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SAI International School

                                             Subject- Biology, Class-VIII
                                      Topic- Microorganisms: Friend and Foe
                                       Subtopic- Friendly Microorganisms 2
                                                     Lesson Notes


               Vaccines – Protection against Diseases

                   •  Vaccines are weak or dead microbes introduced into the body.
                   •  They stimulate the immune system to produce antibodies.
                   •  Antibodies protect us from future infections by the same microbe.
                   •  Common vaccines:
                          ❖  BCG (for tuberculosis),
                          ❖  DPT (for diphtheria, pertussis, tetanus),
                          ❖  Polio, Hepatitis
                   •  Edward Jenner discovered the first vaccine (for smallpox).




               Increasing Soil Fertility – Role of Nitrogen-fixing Bacteria


                   •  Certain bacteria and blue-green algae improve soil fertility.
                   •  Example: Rhizobium lives in root nodules of leguminous plants (peas, beans).
                   •  Rhizobium fixes nitrogen from the air into a form plants can absorb.
                   •  This natural nitrogen enrichment reduces the need for chemical fertilizers.
                   •  Cyanobacteria (blue-green algae) also fix nitrogen in waterlogged fields (like paddy
                       fields).


               Keeping the Environment Clean – Role of Decomposers

                   •  Microorganisms like bacteria and fungi help in decomposing dead plants and
                       animals.
                   •  This process is called decomposition.
                   •  It recycles nutrients back into the soil, supporting plant growth.
                   •  Decomposers help in cleaning up organic waste, making the environment healthy.
                   •  They also help in composting organic kitchen and garden waste.
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