English
Sindh Text Book Board,
Jamshoro.
SECTION 3
BIODIVERSITY
Around two million types of organisms exist on the earth today; much more have
gone extinct, many more are yet to be discovered. To study such a diversified
group it is customary to classify it into groups. Two hundred years ago biologists
divided all the organisms, into two kingdoms, as either plants or animals. But
closer examination with better techniques necessitated three more kingdoms.
Chapter 3
CLASSIFICATION OF LIVING ORGANISMS
It is a human instinct to organize various objects into sets. Likewise biologists,
rather than dealing with millions of different organisms, classify them into major
groups. The science of classifying living organisms is taxonomy. A classification
system is based on shared characteristics. General characteristics allow for large
grouping of very diverse organisms. More specific characters result in smaller
groups. Classification enables biologists to study and identify various organisms
more easily.
Learning objectives:
• The exact meaning of classification.
• The advantages of classifying living organisms.
• Criteria used in the classification of living organisms.
• The units of classification like species, genera, families, orders,
classes, phyla/divisions and kingdoms.
• Binomial nomenclature.
• Common and scientific names of living organisms.
3.1
DEFINITION AND AIMS OF CLASSIFICATION
The scientific study which deals with the classification of living organisms is called
taxonomy (Taxis = Arrangement and Nomos = Law) So, taxonomy deals with
the laws governing the arrangement or classification of living organisms. In a
broader sense, taxonomy can be defined as a branch of biology, which deals with
the description, identification, classification and naming of living organisms
according to structural similarities and dissimilarities.
Technical description means to describe a living organism by using scientific terms.
3.2
BASIS OF CLASSIFICATION
All the living organisms placed in a particular group have many fundamental
similarities in their structure. It is not always easy to recognize these basic
similarities. Many bases and techniques are used to classify organism. It is
principally the homologous structure that one considers in grouping organisms.
Homologous structures are those that are similar because of their common origin.
Sometimes it is impossible to classify organisms using morphological criteria, so
one may compare the chemical substances which they contain. This is particularly
useful when classifying organisms like bacteria which may all look alike and have
an identical cellular structure. Other characteristics used in classifying organisms
include cytological structures with the help of electron microscope, genetic
constitution and their developmental patterns etc.
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3.3
UNITS OF CLASSIFICATION
The basic unit of biological classification is the species. A species is a group of
organisms which has numerous physical features in common and which are
normally capable of inter breeding and producing fertile offspring. Closely related
species are grouped together into genera (singular- genus). Similar genera are
grouped together into families, families into Orders, orders into classes,
classes into phyla (singular -phylum) or divisions and phyla or divisions into
kingdoms. Intermediate categories are also sometimes used; for example a subphylum or sub-division between phylum and class, and sub classes between class
and order.
The name of a species maybe given on the basis of
i) Locality
ii) Character of plant
in) Religious belief
iv) Scientist who first discovered it
For example:
Ficus bengalensis (Banyan tree) named after locality.
Ficus religious (Peepal) named after religious belief.
Ficus elastica (Rubber plant) named after that atex is extracted.
Ficus erica named after Eric a person.
3.4
BINOMIAL NOMENCLATURE
O. Linnaeus adopted the binomial nomenclature system for naming organisms to
eliminate confusion while using native or common names when describing an
organism. He gave each species a scientific name comprising two words. This is
known as binomial nomenclature. The first name refers to the genus and is called
generic name and always begins with a capital letter. The species name follows
the generic name and begins with small letter. Scientific name for mustard is
Brassica campestris, for frog is Rana tigrina and for human is Homo sapiens.
Every scientific name is written in italic or it is underlined.
3.5
COMMON SCIENTIFIC NAMES AND CLASSIFICATION
1)
Common name
KINGDOM
DIVISION
CLASS
ORDER
FAMILY
GENUS
SPECIES
SCIENTIFIC NAME
…
…
…
…
…
…
…
…
…
Mustard
Plantae
Tracheophyta
Dicotyledonae
Capparales
Brassicaceae
Brassica
Campestris
Brasica Campestris
2)
Common name
KINGDOM
PHYLUM
CLASS
ORDER
FAMILY
GENUS
SPECIES
SCIENTIFIC NAME
…
…
…
…
…
…
…
…
…
Man
Animalia
Chordata
Mammalia
Primat
Hominidae
Homo
Sapiens
Homo Sapiens
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3)
Common name
KINGDOM
PHYLUM
CLASS
ORDER
FAMILY
GENUAL
SPECIES
SCIENTIFIC NAME
…
…
…
…
…
…
…
…
…
Frog
Animalia
Chordata
Amphibia
Salientia (Anura)
Ranidae
Rana
Tigrina
Ranatigrina
3.6 MAJOR GRQUPS OF LIVING ORGANISMS
Two Kingdom to five Kingdom classification:
Previously living things were classified into two kingdoms namely Plant Kingdom
and Animal Kingdom. The basis of this division was presence or absence of
cell-wall and chlorophyll. All the living organisms having cell-wall and
chlorophyll were regarded as plants and placed and studied under Kingdom
Plantae. All those living organisms having neither cell-wall, nor chlorophyll were
regarded as animals and placed and studied under Kingdom Animalia. But a
large ruimber of living organisms did not fit cleary into the category of plants and
animals. To solve this problem, Robert H. Whittaker (1969) suggested a new
system of classifying living organisms. According to this new system there are
live kingdoms of living organisms.
