Notes of Ch 1 The Living World| Class 11th Biology

Study Material and Notes of Ch 1 The Living World Class 11th Biology

Topics in the Chapter

• Introduction
• What is ‘Living’?
• Diversity in the Living World
• Taxonomic Categories
• Taxonomical Aids


The life is life is full of amazing diversity of living organism. The diversity of habitats are very vast and deeply reflects on “What indeed is life”. This question has two implicit questions within it. The first is a technical one and seeks answer to what living is as opposed to the non-living, and the second is a philosophical one, and seeks answer to what the purpose of life is.

What is Living?

The main characteristics of living are:
(i) Growth
(ii) Reproduction
(iii) Metabolism
(iv) Cellular organization
(v) Consciousness

→ Those characteristics which have no exception is called defining property of life.

→ Growth and Reproduction are not the defining property of life as well as metabolism, cellular organization, consciousness is the defining property of life.

(i) Growth

→ Overall increase in mass or size of tissue or organism or its parts is called growth.

→ Increase in mass and increase in number are the twin characteristics of growth. This is an irreversible permanent increase in size of the organ or its part or even of an individual cell.

→ Growth is of two types:

• Intrinsic growth: Growth from inside of the body of living organism. This is the defining property of life.

• Extrinsic growth: Growth from outside of the body of the organism. Like accumulation of material on any body surface . Non-living exhibits this type of growth.

→ Intrinsic Growth is of two types:

• Indeterminate growth\Unlimited growth:  Growth which occurs continuously throughout their life span. It occurs only in plants.

• Determinate growth\ limited growth: Growth which occurs only up to certain age. It occurs only in animals. Cell division occurs only in certain tissues to replace lost cells.

(ii) Reproduction

→ Production of new individual or progeny is called as reproduction.

→ Reproduction in case of multicellular organism is production of progeny possessing features more or less similar to those of parents.

→ Reproduction in case of unicellular organism like bacteria, unicellular algae or amoeba is increaser in number of cell. Means in unicellular organism the growth and reproduction are synonyms or same.

→ Reproduction is not found in any nonliving object. There are many living organism which can\do not reproduce like mules, sterile human couples, worker bees. This is also not taken as defining property of life.

→ Reproduction is of two types:

• Asexual reproduction:  Reproduction in which fertilization or gametic fusion and meiosis is not involved is called asexual reproduction.

(a) By Asexual spores: In algae and fungi.
(b) By Budding: In Yeast and Hydra.
(c) By Fragmentation: In filamentous Algae, Fungi and Protonema of moss plants.
(d) By True Regeneration:  Fragmented organism regenerate the lost parts of its body and becomes a new organism i.e.  Planaria.

→ Regeneration is a process in which only lost part of the body is repaired or regenerated. Ex: Star fish, Lizards.

• Sexual Reproduction: Reproduction in which gametes are formed by meiosis and fertilization takes place to form progeny is called as sexual reproduction.

(iii) Metabolism

→ The sum total of all the chemical reaction occurring in our body is metabolism.

→ All organism, both unicellular as well as multicellular exhibit metabolism. No nonliving objects show metabolism.

→ It is the defining property of life.

→ The isolated metabolic reaction outside the body of an organism, performed in a test tube (in vitro) is neither living nor living. These isolated reactions cannot be regarded as living things, but they are definitely living reactions because they are similar to the reaction performing in our body.

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

(iv) Cellular organization

→ Cell is the basis unit of life. All organisms are composed of cells.

→ Some are composed of single cell and are called as unicellular organism while other are composed of many cells, are called multicellular organism.

→ Unicellular organism is capable of independent existence and performing essential functions of life. Anything less than a complete structure of a cell, does not ensure independent living.

→ Cell is the fundamental structure and functional structural and functional unit of all living organism. This is the defining property of life.


Ability to sense the surrounding environment and respond to these environment stimuli is called as consciousness. This is the most obvious and technically complicated features of all living organism. We sense these physical, chemical or biological stimuli through our sense organs. Plants also sense and respond to external factors like light, water, temperature, other organism, pollutants etc. All organisms from the prokaryotes to complex eukaryote show consciousness to environmental clues. Some common examples  of consciousness can be seen in organism, like plants performs flowing in a particular seasons (photoperiodism), Some animals perform breeding  in a particular season only (seasonal breeders), and all organism handle the chemicals entering their bodies etc. When human is concerned a very well developed nervous system and supreme level of skill of communication which is called as self-consciousness. Human is very fast to respond towards the external  stimuli and even it can think or predict about possible changes of surrounding so it can prepare itself according to the surrounding situations. Further human can even change its surrounding situation up to a limit so this topmost or climax level of consciousness is regarded as self-consciousness, which cannot be seen elsewhere. Self –consciousness is thought to be present only in human. The brain dead coma patient who is supported who is supported by machines which replace heart and lungs also has consciousness so it is living but it does not has self-consciousness because it has lost the co-ordination of organs of different body parts. Means all the living phenomena are due to underlying interactions between different component of an individual or organ or tissue or cell. Living organism is self-replicating and self-regulating interactive system capable of responding to external stimuli. Adaptations and homeostasis are also very important characters of living.

