Chapter 2 : Micro-organisms - PPT Class 8 Notes | EduRev

 Page 1


CHAPTER - 2 
 
MICROORGANISMS : FRIEND 
AND FOE 
Page 2


CHAPTER - 2 
 
MICROORGANISMS : FRIEND 
AND FOE 
1) Microorganisms (Microbes) :- 
 i)  Microorganisms are very small organisms which cannot be seen 
with the unaided eye. They can be seen only with a magnifying glass 
or microscope. 
ii) Microorganisms may be unicellular or multicellular. 
iii) Microorganisms may exist alone or in colonies. 
iv) Microorganisms are found in all kinds of environment like ice cold 
climate, hot springs, deserts, marshy lands etc. They are also found 
inside the bodies of other organisms. 
      
Page 3


CHAPTER - 2 
 
MICROORGANISMS : FRIEND 
AND FOE 
1) Microorganisms (Microbes) :- 
 i)  Microorganisms are very small organisms which cannot be seen 
with the unaided eye. They can be seen only with a magnifying glass 
or microscope. 
ii) Microorganisms may be unicellular or multicellular. 
iii) Microorganisms may exist alone or in colonies. 
iv) Microorganisms are found in all kinds of environment like ice cold 
climate, hot springs, deserts, marshy lands etc. They are also found 
inside the bodies of other organisms. 
      
2) Types of microorganisms :- 
   There are four main types of microorganisms. They are :- bacteria, 
fungi, algae and protozoans.  
   Viruses are also considered as microorganisms. They are different 
from other microorganisms because they reproduce only in the body of 
host organisms like bacteria, plants or animals. 
  Eg :-    Algae – Chlamydomonas, Spirogyra etc. 
              Fungi –  Bread mould, Penicillium, Aspergilles etc. 
              Protozoans – Amoeba, Paramaecium etc.  
 
Page 4


CHAPTER - 2 
 
MICROORGANISMS : FRIEND 
AND FOE 
1) Microorganisms (Microbes) :- 
 i)  Microorganisms are very small organisms which cannot be seen 
with the unaided eye. They can be seen only with a magnifying glass 
or microscope. 
ii) Microorganisms may be unicellular or multicellular. 
iii) Microorganisms may exist alone or in colonies. 
iv) Microorganisms are found in all kinds of environment like ice cold 
climate, hot springs, deserts, marshy lands etc. They are also found 
inside the bodies of other organisms. 
      
2) Types of microorganisms :- 
   There are four main types of microorganisms. They are :- bacteria, 
fungi, algae and protozoans.  
   Viruses are also considered as microorganisms. They are different 
from other microorganisms because they reproduce only in the body of 
host organisms like bacteria, plants or animals. 
  Eg :-    Algae – Chlamydomonas, Spirogyra etc. 
              Fungi –  Bread mould, Penicillium, Aspergilles etc. 
              Protozoans – Amoeba, Paramaecium etc.  
 
Virus 
Page 5


CHAPTER - 2 
 
MICROORGANISMS : FRIEND 
AND FOE 
1) Microorganisms (Microbes) :- 
 i)  Microorganisms are very small organisms which cannot be seen 
with the unaided eye. They can be seen only with a magnifying glass 
or microscope. 
ii) Microorganisms may be unicellular or multicellular. 
iii) Microorganisms may exist alone or in colonies. 
iv) Microorganisms are found in all kinds of environment like ice cold 
climate, hot springs, deserts, marshy lands etc. They are also found 
inside the bodies of other organisms. 
      
2) Types of microorganisms :- 
   There are four main types of microorganisms. They are :- bacteria, 
fungi, algae and protozoans.  
   Viruses are also considered as microorganisms. They are different 
from other microorganisms because they reproduce only in the body of 
host organisms like bacteria, plants or animals. 
  Eg :-    Algae – Chlamydomonas, Spirogyra etc. 
              Fungi –  Bread mould, Penicillium, Aspergilles etc. 
              Protozoans – Amoeba, Paramaecium etc.  
 
Virus 
3) Friendly microorganisms (Useful microorganisms) :- 
   i) Microrganisms  like bacteria decomposes organic waste into manure 
and increases the fertility of the soil.  
  ii) Microorganisms help in fixing atmospheric nitrogen into nitrogen 
compounds in the soil and increases the fertility of the soil. 
 iii) Microorganisms are used for making curd from milk, for making 
cheese, pickles, bread, cakes, pastries, alcohol, wine, vinegar (acetic 
acid) etc.  
iv) Microorganisms are used for making medicines. 
a) Making curd from milk :- The bacterium called Lactobacillus 
reproduces in milk and helps to convert milk into curd. 
b) Making bread :-  The fungus called yeast reproduces in flour dough 
and produces carbon dioxide during respiration which makes the dough 
soft and helps in making bread, cakes, biscuits, pastries etc. 
c) Making alcohol :- The fungus called yeast reproduces in sugar solution 
and converts it into alcohol. This process is called fermentation. 
d) Making medicines :-  Some bacteria and fungi are used to make 
medicines which kill or stops the growth of disease causing 
microrganisms. Such medicines are called antibiotics. Eg :- 
streptomycin, tetracycline, erythromycin etc. 
    Vaccines are dead or weakened microbes introduced into the body to 
produce antibodies. These antibodies protect the body from disease 
causing microbes. Diseases like polio, cholera, typhoid, small pox, 
hepatitis etc. can be prevented by taking vaccines.