CHAPTER - 2 MICROORGANISMS : FRIEND AND FOE

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CHAPTER - 2MICROORGANISMS FRIEND AND FOE
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Microorganisms (Microbes) -

• Very small organisms which cannot be seen with
  the naked eye.
• may be unicellular or multicellular
• may exist alone like amoeba or in colonies like
  Fungi Bacteria
• found in all kinds of environment like ice cold
  climate, hot springs, deserts, marshy lands etc.
  They are also found inside the bodies of other
  organisms.

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Types of microorganisms -

• Bacteria
• Fungi Bread mould, Penicillium,
• Algae Chlamydomonas, Spirogyra
• Protozoan Amoeba, Paramaecium

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Virus
They are different from other microorganisms as
they reproduce only in the body of host organisms
like bacteria, plants or animals.
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Friendly microorganisms

• a) Making curd from milk - The bacterium called
  Lactobacillus reproduces in milk and helps to
  convert milk into curd.
• b) Making bread - The fungus called yeast
  reproduces in flour dough and produces carbon
  dioxide during respiration which makes the dough
  soft and helps in making bread, cakes, biscuits,
  pastries etc.
• c) Making alcohol - Yeast is used for commercial
  production of alcohol wine.
• The fungus called yeast reproduces in sugar
  solution and converts it into alcohol. This
  process is called fermentation.
• Louis Pasteur discovered fermentation in 1857.
• d) Making medicines - Some bacteria and fungi
  are used to make medicines which kill or stops
  the growth of disease causing microrganisms. Such
  medicines are called antibiotics.
• Eg - streptomycin, tetracycline, erythromycin
  etc.

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Increasing Soil Fertility

• Some Bacteria and Blue Green Algae are able to
  fix nitrogen from the atmosphere to enrich soil
  with nitrogen and increase its fertility.
• These microbes are called Biological Nitrogen
  Fixers.

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Cleaning the Environment

• Micro organisms decompose dead organic
• waste of plants and animals and convert them
• into simple substances which are again used by
• other plants and animals.

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Harmful microorganisms

• i) Some micro organisms cause diseases in plants
  and animals. Such disease causing microorganisms
  are called pathogens.
• ii) Some micro organisms grow in food substances
  and produce toxic substances and makes the food
  poisonous. Food poisoning causes illness and even
  death.
• iii) Some microorganisms spoil materials like
  clothing, leather, wood etc.

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Pathogens

• Disease causing microorganisms.
• Enter our body through air, water, food, contact
  or insects.
• Diseases which can spread from an infected person
  to a healthy person are called communicable
  diseases.
• Eg - cholera, common cold, chicken pox,
  tuberculosis etc.
• Some insects and animals act as carriers of
  disease causing microbes.
• Eg - House fly, Female anopheles mosquito
  (malaria), Female aedes mosquito (dengue fever)
  etc.

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Female anopheles mosquito
Aedes mosquito
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6) Disease causing microorganisms in plants -

• Microorganisms cause diseases in plants like
  rice, wheat, potato, sugarcane, apple, orange
  etc. These diseases reduce crop yield. They can
  be controlled by using chemicals which kill the
  microbes.

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Some common human diseases caused by
microorganisms-

• Human disease
  Causative Mode of
• 
  microorganism transmission
• Chicken pox
  Virus Air / Contact
• Polio
  Virus Air /
  Water
• Measles
  Virus Air
• Hepatitis B
  Virus Water
• Tuberculosis
  Bacteria Air
• Typhoid
  Bacteria Water
• Cholera
  Bacteria Water / Food
• Malaria
  Protozoa Mosquito
• Some common plant diseases caused by
  microorganisms -
• Plant disease
  Causative Mode of
  
• 
  microorganism transmission
• Citrus canker
  Bacteria Air
• Rust of wheat
  Fungi Air / Seed
• Yellow mosaic of
• Okra (Ladys finger) Virus
  Water

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Some common plant diseases caused by
microorganisms
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Food Poisoning

• Could be due to consumption of food spoilt by
  micro organisms
• So it is important to preserve food.

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Food preservation

• Chemical method
• Pickles can be preserved by using chemicals like
  salts and edible oils.
• Jams and squashes can be preserved by using
  sodium benzoate, sodium meta bisulphate
• These chemicals are called preservatives.

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Salting

• Food items like fish, meat, amla, raw mangoes,
  tamarind etc can be preserved by using common
  salt.
• It prevents the growth of microbes

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By using sugar

• Food items like jams, jellies, squashes etc. can
  be preserved by using sugar solution.
• It reduces the moisture content which inhibits
  the growth of bacteria.

By using Oil Vinegar

• Prevents spoilage of pickles because bacteria
  cannot live in such an environment.
• Vegetable, Fruit, Fish and meat are often
  preserved by this method.

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heat and cold treatments

• Heating food items kills microbes.
• Storing food items at low temperatures prevents
  growth of microbes.

storage and packing

• Many food items are stored in air tight
  containers to protect them from microbes.

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Pasteurisation

• The process of heating milk to about 70oC for 15
  to 30 seconds and then suddenly chilling it to
  prevent the growth of microbes
• This process was discovered by Louis Pasteur.

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• Pasteurisation - The process of heating milk
  to about 70oC for 15 to 30 seconds and then
  suddenly chilling it to prevent the growth of
  microbes is called pasteurisation. This process
  was discovered by Louis Pasteur.
• vi) By storage and packing - Many food items
  are stored in air tight containers to protect
  them from microbes.

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8) Nitrogen cycle -
ATMOSPHERIC NITROGEN
LIGHTNING FIXES NITROGEN
BACTERIA TURN COMPOUNDS OF NITROGEN INTO
GASEOUS NITROGEN
NITROGEN FIXING BACTERIA AND BLUE GREEN ALGAE
FIX ATMOSPHERIC NITROGEN
UPTAKE BY PLANTS
ANIMAL EATS PLANTS
NITROGENOUS WASTE FROM EXCRETION AND DEATH
COMPOUNDS OF NITROGEN IN THE SOIL
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Nitrogen cycle -

• The nitrogen in the atmosphere is converted
  into nitrogen compounds in the soil by nitrogen
  fixing bacteria and blue green algae. Lightning
  also converted into nitrogen compounds in the
  soil. The nitrogen compounds in the soil is used
  by plants for the synthesis of proteins and other
  compounds. Animals feeding on plants get these
  proteins and other compounds. When plants and
  animals die, bacteria and fungi in the soil
  converts the nitrogenous waste into nitrogen
  compounds in the soil which are again use by
  plants. Some other bacteria converts some
  nitrogen compounds in the soil into nitrogen gas
  which goes back into the atmosphere. Hence the
  nitrogen in the atmosphere almost remains
  constant.