The Living World class 11 notes

The Living World class 11 notes

The Living World class 11 notes

The Living World

Living has many definitions depending on the organism’s use and body structure. Some of the most important are Growth, reproduction, sense ability towards environment and response production ability in regards to that environment factor. All these features strike our thought immediately as these are the unique features of almost all the living organisms. Some important characteristics with respect to the living world are metabolism, replication or cloning, well managed and organised, respond towards environment and habitat and act accordingly.

Characteristic of Living Beings

Living organisms as a whole have certain unique and basic characteristic that sets them apart from the non-living world.


This is a common and unique feature of all the living organisms. Growth is observed in twin characters of increase in mass and increase in the number of individuals.

Any multicellular organism will grow by cell division of parent cell. Plants grow continuously throughout their life through cell division. Even animals grow with cell division till a certain age, then cell division is just to repair the wear and tear of the body. Cell division is growth as well as multiplication factor in unicellular organisms. This cell division as growth factor is visible in in-vitro culturing of tissues. Higher multicellular organisms grow and multiply mutually. The growth of an organism is clearly visible from its body mass. Growth property alone cannot define living organisms. Thus, growth is a characteristic of the living world. Simply, an organism which is now dead does not grow.

Growth in cells occurs due to the synthetic property of the cell to produce protoplasmic and non-protoplasmic or apoplasmic substances. Protoplasmic substances are living components used by the cell-like – cytoplasm, nucleus, organelles, etc. while apoplasmic substances are non-living parts like chemicals, gases which are used by cell and then thrown out of the cell.


Reproduction is a major distinguishing characteristic of living organisms. Multicellular organisms reproduce to generate progeny having similar features of parents. Fungi produce asexual spores which spread nearby and give rise to new fungi. Yeast and Hydra multiply by separation of their new bud from themselves which grows into a new organism called as budding. Planaria (flatworms) have special characteristics of regenerating lost parts of the body by fragmentation and the process is called as true regeneration. The fungi, the filamentous algae, the protonema of mosses, use fragmentation as a reproductive feature. Unicellular organisms like bacteria, algae or Amoeba reproduce and grow synonymously, i.e., an increase in the number of cells is an indication of growth as well as reproduction. Hence, single-celled organisms have growth and reproduction at the same time and is a combined feature.

Reproduction is not the fixed feature of organisms as there are organisms that do not multiply (mules, sterile worker bees, infertile human couples, etc.).


Life shows metabolism inside the organism’s body. All living organisms are made of organic components called as biomolecules. These chemicals are constantly produced and modified in the cell. The modification is due to the number of reasons and help of other chemicals resulting in a metabolic reaction or biochemical reaction. There are several metabolic reactions which occur simultaneously in a cell in all living organisms, including all unicellular and multicellular ones.

The sum total of all the chemical reactions that occur in our body is called as metabolism. This metabolic reaction can be forced to take place in systems similar to the body but outside the body in cell-free systems. Such a forced metabolic reaction(s) outside the body of an organism, is carried in a test tube which creates body environments and 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.

The Living World class 11 notes

Cellular Structure

Cellular organisation of the body is the characteristic which can be a defining feature of life forms. Conceivably, the most obvious and scientifically complicated feature of all the living organisms is the presence of a cell in their body. Unicellular body is made of a single cell that performs all the functions of the organism. Multicellular organisms are made of many cells which are differentiated into specific group performing their defined functions. Cells as a whole are made of simple common organelles and chemicals. These cells unite to form and perform an organism and its functions respectively.


The ability of living organisms to sense their surroundings or environment and respond to these environmental stimuli (physical, chemical or biological) is called consciousness. The sense of our environment is through our sense organs in the body and response type changes from organism to organism. Plants respond through their growth pattern and locomotory movements to external factors like light, water, temperature, other organisms, pollutants, etc. All organisms on the planet, be it prokaryotes or the most complex eukaryotes, sense and respond to environmental stimuli. All organisms have their body structure in a way to deal with the chemicals that enter their bodies. Living organisms, therefore, are ‘aware’ of their surroundings. Consciousness thus is the defining property of living organisms.

