Class 11 NCERT Chapter1

1. CHAPTER 1
THE LIVING WORLD

2. What is Living?
Characteristics of living organisms:
• Growth
• Reproduction, Self-replication and self-organization
• Response to stimuli or external environment, for example, phototropism
and chemotaxis
• Show homeostasis (regulation of the internal environment to maintain a
constant state)
• Cellular organization (all organisms are made of one or more cells- the
basic unit of life)
• Metabolism: sum total of all chemical reactions within a living cell or simply
transformation of energy by converting chemicals and energy into cellular
components (anabolism) and decomposing organic matter (catabolism)
• Interactions with other cells and living organisms
• Heredity
• Show adaptation
• Evolve

3. Characteristics of life
• According to one definition, living organisms are open systems that
maintain homeostasis, are composed of cells, have a life cycle,
undergo metabolism, can grow, adapt to their environment, respond
to stimuli, reproduce and evolve.

4. GROWTH
• Increase in mass and /or number of individuals or cells.
• Increase in mass and number are twin characteristics in living creatures.
• Intrinsic property.
• Occurs when rate of anabolism is higher than that of catabolism.
• Growth in multicellular organisms:
- By Cell Division
- In plants: cell division occurs throughout their life at specific
locations, i.e., meristematic tissues; and this is known as
‘growth’.
- In animals, growth occurs up to a certain age only. But the cell
division continues for maintenance, e.g., replacement of lost
tissues.

5. • Growth in unicellular organisms:
- Also by Cell Division
- Cell Division is also a method of reproduction in them, thus,
growth and reproduction are ‘mutually inclusive events’ (occur
simultaneously) in unicellular organisms.
- On the other hand, in multicellular organisms, growth and
reproduction are ‘mutually exclusive events’.
- Cell division in unicellular organisms can be observed in vitro (in
test tube, petri dishes or under microscope, cells can also be
counted.

6. • Difference of growth in non-living objects and living organisms:
- In both increase in mass occurs.
- In non-living objects, increase in size of crystal, snow-mountains,
deserts, sand dunes, etc. are examples of growth.
- But this results from accumulation of materials on the surface,
thus it occurs externally.
- On the other hand, in living organisms, growth occurs internally as
a result of build up of materials though various metabolic activities.
It’s not just accumulation of matter on their bodies.
- Growth is irreversible in living organisms.
• Therefore, though growth is a characteristic of living organisms, but this cannot
be considered a defining property of living organisms.

7. REPRODUCTION
• It is the ability to produce new individual organisms of same kind.
• Non-living things do not have the property of replicating or
reproducing themselves.
• Occurs either sexually (genetic information from two individuals of
different types or sexes is mixed in the offspring) or asexually
(uniparental and offspring that are genetically identical to the parent,
i.e., clone.
• Asexual reproduction is a feature of lower organisms:
- In fungi, millions of
asexual spores are
produced in order to
multiply and spread.

8. - In yeast and hydra, budding is a method of reproduction.

9. - In Planaria (flatworm), fragmentation is a method of asexual
reproduction. This is referred as regeneration.

10. - The fungi, filamentous algae, the protonema of mosses, all
easily multiply by fragmentation.

11. - In bacteria and amoeba, binary fission is a method of
reproduction.
- In Euglena and Paramecium also asexual reproduction
occurs by binary fission.

12. - Sexual reproduction is commonly observed in higher plants and
animals.
- It involves formation of gametes by two parents (opposite sex) of
same species and new individual is developed by fusion of
gametes. The offspring is not a clone of either of the parents.
- Many organisms, however, do not reproduce. For example, mules,
sterile worker bees, infertile human couples, etc.
- Therefore, reproduction is a characteristic of living organisms, but
this cannot be taken as a defining (means essential to what
something is) property of living organisms.

