The Living World

NCERT Class 11 Chapter 1 Class Notes

The Living World

What is Living?

Definition: To define living, we look at the definitive characters that are shown by the organisms.

The characteristics of living organisms

The very range of organisms in terms of size, colour, habitat, physiological and morphological features make us seek the defining characteristics of living organisms. These characters are described below in brief:

Growth:

Young individuals grow in size, biomass, and number.
Multicellular living beings grow in size through cell division.
Plants show cellular division throughout their lifespan, while in animals, this stops after a certain period.
The non-living beings differ here from the living beings as their growth is on the surface, while the growth of the living organisms is from the inside.

Reproduction:

Any living being generates the following generation possessing its features.
Living organisms reproduce through asexual methods such as spore formation, fragmentation, budding, fission, etc.
Alongside it, sexual reproduction, i.e., the production of gametes, is also seen.
Non-living beings are incapable of producing identical offspring i.e., replicating themselves.

Metabolism:

The atoms of different elements and different molecules of chemicals make up living and non-living beings.
But in living beings, these molecules are constantly broken and made into some other molecules.
Such changes or chemical interactions are known as metabolism.
Metabolism taking place outside any living cell is not considered as living or non-living rather it becomes an integral part of the existence of a living being.

Cellular organisation:

The most basic level of organisation of a living being is the cellular level.
Each living being is made up of cells.
Unicellular organisms perform all their life functions using only one cell, while multicellular organisms show different levels of organisation.
We can refer to the cell as a structural and functional unit of life. In multicellular organisms, cells with the same or different features performing common functions are called tissues.
The tissues together form the organs, which unitedly forms an organ system. All the organ systems collectively run the body of multicellular organisms.

Responsiveness:

All living beings can recognise both internal and external stimuli, and they respond to those stimuli accordingly.
Alterations in light intensity, temperature, touch, the presence of chemicals, etc., hormones, and enzymes in the body often act as stimuli.
For example, a plant kept in a shady place near a window moves its branches and leaves towards it to reach more light intensity.

All these properties of living beings are not individually created at the molecular level; rather they develop as a result of interactions among different molecules that constitute the cells and their organelles. Thus, we can define a living being as an interactive system that replicates, evolves and regulates itself and can respond to external stimuli. Also, all the current and extinct living beings are linked to one another through genetic materials.

Diversity in the Living World

The word biodiversity was first used by W. Rosen in 1985.
It refers to the variation of lifeforms on earth from the genetic level to the ecosystems. Examples of variable aspects of diversity can be observed in the following:

The members of one species in an ecosystem show variation in their morphology and structure.
Reproductive variation among species in the same ecosystem.
Morphological variations among species of the same nature in the same ecosystem, etc.

A variety of living organisms are observed around us. The known number of species of a living being may be currently around 1.7–1.8 million, which is maybe only 15-20% of the actual number.
This variety of plants and animals that live in any particular habitat or all around the world includes a diversity of genetic materials, communities, and ecosystems.
For such a large variety of species, studying different aspects of their lives is necessary, and to do so, a universal study system is needed. From there, the development of taxonomy and classification took place, which we are going to discuss here in The Living World Class 11 notes Biology chapter 1 notes.

Concept of Taxonomy

Different species come with different names, which change with languages and places. Thus, a standardised naming process was necessary for scientific purposes. This process is called nomenclature.
But to name an organism, we need to know all of its characters and features. Thus, a standard identification process was also required.
In The Living World Class 11 Biology Chapter 1 Notes pdf, the concept of nomenclature is discussed below.
The nomenclature process is guided by international codes that provide rules and regulations. There are two: the International Code for Botanical Nomenclature (ICBN) and the International Code of Zoological Nomenclature (ICZN).
Each living being has a scientific name composed of a generic name and a specific epithet. Such a two-term composed naming process is known as binomial nomenclature. This process was first described by Carolus Linnaeus in 1753.
In the NCERT notes for Class 11 Biology Chapter 1, all the rules followed while naming an organism through binomial nomenclature are discussed below.

It should be Latinised.
The name must be written in italics, and if handwritten, the two parts of the name must be underlined separately.
The first letter of the generic epithet is a capital letter, while that of a specific epithet is a small letter.
A short form of the scientist’s name who first described the species is added after the specific epithet. This is not italicised.

Example: Mangifera indica L., is the scientific name of mango. The generic epithet here is Mangifera, while the specific epithet is indica. The letter L. at the end represents Linnaeus who named the plant.