Diversity in the Living World

We find a huge degree of variety in living organisms around ourselves, ranging from potted plants to insects, birds, the pets or other animals and plants, huge trees. There is a world of organism which is left unseen with naked eyes but is omnipresent. The dense forest will have a much greater amount and variety of living organisms in it. Every organism that we observe in the surrounding belongs to a particular species and genus. The number of species that are studied and described range anywhere between 1.7- 1.8 million. This indicates the biodiversity or the variety of organisms that are present on earth. Every time a new area is explored, new and even old organisms are being identified and studied.

Need for Classification of Organisms

This was done to make it easier for the study of an organism’s possible scientist has divided organisms into different levels and groups. The basis for differentiation was similarities and differences. This made it possible to bring all organisms into one single table or ground to study. The similarity is common in species placed in one group and decreases as it goes up.

Why the need to classify?

It will help to learn:

  • Importance to estimate the inter-relationship between the organisms.
  • The basics of the development of organisms and thus develop a base for other science streams.
  • Variety of biological studies are dependent on the identification and classification of the organism.

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. Father of taxonomy is Linnaeus as he classified organisms on a broader perspective. Santapau is called as father of Indian Taxonomy. The fundamental sections of taxonomy are as follows:

  • Characterisation and identification: It deals with the determination of the similarities of a new organism with an already known organism, based upon specific characters.
  • Nomenclature: It involves naming of the organism with binomial criteria according to established universal rules.
  • Classification: It is arranging organisms into convenient categories on the basis of visible and easy to study character.

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

  • External and internal structure of the organism along with the structure of the cell in it.
  • Development process of the organism.
  • Ecological information of all the organisms.

Systematics: The word “systematics” is systema meaning systematic arrangement of organisms according to the Latin language. The word was first used by Carolus Linnaeus. He stated that “systematics is the relationships amongst the organisms”.

Generally, the terms like classification, systematics and taxonomy are interchangeably used by taxonomist, but some exceptions like taxonomist Simpson (1961) relate all of them to a separate field. He defined systematics as “The study of the 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:

  • Systematics helps in providing knowledge of the 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, a vivid picture of entire organic diversity.
  • Systematics makes easy for identification which gives useful information about the phylogeny of organisms.
  • It helps to identify newly discovered organisms through systematics.


Nomenclature means the method of naming the organism scientifically and universally. The point arises for the need of nomenclature. There is a common name of the organism in its local language and this name keeps changing with the change in language. Thus there is a need to standardise the names of all the living organisms, such that a particular organism has the same name all over the world. A list of nomenclature methods necessary for assigning a name to the organism are described below:

Vernacular name:

Names in local or regional language are called vernacular names. There are many vernacular names that exist in the world for an organism. These names vary from place to place in a country and even in a state.

Scientific names:

These names are assigned to the organism from scientist based on definite rules and criteria. These are of following types:

  • Polynomial nomenclature
  • Trinomial nomenclature
  • Binomial system of nomenclature: Swedish botanist Carolus Linnaeus established binomial nomenclature, which was first proposed by Caper Bauhin expressed in his book PINAX. In binomial nomenclature, the first word is a generic name having first letter capital and the second word is a specific epithet having first letter small like Mangifera indica.  After the end of the biological name, the name of the author is written in abbreviated form who gave the name to that organism.

Scientific names are in Latin, as Latin was the language known to all the scholars and also called as Language of scholars. Linnaeus was among several scientists who used Latin words and no change can be made in the language. This is because the Latin language lacks synonyms. Linnaeus gave some principles of the binomial nomenclature for around 5900 species of plants with their descriptive briefing in the book “Species Plantarum” (1753). Later he also a book for animals including 4326 species with their respective detailed study and published the book as “Systema Naturae” (1758).

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 (ICBN), International Code of Nomenclature for Cultivated Plants (ICNCP) and currently being developed is International Committee for the Taxonomy of Viruses (ICTV).

