Chapter 1 The Living World class 11th biology Notes

Class 11th biology chapter 1 The Living World
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What is 'Living' ?

'Living' is something that is alive, something that can grow, move, reproduce, respire and carry out various cellular activities.

When it comes to the humans, it is all the more difficult to define the living state. We observe patients lying in the coma in hospitals virtually supported by the machines which replace heart and lungs. The patient has no self consciousness. Are such patients who never come back to normal life, living or non-living? 

Such person exhibit a complete absence of wakefulness and is unable to consciously feel, speak, hear or move . Such a person is called brain dead but as the body system is functioning, the person is considered as living.

Biodiversity 

The Diversity in the living world or biodiversity is the occurrence of the variety of life forms. Each different kinds of plant, animal or microorganisms represents a species.

Currently there are some 1.7 to 1.8 million living organisms known to science. Out of which 1.25 millions are animals and about 0.5 millions are plants.

As stated earlier, there are millions of plants and animals in the world ; we know the plants and animals in our own area by their local names. These local names would vary from place to place, even within a country.

Probably you would recognise the confusion that would be created if we did not find ways and means to talk to each other , to refer to organisms we are talking about.

Hence, there is need to standardized 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.

Systematics

The word ‘Systematics’ is derived from the Latin word Systema, which means systematic arrangement of organisms. Linnaeus used Systema Naturae as the title of his book. He. coined the term Systematics in 1751.

Systematics is the branch of science that deals with unique properties of species and groups to recognise, describe, name and arrange the diverse organisms according to an organised plan.

In 1961, Simpson, defined systematics as the study of diversity of organisms and all their comparative and evolutionary relationships based on comparative’ anatomy, physiology, biochemistry and ecology. The word ‘Systematics’ and ‘Taxonomy’ are often used interchangeably by the biologists. Systematics includes the following:

Identification

It aims at finding the correct name and appropriate position of an organism. The morphological and anatomical characters are examined for proper identification.

Classification

It is almost impossible to study all the living organisms. So, it is necessary to devise some means to make this possible. This can be done by classifying the organisms.

Thus, classification is the process by which organisms are grouped into categories based on some easily observable characters.

Advantages of Classification

(a) It helps to identify an organism easily.

(b) New organisms easily get correct place in their respective groups.

(c) It makes study of fossils easy.

(d) It also helps in building evolutionary pathways.

(e) It becomes easy to know the features of whole group by studying one or two organisms of the group.

Thus, based on these characteristics, all living organisms are classified into different taxa.

Nomenclature

Nomenclature is the system of naming living organism in a way that a particular organism is known by the same name all over the world.

Common Names

The common names or vernacular names are the local names given to an organism in a specific language in a particular region. There are different names of a same organism in different regions even with in a country.

Scientific Names

A scientific name is given by biologists. These names represent a particular organism in every part of the world. The system of providing scientific names is called binomial nomenclature.

The scientific names must be

(a) acceptable in every part of the world.

(b) assigned on agreed principles and criteria.

(c) different for each species and not used for other organisms earlier.

Binomial Nomenclature

Binomial nomenclature was developed by Carolus Linnaeus in 1751 (Philosphica Botanica). All scientific names for animals under binomial nomenclature were given by Linnaeus in the tenth edition of his book Systema Naturae (1758). Linnaeus named plants according to binomial nomenclature in his book Species Plantarum (1753). Binomial nomenclature is the system of providing distinct and appropriate names to organisms, each consisting of two words, first generic name {i.e., name of genus) and second specific epithet (i.e., name of species).

For example, Scientific name of mango is written as Mangifera indica. In this name, Mangifera represents the genus and indica is a particular species or specific epithet.

Rules of Binomial Nomenclature

Rules of binomial nomenclature were initially framed by Linnaeus in his books, Species Plantarum and Systema Naturae.

The rules were revised again by the following nomenclature codes

(i) International Code for Botanical Nomenclature (ICBN).

(ii) International Code of Zoological Nomenclature (ICZN).

(iii) International Code of Bacteriological Nomenclature (ICBN).

(iv) International Code of Viral Nomenclature (ICVN).

(v) International Code of Nomenclature for Cultivated Plants (ICNCP).

Advantages of Binomial Nomenclature

(i) Binomial names are universally acceptable and recognised.

(ii) They remain same in all languages.

(iii) The names are small and comprehensive.

(iv) There is a mechanism to provide a scientific name to every newly discovered organism.

(v) The names indicate relationship of a species with other species present in the same genus.

(vi) A new organism can be easily provided with a new scientific name.

Taxonomy

It is the science of identification, classification and nomenclature. Based on their special / characteristics, all living organisms can be classified into different taxa. This process of classification is called taxonomy. Carolus Linnaeus is known as father of taxonomy.

The basis of modern taxonomy studies are external and internal structure (comparative morphology), along with the structure of cells (cytology), development process (embryology) and ecological information of organisms (ecology).

