Class 11 Biology chapter 1 Living world notes based on NCERT


Class 11 Biology chapter 1 Living world notes based on NCERT The life is full of amazing diversity of living organisms. 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 living is as opposed to the non living and seeks answer to what the purpose of life is.

What is living?

The main characteristics of living are:-

  1. Growth
  2. Reproduction
  3. Metabolism
  4. Consciousness
  5. Cellular organization

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

Growth and reproduction are not the defining property of life. Metabolism, Consciousness, Cellular organization are the defining property of life.


Overall increase in mass or size of tissue or organism or its part is called Growth.


Increase in mass and increase in no. are the twin characteristics pof growth. This is an irreversible permanent increase in size of the organ or its part or even of an individual cell.

Growth are of two type:

  1. Intrinsic Growth-

Growth from inside of the body of living organisms. This is the defining property of life.


2. Extrinsic Growth:

Growth from outside of the body of the living organisms. Like accumulation of material on any body surface. Non living exhibit this type of growth. It is not a defining property of life.

Class 11 Biology 1 Living world notes

Intrinsic Growth are of two types:

  1. Inderminate growth/ Unlimited growth:

Growth which occur continuously throughout the life span. it occur only in plants.

2. Determinate/limited growth:

Growth which occur only up to a certain age. It occur only animals. Cell division occur in certain tissue to replace lost cells.



Production of new individual or progeny is called as reproduction.

The case of multi cellular organisms is the production of progeny possessing features more or less similar to that of parents.

unicellular organisms like bacteria, algae or amoeba is increase in number of cells That means in unicellular organism the growth and reproduction are synonyms or same.

it is not found in any non living thing. There are many living organisms which cannot reproduce like mules, sterile human couples, worker bees. It is not a defining property of life.

Class 11 Biology chapter 1 Living world

Reproduction are of two types:

  1. Asexual reproduction:

Reproduction in which fertilization or gametic fusion or meiosis is not involved is called asexual reproduction

Asexual spores: Algae and Fungi.

Budding: Yeast and Hydra.

Fragmentation: In filamentous algae and fungi and proteome of moss plants.

By True regeneration: Fragmented organism regenerate the lost body part and become a new individual organism i.e. Planaria.

Regeneration: It is a process by which only the lost body part of the body is regenerated. example- star fish, Lizards.

2. Sexual reproduction:

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


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

All organism, both unicellular or multicellular exhibit metabolism. No non living organism show metabolism. It is a defining property of life.

isolated metabolic reaction outside the body of an organism performed in a test tube (in vitro) is neither living nor non living.

These isolated reaction cannot be regarded as living things, but they are living reactions because they are similar to the reaction performing in our body. All plants, animals, fungi and microbes exhibit metabolism.

Cellular organization:-

Cell is the basic unit of life. All the organisms are composed of cells. Some are composed of single cell and are called unicellular organisms

while other are composed of many cells, are called multicellular organisms.

Unicellular organisms is capable of independent existence and performing essential functions of life. Any thing less than a complete3 structure of a cell, dopes not ensure independent living.

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

Class 11 Biology chapter 1 Living world notes based on NCERT
Class 11 Biology chapter 1 Living world notes based on NCERT


All the organisms have excellent ability to sense their surrounding. They respond to various physical, chemical and biological stimuli. The various external factor to which living organisms respond are light, water, temperature, pollutants, other organisms, etc.

Light duration or photo period affect many seasonal breeders, plants as well as animals. All living organisms respond to chemical entering their body.

Human are superior to all living things as they have an additional ability of self consciousness. Therefore consciousness can be also said to be a defining property of life.

However, in human beings, it is more difficult to define living state, e.g. patient lying in coma supported by machines that replace heart and lungs, brains is dead with no self consciousness.

Diversity of 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 or principals and procedures of classification.

There is a need to standardize the naming or living organisms such that a particular living organism is known by the same name all over the world. This process is called nomenclature.

Nomenclature of 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:

  1. ICBN- International code for Botanical nomenclature.
  2. ICZN- International code for zoological nomenclature.

Binomial Nomenclature:-

Carolos Linnaeus- Father of taxonomy.

Name with two parts: Generic name (genus and specific epithet (species).

Guidelines and principles for nomenclature are:

  • Name should be in Latin/ derived from Latin.
  • When it is written in italics when type and underlined when hand written.
  • It contains two parts, first word is Genus; second word is species.
  • Genus name starts with capital while species name starts with small letter.
  • Name should be short, precise and easy to pronounce.

Classification- Grouping of organisms into 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 Natural ( evolutionary relationships among organisms).

Taxonomical Hierarchy- Similarities decrease/ differences increases.

  • species- Panthera leo, Panthera pardus, Panthera tigiris.
  • Genus- Panthera (lion, tiger, leopard).
  • Family- Panthera and felis together into Felidae.
  • Order- Felidae (cat family). Canida (dog family)- carnivore.
  • Class- Carnivore (tiger, cat, dog), primates (Monkeys) Mammalian.
  • Phylum- Pices, Amphibian, Reptilian, Aves and Mammals.
  • Kingdom- Plantae and Animalia.
  • Class 11 Biology chapter 1 Living world notes based on NCERT


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


Family has a group of related genera with still less no of similarities as compared to genus and species. Families are characterized on the basis of both vegetative and reproductive features of plant species.


Order being a higher category, is the assemblage of families which exhibit a few similar characters. The similar character are less in number as compared to different genera includes in a family.

Class 11 Biology chapter 1 Living world notes based on NCERT


This category includes related ordders.


It include all organisms belonging to different classes having a few common characters.


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 plant from various divisions.

Taxonomic aids:-

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


It is a place where dried and pressed plants specimens, mounted on sheets are kept systematically according to a widely accepted system of classification. 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 garden:-

They are specialized gardens having collection of living plants for reference. Plants in these gardens are grown for identification purpose and each plant is labelled indication its scientific name and family. The famous botanical garden includes Royal botanical garden, Kew(London), Indian botanical garden, Kolkata and National botanical garden, Lucknow.


Biological museums is set up in educational institutions like colleges and schools for reference purposes. Specimens are preserved in the containers or jars in preservative solutions or as dry specimens. Insects are preserved in insect boxes after collecting, Killing and pinning.

Zoological Parks:-

These are the places were wild animals are kept in prote4cted environment under human care and which enable us to learn about their food habits and behavior. Natural habitats are provided as far as possible.


Taxonomic key is an artificial analytic device having a list of statements with dichotomic table of alternate characteristics which is used for identifying organisms. Usually two contrasting characters are used. The one present in the organism is chosen while other is rejected. Each statement of a key is called lead. Separate taxonomic category like species, genus, family, etc. Keys are generally analytical in nature.

Flora, manuals, monographs and catalogs are some other means of recording

Class 11 biology ch 18 Body fluid and circulation notes

Class 11 Biology chapter 1 Living world notes based on NCERT


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