1. Kingdom Monera, prokaryotes which feed by a variety of different methods.
2. Kingdom Protista, unicellular eukaryotes which feed by a variety of methods.
3. Kindgdom Fungi, multicellular eukaryotes which feed heterotrophically by
absorption.
4. Kingdom Plantae, multicellular eukaryotes which feed photosynthetically.
5. Kingdom Animalia, multicellular eukaryotes which feed heterotrophically by
ingestion.
Although Whittaker's Scheme received wide spread approval, it had one major
draw back. This relates to the protist kingdom, which contained all unicellular
organisms, including those that formerly had been regarded, as animal
(Protozoan) and those that had been regarded as plant (unicellular algae). Other
problem was that it meant putting the algae into two separate kingdoms, the
protista and the plant kingdom.
This led two other biologists, Margulis and Schwartz, to put forward a
modification of Whittaker's scheme (1989). According to this, there are five
kingdoms of living organisms as listed below:
1. Kingdom Prokaryotae: It includes all the prokaryotes, e.g. bacteria and
cyanobacteria etc.
2. Kingdom Protoctista: It includes all the eukaryotic organisms, which are no
longer classified as animals, plants or fungi, e.g. Euglena, Paramecium,
Chlamydomonas, yeast etc.
3. Kingdom Fungi: It includes non-chlorophyllous, multicellular, eukaryotic
organisms having cell-wall e.g. Agaricus (mushroom) etc.
4. Kingdom Plantae: It includes all the chlorophyllous multicellular eukaryotic
living organisms, having cell-wall and embryonic development e.g. Apple,
Sunflower etc.
5. Kingdom
Animalia:
It
includes
all
the
non-chlorophyllous
multicellular eukaryotic organisms, having no cell-wall, e.g. hydra,
earthworm, man etc.
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SUMMARY
•
•
•
•
•
•
•
•
•
There are uncountable forms of life ranging from VIRUS (border line between
the living and non-living) to the most highly evolved and complex life in the
form of human-beings.
The scientific study which deals with the classification of living organisms is
called Taxonomy (Taxis= Arrangement. Nomos=Law).
All the living organisms placed in a particular group have many fundamental
similarities in their structure.
The basic unit of biological classification is the species.
Closely related species are grouped together into genera.
Each grouping of organisms within the hierarchy is called a taxon (plural taxa)
and each taxon has a rank and a name for example class Mammalia or genus
Homo.
Linnaeus's system of naming give each species a scientific name comprising
two words is known as binomial nomenclature.
Previously living things were classified into two kingdoms namely plant
kingdom and animal kingdom.
Now a days living organisms are classified into five kingdoms.
EXERCISE
1.
i)
ii)
iii)
Fill in the blanks with appropriate terms:
The term biodiversity means variety of ___________.
The study which deals with the classification! of living organisms is
called __________.
The basic unit of biological classification is the __________.
2.
i)
ii)
iii)
Write whether the statements are true or false :
Closely related species are grouped together into genera.
Closely related genera are grouped together into classes.
The plural of taxon is taxa.
3.
i)
Encircle the appropriate answer:
The family of mustard is
(a) Brassicaceae
(b) Poaeceae
(c) Rosaceae
(d) Palmaceae
Closely related species are grouped together into
(a) Family
(b) Genus
(c) Order
(d) Class
Multicellular organisms having no cell-wall and no chlorophyll are
(a) Fungi
(b) Bacteria
(c) Animals
(d) Plants
ii)
iii)
4.
i)
ii)
iii)
5.
i)
ii)
iii)
Write detailed answers of the following questions:
Define taxonomy and describe the aims, bass and units of classification.
Name the five kingdoms of living organisms. Write down the differentiating
characters and examples of each kingdom.
Why is the kingdom protoctista difficult to classify? What is the basis of
their grouping in kingdom protoctista? Give examples of each of its group.
Write short answers of the following questions:
What is the definition of taxonomy?
Define species.
Write a note on binomial nomenclature.
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