Taxonomic Hierarchy

The taxonomic hierarchy is the system of arranging taxonomic categories in a descending order. It was first introduced by Linnaeus (1751) and hence, it is also known as Linnaen hierarchy.

Groups represent category and category further denotes rank. Each rank or taxon represents a unit of classification.

These taxonomic groups/categories are distinct biological entities and not merely morphological aggregates.

Obligate/Common Categories

The taxonomic categories, which are always used in hierarchical classification of organisms are called obligate or common categories.

They are seven in number. In descending order, these are kingdom, phylum or division, class, order, family, genus and species.

i.Species

Taxonomic studies consider a group of individual organisms with fundamental similarities as a species (John Ray).

For example, Mangifera indica (mango), Solarium tuberosum (potato) and Panthera leo (lion).

All the three names indica, tuberosum and leo represent the specific epithets while, the first words Mangifera, Solanum and Panthera are genera and represents another higher level of taxon or category.

ii.Genus

Genus (John Ray) comprises a group of related species, which has more characters common in comparison to species of other genera. In other words, genera are aggregates of closely related species.

iii.Family

Family (John Ray) is a group of related genera with less number of similarities as compared to genus and species. All the genera of a family have some common or correlated features. They are separable from genera of a related family by important differences in both vegetative and reproductive features.

A plant family ends in a suffix -aeae and sub-family -oideae. While, an animal family has a suffix -idae and sub-family -inae.

iv.Order

An order (Linnaeus) is a group of one or more related families that possess some similar correlated characters, which are lesser in number as compared to a family or genera.

Plants and Animal Orders with their Respective Families

Order Animals and Families

Carnivora Canidae (dog, wolf and fox), Felidae (cat, leopard, tiger and lion), Ursidae (bear) and Hyaenidae (hyaena)

v.Class

Class (Linnaeus) is a major category, which includes related orders. For example, order-Primata comprises monkey, gorilla & gibbon and is placed in class—Mammalia along with order—Carnivora that includes animals like tiger, cat and dog.

Class-Mammalia has other orders also.

vi.Phylum or Division

Phylum or Division (Cuvier, Eichler) is a taxonomic category higher than class and lower” in rank to kingdom. The term Phylum is used for animals, while division is commonly employed for plants.

It consists of more than one class having some similar corelated characters.

For example, Phylum— Chordata of animals contain following classes, e.g., Pisces, amphibians, reptiles, aves and mammals.

vi.Kingdom

It is known to be the highest category in taxonomy. This includes all the organisms, which share a set of distinguished characters. For example, all the animals belonging to various phyla are assigned the highest category called kingdom.

For example, Animalia in the classification system of animals. Similarly, all the plants are kept in kingdom—Plantae.

RH Whittaker. (1969) assigned five kingdom classification of organisms.

These are Monera, Protista, Fungi, Plantae and Animalia.

Taxonomical Aids

Taxonomical aids are techniques and procedures to store information as well as specimens or identification and classification of organisms.

The taxonomic studies of various plants, animals and other organisms are useful in areas like agriculture, forestry, industry and knowing our bioresources.

1.Herbarium

Herbarium (Pi. Herbaria) is a store house of collected plant specimens that are dried, pressed and preserved on sheets. These sheets are arranged further according to a universally accepted system of classification. The institutes and universities maintain their own herbarium by collecting specimens from local and far away places.

2.Botanical Gardens

Botanical gardens are specialised gardens that have collections of living plants for reference. These gardens generally have facilities like library, laboratory, herbarium and museum. The botanical gardens are maintained by government, semi-government and other private organisations. Botanists and gardeners look after plants in botanical gardens.

Indian Botanical Garden-Largest Botanical Garden of Asia.

First Botanical Garden-Pisa Botanical Garden, Italy established by Luca Glini (1490-1556).

3.Museums

Museum is a place for collections of preserved plants and animal specimens for study and reference. The universities and educational institutes maintain their own museums in their botany and zoology departments. Plants, which cannot be kept in herbaria are preserved in museums.

For example, algae, fungi, mosses, ferns, fruits, etc. Specimens are preserves in containers or jars in preservative solutions.

4.Zoological Parks

Zoological parks or zoo are the places where wild animals are kept in protected environments under human care and which enable us to learn about their food habits and behaviour. Zoological parks provide natural habitat to the animals.

In India there are about 200 zoological parks. These zoos are managed by the Central Zoo Authority of India. The World Zoo Conservation Strategy (WZCS) refer to all these zoological institutions as zoos.

5.Key

Key is also a taxonomical aid used for identification of plants and animals based on the similarities and dissimilarities.

It helps in the identification of plants and animals by selecting and eliminating the characters according to their presence or absence in the organism under study.

The keys generally use two contrasting characters called couplet. This results in acceptance of one present in organism and rejection of the other. Each statement in the key is called a lead.

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