Microorganisms can be beneficial or harmful. They are classified into five major groups - bacteria, viruses, protozoa, algae, and fungi. Bacteria are single-celled prokaryotes that can be beneficial, parasitic or saprophytic. Viruses are not considered living but can only replicate inside host cells. Protozoa are single-celled organisms that can cause diseases. Fungi include multicellular and unicellular organisms that reproduce via spores. Microorganisms are used in food production, medicine development, pollution reduction and nitrogen fixation in plants. However, they can also cause diseases and food poisoning in humans, animals and plants.

1. MICROORGANISMS
FRIEND AND FOE

2. W H AT A R E
M I C R O O R G A N I S M S ?
A living organism that is very
minute to be seen by the naked
eye , especially a single celled
organism , such as a bacterium is
called a microorganism.
They are classified into five major
groups- bacteria, virus, protozoa,
algae and fungi.

3. CLASSIFICATION OF MICROORGANISMS
• BACTERIA - These are unicellular prokaryotic
microorganisms.
• VIRUS – These are also unicellular and are considered to
be on the borderline between living and non-living
entities.
• PROTOZOA - These are unicellular microorganisms.
• FUNGI – These can be both unicellular and multicellular.

4. BACTERIA
Bacteria are single celled and very small
organisms. They are prokaryotic microorganism
which means they do not have nucleus. They are
among the simplest forms of life known, and,
hence shows the characteristics of both plants and
animals. It was discovered in 1676 by Anton van
Leeuwenhoek. Some species of bacteria are
parasites which attack plants or animals. Some of
them are saprophytes which grow on dead remains
or products of plant and animal life.
Parasitic bacteria are responsible for someof the
diseases of plants and animals, whereas, the
saprophytic kinds may be beneficial in one way or
the other.
They are classified into 5 groups according to their
basic shapes: spherical (cocci), rod (bacilli), spiral
(spirilla), comma (vibrous) or corkscrew
(spirochaetes) .

5. VIRUSES
Viruses are microscopic infectious agents
that can only replicate only inside a host
cell. From a biological perspective, they
cannot be classified either as living nor
non-living. This is due to the fact that they
possess certain defining characteristic
feature of living and non-living entities.
They are inactive when they are present
outside the host cells but become active
within the host cells.
Viruses cause several infections and
reproduce within the host cells by using
the enzymes and raw materials.

6. PROTOZOA
They are single celled organisms. They come in many
different shapes and sizes ranging from amoeba which can
change its shape to Paramecium with its fixed shape and
complex structure. They live in a wide variety of moist
habitats including fresh water, marine environments and
the soil.
They cause diseases in both plants and animals. They are
motile and can move by
• Cilia – tiny hair like structures that cover the outside of
the microbe.
• Flagella – long thread like structures that extend from
the cell surface. The flagella move in a whip-like motion
that produces waves that propel the microbe around.
• Amoeboid movement- the organism moves by sending
out pseudopodia, which are also known as false feet as
in amoeba.

7. FUNGI
They are plant like organisms that do no contain
chlorophyll . They may be unicellular (yeast) or
multicellular ( bread mould) and are found in
warm and moist places. They can be
heterotrophic, saprophytic or parasitic in
nutrition.
 Almost all the fungi have a filamentous
structure except the yeast cells.
 They consist of long thread like structures
known as hypae.
 They reproduce by means of spores.
 Some are parasitic and can infect the host.
 Some of them are edible like mushroom and
yeast which is used in food industry,

8. ALGAE
Algae are simple plant-like organisma
which are usually aquatic in nature.
They contain a cell wall and chlorophyll
and can make their own food by
photosynthesis.
They can be unicellular or multicellular.
They lack a well-defined body, so,
structures like roots, stems or leaves are
absent.
They are found where there is adequate
moisture.
Algae are free living , although some
can form a symbiotic relationship with
other organisms like in lichens.
Some of them are spirogyra, diatoms
and duckweed.

9. USES OF MICROORGANISMS
• Lactobacillus a type of bacteria is used to form curd form milk.
• Rhizobium present in the roots of pulse plants fix nitrogen from air and supply
nitrogen compounds to the pulse (leguminous) plants.
• Micro-organism are also used in winemaking, baking, pickling and other food
making processes.
• Alcoholic fermentation by yeast is widely used in the preparation of wine and bread.
• Microbes are used to reduce pollution. For example: decomposers such as bacteria
and fungi break down dead bodies and excreta to form inorganic compounds which
can be absorbed by plants.
• Microbes also play an important role in the preparation of medicines. Antibiotics are
chemicals produced by micro-organisms to kill bacteria. Penicillin is an antibiotic
made from Penicillium.
• Bacteria present in our intestines helps in proper digestion and release Vitwamin B
which is absorbed by the intestines.
• Many vaccines are prepared from microorganisms. These are given to children to
protect them from diseases.
• Certain microbes are also used in the biological treatment of sewage and industrial
effluents.

10. HARMFUL EFFECTS OF MICROORGANISMS
• Microorganisms cause diseases in humans, animals as well as plants.
• Food poisoning is also caused by the microorganisms that spoils our food by
producing some toxic substances .
HUMAN
DISEASE
CAUSATIVE
ORGANISM
MODE OF
TRANSMISSON
GENERAL PREVENTIWVE MEASURES
1.Covid-19 virus Droplets generated
when an infected
person coughs,
sneezes or exhales
Stay home
Keep a safe distance
Wash hands often
Cover your cough
2. Measles
3. Chickenpox
4. Polio
5. Tuberculosis
Virus
Virus
Virus
Bacteria
Air
Air/contact
Air/water
Air
1. The patient should be kept in complete
isolation.
2. The personal belonging of the patient
should be kept away from others.
3. Vaccination should be done at a suitable
age.

11. HUMAN
DISEASES
CAUSATIV
E
ORGANIS
M
MODE OF
TRANSMISSION
PREVENTIVE MEASURES
6. Cholera
7. Typhoid
Bacteria
Bacteria
Water/food
water
1. Maintain personal
hygiene and good
sanitary habits.
2. Eat properly cooked
food.
3. Drink clean and boiled
water.
4. Vaccination should be
done
8. Hepatitis B Virus Water 1. Drink clean and boiled
water.
2. Vaccination
9. Malaria
10. Dengue
Protozoan
Virus
Mosquito
Mosquito
1. Do not allow to collect
surroundings.
2. Spray insecticides in
homes to kill
mosquitoes.

12. DISEASE CAUSING MICROORGANISMS IN ANIMALS AND
PLANTS
ANIMAL NAME NAME OF THE
DISEASE
CAUSATIVE
ORGANISM
1. CATTLE
2. CATTLE
3. POULTRY BIRDS
FOOT AND MOUTH
DISEASE
ANTHRAX
ASPERGILLOSIS
VIRUS
BACTERIA
FUNGUS
PLANT DISEASE
1. WHEAT
2. CITRUS TREES
3. BHINDI
RUST OF WHEAT
CITRUS CANKER
YELLOW VEIN MOSAIC
FUNGUS
BACTERIA
VIRUS

13. PRESERVATION OF FOOD
1. By Sun-drying
2. By heating
3. By cooling or refrigeration
4. By deep – freezing
5. By adding common salt
6. By adding sugar
7. By adding oil or vinegar
8. By using special chemicals as preservatives ( Sodium
benzoate and citric acid)
9. By Pasteurization (heating milk to about 70degrees
centigrade and cooling very quickly)
10. By Packing in Air-tight packets

14. NITROGEN CYCLE