Diversity in Living World

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


→ This is the study of principles and procedures of classification.

→ 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. This process is called nomenclature.

→ Nomenclature or naming is only possible when the organism is described correctly and we know to what organism the name is attached to. This is identification.

• Rules for nomenclature are provided by:
a) ICBN – International Code for Botanical Nomenclature
b) ICZN – International Code for Zoological Nomenclature

• Binomial Nomenclature

→ Carolous Linnaeus – Father of Taxonomy

→ Name with two parts: - Generic name (Genus) & Specific epithet (Species)

• Guidelines and Principles for Nomenclature:

(a) It should be in Latin / derived from Latin.

(b) If it is written in Italics when types and underlined when handwritten.

(c) It contains two parts, first word is Genus ; second word is Species.

(d) Genus name starts with Capital while species name starts with small letters.

(e) Name should be short, precise & easy to pronounce.

(f) Name of the author is written is an abbreviated form after the species name. Ex: Mangifera indica (Mango), Homo sapiens ( Human), Panthera pardus (Leopard), Felis domestica (Cat)

→ Classification – Grouping of organisms in to categories based on observable characters. (category –taxa)

→ Taxonomy - Characterization, identification , classification and nomenclature are the process of taxonomy.

→ Systematics - Different kinds of organisms and their relationships Linnaeus – Systema Naturae
(evaolutionary relationships among organisms).

→ Taxonomical Hierarchy – Similarities decreases/ Differences increases

(i) Species -Panthera leo, Panthera pardus, Panthera tigris.
(ii) Genus- Panthera (Lion, Leopad,Tiger )
(iii) Family- Panthera and Felis together into Felidae
(iv) Order - Felidae (cat family) , Canidae (dog family) - Carnivora
(v) Class - Carnivora (tiger, cat, dog), Primates (monkeys )- Mammalian
(vi) Phylum – Pisces, Amphibian, Reptilian, Aves & Mammals
(vii) Kingdom – Plantae, Animalia.

• Species: Taxonomic studies consider a group of individual organisms with fundamental similarities as a species. One should be able to distinguish one species from the other closely related species based on the distinct morphological differences.

• Genus: Genus comprises a group of related species which has more characters in common in comparison to species of other genera. We can say that genera are aggregates of closely related species.

• Family: Family, has a group of related genera with still less number of similarities as compared to genus and species. Families are characterized on the basis of both vegetative and reproductive features of plant species.

• Order: Order being a higher category, 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.

• Class: This category includes related orders.

• Division\ Phylum: It includes all organisms belongng to different Classes having a few Common Characters.

• 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.

Taxonomical Aids:

→ Biologists have established certain procedures and techniques to store and preserve the information as well as the specimens.

Some of these are:

• Herbarium: It is the storehouse of collected plant specimens. Collected plant specimens are dried, pressed, and preserved on sheets and then arranged systematically according to the universally accepted system of classification. Herbarium sheet contains label regarding date, place of the collection, scientific name, family, collector’s name, etc. of the specimen.

• Botanical garden: NBRI (Lucknow ) & IBG (Howrah ): It has the collection of living plant species that are grown for identification and reference. Each plant contains labels indicating their scientific name and family. Some famous botanical gardens are Indian Botanical Garden, Calcutta (largest in India), Royal Botanical Garden, Kew (largest in world till date) and National Botanical Research Institute.

• Museum: It is the repository that has a collection of various plant and animal specimens that are preserved for study and reference. The organisms are preserved either in preservative solution or in the form of dry specimen It often has a collection of skeletons of animals also.

• Zoological parks: Zoological parks Wild animals are kept in protected environments. Provides opportunity for studying the behaviour and food habits of the animals.

Key (analytical in nature): Keys are used for identification of plants and animals based on similarities and dissimilarities.

→ Monograph (1 family / genera at a time.)

→ Manuals (particular area , family/ genus/ species)

→ Flora (habitat & description of plants in a given area)

→ Manuals, monographs, and catalogues are other means of recording descriptions.

→ Manuals help in the identification of names of various species of organisms in a given area.

→ Monograph is a detailed and well-documented work on any particular taxon.

NCERT Solutions of Class 11 The Living World

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