The Living World – NCERT Notes- Biology Chapter 1

What is Growth?

To differentiate whether an organism is living or not, various characteristics need to be checked in the case of living organisms.

Growth: All living organisms can undergo the process of growth and development that results in an increase in the Mass and number of cells. Multicellular organisms grow by cell division. The growth of plants and animals takes place with the help of cell division. In the case of plants, the cell division occurs throughout their life while in the case of animals the cell division occurs up to a certain age, and then the cells lose their capability to divide.

It results in an increase in body Mass and increases in the number of cells.

Examples: Mountains, boulders, sand mounds, etc grow by the accumulation of the materials although they are non-living. So, growth cannot be taken as the factor which categorizes the organism as living.

Metabolism: As the body and organs are the constituents of different chemicals, they perform various metabolic functions that result in the conversion of chemicals into other biomolecules. All plants, animals, and microbes exhibit metabolism. It is absent in the case of non-living organisms but may be introduced through the in-vitro method.

Sensitivity: The living organisms whether prokaryotes or eukaryotes respond according to their surroundings and the stimuli present around them, it may be physical, chemical, or biological. The living organisms are sensitive about their surroundings and are responsible in accordance with their stimuli. The stimuli can either be biological, physical, or chemical.

Cellular Organization: It is the defining characteristic of living organisms since all living organisms are made up of cells that help in performing various cellular functions resulting in the growth and development, reproduction, metabolism, etc in the body. Since non-living organisms are not made up of cells so they do not have cellular organization.

Movement: The lining organisms show movement and locomotion and more specifically plants move according to the movement of the sun.

Example: The flame of a candle and a crystal do not show movement while if we take mango trees then we can see they undergo movement, growth, and development along with reproduction and results in the production of more trees through their seeds. Thus mango trees are said to be alive as they show movement while candles flame and crystal are not alive.

Also, the organisms that are aware and are conscious of their surroundings will be living organisms.


We do know that all living organisms reproduce, grow and metabolize. But when we look at the microscopic realm, the actual definition of life is rather blurred. For instance, viruses are basically a nucleic acid that is protected by a protein coat. They exhibit no typical characteristics of living organisms such as reproduction, until and unless it is inside a host.

Another “organism” that borders between the living and non-living are Prions. These are essentially misfolded proteins can reproduce by making other healthy proteins to misfold. These entities are responsible for causing diseases such as Spongiform Encephalopathy, fatal familial insomnia, which are almost always fatal. In conclusion, the realm between the living and the non-living differs even now as the definition of “life” is ambiguous.

Characteristics ofLife

Living organisms exhibit undisputable signs of life – such as growth, reproduction and metabolism. Higher organisms such as humans showcase consciousness – where we become aware of our surroundings. Similarly, consciousness may be observable in many lower forms of life such as bacteria and protozoa. When these organisms engulf food or react to their environment, it is done primarily to ensure survival.

Diversity in the Living World

In response to the sheer number of organisms discovered to date, a system of standardizing names was implemented. Binomial nomenclature assigns a two-part scientific name to an organism. Botanists and zoologists follow set principles and criteria when assigning a scientific name to an organism. For instance – plant names are assigned based on the principles and criteria set by the International Code for Botanical Nomenclature (ICBN). Similarly, animal names are assigned on the basis of the International Code of Zoological Nomenclature (ICZN).

Classification of organisms according to the aforementioned conventions involved a hierarchy of steps, with each step representing a category or a rank. The most basic unit of classification is species.  A species is a group of individual organisms with fundamental similarities.


Reproduction, a characteristic of living organisms is the process of producing off springs, possessing features similar to those of parents. In multicellular organisms, the mode of reproduction is generally sexual. Living organisms also reproduce by asexual means.

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Some examples are given below.

  • Fungi spread and multiply fast by producing millions of asexual spores. Some fungi, the filamentous algae and the protonema of mosses multiply by fragmentation.
  • In yeast and Hydra, budding occurs to produce new organisms. While, in Planaria (flatworm),
  • regeneration of fragmented body parts occur. These parts in turn grow as a new organism.
  • Unicellular organisms like bacteria, algae and Amoeba reproduce by increasing the number of cells, i.e., through cell division (growth is synonymous with reproduction).
  • Some organisms like mules, sterile worker bees, infertile human couples, etc., do not reproduce. Hence, reproduction also cannot be an all-inclusive defining characteristic of living organisms.


Metabolism is an another characteristic and defining feature of all living things. The sum total of anabolic or constructive reactions (anabolism) and catabolic or destructive reactions (catabolism) continuously occurring inside the body is called metabolism.