13. METABOLISM
• All living organisms are made of big or small chemicals of various types,
which exhibit different functions.
• They are constantly being synthesized and transformed into other
biomolecules through different chemical reactions, referred as metabolic
reactions.
• Thousands of metabolic reactions occur simultaneously inside all types
of living organisms in their cells.
• Metabolism is defined as the sum total of all the chemical reactions
occurring in an organism.
• Two types: anabolism and catabolism.
• Non-living objects never exhibit metabolism.
• Metabolic reactions, however, can be carried out in vitro in cell-free
systems in a laboratory (a metabolic reaction carried out in a test tube is
neither living nor non-living, it’s just a reaction).
• Metabolism is a defining feature of all living organisms.

15. CELLULAR ORGANIZATION
• All living organisms are made of CELLS.
• A cell is the smallest basic unit of life,
which can perform life processes
independently.
• No such organization is seen in non-living
objects.
• Therefore, cellular organization is also
considered a defining characteristic of
living organism.

16. CONSCIOUSNESS
• It is the ability to sense their surroundings or environment and respond to
these environmental stimuli (physical, chemical or biological).
• Also known as sensitivity. Example: seasonal breeding & photoperiodism.
• Found in all organisms (from prokaryotes to the most complex
eukaryotes).
• All organisms, therefore, are conscious, i.e., ‘aware’ of their surroundings.
• Human beings (Homo sapiens) is the only species aware of itself (self-
consciousness).
• Consciousness is the defining property of living organisms.
• Patients lying in coma in hospitals: no self-consciousness, not non-living
as many organs or parts are showing all features of being living.

17. THUS
- Living organisms are self-replicating, evolving and self-regulating
interactive systems capable of responding to external stimuli.
- All living organisms (present, past and future) are linked to each
other through a common genetic material.

18. DIVERSITY IN THE LIVING WORLD
• Biodiversity refers to the number and variety of organisms (plants,
animals, fungi, protists and monerans) on the planet earth.
• According to IUCN (International Union of Conservation of Nature and
Natural Resources), till now, 1.7-1.8 million species of different organisms
have been described. Yet millions of unknown organisms are to be
identified.
• These organisms are distributed over a wide range of habitat including
dense forest, thermal vents, dry deserts, hot springs, frost, etc.
• The number of organisms are higher in dense forests.
• Different plants and animals are known by their local names, which vary
from place to place.
• Hence, a need was realized for naming organisms by the same name all
over the world.

19. • The naming the organisms using a set system of terms is referred as
nomenclature.
• Before nomenclature, identification of an organism is essential.
• The scientists all over the world have made a system and
established procedures to assign a scientific name to each known
organism, which is accepted by all.
• Scientific names of plants are based on agreed principles and
criteria provided by International Code for Botanical
Nomenclature (ICBN).
• Animal taxonomists follow International Code of Zoological
Nomenclature (ICZN) for naming animals.
• Name for an organism is universally accepted and unique for it (not
used for any other known organism). It’s description should enable
the people in any part of the world to arrive at the same name.

20. • Similar nomenclature rules are formulated for other organisms also:
• International Code of Nomenclature of Bacteria (ICNB)
• International Code of Nomenclature for Cultivated Plants
(ICNCP)
• International Code of Viruse Classification and Nomenclature
(ICVCN)

21. • The name of each organism has two components:
- the Generic name, & the specific epithet
• This is known as Binomial system of nomenclature.
• It was given by Carolus Linnaeus. He published his book Systema Naturae.
• Example: Mango is called Mangifera indica (Mangifera is genus and indica is
species or specific epithet)
• Other universal rules of nomenclature include the following:
1. Biological names are generally in Latin and written in italics. They are either Latinised
irrespective of their origin or derived from Latin.
2. In the scientific name of an organism, first part is genus and second is specific
epithet.
3. When the scientific name is handwritten, both parts are underlined separately. When
printed, typed in italics to indicate their Latin origin.
4. The genus starts with a capital letter while the specific epithet starts with a small
letter.

