Chapter 2 - Microorganisms: Friend and Foe

MICROORGANISMS

• Definition: living organisms around us which cannot be seen by naked eyes is called microorganism or microbes. We need a microscope to see microbes.

TYPES OF MICROORGANISMS:

There are five major groups of micro-organisms. These are classified as:

1. BACTERIA

2. ALGAE

3. PROTOZOA

4. FUNGI

5. VIRUSES

1.1) bacteria:

• Mostly single celled organism.
• Lived together in colonies of millions.
• Found in basically 3 different shapes:
  • Rod shaped(bacilli)
  • Spherical shaped (cocci).
  • Spiral (spirillia).

Rod shaped(bacilli)	Spherical shaped (cocci)	Spiral (spirillia)

2.2) algae:

• Simple plant like structure organism.
• Aquatic in nature.
• It can be unicellular or multicellular.
• Ex: chlamydomonas, seaweed, diatoms.

3.3) protozoa:

• Unicellular microorganism.
• Mostly aquatic in nature.
• Ex- amoeba, paramecium etc.

4.4) fungi:

• Plant like organism that do not contain chlorophyll
• Can be unicellular or multicellular. Ex- yeast, rizopus etc.

Bread Mould	Penicillium	Aspergillus

5.5) viruses:

• Smaller than any other known cell.
• It can reproduce only inside living bodies, means they need a host.
• It is a borderline between a living and non living thing.

FRIENDLY MICRO-ORGANISMS

USES

• Used in preparation of curd, bread and cake.
• Used in cleaning up of the environment by degrading dead and decay substances.
• Used in increasing soil fertility by fixing nitrogen.

MAKING OF CURD, CHEESE AND BREAD

Bacterium lactobacillus promotes the formation of curd. It multiplies in milk and converts it into curd.

Bacteria convert the natural sugars in milk into lactic acid. Different flavour of milk is due to different types of bacteria used.

Yeast : used in making cakes and bread. Bakers add yeast to dough to increase its volume by filling the gap by bubbles of carbon dioxide produced by yeast.

COMMERCIAL USE OF MICRO-ORGANISMS

• Used for large scale production of alcohol, wine and vinegar (acetic acid).
• Yeast is used for commercial production of alcohol and wine.
• Fermentation- the process of conversion of sugar into alcohol by yeast is known as fermentation.

MEDICINAL USE OF MICRO-ORGANISMS

Antibiotics : these are the medicines that are used to treat infections caused by other bacteria and certain parasites. Antibiotics are produced by the help of other bacteria.

Example: Tetracycline, streptomycin, penicillin, erythromycin etc.

INCREASING SOIL FERTILITY

• Bacteria and blue green algae are able to fix nitrogen from the atmosphere.
• Enrich the soil with nitrogen and increase its fertility.
• These microbes are called as biological nitrogen fixers.

CLEANING THE ENVIRONMENT

• Micro-organism converts dead and decaying part of plants and animals into manures.
• It decomposes organic waste into simple substance.
• It degrades the harmful substance and cleans up the environment.

HARMFUL MICROORGANISMS

Diseases- causing Microorganisms in Humans

FOOD POISONING

• It occurs due to contaminated food products.
• Microorganism that grows on food product sometimes produce toxic elements
• Serious illness or even death may cause due to food poisoning.

Some common human diseases caused by microorganisms

Diseases- causing Microorganisms in Animals

• Anthrax is a dangerous human and cattle disease caused by a bacterium.
• Foot and mouth disease of cattle is caused by a virus.

Diseases- causing Microorganisms in plants

• Disease in plants reduces the yield of crops.
• Example - citrus canker caused by bacteria, rusting of wheat by fungi attack, etc.

METHODS OF FOOD PRESERVATION

Let us study some common method of food preservation in our homes.

CHEMICAL METHOD

• Chemicals are used to protect the food from being spoilt are known as preservatives.
• We add salt or acid to pickles to prevent the attack of microbes.
• Sodium benzoate and sodium metabisulphate are common preservative.

PRESERVATION BY COMMON SALT

• Used to preserve meat and fish for ages.
• Meat and fish are covered to check the growth of bacteria.
• It is also used to preserve amla, raw mangoes, tamarind, etc.

PRESERVATION BY SUGAR

• Jams, jelly and squash are used to preserve by sugar.
• Sugar reduces the moisture content which inhibits the growth of bacteria.

PRESERVATION BY OIL AND VINEGAR

• Oil and vinegar create unfavourable conditions for the growth of microorganisms.
• It is used to preserve fish, fruit, pickles and meat.

HEAT AND COLD TREATMENT

• Both higher and lower temperature prevents the growth of microorganism.
• By boiling or by keeping the food in refrigerator kills the microbes.

NITROGEN FIXATION

In leguminous plant, RIBOZOBIUM helps in the fixation of atmospheric nitrogen. Sometimes nitrogen gets fixed through the action of lightning.

NITROGEN CYCLE

• Our atmosphere has 78% of nitrogen gas.
• Nitrogen constituents as part of proteins, chlorophyll, nucleic acids and vitamins.
• Amount of nitrogen in the atmosphere remain constant.

LET US SEE THE PROCESS BY WHICH THE NITROGEN IN ATMOSPHERE REMAINS CONSTANT.

Nitrogen already present in atmosphere => bacteria likeblue green algae fixes atmospheric nitrogen in the soil=> from the soil nitrogen is used by plants => animals get protein and nitrogen from plants by eating them => when animals and plants die bacteria and fungi decomposes them and converted into nitrogenous compounds => some bacteria convert this nitrogenous compound into nitrogen gas which ultimately goes back to atmosphere.