Metabolism: Anabolism + Catabolism Metabolism occurs in all unicellular and multicellular organisms. Its two stages include, i.e., anabolism, the process of building up or synthesis of complex substances from simpler ones, e.g., Photo synthesis and catabolism, the process of breakdown of complex substances into simpler substances, e.g., Respiration, releasing waste outside.

Metabolic reactions can also be demonstrated outside the body in cell free systems, which are neither living nor non-living. Thus, these reactions in vitro are surely living reactions not living things. Hence, metabolism can be considered as a defining feature of all living organisms without exception.

The important differences between anabolism and catabolism are:

Catabolism Anabolism
Catabolism breaks down big complex molecules into smaller, easier to absorb molecules. Anabolism builds molecules required for the body’s functionality.
The process of catabolism releases energy. Anabolic processes require energy.
Hormones involved in the processes are adrenaline, cytokine, glucagon, and cortisol. Hormones involved in the process are estrogen, testosterone, growth hormones and insulin.
Examples of catabolic processes are proteins becoming amino acids, glycogen breaking down into glucose and triglycerides breaking up into fatty acids. Examples include the formation of polypeptides from amino acids, glucose forming glycogen and fatty acids forming triglycerides.
In catabolism, potential energy is changed into kinetic energy. In anabolism, kinetic energy is converted into potential energy.
It is required to perform different activities in living entities. It is required for maintenance, growth, and storage.

Cellular Organization

The cells are the building blocks of all living things whether plants, animals or humans. The unicellular organisms are made of a single cell, while multi cellular organisms are formed by millions of cells. The cells contain protoplasm (living matter) and cell organelles (inside the cells) which perform several activities at the cellular level and result into various life processes.


All living organisms have excellent ability to sense their environment. They respond to various physical, chemical and biological stimuli.

The various external factors to which living organisms respond are light, water, temperature, pollutants, other organisms, etc. Light duration or photo period affects many seasonal breeders, plants as well as animals. All living things respond to chemicals, entering their * bodies.

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

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


The body of living organisms is organized, i.e., several component and sub-components cooperate with each other for the functioning of whole body.


Physical and Biological Hierarchies

There is a physical (non-living) hierarchy and biological hierarchy in the organization of living body. In physical hierarchy, various non-living components aggregate to form compounds, which finally enter the living world in the form of cells. These cells organize to form Tissues, that form organs and several organs combustive to form organ-systems. Finally, many organ systems organize and form a living organism.

The properties of Tissues are not present in the constituent cells but arise as a result of interactions among the constituent cells. For example, bone is a hard tissue, which provides framework to the body. But the cells present inside it do not have this property. This phenomenon of interactions between various components of the body results in the hierarchy of organization.

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The various life processes are the result of this interaction and coordination. The complexity in organization enables living organisms as to be self-replicating, evolving, self-regulating and responding to external stimuli. All living organisms along with their ancestors and descendants are linked to one another by sharing of common genetic material in the form of DNA in varying degrees. This DNA is responsible for the expression of specific traits in organisms. Thus, Biology is the story of life on earth. It is the story of evolution of living organisms on the earth.

Taxonomic Categories

In 1956 the term Taxon was introduced and in 1964, Mayr defined taxon to be the various categories based on different characters of the organisms that consist of a taxonomic group of any rank.

Taxonomic Hierarchy

Various organisms in different categories depending upon their common characters to make classification easier. These groups together are called taxonomic hierarchies. The taxonomic hierarchy includes. Kingdom, division of the kingdom, phylum, class, order, family, genus, and species. Species are the lowest while the kingdom is the highest rank within the hierarchy. It is also called the Linnaean hierarchy as it was first proposed by Carolus Linnaeus, the Father of Systematic Botany. The hierarchy includes seven obligate categories.

They are as follows:

Species: It is the lowest category of the taxonomic hierarchy. There are around 8.7 million species observed on earth till now while their rest are left undiscovered. It refers to a group of organisms that are similar in shape, form, generative options. Species may be more divided into subspecies. It was first defined by Ernst Mayr in 1964 that the species are the interbreeding populations that are reproductively isolated from other such groups. The term species was first introduced by the biologist John Ray. E.g., sapiens.

Genus: A category that is placed above species as they consist of a group of related species. Genus are of various types based on the number of species present like monotypic (one genus present), and polytypic (several species present). For e.g., the genus Panthera constitutes both lion and tiger.

Family: This taxonomic category consists of related genera having similar characteristics. For e.g., the families Canidae, Felidae, Ursidae, etc. come under one order Carnivora.

Order or Cohort: This taxonomic category is more specific than the class as it consists of one or more similar families. The class Mammalia consists of around twenty-six orders that include primates, Carnivora, etc.

