Chapter-1: The Living World

WHAT IS LIVING?

 Life is a unique, complex organisation of molecules expressing itself through chemical reactions (metabolism) which lead to growth, development, responsiveness, adaptation and reproduction. Hence, "the object by itself exhibiting the growth, development, death, consciousness, reproduction etc. is designated as living being."

A. Characteristics of Living Beings

All the living beings share certain unique and basic characteristics which set them apart from non-living objects. These characteristics are listed below :         

1. Growth                   

2. Reproduction         

3. Metabolism           

4. Cellular structure  

5. Consciousness

1. Growth:

Increase in mass and increase in number of cells are twin characters of growth. Growth refers to irreversible increase in mass or overall size of a tissue, an organism or its parts.

Growth is the result of difference between anabolism (building up reactions) and catabolism (breakdown reactions).

Growth occurs when anabolism or synthetic processes exceeds catabolism.

Degrowth or negative growth will occur when catabolism exceeds anabolism. It will decrease the mass of body.

Unicellular organisms also grow by cell division. In majority of higher animals and plants, growth and reproduction are mutually exclusive events, but in unicelled organisms like Amoeba, reproduction is synonymous with growth, i.e., increase in number of cells.

Non-living objects also grow if we take increase in body mass as a criterion of growth. But in these objects extrinsic growth is present i.e. increase in the mass of body from outside e.g., mountains, boulders and sand mounds. Growth, therefore, cannot be taken as a defining property of living organisms.

2. Reproduction:

Reproduction is the formation of new individuals of similar kind. It is, however, required for survival of the population as it compensates for the loss of life due to death.

Reproduction is of two types, asexual and sexual. Asexual reproduction is uniparental multiplication that occurs through binary fission, multiple fission, spore formation, fragmentation and vegetative multiplication.

Fungi multiply by asexual spores, yeast and Hydra show budding, Planaria exhibits true regeneration. Fungi, filamentous algae, protonema of mosses easily multiplies by fragmentation. But, when we notice single-celled organisms like bacteria, unicellular alga and Amoeba, we are not clear about the usage of these two terms -growth and reproduction, i.e., increase in number of cells.

Hence, reproduction also cannot be an all inclusive property of living organisms. Still, no non-living object is capable of reproducing or replicating by itself. Further, there are some organisms which do not reproduce at all, e.g., worker bees, mules etc.

3. Metabolism:

Life is a never ending flow of energy and materials.

The energy are required by all living cells for building and functioning of their living matter.

Metabolism is the sum total of all chemical reactions occurring in an organism due to specific interactions amongst different types of molecules within the interior of cells.

Metabolism involves exchange of matter and energy between an organism and its environment and transformation of matter and energy within an organism.

Despite vast differences occurring in structure and functioning of cells in different organisms, metabolic reactions are unusually similar.

Metabolic reactions can be demonstrated outside the body in cell free systems.

An isolated metabolic reaction(s) in a test-tube is neither living nor non-living. Hence, while metabolism is a defining feature of all living organisms without exception , isolated metabolic reactions in-vitro are not living things but surely living reactions.

An isolated metabolic reaction(s) in a test-tube is neither living nor non-living. Hence, while metabolism is a defining feature of all living organisms without exception , isolated metabolic reactions in-vitro are not living things but surely living reactions.

4. Cellular structure:

Body of all living organisms consists of cells and their products. Hence, cellular organisation of the body is the defining feature of life forms.

5. Consciousness:

All living beings, plants and animals, are aware of their environment. All organisms sense their surroundings and respond to sudden or smooth changes in it.

All organisms from prokaryota to eukaryota can sense and respond.

Humans also have "self-consciousness" hence, this becomes the defining property of living beings.

It is most obvious and technically complicated feature of all living organisms.

The foregoing discussion, nevertheless concludes that living beings are organized, self-replicating, evolving and self-regulating interactive systems, with consciousness at the head of all.

A question may arise whether a man lying in coma on the life support systems is living or non-living? The answer lies in the quantitative presence of consciousness in the living being in that particular state. Infact, the person in coma has lost the requisite quantity of consciousness to exhibit the features of living being, but still exhibits life. If the requisite consciousness is restored, the person may again start to be as living being or die otherwise.

Other characteristics of living beings are adaptation, life span, homeostasis, healing and repair, movement and variation.

Biodiversity

From a current estimation, approximately 1.7 million species have been scientifically named and classified. These include nearly 1.2 million animals and over 0.5 million species of plants.

Amongst animals, insects form the largest group, i.e., over 10,25,000 species. It is estimated that majority of species diversity is confined to tropical rain forests and huge diversity exist in under water reef formations in tropical oceans.

Existing living species are the outcome of about 3.5 billion years of evolutionary process on this earth. Nearly 15,000 new organisms are discovered every year.

A clearer understanding of this huge variety of organisms can be studied by dividing these into smaller groups or sub-groups (categories) and each group or sub-group comprising of organisms with more or less similar characters.

Method of placing organisms into groups or sub-groups depending upon extent of similarities and differences is called classification.

The division of organisms into different groups follows certain rules, that is why the term called taxonomy is used for classification of organisms following certain rules or principles.

 Need for classification

There are millions of plants and animals varying greatly in their form, structure and complexity.

It is impossible to study all of them individually. To make the study of organisms possible and easier, scientists have divided organisms into different ranks or categories on the basis of similarities and differences.

Classification is just like systematically arranged library where we can easily find out the required book, in the same way, if the organisms are arranged according to a system, it makes their study easy.

Some important needs are

It is essential to understand the inter-relationship among different groups of organisms.

It serves as a base for the development of other biological sciences like biogeography.