Rules for Binomial Nomenclature

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

  • The scientific and universal name of an organism contains two components, 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 of a biological name when handwritten are separately underlined and when printed are typed in italics to indicate their Latin origin and also give respect to the name.
  • The name of the author is also to be mentioned post scientific name in Roman type with a 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 a modern man.
  • Scientific names should not be as small as three letters or as long as twelve letters.
  • Principle of priority: It is the most important of all the rules of ICBN. If the initial name given to the organism is valid and right (in terms of rules), that name will be considered as the name of that organism. Any other valid and right name given later than the initial name will be considered as a synonym. No names are recognised before the names that were used by Linnaeus in 1758 in the 10th edition of Systema Naturae for animals and 1753 for the plants.
  • All the three words (generic name, species epithet and author citation) together form binomial epithet or name of the organism.
  • If a species name has two or more words in its name, a hyphen is put between these words to separate them and yet link them as a single name of that organism. E.g., Hibiscus rosa sinensis for shoe flower).

Taxonomic Categories

Classification involves a hierarchy of steps and levels in which every step represents a rank or a category. Classification of the organism is not a simple process of one step. The category is a part of the overall taxonomic arrangement and it is called the taxonomic category and all categories together constitute the taxonomic hierarchy. Each category is referred as a unit of classification that represents a rank, commonly termed as the taxon (pl.: taxa).

Each rank or taxon, in turn, represents a unit or level of classification. These taxonomic groups or categories are distinct biological entities and not just the morphological aggregates. Taxonomical studies of all known organisms have led to the development of grouping the taxons on the larger scale with common categories such as kingdom, phylum or division (for plants), class, order, family, genus and species.

The Living World class 11 notes

The basic necessity in classifying the organism is the knowledge of the characters of an individual or group of organisms. This knowledge helps to identify the similarities and dissimilarities among the individuals of the similar kind and dissimilar organisms.


A group of individual organisms with similar morphological characters which are able to breed among themselves and produce their own kind is termed as a species. For example, Mangifera indica (mango), indica represent the specific epithets, while the first words Mangifera is genera and represents another higher level of taxon or category. Human beings belong to the species sapiens which is grouped in the genus Homo.


The first higher category above the species level. Genus is a group of related species which has more characters in common in comparison to species of other genera. For example, potato, tomato and brinjal are three different species but all belong to the genus Solanum.


The next category, Family, has a group of related genera differentiated from other related families by certain characteristic differences. For example, three different genera Solanum, Petunia and Datura are placed in the family Solanaceae.


An order is the assemblage of families resembling one another in a few similar characters. The similar characters are less in number as compared to different genera included in a family. 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 Canidae.


This category includes one or more related orders. For example, order Primata comprising monkey, gorilla and gibbon is placed in class Mammalia along with order Carnivora that includes animals like tiger, cat and dog. Class Mammalia has other orders also.


It includes all organisms belonging to different classes like fishes, amphibians, reptiles, birds along with mammals having a few common characters. In case of plants, classes with a few similar characters are assigned to a higher category called Division.


It includes all organisms that share a set of distinguishing common characters. Plants are put in the Plant Kingdom and animals are included in the animal kingdom. It is the highest taxonomic category. The number of similar character to the members of a group decreases from species to kingdom, i.e., the number of a species are most similar while that of kingdom share least similar characters.

Taxonomic Aids

Techniques, procedures and stored information that are useful in identification and classification of organisms are called taxonomic aids.

Some of the important taxonomic aids are:


A collection of plants that usually have been dried, pressed and preserved on shelves for reference is called herbarium.

Botanical Garden:

A collection of living plants maintained for reference. The largest botanical garden is in Moscow. The most famous botanical garden is the Royal Botanical Garden, Kew.

Zoological Parks:

Enclosed areas where animals are kept in open enclosures instead of cages. It helps to study wild animals and their food habits. It is useful for ex-situ conservation through captive breeding of endangered animals.


A place used for storage, preservation and exhibition of objects of natural history, art and objects of natural antiquities. It provides information not only about local flora and fauna but also of other areas.


It was given by John Ray. This scheme is for identification of plants and animals based upon similarities and dissimilarities. It is based on the contrasting characters generally in pairs called couplet, each character of the couplet is called as lead. The one present in the organism is chosen and the other is discarded. Separate keys are used for each category.

Monographs (information on any one taxon), manuals (information for identifying species in an area), flora ( account of habitat and distribution of plants of a given area) and catalogues are some useful taxonomic aids.

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