -micro-organism which is used for the large scale production of alcohol is Yeast.

10. Name any two antibiotics.

Streptomycin and erythromycin are two commonly known antibiotics.

11. Name an antibiotic extracted from fungus (mould). Name the fungus.

An antibiotic Penicillin was extracted from fungus (mould) by Alexander Fleming in 1929. This antibiotic was made from the fungus called penicillium.

12. Name any four diseases which can be prevented by vaccination.

Four diseases which can be prevented by vaccination are Influenza, tuberculosis, Hepatitis B, Measles,

13. Name the scientist who discovered the-vaccine for ‘smallpox.

Edward Jenner discovered the vaccine for smallpox.

14. Name the scientist who discovered ‘penicillin’.

Alexander Fleming discovered the antibiotic Penicillin vaccine in 1929.

15. State an important function performed by blue-green algae.

The blue-green algae help in nitrogen fixation in soil and enrich the soil fertility.

16. Name one ‘biological nitrogen-fixer’.

Blue-green algae is the biological nitrogen fixer.

17. Name two common insects that act as carriers of disease-causing micro-organisms (or disease-causing microbes).

Housefly and mosquito are the two common insects that act as carriers of disease-causing micro-organisms (or disease-causing microbes).

18. Name any two diseases spread by housefly.

The two diseases spread by houseflies are cholera and typhoid.

19. Name the insect which is the carrier of a parasite of malaria.

The insect which is the carrier of a parasite of malaria is female anopheles mosquito.

20. Name the insect which carries the dengue virus.

21. Which of the two spreads dengue: mosquito or housefly?

Female Aedes mosquito spreads dengue.

22. Name two diseases spread by mosquitoes.

Malaria and dengue are the two diseases spread by mosquitoes.

23. Name the microbe which causes malaria disease.

The microbe which causes malaria disease is protozoa plasmodium.

24. Name one disease which spreads by breathing in air containing microorganisms.

Tuberculosis is the disease which spreads by breathing in air containing microorganisms.

25. Name one disease which spreads through insect bites.

The disease which spreads through insect bites is malaria.

26. Name one disease which spreads through infected food or water.

Cholera spreads through infected food or water.

27. Name the causative micro-organisms of the following animal diseases: (a) Foot and mouth disease (b) Anthrax

(a) Virus

(b) Bacteria

28. Name two food materials which are preserved by sun-drying method in our homes.

The two food materials which are preserved by sun-drying method in our homes are vegetable leaves like methi and spinach.

29. Name two food materials that are preserved by using common salt.

Fish and meat are preserved by using common salt.

30. Name two food materials which can be preserved by using sugar.

Food materials that can be preserved by using sugar are jellies and jam.

31. Name two food materials which are usually preserved by deep freezing.

Food materials that can be preserved by using deep freezing are fish and meat.

32. Name some of the preservatives which are used in the preservation of fruits as jams arid jellies.

Sodium benzoate and sodium meta bisulphate is used in the preservation of fruits as jams arid jellies.

33. Name some of the preservatives which are used in the preservation of fruits and vegetables as pickles.

Salt, oil and vinegar are used in the preservation of fruits and vegetables as pickles.

34. Name two food materials which can be preserved by using oil or vinegar.

The food materials which can be preserved by using oil or vinegar are meat and fish

35. Name any two special chemicals which are used as food preservatives.

Sodium benzoate and sodium meta bisulphate are two special chemicals which are used as food preservatives.

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

Blue-green algae is the microorganisms which can fix atmospheric nitrogen in the soil.

37. What type of plants can fix nitrogen gas of the air into compounds of nitrogen?

Leguminous plants can fix nitrogen gas of the air into compounds of nitrogen.

38. Name the microorganisms present in the soil and in the root nodules of leguminous plants which can fix atmospheric nitrogen.

Blue-green algae and Rhizobium bacteria ( nitrogen-fixing bacteria) is present in their root nodules can fix atmospheric nitrogen.

39. Name two leguminous plants that can fix nitrogen.

Leguminous plants like peas and beans can fix nitrogen gas of the air into compounds of nitrogen.

40. Fill in the following blanks with suitable words

(a) Alcohol is produced with the help of_________

(b)Blue-green algae fix _________directly from air to enhance fertility of soil.

(c) Micro-organisms can be seen with help of _________

(d) Cholera is caused by_________.

(e) Common salt has been used to preserve_________ and _________for ages.

(f) The food material which is preserved by pasteurization is _________

(g) As a result of the nitrogen cycle, the percentage of nitrogen in the atmosphere remains more or less_________

(a) Alcohol is produced with the help of Yeast.

(b)Blue-green algae fix nitrogen directly from the air to enhance fertility of soil.

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

(d) Cholera is caused by bacteria.

(e) Common salt has been used to preserve meat and fish ages.

(f) The food material which is preserved by pasteurization is milk.

(g) As a result of the nitrogen cycle, the percentage of nitrogen in the atmosphere remains more or less constant.


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