22. 5. The name of the author (discoverer) is mentioned after the specific
epithet, i.e., at the end of the biological name and is written in an
abbreviated form, e.g., Mangifera indica Linn. (indicating that this
species was first described by Linnaeus).
6. Principle of priority: If first name given to an organism is valid
(based on rules), then it is given preference over the second name
suggested for the same organism at some time later. The second
name is considered as synonym (but is never a preference).
No name is considered valid before Systema Naturae for animals
(1758, 10th edition) and Species Plantarum for plants (1753) by
Linnaeus.

23. Common name Scientific name
Human
Lion
Dog
Onion
Wheat
Brinjal
Rose
Pigeon
Homo sapiens
Panthera leo
Canis familiaris
Allium cepa
Triticum aestivum
Solanum melongena
Rosa indica
Columba livia

24. NEED OF CLASSIFICATION
Because study of all organisms is not possible. So it’s better to classify the
organisms.
Classification is the process by which organisms are grouped
into convenient categories based on some easily observable characters.
• For example, plants having roots, shoots, leaves or flowers.
Mammals having external ears and body hair.
Similarly, certain features make dogs look like a dog.
Same is the case with all organisms.
• ‘Dogs’, ‘Cats’, ‘Mammals’, ‘Wheat’, ‘Rice’, ‘Plants’, ‘Animals’, etc., are
convenient categories we use to study organisms. The scientific term for
these categories is taxa.
• A taxon is a group of one or more populations of an organism or
organisms seen by taxonomists to form a unit.
• The organisms within a taxonomic unit share certain common
characteristics.

25. • Taxa can be big or small.
• Plants is form a taxon, a bigger taxon. Flowering plants is also a taxon but smaller
than plants.
• Similarly, animals is a bigger taxon, mammals smaller and cows even smaller.
They represent taxa ta different levels.
• All living organisms can be classified into different taxa. The process is known as
taxonomy (process of classification of organisms based on their characteristics).
• Basis of modern taxonomy: internal and external structure, cell structure,
development, and ecological information of organism.
• The characterization, identification, classification and nomenclature are the
processes that are basic to taxonomy.
• In modern times, relationships between organisms are also studied in addition to
their diversity and individual studies.
• This is referred as systematics: deals with characterization, identification,
classification and nomenclature of organisms based on their diversities and
evolutionary relationships among themselves.

26. TAXONOMIC CATEGORIES
• Classification is not done in a single step and organisms are classified
among taxa at different levels.
• The same organism, e.g., dog belongs to taxon animals as well as taxon
mammals and to several others taxa also.
• The organisms are actually classified in a hierarchy of taxa (rank or
category: a unit in itself).
• Studies have lead to the development of several taxonomic categories,
i.e., kingdom, phylum or division (for plants), class, order, family, genus
and species; and these taxa are arranged hierarchically.

27. Example of geographical
taxonomical hierarchy
Biological taxonomical
hierarchy: seven obligatory
taxa
In plants, division is used in place
of phylum
Taxonomists have also developed sub-
categories in this hierarchy to facilitate
more sound and scientific placement of
various taxa.
Increasingspecificity

29. SPECIES
• Species are a group of similar organisms which can interbreed freely among
themselves to produce fertile offspring.
• Share common characteristics.
• Two closely related species have distinct morphological difference.
• Examples, Mangifera indica, Solanum tuberosum (potato) and Panthera leo (lion).
• Mangifera, Solanum and Panthera are genera
• indica, tuberosum and leo are specific epithets.
• Genus is a taxon at a level higher than that of species.
• Each genus may have one or more than one specific epithets (or species)
representing different organisms, but having several morphological similarities.
• Solanum includes species like nigrum (black nightshade) and melongena
(eggplant). Similarly Panthera includes tigris (tigers ), leo (lion), and pardus
(leopard).
• Human beings: species- sapiens and genus Homo (Homo sapiens) (only genus
with single species).

