living world - notes class 11th

             CBSE Quick Revision Notes

                  CBSE Class-11 Biology

                            Chapter-1

                   THE LIVING WORLD

Life is a unique, complex organization of molecules that expresses itself through chemical

reactions which lead to growth, development, responsiveness, adaptation and reproduction.

The objects exhibiting growth, development, reproduction, respiration, responsiveness and

other characteristics of life are designated as living beings.

Unique features of living organism:-

1. Growth- Living organisms grow in mass and number. A multicellular organism increases

its mass by cell division. In plants growth continuous throughout life in their

meristematic area but in animals, growth occurs to a certain age. Unicellular organisms

also grow by cell division. Living organisms show internal growth due to addition of

materials and formation of cells inside the body. Non living organism like mountains,

boulders, crystals also grow but due to addition of similar materials to their outer

surface.

2. Reproduction. It is the formation of new individuals of the similar kind. Reproduction is

not essential for survival of the individuals. It is required for perpetuation of the

population. In sexual reproduction two parents are involved to produce more or less

similar kinds of individuals. In asexual reproduction single parent is involved and

individual is copy of the parent. Asexual reproduction may occurs by fission,

fermentation, regeneration, vegetative propagation etc. In unicellular organism, growth

and reproduction are synonyms. Many organisms like mules, sterile worker bees,

infertile human couples do not reproduce. Therefore, reproduction is not an all-inclusive

characteristic of living organism. However, no nonliving object has the power to

reproduce or replicate.

3. Metabolism- The sum total of all types of chemical reactions occurring in an individual

due to specific interactions amongst different types of molecules in the interior of cells is

called metabolism. All activities of an organism including growth, movements,

development, reproduction etc. are due to metabolism. There are two types of metabolism-Catabolism and Anabolism. Anabolism includes all the building up reactions

to increase the mass of the organism like photosynthesis. In catabolism breakdown

reactions are involved, such as respiration, digestion etc. no nonliving object show

metabolism.

4. Consciousness. It is the awareness of the surroundings and responding to external

stimuli. External stimuli may be physical, chemical or biological. Plants also responds to

stimuli like light, water, gravitation, pollution etc. All living organisms prokaryotic to

eukaryotic responds to different kinds of stimuli. Human being is only organism who is

aware of himself. Consciousness therefore, becomes the defining property of living

organisms.

5. Life span- every living organism has a definite life span of birth, growth, maturity,

senescence and death.

6. Living organisms are therefore, self-replicating, evolving and self-regulatory interactive

systems capable of responding to external stimuli.

Diversity in the living world or biodiversity is the occurrence of variety of life forms differing

in morphology, size, colour, anatomy, habitats and habits. Each different kind of plant,

animal or microorganisms represents a species.

Currently there are some 1.7 - 1.8 million living organisms known to science. Out of which

1.25 are animals and about 0.5 millions are plants.

Identification

• Nomenclature

Classification

• Systematics is branch of biology that deals with cataloguing plants, animals and other

organism into categories that can be named, compared and studied.

• Identification is the finding of correct name and place and place of an organism in a

system of classification. It is done with the help of keys. This is carried out by

determining similarity with already known organisms.

Nomenclature is the process of standardize naming of living organism such that a

particular organism is known by the same name all over the world. For plants

scientific names are based on international code of botanical nomenclature (ICBN)

and animals names on international code of zoological nomenclature (ICZN).

Scientific name ensures that each organism has only one name.

Biological nomenclature- It is the universally accepted principles to provide scientific name

to known organisms. Each name has two components-generic name (genus) and specific

epithet (species). This system of nomenclature was provided by Carolus Linnaeus.

Mango- Mangifera indica.

Human beings- Home sapience.

Universal rules of nomenclature:-

1. Biological names are generally in Latina and written in italics.

2. The first word in a biological name represents the genus while the second component

denotes the specific epithet.

3. Both the words in biological name, when handwritten, are separately underlined, or

printed in italics.

4. The first word denoting the genus starts with a capital letter while the specific epithet

starts with small letter.

Classification. It is the process by which anything is grouped into convenient

categories based on some easily observable characteristics. Classification makes the

study of organisms convenient.

Taxonomy- The process of classification on the basis of external and internal

structure along with internal structure of cell, development process and ecological

information is known as taxonomy.

Taxonomic categories

A taxonomic category is a rank or level in the hierarchical classification of organism. There

are seven obligate categories and some intermediate categories. Since the category is a part

of overall taxonomic arrangement, it is called taxonomic category and all categories together

constitute the taxonomic hierarchy.

Taxonomic hierarchy is shown below:-

KINGDOM

介

DIVISION/PHYLLUM

11

CLASS

介

ORDER

11

FAMILY

1

GENUS

11

SPECIES

Species- Species are the natural population of individuals or a group of population

which resemble one another in all essential morphological and reproductive

characters so that they are able to interbreed freely and produce fertile offspring. For

Mango tree indica is species of genus Mangifera(Mangifera indica).

Genus- it is a group of related species which resemble one another in certain

correlated characters. All species of genus presumed to have evolved from a common

ancestor. Lion, Tiger, Leopard are closely related species and placed in same genus

Panther.

• Family- It is a taxonomic category which contains one or more related genera. All

genera of a family have some common features or correlated characters. Family

Solanacaeae contains a number of genera like Solanum, Withania, Datura etc.

• Order- This category includes one or more related families. Families felidae and

canidae are included in same order carnivore.

Class-A class is made of one or more related orders. The class dicotyledoneae of

flowering plants contains all dicots which are grouped into several orders like roales,

polemoniales, renales etc.

Division/Phylum- The term phylum is used for animals while division is used for

plants. They are formed of one or more class. The phylum chordate of animals

contains not only the mammals but also aves, reptiles, amphibians, etc.

• Kingdom- It is the highest taxonomic category. All plants are included in the kingdom

Plantae while all animals belong to kingdom Animalia.

• Taxonomic Aids:- Techniques, procedures and stored information that are useful in

identification and classification of organisms are called taxonomic aids.

Herbarium-Herbarium 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 indicating its scientific name and family. The famous botanical

garden includes Royal botanical garden, Kew (London), Indian botanical garden,

Kolkata and National botanical garden, Lucknow.

Museums- Biological museum is set up in educational institutions like colleges and

school 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 where wild animals are kept in protected

environments under human care and which enable us to learn about their food habits

and behavior. Natural habitats are provided as far as possible.

Key- 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 keys are used for each

taxonomic category like species, genus, family, etc. Keys are generally analytical in nature.

Flora, manuals, monographs and catalogues are some other means of recording descriptions.