2-Microorganisms : Friend and Foe | Science | NCERT | Class 8

Hello students, in this blog you can find important summary notes from the Chapter 2, Science , NCERT Book of Class 8. These notes can be used for preparation of various school Competitive Exams, Olympiads and also developing Fundamentals.

1. Living organisms around us which we normally cannot see, are called microorganisms or microbes

2. Microorganisms are classified into four major groups.
fungi (Bread mould, Pericillium, Aspergillus)
protozoa (Amoeba, Paramecium)
algae (Chlamydomonas, Spirogyra)

3. Common ailments caused by viruses : cold, influenza (flu) and most coughs

4. Serious diseases caused by viruses : polio and chicken pox.

5. Protozoa causes: dysentery and malaria

6. Bacterial diseases: typhoid and tuberculosis (TB)

7. Friendly microorganisms : used for various purposes like making of curd, bread, cake & also alcohol.

8. Bacteria also act in fixing Nitrogen in soil

9. Microorganisms may be :
single-celled, like bacteria, some algae and protozoa
multicellular, such as many algae and fungi

10. For making curd we used the bacterium called : Lactobacillus

11. Yeast reproduces rapidly and produces CO2 during respiration

12. Commercial use of microorganisms are production of:
– alcohol
– wine
– acetic acid (vinegar)

13. The process of conversion of sugar into alcohol is known as fermentation

14. Louis Pasteur discovered fermentation in 1857.

15. Antibiotics are produced from bacteria and fungi

16. Antibiotics play an important role to kill or stop the growth of disease-causing microorganisms

17. Common antibiotics produced from fungi and bacteria are: – streptomycin
– tetracycline
– erythromycin

18. Antibiotics are also used to :
– check microbial infections in animals
– control plant diseases

19. When a disease-carrying microbe enters our body, the body produces antibodies to fight the invader.

20. Several diseases can be prevented by vaccination including cholera, tuberculosis, smallpox and hepatitis.

21. Penicillin was discovered by Alexander Fleming in 1929

22. Vaccine for small-pox was discovered by Edward Jenner in 1798.

23. Some bacteria are able to fix nitrogen from the atmosphere to enrich soil with nitrogen and increase its fertility, these microbes are commonly called biological nitrogen fixers.

24. Microorganisms decompose dead organic waste of plants and animals converting them into simple substances

25. Some microorganisms cause diseases in human beings, plants and animals and are called as pathogens

26. Microbial diseases that can spread from an infected person to a healthy person through air, water, food or physical contact are called communicable diseases
• Examples of communicable diseases include cholera, common cold, chicken pox and tuberculosis

27. There are some insects and animals which act as carriers of disease-causing microbes. Housefly is one such carrier.

28. Female Anopheles mosquito, acts as a carrier of the parasite of malaria (Plasmodium).

29. Female Aedes mosquito acts as carrier of dengue virus.

30. Robert Köch (1876) discovered the bacterium (Bacillus anthracis) which causes anthrax disease.

31. Anthrax is a dangerous human and cattle disease caused by a bacterium

32. Foot and mouth disease of cattle is caused by a virus.

33. Food poisoning could be due to the consumption of food spoilt by some microorganisms.

34. Salts and edible oils are the common chemicals generally used to check the growth of microorganisms, hence they are called preservatives.

35. Sodium benzoate and sodium metabisulphite are common preservatives.

36. Salting is also used to preserve amla, raw mangoes, tamarind, etc.

37. Sugar is used to preserve jams, jellies and squashes.

38. Oil and vinegar are used in preservation of vegetables, fruits, fish and meat

39. Pasteurisation is a process in which the milk is heated to about 70◦C for 15 to 30 seconds and then suddenly chilled and stored

40. Pasteurisation was discovered by Louis Pasteur.

41. The bacterium Rhizobium is involved in the fixation of nitrogen in leguminous plants (pulses)

42. There is a symbiotic relationship between Rhizobium and leguminous plants, such as beans and peas

43. Our atmosphere has 78% nitrogen gas

44. Nitrogen is one of the essential constituents of all living organisms as part of proteins, chlorophyll, nucleic acids and vitamins.

45. The atmospheric nitrogen cannot be taken directly by plants and animals

46. Certain bacteria and blue green algae present in the soil fix nitrogen from the atmosphere and convert it into compounds of nitrogen

47. Nitrogen is used for the synthesis of plant proteins and other compounds



Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

This site uses Akismet to reduce spam. Learn how your comment data is processed.