Diversity in Organisms

Chapter-1

Diversity in Organisms

Biology is the branch of science which deals with the study of living things. The word biology is derived from two words: Bio means living things and logy means study or discourse. Aristotle is called the father of biology.The main branches of biology are 1. Botany and 2. Zoology.Botany is the branch of biology which deals with the study of plants. The father of botany is Theophrastus.Zoology is the branch of biology which deals with the study of animals. Aristotle is known as the father of zoology.Things which show growth, reproduction, metabolism, ability to sense environment and respond to it and having cellular organization is called “living”.

Characters of living things

Growth.

This is a property of living things. Growth leads to increase in body mass. The growth in living things is internal but in non-living things it is external. In plants growth is continuous but in animals it is limited. Hence growth is not a defining property of living things.

Reproduction

Reproduction may be sexual or asexual. But some living things cannot reproduce, for example mule, sterile worker bees, infertile human couples etc. Hence reproduction is not a defining property of living things.

Metabolism

The sum total of all the biochemical reaction going on inside the living system is called metabolism. Non-living things do not show metabolism, but metabolic reactions can be demonstrated in cell free system (in vitro), hence metabolism and cellular organization is a defining property of living things.

Sensitivity and response to environmental changes

All the living things have ability to sense their environment and to respond it. To respond environmental factors like light, temperature, water etc is the innate tendency of all living things. This is called consciousness. Hence consciousness is the property of living things.

Biodiversity.

The living world comprises an amazing diversity of living organisms-like plants, animals, insects and microorganisms, which we cannot see by naked eyes. Living organisms are present on land, water, air and glaciers. Organisms living in different habitat shows differences concerned with some aspects and similarity concerned with some other aspects. The numbers of kinds of living organisms are between 1.7-01.8 million. This is called biodiversity. Organisms range in size from smallest living organism PPLO (Pleuro Pneumonia like Organism, 80nm) to giant blue whale or sequoia plant.

“Diversity in the living world”-explain.

Organisms are different in colour, structure, behavior, reproduction, physiology and in many more characters. These aspects of the living organisms are known as diversity in the living world. 

Systematics

Systematic is the scientific study of similarities and differences among different kinds of organisms and it also includes their identification, nomenclature and classification. Systematics takes in to account evolutionary relationships between organisms. Linnaeus published the book “Systema naturae” (1735).

Taxonomy

Taxonomy is the branch of biology which deals with the collection, identification, nomenclature, description and classification of living things.

Objectives of taxonomy/ systematics?

1. To know various kinds of plants on the earth with their names, affinities, geographical distribution, habit, characteristics and their economic importance.
2. To make reference system.
3. To demonstrate diversity of organisms and their phylogenetic relationships.
4. To give scientific name for every organisms.

Classification?

Arrangement of organisms according to their differences and similarity into different groups. These categorizing organisms are called classification.

Need of classification?

To study the entire living organisms in the life of a man is impossible. If we categorize the living things into smaller groups and study the general character of this group, which represent the character of the entire organisms in that group, then only we can study the entire living things in the universe. Hence we need a system of classification.

Three domains of life

The three domain system was developed by Carl Woes in 1990. The previous system of classification was based on the phenotypes of organisms, but the three domain system is based on differences in ribosomal RNA structure of different groups of organisms. According to this organisms are classified into three domains and six kingdoms. The three domains are archae, bacteria and eukarya. The domain archae and bacteria include prokaryotic organisms. It includes the kingdom archae bacteria and the kingdom eubacteria. The domain eukarya include all eukaryotics. The four kingdoms under this domain are kingdom protista, fungi, plantae and animalia.

Taxonomic hierarchy

Classification is not a single step process but involves hierarchy of steps in which each step represents a rank or category. The entire taxonomic category together constitutes the taxonomic hierarchy. Each category is referred as a rank and is commonly called taxon (Pl: taxa).

Taxon?

Taxon is a group of living organisms which is used to represent a concrete unit of classification. The term taxon was coined by H.J.Lam in 1948 for plants.

Category?

A category is a rank or level in the heirachial classification of organisms. Species is the smallest and kingdom is the largest category.

                            Classify China rose and cobra with all the categories and taxon.

                   Schematic diagram to show the units of classification

Taxonomic categories

1. Species

Species are the lowest unit of classification. It is a group of closely related organisms which can be interbreed and produce fertile offspring.

e.g.: Masngifgera indica, Solanum tuberosum, Panthera leo. All the three names indica, tuberosum and leo represents species name and Mangifera, Solanum and Panthera represents  another higher level of taxon or category. Each genus contains one or more species representing different organisms, but has morphological similarities. E.g. Panthera has another species tigris and Solanum includes species like nigrum and melonena.

      Human being belongs to the genus Homo and species sapiens; hence the scientific name of human being is Homo sapiens.

