We know that the
microorganisms are livings
things, but, What are they?
Are they harmful or useful?
What do they produce? We
are going to know about the
world of the microorganisms.
Microorganisms are unicellular or
multicellar organisms, that are microscopic
(you can not see them with your naked eye).
Micro-organisms are classified into four major
Bacteria constitute a large domain or
kingdom of prokaryotic microorganisms.
Typically a few micrometres in length,
bacteria have a wide range of shapes,
ranging from spheres to rods and
spirals. Bacteria were among the first
life forms to appear on Earth, and are
present in most habitats on the planet.
A virus is a small infectious agent that can
replicate only inside the living cells of organisms.
Viruses infect all types of organisms, from animals
and plants to bacteria and archaea .
viruses are both living and non-living. viruses are
living inside the host and non-living outside the host
viruses cause diseases like polio,chickenp0x,and
Protozoa caused diseases like Dysentery and
Protozoa, a diverse group of unicellular
eukaryotic organisms, many of which are motile.
Originally, protozoa had been defined as unicellular
protists with animal-like behaviour, e.g., movement.
Protozoa were regarded as the partner group of
protists to protophyta, which have plant-like
behaviour, e.g., photosynthesis.
Fungi is a group of simple plants that
have no chlorophyll. There are some
species of fungi that are single celled
organisms, and there are other kinds
of fungi that are multi-cellular
Fungi caused diseases like
WHERE DO MICROORGANISMS
• Micro-organisms may be single-celled like Bacteria,
some Viruses and some Protozoa, or Multicellar, such
as Virus and Fungi.
• They can survive under all types of environment,
ranging from ice cold climate to hot springs and
deserts to marshy lands.
• Microorganisms like amoeba can live alone, while
fungi and bacteria may live in colonies.
HOW DO MICROORGANISMS
• In agriculture they are used to increase soil fertility by
• Milk is turned into curd by bacteria.
• Of these, the bacterium Lactobacillus promotes the
formation of curd. Bacteria are also involved in the
making of cheese, pickles and many other food items
• Microorganisms are used for the large scale
production of alcohol, wine and acetic acid
(vinegar. For this purpose yeast is grown on natural
sugars present in grains like barley, wheat, rice and
crushed fruit juices, etc.
• The process of conversion of sugar into alcohol is
known as fermentation.
• Microorganisms are used in the production
of antibiotic tablets, capsules or injections
such as of penicillin.
• Such medicines are called antibiotics. These
days a number of antibiotics are being
produced from bacteria and fungi.
Streptomycin, tetracycline and erythromycin
are some of the commonly known
• When a disease-carrying microbe
enters our body, the body produces
antibodies to fight the invader.
• Children are given injections to protect
themselves against several diseases.
• Polio drops given to children are
actually a vaccine.
• These days vaccines are made on a
large scale from microorganisms to
protect humans and other animals from
• 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 commonly called biological nitrogen fixers.
Microorganisms are harmful in many ways. Some of the
microorganisms cause diseases in human beings, plants and
animals. Such disease-causing microorganisms are called
Examples of such diseases include cholera, common cold,
chicken pox and tuberculosis.
There are some insects and animals which act as carriers of
Housefly is one such carrier.
Examples of carriers are: the female Anopheles
m o s q uito which carries the parasite of malaria;
Female A d e s m o s q uito a c ts a s c a rrie r of dengue virus.
kills many microorganisms in milk. Low
temperature inhibits the growth of microbes.
• The milk is heated to about 70 Degrees Celsius
for 15 to 30 seconds and then suddenly chilled
and stored. By doing so, it prevents the growth
of microbes. This process was discovered by
Louis Pasteur. It is called pasteurization.
ba c te ria is involved in
the fixation of nitrogen in
leguminous plants (pulses).
Rhiz o bium liv e s in the ro o t
no d ule s o f leguminous plants ,
such as beans and peas, with
which it has a symbiotic
• Rhiz o bium
• Sometimes nitrogen gets fixed
through the action of lightning.