Class 8 Notes

SCIENCE MICROORGANISMS: FRIEND AND FOE

Microorganisms: Friend and Foe
Microorganisms
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Organisms too small to be seen with our naked eyes are called microorganisms or microbes.
They can only be seen using a microscope.
Microorganisms are found in a variety of habitats such as air, soil and water.
They can live and survive in extreme environments, from ice cold regions to hot springs, from deserts
to marshy lands.
 Some microorganisms are useful to us in many ways. They are called beneficial microbes. Example:
Bacterium Rhizobium helps in nitrogen fixation.
 Some microorganisms cause diseases in plants, animals and human beings. They are called
pathogens. Example: Anthrax bacillus causes anthrax in animals.
 Robert Hooke and Anton Van Leeuwenhoek discovered the existence of microbes during the period
1665 - 1683.

Major Groups of Microorganisms

GROUP
Algae

Fungi

Protozoa

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DESCRIPTION
 Found on walls, in fields and in small
puddles.
 May be unicellular or multicellular with a
size of 1 µ-1 m.
 Oscillatoria, Nostoc and Anabaena are
examples of this type of algae.
 Sexual reproduction occurs by
conjugation.
 Grows on stale bread, chapati, pickles,
damp clothes and shoes in monsoon.
 Respires aerobically or anaerobically.
 Lives a saprophytic or parasitic life.
 Mucor, Rhizopus and Aspergillus are
examples of fungi.

 Amoeba, Paramoecium and Plasmodium
are examples of protozoa.
 Amoeba has an irregular shape.
 Locomotion occurs through pseudopodia.
 Paramoecium is slipper shaped.
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SCIENCE MICROORGANISMS: FRIEND AND FOE
 It has numerous cilia for locomotion.
 Plasmodium is a protozoan living a
parasitic life. It is responsible for the
spread of malaria.

Bacteria

Virus

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 Found in any kind of environment from
deserts to Polar Regions.
 Range in size is from 0.2 to 10 µ.
 Reproduces sexually and asexually.
 Respires...