2.Genus

Genera are aggregates of closely related species. For example, potato and brinjal are two different species but both belong to the genus Solanum. Leo (Panthera leo), leopard (P.pardus) and tiger (P.tigris) with several common features are all species of the genus Panthera. This genus differ from another genus Felis which includes cats.

3.Family

Family is an aggregate of closely related genus. Families’ area characterized both vegetative and reproductive features of plants species. For example, three different genera Solanum, Pentunia and Datura are placed in the same family Solanaceae. The genus Panthera, comprising lion, leopard and tiger is put along with genus Felis (Cat) in the same family Felidae.

4.Order

Order is the aggregate of families which exhibit a few similar characters. For example, the family solanaceae, Convolvulaceae are included in the order Polymoniales based on the floral characters. The animal family canidae and felidae are included in the order carnivore.

5.Class

Related order forms class. For example, order primate comprising monkey, gorilla and gibbon is placed in class mammalian along with order Carnivora that includes animals like tiger, cat and dog.

6.Phylum

Classes comprising animals like fishes, amphibian, reptiles, and birds along with mammals constitute the next higher category called phylum. All these are based on the common features like presence of notochord and dorsal tubular nerve cord. In plants instead of phylum we say division.

7.Kingdom

All animals belongs to various phyla are assigned to the highest category called Kingdom animalia, similarly kingdom plantae. Each category may include sub category also.

[King Philip Came Over For Good Soup]

Thus there are seven obligatory taxonomic categories

Nomenclature

The process of naming an organism which can be agreed all over the world is known as nomenclature. For this purpose scientist all over the world established procedures which can be acceptable to biologists all over the world. For plants scientific names are based on some criteria which are provided in International Code for Botanical Nomenclature (ICBN), similarly for animals International Code of Zoological Nomenclature (ICZN).

Vernacular name

These are the names given to organisms in a particular region and language by local people. All plants and animals are known by different common names in different parts of the world. Some times in different sates of a country plants and animals known differently.

E.g.  Ipomea batatas

In English it is known as sweet potato

In Hindi it is known as Shakarkand

In Asamese and Bengali it is known as Meetha alu

In Telugu it is known as kandamul

In Marathi it is known as Ratalu

In Kannada it is known as Jenasu etc

More over single vernacular name is used for several species is also in practice. For example the name “lily” is used for water lily, spider lily etc. vernacular names are misleading also, for example star fish, jelly fish, silver fish are not fishes at all. Thus vernacular names are fully confusing. Another demerit of the vernacular name is it is very short, do not communicate any necessary information and do not indicate proper relationships.

Scientific name

These names are based on some principles and criteria which are accepted all over the world. In early times the scientific names was polynomial and lengthy. For example Sida acula was named as Chrysophyllum follies avails supreme glabris parallel striates subtis tomento sonitidis. Hence to make it easier and meaningful, binomial system of nomenclature was introduced.

Binomial nomenclature

A system of providing name with two components is called binomial nomenclature. This naming system was given by Carolus Linneus (Swedish botanist and physician, Carl von Linné, 1707–1778). He introduced this system in his book “Species plantarum”. By this system name of each organism has two components-the generic name and specific name.

Example: The scientific name of mango tree is Mangifera indica .Here Magifera represents the genus name and indica represents the species name or specific epithet.

Rules for Binomial nomenclature

1. The names are generally in Latin or Latinized and written in italics.
2. The first word in the binomial nomenclature is the genus name and the second component is specific name.
3. Both words in a biological name, are separately underlined in hand written and in italics in print.
4. The genus name must start with capital letter while specific name start with small letter.
5. The genus name is always a noun or an adjective, species name has no grammatical rule.
6. The generic name and species name should not contain less than three letters and more than thirteen letters.
7. The generic name should not be repeated, but species name can be repeated, for example mangifera indica (Mango) and Azadirachta indica (neem).

Eg: Mangifera indica  

Name of the author appears after the species name, in the abbreviated form.e.g: Mangifera indica Linn. It indicates this species was first described by Linnaeus. This nomenclature is only possible when the organism is described correctly and we know to what organism the name is attached. This is called identification. 

Advantages of binomial nomenclature?

Advantage of binomial nomenclature

1. These names are simple, meaningful, precise and standard.
2. These are accepted universally.
3. By this system confusion due to local names are avoided.
4. The binomial names are easy to understand and remember.
5. It indicates phylogenetic relationship.

Biological classification

The first known classification system was developed more than 2000 years ago by the Greek philosopher and naturalist Aristotle.  He classified all organisms as either plant or animal.  He further classified the animals depending on where they lived: land animals, water animals, and air animals.  Theophrastus, one of Aristotle’s students, further classified plants according to their kind of stem: herbs, shrubs, and trees. Aristotle’s system had problems.  For example – bats, birds, and mosquitoes were all classified in the same group because they fly, however, they a