30. GENUS
• a group of related species which has more characters in common in
comparison to species of other genera.
• Aggregates of closely related species, e.g., potato, tomato and brinjal are
three different species (tuberosum, lycopersicum, melongena respectively)
but all belong to the genus Solanum.
• Lion (Panthera leo), leopard (P. pardus) and tiger (P. tigris) with several
common features, are all species of the genus Panthera.
• Panthera genus differs from Felis including cats.

31. FAMILY
• A group of related genera with considerable number of similarities but
lesser than the genus and species.
• In plants, families are characterised on the basis of both vegetative and
reproductive features, for example, three different genera Solanum, Petunia
and Datura are placed in the family Solanaceae.
• Among animals for example, genus Panthera, comprising lion, tiger, leopard
is put along with genus, Felis (cats) in the family Felidae.
• Cats and dogs, on the other hand, are placed in different families, i.e.,
Felidae and Cancidae, respectively (but same order).

32. ORDER
• Order is an assemblage of families which exhibit a few similar characters.
• The similar characters, however, are less in number as compared to
different genera included in a family.
• Plant families like Convolvulaceae, Solanaceae are included in the order
Polymoniales mainly based on the floral characters.
• The animal order, Carnivora, includes families like Felidae and Cancidae.

33. CLASS
• This category includes related orders.
• For example, order Primata comprising monkey, gorilla and gibbon is
placed in class Mammalia along with order Carnivora that includes animals
like tiger, cat and dog. Class Mammalia has other orders also.
• Class Dicotyledonae includes order polymoniales and sapindales (mango).
PHYLUM
• This category includes classes with few similarities.
• Phylum Chordata includes classes fish, amphibia, reptilia, aves and
mammalia (because of common feature: presence of notochord and dorsal
hollow neural system).
• Division Angiopermae includes class dicotyledonae and monocotyledonae.

34. KINGDOM
• Highest category of taxonomy.
• Animals in kingdom Animalia.
• Plants in kingdom Plantae.
• Lower the taxa, more are the characteristics that the members within the
taxon share. (the number of similar characters decreases as we go higher
from species to kingdom taxa).
• Higher the category, greater is the difficulty of determining the relationship
to other taxa at the same level.

37. TAXONOMIC AIDS
Economical Significance of taxonomical studies :
• Study of plants, animals and other organisms can be helpful in knowing the
bio-resources and bio-diversity of our planet, which can be utilized in
agriculture, forestry and other industries.
Need of taxonomical aids:
• Identification and classification of an organism requires its study in a lab as
well as in field.
• The collection of an organism is essential for this.
• The study also involves gathering and storage of information along with
preservation of many organisms for future studies.
• Biologists have, therefore, established certain procedures and techniques to
store and preserve the information as well as the specimens, which act as
taxonomic aids.

38. HERBARIUM (plural: herbaria)
• It’s is a store house of collected plant specimens that are dried, pressed and
preserved on sheets (or collection of preserved plant specimens and
associated data used for scientific study).
• Arrangement of sheets is done according to a universally accepted system of
classification.
• Specimens + descriptions on herbarium sheets= repository for future use.
• Label at the base on the sheet for providing information about: date and place
of collection, English, local and botanical names, family, collector’s name, etc.
• Steps involved: Collection, Drying, Poisoning (using 0.1% corrosive sublimate
or HgCl2), Stitching, Labeling & Deposition.
• International size of herbarium sheet: 41 x 29 cm2 (16.5 x 11.5 inch2)
• Size of label: 7 x 12cm.
• Fragment packets are used for seeds, extra flowers or loose plant parts).

40. Collection of herbaria
Herbarium press

41. Two types of herbaria:
• Major (National) and
• Minor (regional/ local/ college or university)
Important Herbaria of the World:
• Royal Botanical Garden, Kew (England): over 6 x 106 number of specimens
• British Museum of natural History (BM): 6 x 105 number of specimens
• Royal Botanical Garden, Edinburgh (E): 15 x 105 number of specimens
• Central National Herbarium, Calcutta (CAL): 2 x 106 number of specimens
• Herbarium of forest Research Institute, Dehradun (DD): 3 x 105 number of
specimens
• Herbarium of NBRI, Lucknow: 8 x 104 number of specimens

