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SAI International School
                                            Subject- Biology, Class-VIII
                                    Topic- Microorganisms: Friend and Foe
                     Subtopic- Friendly Microorganisms II - Cleaning Environment
                                                       Module-13

                                                     Lesson Notes

               Vaccine:  A  vaccine  is  a  biological  preparation  that  contains  dead  or  weakened
               microorganisms. It improves immunity of our body against a particular disease.


               When  the  disease-causing  microorganisms  enter  our  body,  our  immune  system
               produces  some  special  proteins  called  antibodies  to  fight  against  them.  Our  immune
               system remembers how to fight against, if similar type of microbe enters again.

               When vaccine is introduced into our body, our immune system produces antibodies and
               alsoremembers  it.  Thus,  it  protects  our  body  from  similar  type  of  microorganisms  in
               future.

               Edward Jenner discovered the vaccine for small pox in 1798.

               Vaccination prevents the diseases against which the vaccines are given. Vaccines are
               available for several diseases like -

                     Polio (Oral polio vaccine)

                     Tuberculosis (Bacillus Calmette Guerin)
                     Small pox
                     Cholera
                     Hepatitis

               In pulse polio programme, polio drops are given as the vaccine of polio. Small pox has
               been eradicated across the globe by mass campaign and vaccination.

               Increasing  soil  fertility:  Bluegreen  algae,  the  free-living  bacteria  found  in  soil,  fixes
               atmospheric nitrogen and enriches soil with nitrogen.

               Rhizobium  is  symbiotic  bacteria  found  in  root  nodules  of  leguminous  plants.  It  fixes
               atmospheric nitrogen and enriches soil with nitrogen.


               In this way, these biological nitrogen fixers improve fertility of soil.

               Cleaning  the  environment:Microorganisms  play  important  role  in  decomposing
               complex organic substances into simpler forms and those are again used by plants as
               nutrients. Microorganisms can be used to degrade harmful and smelly substances. So,
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