1. The Living World

Definitions of Life are:

1. The quality that distinguishes a vital and functional being from a non-living or dead body or purely chemical matter.
2. The state of a material complex or individual characterized by the capacity to perform certain functional activities including metabolism, growth, and reproduction.
3. The sequence of physical and mental experiences that make up the existence of an individual.

CHARACTERISTICS of LIVING

• Growth
• Reproduction
• Metabolism
• Cellular Organisation
• Consciousness.

Growth

●Increase in mass and increase in number of individuals are twin characteristics of growth.

●A multi cellular organism grows by cell division.

●In plants, this growth by cell division occurs continuously throughout their life span.

●In animals, this growth is seen only up to a certain age.

Unicellular organisms also grow by cell division.

●Non-living objects also grow if we take increase in body mass as a criterion for growth. ●Growth exhibited by non-living objects is by accumulation of material on the surface.

●In living organisms, growth is from inside.

Growth, therefore, cannot be taken as a defining property of living organisms.

Reproduction

●Reproduction refers to the production of progeny possessing features more or less similar to those of parents.

●Organisms reproduce by sexual and asexual means.

Some methods of asexual reproduction –

Spores – Fungi.

Budding – yeast and hydra.

True regeneration – Planaria (flat worms).

Fragmentation – The fungi, the filamentous algae, the protonema of mosses.

●In unicellular organisms, reproduction is synonymous with growth.

►There are many organisms which do not reproduce (mules, sterile worker bees, infertile human couples, etc).

Hence, reproduction also cannot be an all-inclusive defining characteristic of living organisms.

Metabolism –

●The sum total of all the chemical reactions occurring in our body is metabolism.

●All plants, animals, fungi and microbes exhibit metabolism.

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

●An isolated metabolic reaction(s) outside the body of an organism, performed 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.

Cellular organization –

Cellular organization of body is defining feature of all life forms as body of all living being consist of cell(s).

Cell is smallest independent possible unit of life which can sustain itself.

Consciousness : Ability to sense environment–

●The most obvious and technically complicated feature of all living organisms is this ability to sense their surroundings or environment and respond to these environmental stimuli.

●We sense our environment through our sense organs.

●All organisms, from the prokaryotes to the most complex eukaryotes can sense and respond to environmental cues.

●All organisms are aware of their surroundings.

●Human being is the only organism who is aware of himself, i.e., has self-consciousness.

 ►Consciousness therefore, is the defining property of living organisms.

All living phenomena are due to underlying interactions. Properties of tissues are not present in the constituent cells but arise as a result of interactions among the constituent cells. Similarly, properties of cellular organelles are not present

in the molecular constituents of the organelle but arise as a result of interactions among the molecular components  comprising the organelle.

These interactions result in emergent properties at a higher level of organisation. This phenomenon is true in the hierarchy of organizational complexity at all levels.

Therefore, we can say that living organisms are self-replicating, evolving and self-regulating interactive systems capable of responding to external stimuli.

Diversity In The Living World

● The number of species that are known and described range between 1.7-1.8 million. ●Biodiversity refers to the number and types of organisms present on earth.

Nomenclature: Different organisms are known by their local names in different areas so there is a need to standardise the naming of living organisms such that a particular organism is known by the same name all over the world.

Identification: Nomenclature or naming is only possible when the organism is described correctly and we know to what organism the name is attached to.

►For plants, scientific names are based on agreed principles and criteria, which are provided in International Code for Botanical Nomenclature (ICBN).

►For animal there is International Code of Zoological Nomenclature (ICZN).

The scientific names ensure that each organism has only one name.

Binomial nomenclature: The system of providing a name with two components is called Binomial nomenclature. This naming system given by Carolus Linnaeus.

●Each name has two components – the Generic name and the specific epithet.

Universally accepted principles to provide scientific names –

1. Biological names are generally in Latin and written in italics. They are Latinised or derived from Latin irrespective of their origin.

2. The first word in a biological name represents the genus while the second component denotes the specific epithet.

3. Both the words in a biological name, when handwritten, are separately underlined, or printed in italics to indicate their Latin origin.

4. The first word denoting the genus starts with a capital letter while the specific epithet starts with a small letter. Example: Mangifera indica.

Name of the author appears after the specific epithet, i.e., at the end of the biological name and is written in an abbreviated form, e.g., Mangifera indica Linn. It indicates that this species was first described by Linnaeus.

Classification is the process by which anything is grouped into convenient categories based on some easily observable characters.

The scientific term for these categories is taxa.

Taxonomy :. The process of classification of all living organisms  into different taxa on the basis of characteristics.

External and internal structure, along with the structure of cell, development process and ecological information of organisms are essential and form the basis of modern taxonomic studies.

Characterisation, identification, classification and nomenclature are the processes that are basic to taxonomy.

Systematics: The word systematics is derived from the Latin word ‘systema’ which means systematic arrangement of organisms.

