Microorganisms Friend and Foe Notes || Class 8 Chapter 2 Science ||





Chapter – 2, Science
MICROORGANISMS: FRIEND AND FOE
1.      Microorganisms/microbes are very small which cannot be seen with the help of eyes.
2.      We use microscope or magnifying glass to see them.
3.      E.g. fungus that grows on bread
                  

Classification of Microorganisms
1.      It is classified into four major groups
2.      Bacteria, fungi, protozoa and algae
3.      Viruses are other kind of microorganisms.
4.      They are explained below –
Bacteria
1.      Bacteria are very small, single celled micro-organisms which have cell walls but do not have an organised nucleus & other structure
2.      These are found everywhere like in air, soil, water, every surface around us, on our bodies or inside our body.
3.      Two common examples are Lactobacillus & Rhizobium 
4.      Some are useful & help in making foods (like curd (दही)) & some can cause disease like cholera (हैजा), typhoid (मियादी बुखार), tuberculosis (TB) & food Poisoning (पेट दर्द).
      

Protozoa
1.      It is a single celled micro-organism.
2.      It is mainly found in ponds (तालाब), lakes, dirty water drains & rivers.
3.      Some common examples of protozoa are Amoeba, paramecium, Plasmodium.
4.      Disease produced by protozoa like dysentery (पेचिश  or दस्त) & malaria.
                         

Algae
1.      It is a large group of simple, plant like organisms.
2.      They contain chlorophyll & produce food by photosynthesis just like plants.
3.      Some of the examples are blue-green algae, diatoms & seaweeds (समुद्री शैवाल).
4.      Some are unicellular & most of the algae are multicellular.
         


Fungi
1.      Fungi are a large group of organisms which do not have chlorophyll & photosynthesis.
2.      Some examples are Yeast, Moulds (such as bread mould, penicillium), Mushrooms etc.
3.      Some fungi look like plants but they cannot make their own food like the plants.
4.      They food on dead things like remains of dead plants & animals
5.      Fungi need moist & warm conditions to grow.

Viruses
1.      Viruses are the smallest micro-organisms which can develop only inside the cells of the host organisms (may be animals, plants)
2.      Viruses can reproduce & multiply only inside the cells of other organisms (such as animal cell, plant cell or organisms cell)
3.      Thus, as long as viruses are outside the living cells, they behave as non-living things.
4.      Diseases produced by them are common cold, influenza (ज़ुकाम) (flu), measles (खसरा), polio, chickenpox & smallpox etc
                                    

Where do Microorganisms Live?
1.      Microorganisms may be single-celled like 
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