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NCERT Solutions for Class 8th Science


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Chapter 2. Microorganisms : Friend And Foe

Chapter Review




Chapter Review:

  • There are other living organisms around us which we cannot see with eyes alone. These are called microorganisms or microbes.
  • Microorganisms are classified into four major groups. These groups are bacteria, fungi, protozoa and some algae.
  • Viruses are quite different from other microorganisms. They reproduce only inside the host organism; bacterium, plant or animal cell.
  • Microorganisms are found in air, water and in the bodies of plants and animals.
  • They can live in all kinds of environment, ranging from ice cold climate to hot springs and deserts to marshy lands.
  • Some microorganisms are useful for commercial production of medicines and alcohol.
  • Some microorganisms decompose the organic waste and dead plants and animals into simple substances and clean up the environment.
  • There are some insects and animals which act as carriers of disease causing microbes. Like housefly.
  • Disease causing agents are called pathogens.
  • When a disease-carrying microbe enters our body, the body produces antibodies to fight the invader.
  • Several diseases, including cholera, tuberculosis, smallpox and hepatitis can be prevented by vaccination.
  • Process of conversion of sugar into alcohol is known as fermentation.
  • Medicines which kill or stop the growth of the disease-causing microorganisms. Such medicines are called antibiotics.
  • Microorganisms like amoeba can live alone, while fungi and bacteria may live in colonies.
  • Microorganisms are used to increase soil fertility by fixing nitrogen.
  • Lactobacillus bacteria are found in curd, which promotes the formation of curd.
  • Sugar is converted into alcohol by yeast. 


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