Classification

As studying all individual organisms separately is not possible for one person in his lifetime, scientists can come up with the idea of classification, where all organisms are grouped according to similar characteristics. In NCERT notes for class 11 biology chapter 1, the concept of classification is discussed below.

Based on similar characteristics, living beings are placed in different groups. These groups are called taxa.
This process of placing different organisms into taxa is known as taxonomy.
According to G. H. M. Lawrence, taxonomy handles three aspects—identification, nomenclature, and classification of organisms.
The man did not stop after classification. Their curiosity has led them to learn about relationships among different species.
The branch of biology dealing with this interrelationship among species leading towards their origin and evolution is known as systematics. This word was coined by Linnaeus in his book Systema Naturae.

Taxonomic Categories

Each step of classification involves several steps, each of which expresses a rank or category, and these are arranged in a definite higher-to-lower order. This is known as a taxonomic hierarchy. These ranks are the taxa (singular: taxon) of seven types. In The Living World Class 11 notes Biology Chapter 1 notes, different taxonomic categories are discussed separately below:

Species

This is the group of organisms with similar characters and an interbreed. They are reproductively isolated.

Example: Mango plants found all over the world are included in indica species.

Genus

Different species of similar characters are accumulated under the genus taxon.

Example: Ficus benghalensis, Ficus religiosa and Ficus elastica are all added under the Ficus genus even though these three are entirely different plants.

Family

Taxa of one or more genera with similar characters.

Example: Solanum, Petunia, Atropa, etc. are members of Family Solanaceae.

Order

This taxonomic category includes related families (one or more) with some common characteristics.

Example: Felidae and Canidae are added under order Carnivora.

Class

This taxonomic category includes closely related orders of one or more numbers.

Example: Class Mammalia includes order Carnivora and order Primata.

Division or Phylum

This taxon includes classes of common features.

Example: The spermatophyta division includes two classes: gymnosperms and angiosperms. In animals, the division named as phylum.

Kingdom

The largest or highest taxonomic category is called a kingdom.
All the plants are placed under Kingdom Plantae while all animals are placed under Kingdom Animalia.

To store and preserve these data of taxonomy and systematics as well as utilise them, we need some aids or tools. Here in The Living World Class 11 Biology chapter 1 notes, we will discuss them.

Taxonomical Aids

Taxonomic tools can be defined as means to preserve, identify and classify different specimens. These specimens may be in living condition or maybe in preserved condition. Different taxonomic aids are discussed separately in The Living World Class 11 notes Biology chapter 1.

Herbarium

A herbarium is a depository of plant specimens dried, pressed, and preserved on special sheets. These specimens are arranged according to any known and accepted system of classification.

In biology class 11 chapter 1 notes pdf, the importance of herbarium is given below:

It gives us knowledge and information regarding the flora of a specific location.
It helps to give information and general features of the species. It helps in the identification of species.
It helps regarding the classification of new species.
It provides research and job facilities to taxonomists.

Botanical garden

Botanical gardens are places to cultivate and maintain species of plants of local flora as well as those brought from distant countries.

The ch 1 biology class 11 notes, the Botanical garden is given below:

Helps in the conservation of endangered and threatened plant species.
Ex-situ conservation of many plant species is done.
Most of the botanical garden serves as a herbarium depository.
It provides materials for the study of biosystematics.

Museum

Museums are places where art and educational material are exhibited to common people and those collections are available for study and observations.

In the living world class 11 notes, the importance of museums is given below:

Museums help in the preservation of collected plants and animal species.
The collections are used for the taxonomic study of different taxa.
Provides information regarding local flora and fauna.

Zoological Parks

Zoo or zoological parks are enclosed areas where wild animal species are conserved in captivity. In many zoological parks, high standard and care is maintained so the animals may live under more natural conditions.

In the class 11 biology chapter 1 notes, the importance of Zoological Park is given below:

Zoological parks are important for the ex-situ conservation of wild animals.
Breeding programmes are carried out in zoological parks.
These are important recreation centres and are used for mass awareness about wild species.
Important research tool for studying animal behaviour and life.

Key

Based on contrasting characters, especially similarities and dissimilarities among different species, the key is prepared as a taxonomic aid for the identification of plants and animals. The two-opposite option for each character is given and each choice leads us to different species. Though we need different taxonomic keys for different taxa.

Apart from these aids, Flora, manuals, monographs and catalogues also help us to identify, classify and name different species