Various applied biology fields also depend upon exact identification and classification.

Taxonomy and Systematics

Taxonomy: The branch of science dealing with the study of principles and procedures of classification is called taxonomy. The term taxonomy was coined by A.P. de Candolle. Linnaeus is considered as Father of Taxonomy. Santapau is considered as Father of Indian Taxonomy. The fundamental elements of taxonomy are as follows :

• Characterisation and identification : It is the determination of the similarities of an organism with an already known organism, based upon specific characters.
• Nomenclature: It is the determination of correct name of an organism according to established universal rules.
• Classification: It is grouping of organisms into convenient categories on the basis of easily observable characters.

• The classical taxonomy is based on observable morphological characters, however the modern taxonomy deals with several characters for the classification of organisms like

 (a)     External and internal structure alongwith the structure of cell.

 (b)    Development process.

 (c)    Ecological information of organisms

Systematics : The word "systematics" is derived from Latin word systema which means systematic arrangement of organisms. It was first used by Carolus Linnaeus. According to him, "systematics is the discipline of biology which deals with the kind and diversity of all organisms and the existing relationships amongst them."

Generally, the terms such as classification, systematics and taxonomy are used interchangeably but some taxonomists like Simpson (1961) relate them with a separate field. He defined systematics as

"The study of diversity of organisms and all their comparative and evolutionary relationships based on comparative anatomy, comparative ecology, comparative physiology and comparative biochemistry."

The main uses of systematics are as given below :

(i)      It helps in providing knowledge of great diversity of animals and plants. It provides information regarding evolution which took place among plants and animals by knowing the distinction, relationship, habitat and habits. It thus, gives a vivid picture of entire organic diversity.

(ii)    It helps in the identification of fossils which gives useful information about the phylogeny of organisms.

(iii)   Newly discovered organisms can be identified through systematics. well as the specimens

Concept Builder

1. The reasons for large scale biodiversity amongst living beings are :

1. 1. Adaptations in organisms to diverse habitat in order to reduce competition.
   2. Change in genetic constitution.
   3. Isolation

2. Ontogeny is the life history of organisms. Phylogeny is the evolutionary history of organisms.

3. Systematics is taxonomy alongwith phylogeny.

4. Classical or old or descriptive systematics is based upon morphological characters. According to it basic unit of classification is species. Pioneer workers are Aristotle and linnaeus.

5. New systematics / Biosystematics / Neosystematics is based upon all characters" i.e., morphological, cytological, ecological, biochemical, genetical etc. The term was coined by Julian Huxley. Basic unit of classification is population or sub-species for the new systematics.

6. Founder of taxonomy / Father of biology / Zoology–Aristotle, Father of Botany –Theophrastus, Father of Indian Botany/Indian herbaria -William Rouxburgh.

7. About 5-30 million species of living organisms exist today. Taxonomically or scientifically known number of species is 1.7 million or 13 percent.

Representing global biodiversity: proportionate number of species of major taxa of plants, invertebrates and vertebrates

 Need for classification

• There are millions of plants and animals varying greatly in their form, structure and complexity.
• It is impossible to study all of them individually. To make the study of organisms possible and easier, scientists have divided organisms into different ranks or categories on the basis of similarities and differences.
• Classification is just like systematically arranged library where we can easily find out the required book, in the same way, if the organisms are arranged according to a system, it makes their study easy.

Some important needs are

• It is essential to understand the inter-relationship among different groups of organisms.
• It serves as a base for the development of other biological sciences like biogeography.
• Various applied biology fields also depend upon exact identification and classification.

Biodiversity

• From a current estimation, approximately 1.7 million species have been scientifically named and classified. These include nearly 1.2 million animals and over 0.5 million species of plants.
• Amongst animals, insects form the largest group, i.e., over 10,25,000 species. It is estimated that majority of species diversity is confined to tropical rain forests and huge diversity exist in under water reef formations in tropical oceans.
• Existing living species are the outcome of about 3.5 billion years of evolutionary process on this earth. Nearly 15,000 new organisms are discovered every year.
• A clearer understanding of this huge variety of organisms can be studied by dividing these into smaller groups or sub-groups (categories) and each group or sub-group comprising of organisms with more or less similar characters.
• Method of placing organisms into groups or sub-groups depending upon extent of similarities and differences is called classification.
• The division of organisms into different groups follows certain rules, that is why the term called taxonomy is used for classification of organisms following certain rules or principles.

Taxonomy and Systematics

Taxonomy: The branch of science dealing with the study of principles and procedures of classification is called taxonomy. The term taxonomy was coined by A.P. de Candolle. Linnaeus is considered as Father of Taxonomy. Santapau is considered as Father of Indian Taxonomy. The fundamental elements of taxonomy are as follows :

• Characterisation and identification : It is the determination of the similarities of an organism with an already known organism, based upon specific characters.
• Nomenclature: It is the determination of correct name of an organism according to established universal rules.
• Classification: It is grouping of organisms into convenient categories on the basis of easily observable characters.

• The classical taxonomy is based on observable morphological characters, however the modern taxonomy deals with several characters for the classification of organisms like

 (a)     External and internal structure alongwith the structure of cell.

 (b)    Development process.

 (c)    Ecological information of organisms

Systematics : The word "systematics" is derived from Latin word systema which means systematic arrangement of organisms. It was first used by Carolus Linnaeus. According to him, "systematics is the discipline of biology which deals with the kind and diversity of all organisms and the existing relationships amongst them."

    Generally, the terms such as classification, systematics and taxonomy are used interchangeably but some taxonomists like Simpson (1961) relate them with a separate field. He defined systematics as

   "The study of diversity of organisms and all their comparative and evolutionary relationships based on comparative anatomy, comparative ecology, comparative physiology and comparative biochemistry."

