MICRO ORGANISMS FRIEND AND FOE | SPEED NOTES | SCIENCE | CBSE | CLASS 8

Chapter – 2 Micro-organisms: Friend and Foe

Micro-organisms: Micro-organisms aretoo small andare not visible to the unaided eye. Theycan survive underall types ofenvironment, ranging fromice cold climate to hot springs and deserts to marshy lands. They are also found inside the bodies of animals including humans. Micro-organisms are foundin air, waterand in thebodies of plants and animals. Theymay be unicellular or multicellular. Micro-organisms are classified into four major groups. These groups are bacteria, fungi, protozoa and somealgae. Viruses are quitedifferent from othermicro-organisms. They reproduce only inside the hostorganism; bacterium, plantor animal cell. Based on thesignificance, micro-organisms canbe useful or harmful to us. Uses of microorganisms

Protozoan causeserious diseases likedysentery andmalaria. Some bacteria andblue green algaepresent in thesoil fix nitrogen from the atmosphere and convert intonitrogenous compounds. Certain bacteria convert compounds ofnitrogen present inthe soil intonitrogen gas which is released tothe atmosphere.

Pathogens: Some ofthe microorganisms cause diseases in humanbeings, plants and animals. Such disease causing microorganisms arecalled pathogens.

Cleaning of Environment: The microorganisms decompose dead organic waste of plants and animals converting them into simple substances. These substances are again used by other plants and animals. Microorganisms can be usedto degrade theharmful and smelly substances and thereby clean up theenvironment.