Two-Kingdom classification : In 1735, a well-known scientist Linnaeus divided all the living beings into two classes, namely all plants under the kingdom ‘Plantae’ and all the animals under ‘Animalia’.
Three-kingdom classification : In 1866 Haeckel classified all living beings into three. Plants, Animals and third was Protista. Third was to give a place for primitive organisms of simple structure.
Five-kingdom classification : In 1969, R.H. Whittaker classified the living beings into five kingdoms namely
1. Monera, 2. Protista, 3. Fungi, 4. Plantae and 5. Animalia.
The earth is 4.6 billion years old and the great diversity of life is the result of this long period in evolution on earth. Many forms have become extinct which were 50-100 times more in number than the living forms.
More than 30 million species of living beings exist on the earth. About 1.7 million species have been given scientific names of which insects form the major part.
Aristotle was the first who in 4th century, made an attempt to classify the organisms into plants and animals.
Two kingdom classification was given by a well-known naturalist, Linnaeus in 1735. It was based on gross similarties and differences. He also gave a scientific way of naming the species known as Binomial Nomenclature.
Organisms groups like like Euglena, slime-moulds, fungi, lichens and bacteria could not be clearly classified into plants and animals by many taxonomists.
The areas of dispute were the classi-fication of putting together of prokaryotes and eukaryotes, non-photosynthetics and photosynthetics.
Viruses are so small that they are visible only through electron microscope. They are smaller than bacteria. No virus has either DNA or RNA as the hereditary material enclosed in a protein cover. The viral nucleic acid uses the host-cell metabolic apparatus to produce its own kind and ultimately the host cell bursts. Viruses form a special group as they replicate when present in a living cell. Viruses can be stored for several years in a bottle just like non-living objects.
The five kingdom classification is based on complexity of cell structure, nutritional way, and complexity of the body of the organism.
Summary of five Kingdom Classification
Kingdom Important Features
(i) Monera This kingdom is Unicellular, Prokaryo-tes Autotrophic and Heterotrophic nutrition important decomposers and mineralisers.
Important examples of this class are Bacteria, Blue-green algae.
(ii) Protista This is the second kingdom which is Unicellular, Eukaryotes
Autotrophic and Heterotrophic nutrition Producers, consumers and decomposers. The examples of this class are Phytoplankton, Zoo-plankton, Protozoans.
(iii) Plantae This kingdom is Multicellular. Cells have cellulose wall and contain chlorophyll. Mainly autotrophic nutrition. Major Producers on land. Examples of this class are Red, brown green algae, Mosses, Ferns, Seed plants.
(iv) Fungi This kingdom is both Unicellular or Multi-cellular. Body made of filaments, mainly sapro-phytic nutrition, major decomposers. The examples of this class are Yeast (unicellular) Moulds, Mushrooms.
(v) Animalia The organisms of Animalia kingdom are Multicellular, cells without cells walls or chloroplast. Hetero-trophic nutrition. Basic consumers on earth. The examples of this class are Sponges, Invertebrates and Vertebrates.
Viruses
These are simple acellular, sub-microscopic organisms consisting of one or more molecules of either DNA or RNA enclosed in a coat of protein. They can reproduce in other organisms.
Virology is the branch which deals with the study of viruses.
Important discoveries made in the history of virology:
Scientist Discovery
Edward Jenner Small pox Vaccine
Iwanowski Causal agents of tobacco mosaic disease are filterable.
Beijerinck Contagium virum fluidum causes Tobacco Mosaic disease
F.d’ Herelle & Bacteriophages
F.W. Twort
W.M. Stanley TMV
crystallization
N.W. Pierie & Nucleoprotein
F.C. Bawden nature of viruses
R.C. Gallow & Human Immuno
L.Montagnier Virus (HIV) (AIDS virus)
Types of Viruses
Plant viruses : Plant viruses attack mainly plants and cause diseases.
Animal viruses : These viruses attack the various types of animals and produce diseases in them.
Bacteriophages : The viruses that infect the bacteria are called bacteriophages.
Mycophages : Fungi are made diseased by these viruses.
Zymophages : Zymophages attack yeast cells and make them diseased.
Cyanophages : Blue green algae is attached by these viruses.
Structure of Viruses
Size : Viruses range in size from about 10 to 300 nm in diameter. These are called virious. They are rod shaped, rectangular, polyhedral, spheriodal, bullet shaped etc. Examples of each are given below—
Shape
Rod shaped Tobacco mosaic virus
Rectangular Vaccinia virus
Polyhedral Adenovirus
Spheroidal Polio virus
Tadpole shaped Bacteriophages
Bullet shaped Rhabdovirus
Plant diseases caused by Viruses
Chlorosis : In this disease, entire leaf becomes white or yellow due to the loss of chlorophyll. Rice leaves become yellow in this disease.
Mosaic : Tobacco Mosaic disease is caused by viruses. In this disease colour change occurs in isolated patches in the green lamina.
Vein clearing : In this disease the tissues of the veins turn yellow, while the remaining areas remain green. e.g: Bhendi vein clearing.
Vein banding : Veinbending is the condition in which the tissues close to the vein remain green and the remaining areas of the lamina undergo chlorosis. e.g: Citrus vien banding.
Ring spots : In this disease chlorophyll is lost and circular rings or spots are formed.
Dwarfing or Stunting : In this disease plant growth is reduced making the plant dwarf e.g. Rice stunting
Malformation : In this the growth of the plant is not normal e.g: Swollen shoot of Coco.
Breaking of flowers : In this disease there is a loss of colour in petals at certain parts and formation of dark colours at other parts takes place e.g: Tulip mosaic break.
Animal Diseases caused by Viruses
Viral disease caused to humans and aminals are
Diseases Symptoms
Chicken pox External lesions, body-ache and fever.
Encephalitis High fever, body-ache and headache
Hepatitis Liver does not work properly and jaundice. It is a very dangerous disease.
Influenza Chill, fever and generalised ache of the limbs.
Polio Paralysis of the limbs and fever. Movement becomes almost impossible.
Rabies Hydrophobia, diffi-culty in swallowing and increased muscle tone leading to spasmodic contrac tion. It is mainly caused by dog bite.
Small pox External and internal lesions filled with watery substance.
Common cold Fever and
and related nasopharyngeal
diseases secretions.
Gastro- Fever, occasional rash
intestinal and digestive
diseases disorders.
AIDS Destruction of immune system.
Control of Viral Diseases
1. Isolation and exclusion of source of infection.
2. Immunization
3. Eradication of vector
4. Chemotheraphy
5. Breeding of disease resistant varieties.
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