Classification of Living World
From the Previous chapter we know that the planet
earth is endowed with living and non -living things. In our daily life we see
several things in and around us. Imagine you are on a trip to Hill station. You
are enjoying the beauty of mountains, dazzling colour of the flowers, and
melodious sound of the birds. You may be capturing most of the things you come
across in the form of photography. Now, from this experience can you mention
the objects you came across? Can you record your observations and tabulate
them. How will you organize the things? Will you place mountain and flowers
together or tall trees and trailing herbs in one category or place it in
different category? If you place it in different category, what made you to
place them in different category? So classification is essential and could be
done only by understanding and comparing the things based on some characters.
In this chapter we shall learn about classification of living world.
Many attempts have made in the past to classify the
organisms on earth.
Theophrastus, “Father
of botany” used the morphological
characters to classify plants into trees, shrubs and herbs. Aristotle
classified animal into two groups. i.e., Enaima
(with red blood) and Anaima (without
red blood). Carl Linnaeus classified living world into two groups namely Plants
and Animals based on morphological characters. His classification faced major
setback because prokaryotes and Eukaryotes were grouped together. Similarly
fungi, heterotrophic organisms were placed along with the photosynthetic
plants. In course of time, the development of tools compelled taxonomists to
look for different areas like cytology, anatomy, embryology, molecular biology,
phylogeny etc., for classifying organisms on earth. Thus, new dimensions to
classifications were put forth from time to time.
Classification is essential to achieve following
needs
•
To relate things based on common characteristic
features.
•
To define organisms based on the salient features.
•
Helps in knowing the relationship amongst different
groups of organ-isms.
•
It helps in understanding the evolu-tionary
relationship between organ-isms.
A comparison of classification proposed for
classification of living world is given in Table 1.4.
R.H.Whittaker, an American taxonomist proposed five
Kingdom classification in the year 1969. The Kingdoms include Monera, Protista, Fungi, Plantae and
Animalia (Figure 1.7). The criteria adopted
for the classification include cell structure, thallus organization, mode of
nutrition, reproduction and phylogenetic relationship. A comparative account of the salient features of each Kingdom is
given in Table 1.5
•
The classification is based on the complexity of
cell structure and organization of thallus.
•
It is based on the mode of nutrition
•
Separation of fungi from plants
•
It shows the phylogeny of the organisms
The Kingdom Monera and protista accommodate both
autotrophic and heterotrophic organisms, cell wall lacking and cell wall
bearing organisms thus making these two groups more heterogeneous.
•
Viruses were not included in the system.
Carl Woese and co-workers in the year 1990 introduced three domains of life viz., Bacteria, Archaea and Eukarya based on the difference in rRNA nucleotide sequence, lipid structure of the cell membrane. A revised six Kingdom classification for living world was proposed by Thomas Cavalier-Smith in the year 1998 and the Kingdom Monera is divided in to Archaebacteria and Eubacteria. Recently Ruggerio et al., 2015 published a seven Kingdom classification which is a practical extension of Thomas Cavalier’s six Kingdom scheme. According to this classification there are two SuperKingdoms (Prokaryota and Eukaryota) Prokaryota include two Kingdoms namely Archaebacteria and Eubacteria.
Eukaryota include the Protozoa,
chromista, fungi, Plantae and Animalia.
A new Kingdom, the Chromista was
erected and it included all algae
whose chloroplasts contain chlorophyll a and c, as well as various colorless
forms that are closely related to them. Diatoms, Brown algae, cryptomonads and
Oomycetes were placed under this Kingdom.
Visit to a pond and record the names of the biotic
components of it with the help of your teacher. Tabulate the data and segregate
them according to Five Kingdom classification
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