The main uses of systematics are as given below :

  (i)      It helps in providing knowledge of great diversity of animals and plants. It provides information regarding evolution which took place among plants and animals by knowing the distinction, relationship, habitat and habits. It thus, gives a vivid picture of entire organic diversity.

  (ii)    It helps in the identification of fossils which gives useful information about the phylogeny of organisms.

(iii)   Newly discovered organisms can be identified through systematics.

TAXONOMIC CATEGORIES

•  Classification is not a single step process. It involves hierarchy of steps in which each step represents a rank or category.  
•  The category is a part of overall taxonomic arrangement. All categories together make taxonomic hierarchy.  
• Each category is also termed as a unit of classification. It represents a rank and is commonly called as taxon.  
• The taxon must be recognisable and order should belong to a category.  
• Taxonomic hierarchy is a series of different ranks placed in ascending or descending order.
• It was Linnaeus who for the first time introduced five categories in the taxonomic hierarchy, viz., class, order, genus, species and variety.
• Later on three more categories, viz., kingdom, division or phylum and family were added.
• Variety was Species discarded to make a hierarchy of seven obligate categories.     
• Taxonomic categories kingdom -division (in plants) or phylum (in animals) -class -order -family -genus -species. (descending order)
• Higher the category, higher is the number of organisms in it. Higher the category, fewer will be the number of common characters and greater is the difficulty of determining the relationship to other taxa at the same level. Hence, the problem of classification becomes more complex.
• Taxonomic categories and hierarchy can be illustrated by an example. Insects represent a group of organisms sharing common features like three pairs of jointed legs.
• It means insects are recognisable concrete objects which can be classified, and thus were given a rank or category.
• Similarly, mammals represent animals with external ears, body hairs, mammary glands etc. Dog, mammals, animals are all taxa but of different categories.
• Taxon dog, mammals and animals represent categories like species, class and kingdom respectively.  

 Species:

• Term given by John Ray. It is lowest category of classification. It is a group of closely related individuals with similar morphological, anatomical, biochemical and cytological characters.
• It is a group of naturally interbreeding population with the ability to produce fertile offsprings.
• Individuals of a species share common gene pool.
• It is reproductively isolated, thus genetically closed system.

      e.g,  Pisum sativum                    – Pea

Mangifera indica                 – Mango

Solanum tuberosum            – Potato

Panthera leo                         – Lion

 Homo sapiens                      – Human being

 In these, sativum, indica, tuberosum, leo, sapiens represent the specific epithet, while Pisum, Mangifera, Solanum, Panthera and Homo represent genus.

Genus:

• Genus is a group of related species. Species has more characters in common in comparison to species of other genera. 
•  e.g., Potato, (Solanum tuberosum), makoi (S. nigrum) and brinjal (S. melongena) are three different species belonging to same genus Solanum.  
•  Lion, leopard and tiger with several common features belong to the same genus Panthera.

Family:

It is a group of related genera with still less number of similarities as compared to genus and species. Families are characterised on the basis of both vegetative and reproductive features of plants.

• For example, four related genera Solanum, Petunia, Datura and Atropa belong to the family Solanaceae. Genus Panthera and Felis (cat) are put together in family Felidae.

Order:

•  It is a group of related families which exhibit a few similar characters. The similar characters are less in number as compared to different genera included in a family. 
•   For example, plant families like Convolvulaceae and Solanaceae are included in order Polymoniales mainly based on floral characters.
•    In animals, order carnivora includes families like Felidae (cat) and Canidae (dog).

Class:

•   It is a group of related orders. 
•  For example , plants order like Sapindales (mango) and Polymoniales are included in   Class -Dicotyledonae, Order -Volvocales (Volvox) and Conjugales (Spirogyra) are included in Class -Chlorophyceae (green algae).In animals, order Primata (man, monkey) and Carnivora (cat, dog) are included in class -Mammalia.

Phylum/Division :

• It is a group of related classes.
•  The phylum Chordata of animals contains not only the class mammalia but also aves (birds), reptilia (reptiles) amphibia (amphibians) and osteichthyes (fishes).
• In case of plants, classes with few similar characters like dicots and monocots constitute division -Angiospermae.
• The category phylum is used in animalia while division is used in plantae.

Kingdom:

•  It is highest category in hierarchy with related phylums or divisions.

           Kingdom animalia includes all animals belonging to different phyla. Kingdom Plantae includes all plants of various divisions.

 

Concept of Species :

            Biological concept of species (was given by Ernst Mayr) : Species is the fundamental unit of classification. A species is a group of organisms (i) which are closely related (structurally and functionally) sharing a common gene pool (ii) which can interbreed freely in nature and produce fertile offspring in a natural environment. This concept of species is based upon reproductive isolation and called biological concept.

           Some important interspecific hybrids (exception of biological concept of species)

  (i)      Sterile Hybrid (under natural conditions)
Mule = Between male donkey and female horse (Mare)
Hinny = Between male horse (Stal'lion) and female donkey

  (ii)     Fertile Hybrid (under captive conditions)
Tigon = Between male tiger and female lion
Liger = Between male lion and female tiger

Types of Species :

TAXONOMICAL AIDS

• The laboratory and field studies are required for identification of various species and their placement in taxonomical hierarchy.
• The information thus gathered about the species, needs to be stored for future use.
• The taxonomical aids developed by biologists have established certain procedures and techniques to store and preserve the information as well as the specimens

NOMENCLATURE

There is a need to standardize the naming of living organisms, such that a particular organism is known by same name all over the world. A variety of nomenclatural methods are described below :

  1.Vernacular name: Names in local or common language are called vernacular names. So, many vernacular names exist for an organism in different languages. These may vary from place to place.

