Micro-organism, Grade-8 Science, CDC based course

1. The System
of
classification

2. • What is classification of living organisms?
The system of grouping of living organisms
on the basis of the similarities and
dissimilarities is known as classification of
living organisms.
The branch of biology that deals with the
classification of living organisms is called
taxonomy.
A great Swedish biologist “Carolus Linnaeus”
is known as father of taxonomy.

3. In 1758 Carolus Linnaeus classified all living
organism into two kingdoms:-
1. Plantae
2. Animalia
He formulated a framework for the
classification under seven categories as;
Kingdom
Phylum(for animals)/ Division(for plants)
Class
Order
Family
Genus
Species

4. Some merits of two kingdom system of
classification are;
• It is the first systematic classification of
organisms.
• All living organisms can be categorized
into plant kingdoms and animal
kingdoms on the basis of characteristics
of the organisms.

5. Some demerits of two kingdom system of
classification are;
• The position of connecting animals, like euglena,
was uncertain as it has some feature similar to
those of plants and some features as those of
animals.
• Prokaryotes and eukaryotes are not separated.
• Unicellular and multicellular organisms are not
separated
• Green plants and non-green plants(fungi) are not
kept in separate groups.
• This system of classification does not include all
living organisms like Lichens

6. After 234 years of introduction of two-kingdom
classification, an American taxonomist, Robert H.
Whittaker, in 1969 gave a concept of five
kingdom system of classification to overcome the
demerits of two-kingdom system.
The kingdom of living beings of the Five-
Kingdom System of Classification are;
1. Monera (Prokaryotic like bacteria)
2. Protista (Unicellular like amoeba)
3. Fungi (non-green plants like mushroom,yeast)
4. Plantae
5. Animalia

7. The advantages of five-kingdom system of
classification are;
1. Prokaryotic and eukaryotic organisms are
placed under separate kingdom
2. Unicellular and multicellular organisms are
separated
3. Autotrophs and heterotrophs are also separated
4. This system of classification is based on the
evolution of organisms.
However, five kingdom system of classification
has not considered the position of virus.

8. The organisms which cannot be seen through our naked eyes are
known as microscopic organisms or micro-organisms. Most of
the micro-organisms are unicellular.

9. The study of micro-
organisms is
microbiology, whereas
the person who studies
microbiology is called
microbiologist.
Classification of micro-
organisms:
The micro-organisms
are further divided as;

10. Bacteria (Singular- Bacterium)
Bacteria are unicellular, microscopic prokaryotic
organism kept in ‘Kingdom-Monera’ in five-kingdom
system of classification.
They were discovered by Anton Van Leeuwenhoek in
1676 and term bacteria was coined by CG Ehrenberg in
1828.
The study of bacteria is called bacteriology.
Cynobacteria, Rhizobium, Salmonella, Azotobacter,
Psedudomonas etc. are some examples of bacteria.

12. Based on their structure bacteria are classified into four
types;
• Coccus or Spherical Bacteria
Examples: Staphylococcoi, Diplococci, Streptococci
• Bacillus or Rod-shaped Bacteria
Examples: Escheichia coli, Bacillus anthracis
• Spirillum or Spiral Bacteria
Examples: Leptospira, Spirillum
• Vibrio or Comma-shaped Bacteria
Examples: Vibrio cholera

13.  Bacterial cell “shapes” A=bacillus or pl. bacilli B= round, coccus, cocci
pl., in chains “Streptococcus) C. Staphylococcus – clusters D= diplococcus
E=Spirillum, spirilla pl. F= vibrio, more comma shaped

14.  Characteristics of Bacteria:
i. They have prokaryotic cell i.e. they lack well-
developed nucleus and many cell organelles
ii. They have a cell wall made up of peptydoglycan
iii. Many bacteria found single cell while some exist in a
group for eg: Neisseria form a pair, Streptococci
form a chain, Staphylococci group together to form
like a bunch of grapes.
iv. They show autotrophic as well as heterotrophic mode
of nutrition
v. Their size range from 0.5 µm to 5 µm, for eg. Size of
coccus is about 1.5µm, size of bacillus is about 1µm
vi. They reproduce asexually by fission

15.  Effects of bacteria;
Bacteria have both useful and harmful effects;
 Some harmful effects of bacteria;
i. Bacteria cause many harmful diseases to plants and
animals
ii. Saprophytic bacteria spoil milk, meat, vegetables,
cooked food etc.
iii. Certain denitrifying bacteria reduce the fertility of
soil
iv. Some bacteria releases toxin that cause food
poisoning.

16.  Some useful effects of bacteria;
i. Bacteria like Rhizobium, Nitrobacter, Nitrosomonas etc.
regulates nitrogen cycle and help to increase fertility of soil.
ii. Bacteria decompose organic matter and dead bodies of plants
and animals which helps to recycle materials
iii. Bacteria are also used in (Lactobacillus, Lactococcus) curding
of milk, (processing of coffee, production of vinegar,
(Streptococcus lactis) cheese making etc.
iv. Intestinal bacteria check the growth of harmful bacteria and
helps on digestion of cellulose
v. Many bacteria are used for making medicines; for example
Streptomuces are used to produce streptomycin, aureomycin
etc.