Class: It was the most general taxonomic category before the introduction of phyla. In the animal kingdom, there are around 108 classes that include Pisces, reptilia, aves, etc. The categories used in classification now are different from those of the Linnaeus taxonomy.

Phylum: This category is more specific than the kingdom. In the animal kingdom, there are around thirty-five phyla that include phylum Arthropoda, Chordata, etc.

Kingdom: The highest level of classification is the kingdom which is further divided into various subgroups. The total kingdoms of the living organisms are five in number that includes Monera, Protista, Fungi, Plantae, and Animalia.


Generic Name Specific Epithet Common Name
Mangifera indica Mango
Solanum tuberosum Potato
Solanum nigrum Nightshade
Panthera leo Lion
Panthera tigris Tiger
Homo Sapiens Man



Common Name Biological Name  












Man Homo sapiens Homo Hominidae Primata Mammalia Chordata
Housefly Musca domestica Musca Muscidae Diptera Insecta Arthropoda
Mango Mangifera indica Mangifera Anarcardiaceae Sapindales Dicotyledonae Angiospermae
Wheat Triticum aestivum Triticum Poaceae Poales Monocotyledonae Angiospermae



A herbarium is a collection of preserved plant specimens that are dried and labelled. The plant species that are collected are first dried, pressed, mounted, and then labelled on the herbarium sheets.

The steps involved in the herbarium technique are as follows:

  • Collecting various specimens from different areas.
  • Drying the particular specimen by placing them in between the various folds of newspapers or by iron drying them.
  • By dipping the specimens in mercuric chloride poisoning is done.
  • With the help of a cello tape or glue, mounting the dried specimens on the herbarium sheets.
  • Certain specimen parts that are difficult to attach to the sheet, like stems, are stitched so that they stick to their position on the sheet.
  • To keep them for a longer time, preserves must be sprayed.
  • The labeling for identification of all the specimens must be done at the left side of the bottom corner. The name, date of collection, area of collection, habit, etc must be written.
  • Lastly, these herbarium sheets are deposed under the herbarium covers where the rest of the herbarium sheets are covered and packed.
  • These herbarium sheets are stored in the cupboards named under their category.

To avoid any confusion each herbarium sheet is to be labeled properly on the right-hand corner at the bottom of the herbarium sheet which includes the scientific name along with author’s name, local name, name of family, locality, date of collection, name of the collector, etc.

The book flora consists of information about the collected specimens, this book gives the information regarding the number of plant species present in the various regions along with their brief description.  is published in the form of a book called flora.

Some important floras of India are Flora of British India, Flora of Delhi, Flora of Madras, Flora of Travancore, etc.

In England, the Royal Botanical Garden at Kew is the largest Herbarium in the world. Central National Herbarium is the largest Herbarium in India located in the Indian Botanical Garden at Kolkata established in 1787.

Botanical Gardens

They are those gardens that are responsible for the cultivation and preservation of a wide range of plants. These plants are reserved along with their botanical names that are tagged as a label. It is a collection of many species of plants such as succulent plants, garden herbs, and many more exotic plants. Visitors include educational displays, art exhibitions, and open-air theatre musical performances with tours and other entertainments. They are under the control of the universities or the scientific research organizations that relate both herbaria and the research programs together in the botanical sciences. There are more than 600 botanical gardens present all around the world.

The ancient Botanical Garden in the world is the Hanging Gardens of Babylon and comes under the Wonders of the world.

The Royal botanical garden at Kew in England is the largest Botanical Garden in the world and is known as the botanical capital of the world. It was discovered by Bentham and Hooker.

In India Indian Botanical Garden at Kolkata is the largest botanical garden while Tropical Botanical Garden at Thiruvananthapuram in Kerala is the largest tropical botanical garden in Asia.


The museum is the place where the artistic and educational plants or animals are preserved, stored, and exhibited to the public. Museums are of various types that include the natural science museum, Science Museum and Zoological Museum.

The Botany and Zoology Departments of all the college’s museums are maintained. Animals can also be preserved as they are placed in jars or containers having chemical solutions which help them to preserve for a longer time. The specimens are then identified and labelled and are then stored after their catalog is prepared.

The plants and animal specimens are also preserved as dry specimens. Like insects after collecting, killing, and pinning are then preserved in insect boxes while in the case of the birds and mammals they are first stuffed and then preserved. The skeletons of the animal are preserved in the museums.


They are animal parks within enclosures that display to the public and replicate their natural habitats for behavioral patterns which benefit the animals and visitors. Special climatic conditions are created for the animals and the walkthrough exhibits are there for visitors for non-aggressive species. Visitors are how to avoid eating foods that animals might snatch or to keep their paths away.

The zoological park of Kruger in South Africa is the largest zoo in the world.

The Zoo of Kolkata in India is the largest zoo.