  2.Scientific names: These names were based on definite rules and criteria. These are of following types :

(i) Polynomial nomenclature

(ii) Trinomial nomenclature [both given in concept builder]

(iii) Binomial system of nomenclature:

a.Swedish naturalist Carolus Linnaeus established binomial nomenclature though, it was first proposed by Casper Bauhin in his book PINAX.

b. In binomial nomenclature, the first word is a generic name and second word is a specific epithet like Mangifera indica Linn.

c. After end of biological name, the name of author is written in abbreviated form who gave the name of the organism.

d.Scientific names are in Latin, because Latin was the language of scholars at the time of Linnaeus, and no change is possible in the language because this language has no synonyms.

e.Linnaeus gave some principles of the binomial nomenclature in Philosophia Botanica.

f. The nomenclature was used first in Species Plantarum (1753), where names and description of 5900 species of plants were given.

g.He published Systema Naturae (1758), where 4326 species of animals were described.           

A. International Code of Nomenclature

Scientific names have been standardised through some international agencies, viz., International Code of Botanical Nomenclature (ICBN, 1961) and International Code of Zoological Nomenclature (ICZN, 1964), International Code for Nomenclature of Bacteria (ICNB), International Code of Nomenclature for Cultivated Plants (ICNCP) and currently being developed is International Committee for the Taxonomy of Viruses (ICTV).

B. Rules for Binomial Nomenclature

ICBN and ICZN formulated certain rules and regulations for giving scientific names to all organisms. These rules are as follows :

• The valid name of an organism has two components, i.e., a generic name and a specific epithet. The generic name should begin with a capital letter and species name should begin with a small letter.
• Both the words in a biological name when handwritten are separately underlined or printed in italics to indicate their Latin origin.
• The name of the author should be written after the scientific name in Roman type with capital letter without any comma in between and is written in an abbreviated form, e.g., Homo sapiens Linn. is the complete scientific name for modern man. This shows that Linnaeus was the first scientist who named man as Homo sapiens.
• Scientific names should not contain less than three and more than twelve letters.
• Principle of priority: It is the most important of all the rules of ICBN. If first name given to the organism is valid (in terms of rules), that will be considered at the first preference. Any other valid name given after that will be considered as synonym. No names are recognised prior to those used by Linnaeus in 1758 in the 10th edition of Systema Naturae for animals and 1753 for plants.
• All the three words (generic name, species epithet and author citation) collectively form Binomial epithet.
• If a species name has two or more words in its name, a hyphen is put between these. Such names are compound specific names (e.g., Hibiscus rosa-sinensis).

 Zoological Parks

• Zoos or zoological gardens (parks) are protected areas or enclosed space where live wild animals are kept, under human care. This enables us to learn their food habits and behaviour.
• Objectives are public exhibition to understand wild life, recreation, education, ex situ conservation and breeding of rare fauna.
• Largest zoo of the world is situated in Kruger (S. Africa).
• National Zoological Park (Delhi) is one of the finest zoo of Asia.

  

    Herbarium (Dry Garden)

• It is defined as "a store house of collected plant specimens that are dried, pressed and preserved on sheets."
• These sheets are arranged in the sequence of an accepted classification system.
• These specimens, along with their description on herbarium sheets, become a store house or repository for future use. The herbarium sheet contains a label on the right-hand side at lower corner.
• Label provides information about date and place of collection, English, local and botanical names, family, collector's name etc.
• Herbaria also serve as quick referral systems in taxonomical studies.

Herbarium Sheet

Functions of a Herbarium

The two primary functions of herbarium are accurate identification and alpha taxonomic research (based on gross morphology).

The secondary functions include closer interaction between the student of general systematics and the herbarium.

Other important functions of a herbarium are –

  1.To preserve plant wealth including type material and palaeobotanical collections.

  2.To carry out exchange and loan of preserved plant material for research, exhibitions etc.

A list of important herbaria of the world is given below along with their standard abbreviations and the approximate number of specimens they hold

TYPE SPECIMEN (HERBARIUM SHEET)

Type specimen (Herbarium Sheet) of newly discovered plant should be place in herbarium (Dry garden). Standered size of herbarium sheet is 11.5 × 16.5 inches.

Holotype - Herbarium sheet on which the first description of plant is based.

Isotype - Duplicate of holotype - In presence of holotype a second herbarium sheet prepared from the original plant is called isotype.

Paratype - Additional herbarium sheet used in the first description of plant is called paratype. It is prepared from some other plant of same species having some variations.

Lectotype - In case of holotype is lost, second herbarium sheet prepared from the original plant is called lectotype.

Neotype - In case of holotype and original plant is lost, then herbarium sheet prepared from some other plant of same species is called neotype.

Syntype - In case of holotype and original plant is lost then many herbarium sheet prepared from many plants of same species is called syntype.

Note : Nomenclature is invalid in absence of Herbarium sheet.

Botanical Gardens

• From the time of Theophrastus, gardens have contributed to the science of botany. But, there was an impetus to the botanical explorations only in the Post-Linnean period.
• In ancient Indian culture, cultivation of food and medicinal plants is known since 4000 to 2000 B.C. The 'Hanging Gardens of Babylon' are amongst the wonders of the ancient world.
• During the Middle Ages, from A.D. 600-1600, there was a lapse in learning and introduction of plants.
• In the seventeenth century, there was a revival in the interest and by eighteenth century, most of the famous Botanical Gardens known today had already been established.

