The living world

Biology is the branch of science deals with the study of living things and a relationship between the structure of an organism and adaptation to its function or environment. Organisms are living things such as plants or animals. They have a unique feature of growth, reproduction, metabolism, movement,ability to sense the environment and mount a suitable response etc..

Characteristics of living organisms
The permanent and irreversible increase in cell number and size is called growth Increase in mass and increase in numbers of cells are two characteristics of growth. .
Growth is seen in all living organisms.In plants, growth occurs continuously throughout their life span but in animals, growth is seen only up to a certain age.
Non -living objects grows by an accumulation of particles in their outer surfaces .eg – A snowball due to accumulation of its own of the outer surfaces.

All living organisms have the ability to produce offspring having feature more or less similar to those of parents.
All living things reproduce in one of the following ways
Asexual reproduction– Producing offspring without the use of gametes .
Sexual reproduction– Producing offspring by the joining of a sex cell.
There are many organisms which do not reproduce (Mules, sterile, infertile human couples etc). So, we can say reproduction can-not be all-inclusive defining characteristics of living organisms.


The sum total of all chemicals reaction occurring inside the living body called metabolism. There are two types of metabolic reaction.
a. Catabolic reaction – Complex substances break down into simpler substances. It releases energy .eg. glycogen breaking down into glucose, Protein into amino acids
b. Anabolic reaction – simpler substance converted into complex substances. They require energy .eg.Photosynthesis

Organisms are very sensitive and possess wonderful power of responding to an external influence called stimuli. A stimulus may be physical(Heat or light), chemical(acids or base)and mechanical (Touch or contact). All organisms from the prokaryote to the most complex eukaryotes can sense and respond to environmental cues. The roots of the plant go deep into the soil under the influence of the force of gravity, and a muscles contracts when stimulated by an electric shock.
Photoperiods affects reproduction in seasonal breeders.

5.Maintain a stable environment
The ability of an organism to maintain its internal environment despite the condition in the external environment called Homeostasis.
Shivering is an example of Homeostasis to keep the body warm.

6.Cellular organisation
A Living body is highly organised and it consists of closely correlated parts organs such as leaves of plants or lungs .Each organ assigned to a particular function .
An orgn is composed of small protoplasmic unit known as the cells .Group of similar cells which have a particular function are organised to form a tissue and collection of tissues constitute an organ .The orgns are interrelated with one another and work together in a spirit of cooperation .
In the lowest form of life the entire protoplasm into a single cell which by differentiation of its parts carry on the essential life function .

7.Life cycle
A living organisms has a definite life cycle .In the young or trophic stage it takes food and grows actively .when fully grown ,it reproduce . After a definite life span they become old and finally dies out.
Every organisms has a definite life span and it varies different kind of plant and animals .The tiny Diwali insects completed its life span in few hours and dies out where gigantic Banyan tree lives for more than one hundred years.

Diversity in the living world
Biodiversity is the sum of total and different types of organisms present on Earth. There are different organisms present on Earth ,some have similar to one another and some are dissimilar so it’s important them to categorise in a group . This categorise called nomenclature .

Identification is the comparison similarities and different with already ones .
Nomenclature – Naming of organisms .The names are unique and universal .

Universal rule of nomenclature are as follows
1. Biological names are generally in latin and written in italics

2.The world in biological name represent the genus while the second component denotes the specific epithet .

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

4.The first world denoting the genus starts with small letter .It can be illustrated with example of mangifera indica.

Binomial Nomenclature – Bionomenclature is Naming of organisms with two parts – Generic name and specific epithet.

Rules for Nomenclature are provided by as follows
1.ICBN– International code for Botany nomenclature .

2.ICZN– International code for Zoological nomenclature .

species is commonly used and basic unit of classification.Species is group of organisms with fundamental similarities .eg – mangifera indica,. panthera Leo

Genus comprises ,group of related species which has more characteristics in common in comparison to species of other genera .
Eg- potato and brinjanl are two different species but both belongs to genus solanum
Lion(panthera Leo) ,leopard(panthera pardus) and tiger(panthera Tigris) with common several features are all spescis of genus panthera .

Family has a group of related genera with stil less number of similarities as compared to genus and species.
Eg- solanum,petunia and dathura placed in the family solanaceae .

You have seen earlier that categories like species genus and families are based on number of similar charector .Generally, order and other higher taxonomic categories are identified on the basis of aggregate charector .
Eg- plant families like convovolvulaceae, solanaceae are included in the order polynomials .

This category includes related order .

Class comprising animals like fishes ,amphibians ,reptiles bird along with mammals constitute .In case of plants, Class with a few similar charector are assigned to a higher category called divisions .

Kingdom is a highest category in this system.All animal belonging to various phyla comes under kingdom animal and plants belonging to various phyla comes under kingdom plantae.

Taxonomic aids
Taxonomic studies is used in various fields (agricultural, forestry, etc) and helps us to know about our biodiversity .some of common taxonomical aids are herbaria, botanical gardens,Museum, zoological park etc

Herbarium is a store house of collected plant speciman that are dried passed and preserve on sheet .The herbarium sheets also carry a labelling providing information about date and place of collection ,English ,local and botanical names ,family ,collector’s names etc
Herbarium also serve as quick referral system in taxonomic studies.

Botanical garden
Specialised garden have collection of living plants for reference .Each plant is labelled indicating his botanical/scientific name and its family .
The famous botanical gardens are at Kew (England),Indian botanical garden Howrah (India) etc.

Biological museum are generally set up in educational set up in educational institutes such as school and college .They have collection of presented plant and animal speciman for study and reference where speciman are preserved in containers and jars in preservative solution .
They are preserved in insects boxes after collecting,killing and dinning whole larger animal like birds are usually stuffed and preserved .

Zoological park
A place where wild animals are kept in a protected environment under human care and which enable us to learn about their food habits and behaviour

Key is taxonomical aid used for identification of organisms based on similarities and dissimilarity. Key is based on contrasting character generally in a pair called a couplet. It is basically analytical in nature.

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