42. BOTANICAL GARDENS
• Specialized gardens, where living plants are grown for scientific studies
(taxonomic) or reference.
• Each plant is well-labeled indicating its botanical/scientific name and its
family.
• Famous botanical gardens:
o Riyal Botanical Garden, Kew (England)
o Indian Botanical Garden, Howrah (India)
o National Botanical Research Institute, Lucknow (India)
o Lloyd Botanical Garden, Darjeeling (India)

43. ZOOLOGICAL PARKS
• Specialized places where living animals are kept in protected environments
under human care. Example: National Zoological Park (Delhi).
• All animals in a zoo are provided, as far as possible, the conditions similar
to their natural habitats.

44. MUSEUMS
• Set up for educational purposes primarily.
• Have collections of preserved plant and animal specimens for study and
reference.
• Specimens are preserved in the containers or jars in preservative solutions.
• Dry specimens of plants and animals are also preserved.
• Insects are preserved in insect boxes after collecting, killing and pinning.
• Larger animals like birds and mammals are usually stuffed and then
preserved.
• Skeletons of animals are also reserved.
• Information as labels are provided along with all specimens in the
museums.
• Example: National Museum of Natural History (NMNH) in Delhi.

46. KEY
• Key is another taxonomical aid used for identification of plants and animals
based on the similarities and dissimilarities (or a device used by biologists for
identifying unknown organisms).
• Keys are generally analytical in nature. They are based on the contrasting
characters generally in a pair called couplet: two opposite options from which a
choice is made. Thus one is accepted and the other is rejected.
• Each statement in the key is called a lead.
• Separate taxonomic keys are required for each taxonomic category such as
family, genus and species for identification purposes.

47. https://www.tes.com/lessons/q14cf_HkAxg6pA/classwork-5-4

48. OTHER TAXONOMICAL AIDS
• Flora, manuals, monographs and catalogues: RECORDED DESCRIPTIONS.
• Help in correct identification.
• Flora is the account (habitat and distribution) of plant life occurring in a particular
region or time, generally the naturally occurring or indigenous—native plant life.
• Manual contains listing and description of the plant species found in an area.
This is not necessarily exhaustive and is usually user defined.
• Monograph contains systematic study of a particular taxonomic group (one
taxon).
• Catalogue is simply a listing of all species organized alphabetically.

49. KNOWLEGDE CLOUD
• Founder of Biology/ Zoology/ Taxonomy: Aristotle
• Father of Botany: Theophrastus
• Father of Indian Botany/ Indian herbaria: William Rouxburgh
• Today around 5-30 million species of different organisms are estimated to exist
on earth, from which 1.7 million (13%) are known scientifically (identified) to
taxonomists.
• Reasons for large scale biodiversity are: adaptation of organisms to different
habitats, genetic variability & geographical isolation of organisms.
• Phylogeny: evolutionary history of organisms.
• Ontology: history of organisms.
• Old Classification by Aristotle and Linnaeus: Classical or Descriptive systematics:
based on morphological characters.
• New Systematics/ Biosystematics/ Neosystematics: based on all characters
(morphological, cytological, ecological, genetical, biochemical, etc.). Term was
given by Julian Huxley. Basic unit of classification for the new systematics is
population or sub-species.

50. KNOWLEGDE CLOUD
• Trinomial Nomenclature: proposed by Lamarck
Additional word: subspecies for animals and variety for plants.
Examples: Brassica oleracae var. capitata (cabbage)
Acacia nilotica var. indica (Indian babul)
Corvus splendens splendens (Indian cow)
Gorilla gorrila gorilla (Gorilla)
• According to ICBN, names of different taxa end with standard suffixes:
Division: -phyta
Class: - phyceae or –opsida or –ae
Order: - ales
Family: - aceae
Tribe: - eae
Animal Kingdom: Family: -idea; Tribe: -ini
Tribe is intermediate category between sub-family and genus.

51. Thank You