  The functions of a botanical garden are:

1. Provide records of local flora for monographic work.
2. Provide facilities for collections and identification of living plant material for biosystematic studies / references.
3. Supply seeds and material for botanical investigations.
4. Botanical gardens have an aesthetic appeal and attract a large number of visitors for observing general plant diversity.
5. Provides means of ex-situ conservation strategies.

• There are about 525 botanical gardens in various countries, but only about 125 have documented collections of authenticated taxa.

       6.The International Association of Botanical Gardens was established in 1962. This association has published the International Directory of Botanical Gardens (1983).

BOTANICAL GARDENS OF INDIA

• The Indian Botanical Garden, Kolkata, India: It was founded in 1787, by Lt.Col. Robert Kyd. It covers an area of 273 acres and contains collections of world's tropical plants.
• It is one of the greatest botanical gardens of the world and one of the first to be established in tropics.
• William Roxburgh, 'Father of Indian Botany' was its director from 1793 to 1813.
• It has the largest herbarium of east and is famous for the Great Banyan tree, Ficus benghalensis, which is two centuries old, the palm houses, nurseries and the Amazon lily, Victoria amazonica (Nymphaeaceae), the plant with the largest leaves.

It is now under control of BSI (Botanical Survey of India).

Other botanical gardens of India are -   

Lloyd Botanical Garden                    – Darjeeling
National Botanical Garden               – Lucknow
Lalbag Gardens                                – Bangalore
Saharanpur Botanical Garden          – Saharanpur

Diversity in the Living World

From a current estimation, approximately 1.7 million species have been scientifically named and classified. These include nearly 1.2 million animals and over 0.5 million species of plants.

Amongst animals, insects form the largest group, i.e., over 10,25,000 species. It is estimated that majority of species diversity is confined to tropical rain forests and huge diversity exist in under water reef formations in tropical oceans.

Existing living species are the outcome of about 3.5 billion years of evolutionary process on this earth. Nearly 15,000 new organisms are discovered every year.

A clearer understanding of this huge variety of organisms can be studied by dividing these into smaller groups or sub-groups (categories) and each group or sub-group comprising of organisms with more or less similar characters.

Method of placing organisms into groups or sub-groups depending upon extent of similarities and differences is called classification.

The division of organisms into different groups follows certain rules, that is why the term called taxonomy is used for classification of organisms following certain rules or principles.

 TAXONOMIC CATEGORIES

Classification is not a single step process. It involves hierarchy of steps in which each step represents a rank or category.  

The category is a part of overall taxonomic arrangement. All categories together make taxonomic hierarchy.  

Each category is also termed as a unit of classification. It represents a rank and is commonly called as taxon.  

The taxon must be recognisable and order should belong to a category.  

Taxonomic hierarchy is a series of different ranks placed in ascending or descending order.

It was Linnaeus who for the first time introduced five categories in the taxonomic hierarchy, viz., class, order, genus, species and variety.

Later on three more categories, viz., kingdom, division or phylum and family were added.

Variety was Species discarded to make a hierarchy of seven obligate categories.     

Taxonomic categories kingdom -division (in plants) or phylum (in animals) -class -order -family -genus -species. (descending order)

Higher the category, higher is the number of organisms in it. Higher the category, fewer will be the number of common characters and greater is the difficulty of determining the relationship to other taxa at the same level. Hence, the problem of classification becomes more complex.

Taxonomic categories and hierarchy can be illustrated by an example. Insects represent a group of organisms sharing common features like three pairs of jointed legs.

It means insects are recognisable concrete objects which can be classified, and thus were given a rank or category.

Similarly, mammals represent animals with external ears, body hairs, mammary glands etc. Dog, mammals, animals are all taxa but of different categories.

Taxon dog, mammals and animals represent categories like species, class and kingdom respectively.  

 Species:

Term given by John Ray. It is lowest category of classification. It is a group of closely related individuals with similar morphological, anatomical, biochemical and cytological characters.

It is a group of naturally interbreeding population with the ability to produce fertile offsprings.

Individuals of a species share common gene pool.

It is reproductively isolated, thus genetically closed system.

e.g,  Pisum sativum                    – Pea

Mangifera indica                 – Mango

Solanum tuberosum            – Potato

Panthera leo                         – Lion

 Homo sapiens                      – Human being

 In these, sativum, indica, tuberosum, leo, sapiens represent the specific epithet, while Pisum, Mangifera, Solanum, Panthera and Homo represent genus.

Genus:

Genus is a group of related species. Species has more characters in common in comparison to species of other genera. 

 e.g., Potato, (Solanum tuberosum), makoi (S. nigrum) and brinjal (S. melongena) are three different species belonging to same genus Solanum.  

 Lion, leopard and tiger with several common features belong to the same genus Panthera.

Family:

It is a group of related genera with still less number of similarities as compared to genus and species. Families are characterised on the basis of both vegetative and reproductive features of plants.

For example, four related genera Solanum, Petunia, Datura and Atropa belong to the family Solanaceae. Genus Panthera and Felis (cat) are put together in family Felidae.

Order:

 It is a group of related families which exhibit a few similar characters. The similar characters are less in number as compared to different genera included in a family. 

  For example, plant families like Convolvulaceae and Solanaceae are included in order Polymoniales mainly based on floral characters.

   In animals, order carnivora includes families like Felidae (cat) and Canidae (dog).

Class:

It is a group of related orders. 

 For example , plants order like Sapindales (mango) and Polymoniales are included in   Class -Dicotyledonae, Order -Volvocales (Volvox) and Conjugales (Spirogyra) are included in Class -Chlorophyceae (green algae).In animals, order Primata (man, monkey) and Carnivora (cat, dog) are included in class -Mammalia.