17. Some harmful bacteria and their effects
Name of Bacteria Diseases
1. Mycobacterium tuberculosis Tuberculosis
2. Salmonella typhi Typhoid
3. Vibrio cholera Cholera
4. Spirillum minus Rat-bite fever
5. Escherichia coli Diarrhoea

18.  Viruses (Latin ‘venom’ means poison):
Viruses are smallest entity(size: 25nm-250nm), which are
parasitic, acellular(i.e. no cell membranes and cell
organelles), ultra-microscopic, non-protoplasmic and
disease causing bodies.
The study of virus is called virology.
Note:
• In free-state, viruses are inactive. But they become
active and can reproduce inside the living cell of the
host, so they are called obligatory parasites.
• Viruses are placed on the boundary between the living
world and non-living world.

20. Types of viruses:
On the basis of host, viruses are of three types;
•Bacteriophages
•Plant viruses
•Animal viruses
On the basis of
genetic materials,
viruses are
classified as DNA
and RNA virus.

21. Some examples of viruses:
Viruses Plant virus Animal virus Bacteriophage
DNA virus Rice tungro
virus (RTV),
Cauliflower
mosaic virus
(CaMV)
Small pox
virus, Adeno
virus
Bacteriophage
virus, T4
phage, T2
phage
RNA virus TMV(Tobacco
Mosaic Virus),
Tobacco
necrosis virus
(TNV)
Polio virus,
Rhino virus,
Retro virus,
Rhabdo virus,

22.  Characteristic of viruses:
a. Living characteristics (i.e. inside living host cells)
i. They have hereditary materials i.e. DNA and
RNA
ii. They can divide and reproduce also transfers their
hereditary characters
iii. They infect living organism and cause various
disease.
For example: Rhinovirus cause common cold,
Retrovirus cause AIDS etc.
• Differentiate between bacteria and viruses.

23. b. Non-living characteristics (i.e. outside the living host)
i. They do not have any cellular structure
ii. They can be crystallized as non-living things
iii. They do not show respiration and metabolism
iv. They become inert and cannot reproduce outside
the living cell
Ebola
Bacteriophage

24.  Modes of transmission of viruses;
 By direct contact with the infected organism or the
materials used by the infected
 Through the medium of air, water and food
 By the means of insects mouthparts, legs of flies,
animal bite etc.
 By means of droplets during coughing, sneezing,
laughing, talking etc.
 From infected mother to the child

25. Fungi (Singular fungus) (yeasts):
In two kingdom system, fungi were kept in Kingdom
plantae whereas in five kingdom system, they are kept in
separate kingdom, Fungi or Mycota.
They get their food from dead and decaying organic
matter, so they are called saprophytes. (while some are
plants and animals).
The study of fungi is called mycology.
Some examples: Unicellular fungi; yeast, multicellular;
mucor, mould, mushroom, penicillium etc.

26. Fungi can be saprophytic, symbiotic or parasitic;

27.  Characteristics of fungi:
• They are non-green eukaryotes
which may contain more
than one nucleus
(mushroom: Agaricus bisporus).
• Fungi consists of small threads like structure
called hypae (collection mycelia)
• They may be unicellular (yeast) or multicellular
(mushroom)
• Mode of nutrition may be saprophytic, symbiotic
or parasitic.
• They have a cell wall made up of cellulose and
chitin.
• Asexual reproduction; budding, fragmentation,
sporulation

28.  Effects of fungi:
a. Harmful effects:
• Many skin diseases, allergies, infections are caused due to
fungal infection
• Many fungi attack food grains, vegetables, fruits, and dairy
products and spoil them.
• Fungi also spoil leather foods, clothes, photographic
materials, different electrical equipments etc.
b. Useful effects:
• Edible mushroom acts as food sources of nutrition
• Some fungi are used as the sources of medicine for
example Penicillin widely used antibiotics is derived from
Penicillium notatum.
• Saprophytic fungi act on dead bodies and decompose them
which help to increase the fertility of the soil
• Fungi like yeast are used in wine industries and bakeries

29. Amoeba: (Gr. amoibe = change)
In five-kingdom system Amoeba is placed in Phylum-Protists. It is a
unicellular microscopic organism which measure about 250-600µm in
diameter. Its all life processes is completed by a single cell.
Structure of Amoeba

30.  Characteristics of Amoeba
• They are microscopic, irregular and colorless organisms.
• The body is covered with a very thin, elastic and semi-
permeable layer called plasmalemma.
• They locomote by the formation of finger-like temporary
projections called pseudopodia.
• The mode of nutrition is holozoic (i.e. mechanism in
which the food is
engulfed in a solid
form).
• They breathe through
general body surface.
• Asexually
reproduction by
binary fission or
multiple fission.

31.  Effects of Amoeba on Human Beings:
There are different species of amoeba, where some are
found free-living in water, on land or as parasite in host.
• Entamoeba hystolytica are found in intestine of human
beings which causes Amoebiasis (dysentry).
• Entamoeba coli is a non-pathogenic species of amoeba
found in lumen of intestine which may cause digestive
complications.
• Naegleria fowleri are mostly free-living amoeba but on
entering human body it may also cause disease.
• Enatamoeba ginfivalis (non-pathogenic species) are found
in the mouth of nearly 70% of people, which help bacteria
to cause pyorrhoea by destroying the tissues of gums.

32.  Methods of food preservation:
Food preservation is a process or action of maintaining the food
items at its desired level of quality.
Some common traditional methods of food preservation are:
• By drying or dehydration
• By sugaring
• By salting
• By smoking
• By canning
• By organic acids
• By oiling
• By pasteurization
• By freezing