It is the branch of study about different kinds of organisms, their diversities and the relationships among them.

Linnaeus used Systema Naturae as the title of his publication.

The scope of systematics was later enlarged to include identification, nomenclature

and classification. Systematics takes into account evolutionary relationships between organisms.

Taxonomic Categories

●Classification involves hierarchy of steps in which each step represents a rank or category.

●Since the category is a part of overall taxonomic arrangement, it is called the taxonomic category and all categories together constitute the taxonomic hierarchy.

●Each category, referred to as a unit of classification, represents a rank and is commonly termed as taxon.

Species → Genus → Family → Order → Class → Phylum or Division → Kingdom

Species: is the basic unit of biological classification and a taxonomic rank.

●A species is often defined as the largest group of organisms in which two individuals can produce fertile offspring, typically by sexual reproduction.

Ex:-

Mango:  Mangifera indica

Potato:  Solanum tuberosum

Lion:      Panthera leo

Makoi:   Solanum nigrum

Brinjal:  Solanum melongena

Genus: a group of related species.

Ex:

●Potato,tomato and brinjal are three different species but all belong to the genus

Solanum.

●Lion (Panthera leo), leopard (P. pardus) and tiger (P. tigris) with several common features, are all species of the genus Panthera.

● This genus differs from another genus Felis which includes cats.

Family: a group of related genera with less number of similarities as compared to genus and species.

● Families are characterised on the basis of both vegetative and reproductive features of plant species.

Ex:

●Genera Solanum, Petunia and Datura are placed in the family Solanaceae.

 ●Genus Panthera, comprising lion, tiger, leopard is put along with genus, Felis (cats) in the family Felidae.

●Similarly, cat and a dog are separated into two different families – Felidae

and Cancidae, respectively.

Order: is the assemblage of families which exhibit a few similar characters.

●The similar characters are less in number as compared to different genera included in a family.

Ex:

●Plant families like Convolvulaceae, Solanaceae are included in the order Polymoniales mainly based on the floral characters.

●The animal order, Carnivora, includes families like Felidae and Cancidae.

Class: This category includes related orders.

Ex:

●Order Primata comprising monkey, gorilla and gibbon is placed in class Mammalia along with order Carnivora that includes animals like tiger, cat and dog.

Phylum / Division(Plants): Classes comprising animals like fishes, amphibians, reptiles, birds along with mammals constitute the next higher category called

Phylum.

●All these, based on the common features like presence of notochord and dorsal hollow neural system, are included in phylum Chordata.

Kingdom: All animals belonging to various phyla are assigned to the highest category called Kingdom Animalia in the classification system of animals.

●The Kingdom Plantae, on the other hand, is distinct, and comprises all plants from various divisions.

► As we go higher from species to kingdom, the number of common characteristics goes on decreasing.

Common Name	Biological Name	Genus	Family	Order	Class	Phylum/ Division
Man	Homo sapiens	Homo	Hominidae	Primata	Mammalia	Chordata
Housefly	Musca domestica	Musca	Muscidae	Diptera	Insecta	Arthropoda
Mango	Mangifera indica	Mangifera	Anacardiaceae	Sapindales	Dicotyledonae	Angiospermae
Wheat	Triticum aestivum	Triticum	Poaceae	Poales	Monocotyledonae	Angiospermae

TAXONOMICAL AIDS

Herbarium

Herbarium is a store house of collected plant specimens that are dried, pressed and preserved on sheets.

These specimens, along with their descriptions on herbarium sheets, become a store house or repository for future use.

The herbarium sheets also carry a label providing information about date and place of collection, English, local and botanical names, family, collector’s name, etc.

Botanical Gardens

●These specialised gardens have collections of living plants for reference.

●Plant species in these gardens are grown for identification purposes and each plant is labelled indicating its botanical/scientific name and its family.

►Some famous botanical gardens:

●Kew (England)

●Indian Botanical Garden, Howrah (India)

●National Botanical Research Institute(NBRI), Lucknow (India).

Museum

●Biological museums are generally set up in educational institutes such as schools and colleges.

●Museums have collections of preserved plant and animal specimens for study and reference.

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

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

●Larger animals like birds and mammals are usually stuffed and preserved. Museums often have collections of skeletons of animals too.

Zoological Parks

●These are the places where wild animals are kept in protected environments under human care and which enable us to learn about their food habits and behaviour.

Key

●Key is taxonomical aid used for identification of plants and animals based on the similarities and dissimilarities.

●The keys are based on the contrasting characters generally in a pair called couplet.

●It represents the choice made between two opposite options. This results in acceptance of only one and rejection of the other.

●Each statement in the key is called a lead.

●Separate taxonomic keys are required for each taxonomic category such as family, genus and species for identification purposes.

Keys are generally analytical in nature.

Flora, Manuals, Monographs, 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.

Manuals are useful in providing information for identification of names of species found in an area.

Monographs contain information on any one taxon.

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