Phylum/Division :

It is a group of related classes.

The phylum Chordata of animals contains not only the class mammalia but also aves (birds), reptilia (reptiles) amphibia (amphibians) and osteichthyes (fishes).

In case of plants, classes with few similar characters like dicots and monocots constitute division -Angiospermae.

The category phylum is used in animalia while division is used in plantae.

Kingdom:

 It is highest category in hierarchy with related phylums or divisions.

Kingdom animalia includes all animals belonging to different phyla. Kingdom Plantae includes all plants of various divisions.

Concept of Species :

Biological concept of species (was given by Ernst Mayr) : Species is the fundamental unit of classification. A species is a group of organisms (i) which are closely related (structurally and functionally) sharing a common gene pool (ii) which can interbreed freely in nature and produce fertile offspring in a natural environment. This concept of species is based upon reproductive isolation and called biological concept.

Some important interspecific hybrids (exception of biological concept of species)

  (i)      Sterile Hybrid (under natural conditions)
Mule = Between male donkey and female horse (Mare)
Hinny = Between male horse (Stal'lion) and female donkey

  (ii)     Fertile Hybrid (under captive conditions)
Tigon = Between male tiger and female lion
Liger = Between male lion and female tiger

Types of Species :

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In accordance with International Code of Botanical Nomenclature, the names of different categories must end in the standard endings (suffixes) given below :

Tournefort gave the term genus and John Ray gave the term species 
    (b)     Names of some families are changed according to ICBN rules for suffixes. 

Old Name          New Name

Palmae               Arecaceae

Graminae            Poaceae

Leguminosae      Fabaceae

Compositae         Asteraceae

Cruciferae           Brassicaceae

Umbelliferae        Apiaceae

Labiatae               Lamiaceae

Guttiferae            Clusiaceae

(c)     Tribe is an intermediate category between sub-family and genus. 
(d)     In asexually reproducing organisms, physical resemblances and differences are used for delimiting species. 
(e)     Basic function of biological classification : 

• (a) Recognition and description of species. 
• (b) Grouping the species on the basis of similarities and relationship. 
• (c) To establish evolutionary relationship amongst different organisms. 

(f)    The genera which have more than one specific epithets, are known as polytypic. 

Lion    – Panthera leo 
Leopard    – Panthera pardus 
Tiger    – Panthera tigris 

(g)    There are 7 obligate categories and about 21 intermediate categories. Prefixes: sub-and super-used for intermediate categories. 
(h)    Species name is given on the basis of some characters or habit, colour and distribution, e.g., niger (black), alba (white), tuberosum (tuber). 
(i)    Taxon is a group of real organisms which is assigned for any category. It is the unit of classification for any rank. Term taxon was introduced by ICBN in 1956 and defined by Mayr (1964). 
(j)    Category is an abstract term and represents only rank or level in a hierarchy and does not represent the living organisms. Example: Reptile is taxon but reptilia is category.

(k)    Typological concept of Species

It was proposed by “Aristotle” and “Plato”. According to this concept, “There is a definite type or pattern of characters are present in the each species and all the members of species shows maximum resemblance with this pattern”. The species in which one fixed pattern of characters is present are called as monotypic species. e.g., Bacteria, Blue green algae if more than one type of pattern of characters are present. These are called “Polytypic species” or “Macrospecies”. e.g., Brassica oleracea  Cauliflower, Cabbage, Knol-Knol.

Type of Polytypic Species :

Biotype : Members of same species inhabiting similar environment and having some genetic variations are known as biotypes. Variations found in these members are permanent. These members can not interbreed among themselves. e.g. Cauliflower, Cabbage, Knol-Khol are three biotypes of one species
Ecotypes : Members of same species inhabiting different environment and having some genetic variations are known as ecotypes. Variations are permanent. These members can interbreed among themselves but due to geographical barrier they can not interbreed.
e.g., Crow (Corvus splendense) found in different regions are ecotype of one species
Corvus splendense splendense - Indian crow
Corvus splendense insolense - Myanmar crow
Corvus splendense protegatus - Srilankan crow
Ecospecies : It contains one or more ecotype which although interfertile (capable of interbreeding), but do not produce viable offsprings due to some natural interruption (mountain, ocean etc).
Ecads or Ecophenes : Members of same species having some non genetic variation due to environment. These variations are temporary. 
e.g.,    

TAXONOMICAL AIDS 

The laboratory and field studies are required for identification of various species and their placement in taxonomical hierarchy. 

The information thus gathered about the species, needs to be stored for future use. 

The taxonomical aids developed by biologists have established certain procedures and techniques to store and preserve the information as well as the specimens. 

1. Botanical Gardens 

From the time of Theophrastus, gardens have contributed to the science of botany. But, there was an impetus to the botanical explorations only in the Post-Linnean period. 

In ancient Indian culture, cultivation of food and medicinal plants is known since 4000 to 2000 B.C. The 'Hanging Gardens of Babylon' are amongst the wonders of the ancient world. 

During the Middle Ages, from A.D. 600-1600, there was a lapse in learning and introduction of plants. 

In the seventeenth century, there was a revival in the interest and by eighteenth century, most of the famous Botanical Gardens known today had already been established. 

    The functions of a botanical garden are: 

1.    Provide records of local flora for monographic work. 

2.    Provide facilities for collections and identification of living plant material for biosystematic studies / references. 

3.    Supply seeds and material for botanical investigations. 

4.    Botanical gardens have an aesthetic appeal and attract a large number of visitors for observing general plant diversity. 

