Life is a complex organization of molecules that is unique and leads to growth, development, responsiveness adaptation, and reproduction. Living organisms are evolving, self-replicating, and self-regulating interactive systems.
1.Distinctive Characteristics Exhibited By Living Organisms
The fundamental characteristics of livings are those which are found in livings and absent in non-livings. The characteristics of livings found in all livings are called defining features. The fundamental characteristics are
Growth,
Reproduction,
Ability to sense the environment,
Metabolism,
Ability to self-replicate,
Self-organize,
Interact and Emergence.
I.Growth
An increase in mass and an increase in the number of individuals are twin characteristics of growth.
A multicellular organism grows by cell division.
In plants, this growth by cell division occurs continuously throughout their life span while 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.
However, this kind of growth exhibited by non-living objects is by accumulation of material on the surface while in living organisms, growth is from inside.
Growth, therefore, cannot be taken as a defining property of living organisms.
II. Reproduction
In multicellular organisms, 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 allinclusive defining characteristic of living organisms.
III. Metabolism
The sum total of all the chemical reactions occurring in our body is called 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. It is called living reaction.
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.
IV. 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.
V. Ability to sense the environment and mount a suitable response
The most obvious and technically complicated feature of all living organisms is the 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 selfconsciousness.
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.
2. Diversity In The Living World
Our earth has high bio-diversity as it has about 1.7-1.8 million species.
These include nearly 1.2 million animal and over 0.5 million species of plants. Amongst animals insects form the largest group i.e, over 1025000 species.
On the basis of similarities and differences, organisms are placed into groups or subgroups. It is called classification.
Claasification throws light on the origin of organisms gives information about evolutionary relationship between organisms and it is important to know bio-resources and bio diversity.
Taxonomy the branch dealing with the study of principles and procedure of classification of organisms.
Characterisation, identification, nomenclature and classification are steps of taxonomy.
Carolus Linnaeus is known as father of taxonomy.
Systematics is taxonomy and evolutionary history of organisms (phylogeny).
Nomenclature
Different organisms are known by their local names in different areas so there is a need to standardize the naming of living organisms such that a particular organism is known by the same name all over the world. This process is called nomenclature.
Standardisation of scientific names is provided by
ICBN (1961): International code of Botanical Nomenclature.
ICZN (1964): International code of Zoological Nomenclature.
ICNB : International code for nomenclature of Bacteria.
ICNCP : International code of nomenclature for cultivated plants.
ICTV : International committe for taxonomy of Virus.
Universally accepted principles to provide scientific names –
Each name has two components – the Generic name and the specific epithet. This system
of providing a name with two components is called Binomial nomenclature – given by
Carolus Linnaeus.
e.g., mango – Mangifera indica. (Mangifera – genus name, indica – species epithet).
Biological names are generally in Latin and written in italics.
Both the words in a biological name, when handwritten, are separately underlined, or printed in italics to indicate their Latin origin.
The first word denoting the genus starts with a capital letter while the specific epithet starts
with a small letter.
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.
Linnaeus used Systema Naturae as the title of his publication.
I. 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 lowest category and kingdom is the highest category. There are seven obligate
categories.
The number of organisms increases when one goes from lower to higher category.
The number of common characters decreases from species to kingdom but the number of general characters increases from species to kingdom.
So as one move from species to the kingdom, classification becomes more complex and it becomes difficult to establish relationship among organism at higher category.
3. TAXONOMICAL AIDS
I. 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.
II. 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, Lucknow (India).
III. 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.
IV. 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 behavior.
V. 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.
VI. 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. e.g. Flora Indica, Flora of Delhi.
Manuals are useful in providing information for identification of names of species found in an area. It is handy book. e.g The manual of cultivated plants.
Monographs contain information on any one taxon like family or genus. e.g the Pinus.
Catalouge is a list of all species arranged methodically found in a particular area often with brief description.
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