Class XI Biology

2.  Biology - The term biology is derived from the
Greek word bios means ‘life’ and logia means
‘study of’.
 Biology is the study of life and living organisms.
 Life - Life can be defined as the property or
quality of the living organisms that distinguishes
from dead or non-living in some functions like:
 growth
 metabolism
 response to stimuli
 reproduction

3. CHARACTERISTICS OF LIVING THINGS
1. Growth
2. Reproduction
3. Metabolism
4. Response to stimuli

4.  Growth is an important characteristic feature of living
beings.
 They increase in mass and number.
 Non-living objects also grow in mass by accumulation
of material on its surface.
 Growth in a living being takes place due to internal
processes, i.e. cell division.
 Plants show continuous growth throughout their life
span, while animals show growth up to a certain age.

5.  All living beings produce their offspring by the process of
reproduction.
 Reproduction is an important process for continuing the
lineage of a species.
 Fungi reproduce by asexual spores.
 Yeast and Hydra by budding.
 Planaria (flat worms) by regeneration.
 Unicellular organisms like bacteria, unicellular algae or
Amoeba, reproduction is synonymous with growth, i.e.,
increase in number of cells.
Reproduction
Sexual Asexual

6.  All living organisms are made of chemicals belonging to
various classes, sizes and functions.
 The chemicals within a living organism are constantly
being made and changed into some other biomolecules.
 The sum total of all the chemical reactions occurring in
our body is metabolism.
 No non-living object exhibits metabolism.
Metabolism
Anabolism Catabolism

7.  Living organisms respond to their surroundings or
environment.
 Respond to environmental stimuli could be physical, chemical
or biological.
 Plants respond to external factors like light, water,
temperature, other organisms, pollutants, etc.
 Organisms can sense and respond to environmental cues.
 Photoperiod affects reproduction in seasonal breeders, both
plants and animals.
 Organisms handle chemicals entering their bodies and aware
of their surroundings.
 Human being, the only organism, which has self-
consciousness.

8.  Biodiversity - The diverse form of organisms present on
earth is called biodiversity.
 Nomenclature – It is a system of naming of organisms.
 There are millions of plants and animals in the world.
 Plants and animals are known in the local area by their local
names.
 These local names are vary from place to place, region to
region and within a country also.
 So, it is impossible for any person to remember the names
of an organism in all the languages.
 Hence, there is need for a uniform system of nomenclature
of organisms.

9.  Identification - Identification is the process of
assigning a pre-existing taxon name to an
individual organism.
 ICBN - International Code for Botanical
Nomenclature
 ICZN - International Code for Zoological
Nomenclature

10.  Bionomial nomenclature is a
system of naming species by
giving each a name composed
of two components, generic
name and species name.
 Carolous Linnaeus invented
the modern system of binomial
nomenclature.
Carolous Linnaeus

11.  Biological names are usually written in Latin word
and in italics font.
 Scientific name usually contains two parts: first word
is Genus and second word is Species or specific
epithet.
 Genus name starts with a Capital letter while species
name starts with a small letter.
 Biological name is or printed in italics to indicate their
Latin origin and underlined, when it is handwritten.
 Example: Mangifera indica ( Mango), Homo sapiens
( Human), Oryza sativa (Rice), Triticum aestivum
(Wheat)

12.  Classification – It is the process of grouping of organisms
into categories based on easily observable characters.
 Taxon - The scientific term for any unit used in the science of
biological classification is called taxon.
 Taxonomy - Taxonomy is the science of defining groups of
biological organisms on the basis of shared characteristics
and giving names to those groups.
 Carolus Linnaeus is regarded as the father of taxonomy.
Process of Taxonomy
Characterization
Identification
Classification
Nomenclature

13.  Systematics
 The word systematics is derived from the Latin
word ‘systema’ means systematic arrangement of
organisms.
 Systematics is the study of the diversification of
living forms, both past and present, and the
relationships among living things through time.
 Linnaeus used Systema Naturae as the title of his
publication

14.  TAXONOMIC CATEGORY
 Classification involves hierarchy of steps where
each step represents a rank or category.
 Various steps of the classification hierarchy are
called taxonomic categories.
 Each level in the hierarchy represents an increase
in organisational complexity.

15.  Species is a group of individuals in which the
individuals can interbreed among themselves.
 Members of a species have a large number of
similar characters.
 Example:-
 Mangifera indica (Mango),
 Solanum tuberosum (potato)
 Panthera leo (lion);
SPECIES

16.  A group of closely related species is called genus.
 Example –
 Potato,tomato and brinjal are three different species
but all belong to the genus Solanum.
 Lion (Panthera leo), leopard (Panthera pardus) and
tiger (Panthera tigris) are members of the genus
Panthera.