5.    Provides means of ex-situ conservation strategies. 
        There are about 525 botanical gardens in various countries, but only about 125 have documented collections of authenticated taxa. 
6.    The International Association of Botanical Gardens was established in 1962. This association has published the International Directory of Botanical Gardens (1983). 

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Some of the important Botanical Gardens are listed below :

1. Royal Botanical Garden, Kew, England : It was founded in 1759 by William Alton, but was officially opened in 1841 and was called the Botanical Capital of the World. Sir J.D. Hooker was one of its directors. It is famous for its Alpine house, Rose Garden, Green house, Temperature house, Bamboo garden and Lily pond. It is associated with Jodrell laboratory of experimental taxonomy. It is spread in 200 acres. It is famous for collection of Acacias, Acer, Rhus, Citrus, Rosa, Prunus, Magnolia. It has Chelsa Physic Garden for horticulturists. Kew

2. Orto Botanico (Padua Gardens), Italy: It is said to be the first botanical garden. It is famous for collections of grasses, Alliums, Irids, Paeonias, succulents and hydrophytes.

3. Pisa, Italy: Almost as old as Padua Gardens, it was the first to introduce palaeontological practises; for the study of plants fossils. It is known for trees like Magnolia grandiflora, Liriodendron tulipifera etc. Caesalpino and John Ray have been associated with this garden.

4. Villa Taranto, Italy: It is the most beautiful garden of Italy and important from the horticultural study point of view.

5. Main Botanical Garden, Moscow: Largest Botanical Garden, spread over an area of 900 acres.

BOTANICAL GARDENS OF INDIA

The Indian Botanical Garden, Kolkata, India: It was founded in 1787, by Lt.Col. Robert Kyd. It covers an area of 273 acres and contains collections of world's tropical plants.

It is one of the greatest botanical gardens of the world and one of the first to be established in tropics.

William Roxburgh, 'Father of Indian Botany' was its director from 1793 to 1813.

It has the largest herbarium of east and is famous for the Great Banyan tree, Ficus benghalensis, which is two centuries old, the palm houses, nurseries and the Amazon lily, Victoria amazonica (Nymphaeaceae), the plant with the largest leaves.

It is now under control of BSI (Botanical Survey of India).

Other botanical gardens of India are -

Lloyd Botanical Garden                – Darjeeling
National Botanical Garden           – Lucknow
Lalbag Gardens                           – Bangalore
Saharanpur Botanical Gardens   – Saharanpur

Herbarium (Dry Garden)

It is defined as "a store house of collected plant specimens that are dried, pressed and preserved on sheets."

These sheets are arranged in the sequence of an accepted classification system.

These specimens, along with their description on herbarium sheets, become a store house or repository for future use. The herbarium sheet contains a label on the right-hand side at lower corner.

Label provides information about date and place of collection, English, local and botanical names, family, collector's name etc.

Herbaria also serve as quick referral systems in taxonomical studies.

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Herbarium Technique 
The herbarium technique involves the following steps: 

• (a) Collection    
• (b) Drying    
• (c) Poisoning    
• (d) Mounting      
• (e) Stitching     
• (f) Labelling    
• (g) Deposition 

(a)    Collection: Collection of plant material is done with an aesthetic sense and scientific mind. 
The material should be perfect and complete for determination, i.e., must have fully grown 
leaves, complete inflorescence etc. 
Woody elements are well represented by flowering twigs with 30-40 cm in lengths, while 
herbaceous plants are collected alongwith underground parts. 
Diseased plants, infected twigs should be avoided. 
The collections are kept inside metallic vasculum or polythene bags. 

(b)     Drying: The plant collections are pressed in ordinary newspaper folders, avoiding overlapping. The folders, in turn, are pressed in a field press. The moistened folders are changed frequently to avoid blackening and decay of plant material. 

(c)     Poisoning: The specimens are poisoned to keep away the microbes. When the specimens are partially dehydrated, they are poisoned by using chemicals like 0.1% of corrosive, sublimate (HgCl2).

(d-f)     Mounting, Stitching and Labelling : Dried specimens are glued and stitched on herbarium sheets made up of thick card sheets cut to the required size. The international size of the herbarium sheet is 41× 29 cm (16  ×11  inches) . The field data is entered on label on the right hand side lower corner of the herbarium sheet. Size of label is commonly 7 × 12cm. The small paper envelopes called fragment packets are often attached to the herbarium sheet to hold seeds, extra flowers or loose plant parts. 

(g)    Deposition: Arrangement of specimen, according to accepted classification, is called deposition. In India, herbaria are arranged according to Bentham and Hooker system of classification. 
The specimens so preserved are sprayed with repellents or disinfectants such as DDT powder, copper sulphate solution at intervals of 4 to 6 months to keep off small insect pests such as silver fish. 

Functions of a Herbarium 

The two primary functions of herbarium are accurate identification and alpha taxonomic research (based on gross morphology). 

The secondary functions include closer interaction between the student of general systematics and the herbarium. 

Other important functions of a herbarium are 

1.  To preserve plant wealth including type material and palaeobotanical collections. 

2.  To carry out exchange and loan of preserved plant material for research, exhibitions etc. 
A list of important herbaria of the world is given below along with their standard abbreviations and the approximate number of specimens they hold 
1.Royal Botanical Gardens, Kew (K)         over 6,000,000
4. Central National Herbarium, Calcutta (CAL)       2,000,000 

TYPE SPECIMEN (HERBARIUM SHEET)

Type specimen (Herbarium Sheet) of newly discovered plant should be place in herbarium (Dry garden). Standered size of herbarium sheet is 11.5 × 16.5 inches.

Holotype - Herbarium sheet on which the first description of plant is based.

Isotype - Duplicate of holotype - In presence of holotype a second herbarium sheet prepared from the original plant is called isotype.

Paratype - Additional herbarium sheet used in the first description of plant is called paratype. It is prepared from some other plant of same species having some variations.

Lectotype - In case of holotype is lost, second herbarium sheet prepared from the original plant is called lectotype.

Neotype - In case of holotype and original plant is lost, then herbarium sheet prepared from some other plant of same species is called neotype.

Syntype - In case of holotype and original plant is lost then many herbarium sheet prepared from many plants of same species is called syntype.

Note : Nomenclature is invalid in absence of Herbarium sheet.

3. Keys [Given by John Ray] 

The scheme for identification of plants and animals based upon similarities and dissimilarities is known as a key. It is based on the set of contrasting characters known as couplet, each character of couplet is called as lead. Separate taxonomic keys are required for each taxonomic category. Keys are generally analytical in nature and are of two types (1) Indented key (2) Bracketed key –
1. Indented Key: It has a sequence of choice between two or more statements of characters of species. These require great taxonomic skills to prepare, so are generally less followed. 
2 Bracketed Key: In the Bracketed key the pairs of contrasting statements are used for identification. The bracketed number on the right side indicates the next choice of paired contrasting statements. These are most popular keys. 

4. Zoological Parks

Zoos or zoological gardens (parks) are protected areas or enclosed space where live wild animals are kept, under human care. This enables us to learn their food habits and behaviour.

Objectives are public exhibition to understand wild life, recreation, education, ex situ conservation and breeding of rare fauna.

Largest zoo of the world is situated in Kruger (S. Africa).

National Zoological Park (Delhi) is one of the finest zoo of Asia.

5. Museums

These have collections of preserved plants and animals for study and reference.

Specimens are preserved in jars or containers in preservative solution.

Plant and animal specimens may also be preserved as dry specimens.

Insects are preserved in insect boxes after collecting, killing and pinning.

Larger animals are usually stuffed and preserved.

These often have collections of skeletons of animals too.

Museums are prepared to preserve algae, fungi, mosses, ferns and organs of gymnosperms since they cannot be kept in herbaria. These differs from parks because no living object is displayed in museums.

Some important Museums: 

(i) Natural History Museum, London (England) 

(ii) United States National Museum, Washington 

(iii) National Museum of Natural History (NMNH), Delhi 

(iv) Prince of Wales Museum, Mumbai etc.
Comperative Study of Botanical Garden, Herbarium and Museum : 

6.Flora, Manuals, Monographs and Catalogues 

Flora: Contains the actual account of habitat and distribution of plants of a given area. These provide the index to the plant species found in a particular area. 
Some important flora are given below: 

(i) Flora of British India by J.D. Hooker. 

(ii) Flora of Delhi by J.K. Maheshwari. 

(iii) Flora Indica by William Roxburgh. 

(iv) Flora Simlensis by H. Collet 

Manuals: The complete listing and description of the plants growing in a particular area. 
e.g., Manual of Cultivated Plants by L.H. Bailey 

 Monographs: Contain information on anyone taxon. 
e.g., The Genus Pinus by N.T. Mirov 

Catalogues: This includes the alphabetical arrangements of species describing their features.

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1.    Ex-situ / Off-site conservation strategies for organisms includes Botanical gardens and Zoological parks. 

2.    Succulent plants or those plants which are unsuitable for pressing and drying techniques, are fixed in suitable liquid preservative like 2.5% solution of formaldehyde, glacial acetic acid and ethyl alcohol [FAA]. 

3.    Herbarium technique was first introduced by Caesalpino et. al. 

4.    Botanical gardens of world have 15% or 35,000 plants species of the world flora.
Tapiary -Beautifying areas 
Bonsai trees -Dwarf trees are grown,in pots 

5.    According to WZCS (World Zoo Conservation Strategies), zoological parks are meant to conserve the species that are particularly endangered in their natural environment. India has about 200 zoological parks. 

 

SUMMARY
1.    The living world is rich in variety. Millions of plants and animals have been identified and described but a large number still remains unknown. 

2.    The very range of organisms in terms of size, colour, habitat, physiological and morphological features make us seek the defining characteristics of living organisms. 

3.    In order to facilitate the study of kinds and diversity of organisms, biologists have evolved certain rules and principles for identification, nomenclature and classification of organisms. 

4.    The branch of science dealing with these aspects is referred to as taxonomy. 

5.    The taxonomic studies of various species of plants and animals are useful in agriculture, forestry, industry and in general for knowing our bio-resources and their diversity. 

6.    The basics of taxonomy like identification, naming and classification of organisms are universally evolved under international codes. 

7.    Based on the resemblances and distinct differences, each organism is identified and assigned a correct scientific/biological name comprising two words as per the binomial system of nomenclature. 

8.    An organism represents/occupies a place or position in the system of classification. There are . many categories/ranks and are generally referred to as taxonomic categories or taxa. All the categories constitute a taxonomic hierarchy. 

9.     The basis of modern taxonomic studies is : External and internal structure, along with the structure of cell, development process and ecological information of organisms 

10.     Taxonomists have developed a variety of taxonomic aids to facilitate identification, naming and classification of organisms. These studies are carried out from the actual specimens which are collected from the field and preserved as referrals in the form of herbaria, museums and in botanical gardens and zoological parks. It requires special techniques for collection and preservation of specimens in herbaria and museums. 

11.     Live specimens, on the other hand, of plants and animals, are found in botanical gardens or in zoological parks. 

12.     Taxonomists also prepare and disseminate information through manuals and monographs for further taxonomic studies. 

13.     Taxonomic keys are tools that help in identification based on characteristics.