17.  A group of closely related genera is called a family.
 Families are characterised on the basis of both
vegetative and reproductive features of plant species.
Example :-
 Three different genera Solanum, Petunia and Datura
are placed in the family Solanaceae.
 In animals, genus Panthera and genus Felis belong to
the family Felidae.
FAMILY

18.  A group of closely related families is called order.
 Order and other higher taxonomic categories are
identified based on the aggregates of characters.
Example :–
 Plant families like Convolvulaceae, Solanaceae are
included in the order Polymoniales.
 In animals, Felidae and Concidae belong the order
Carnivora.

19.  Class is a major category made of one or more
related orders that posses certain similar correlated
characters.
 Example –
 Class mammalia has a number of orders like
carnivora, rodentia, primata, insectivora, etc. all
possess mammary glands, external ears and hair.


20.  A group of closely related classes is called phylum.
 In the Plant Kingdom phylum has been replaced
with division.
 Example - Pisces, Amphibia, Reptilia, Aves and
Mammalia belong to the Phylum Chordata.

21.  A group of all the related phyla is called the Kingdom.
 Example :–
 The Kingdom Plantae comprises all plants from
various divisions.
 All heterotrophic organisms which are eukaryotic and
lack a cell wall are kept under Animal Kingdom.
KINGDOM

22. Kingdom
Phylum or
Division
Class
Order
Family
Genus
Species

23. ORGANISMS WITH THEIR
TAXONOMIC CATEGORIES
Common
Name
Biological
Name
Genus Family Order Class Phylum/
Division
Man Homo
sapiens
Homo Hominidae Primate Chordate Mammalia
Housefly Musca
domestica
Musca Muscidae Diptera Insecta Arthropoda
Mango Mangifera
indica
Mangifera Anacardiac
eae
Sapindal
es
Dicotyledo
nae
Angiospermae
Wheat Triticum
aestivum
Triticum Poaceae Poales Monocotyle
donae
Angiospermae

24.  Storehouses of information and specimens which
can help in identification and classification of
organisms are called taxonomic aids.
 Study of various species of plants, animals and
other organisms are useful in agriculture, forestry,
industry, etc.
 These studies are useful to know about our bio-
resources and their diversity.
 These help in identification, naming, and
classification of organisms.

25.  1. Herbarium
 Herbarium is the storehouse of plant specimens.
 Specimens are dried, pressed, and preserved on
sheets.
 These sheets are arranged systematically
according to the universally accepted system of
classification.
 Herbarium sheet contains information about date
and place of the collection, collector’s name, local
and scientific name, family, etc.
 It provides quick referral systems in taxonomical
studies.

26.  2. Botanical gardens
 A botanical garden is a place where plants are grow
and displayed for the purposes of research and
education.
 Each plant contains labels indicating their scientific
name and family.
Some famous botanical gardens:
 Indian Botanical Garden, Calcutta
 National Botanical Research Institute, Lucknow
 Garden of Medicinal Plants, North Bengal University,
West Bengal

27.  3. Museum
 Musium is the place of collection of preserved plant
plant and animal specimens for study and
reference.
 Specimens are preserved in containers or jars in
preservative solutions and can be preserved as dry
also.
 Insects are preserved in insect boxes after
collecting, killing, and pinning.
 Large animals are stuffed and preserved.

28.  4. Zoological parks
 Zoological park is the place where wild animals are
protected under similar to their natural habitat.
 It provides opportunity for studying the behaviour and
food habits of the animals.
Some famous Zoo in India:
 Zoological Park, Mysore
 Nehru Zoological Park, Hyderabad
 Trivandrum Zoo
 Chennai Zoo

29.  5. Key
 Keys are used for identification of plants and
animals based on similarities and dissimilarities.
 Keys are analytical in nature and based on
contrasting characters in a pair called couplet.
 Out of two proposed characters, only one which is
relevant is accepted while the other is rejected.
 Each statement in a key is called a lead.
 Separate taxonomic keys are required for each
taxonomic category such as family, genus, order,
etc.

30.  Flora, manuals, monographs, and catalogues are
other taxonomical aids.
 They help in correct identification
 Manuals provide information for identification of
names of various species in a given area.
 Monograph contain information on any particular
taxon.