The Living World 11TH BIOLOGY

The Living World

1. The Living world (Topic)
Class-11th Sub-Biology
Balbeer Kour 1
Living Beings
Characteristics of Living Beings
Growth: All living beings grow in size. Some non-living beings also grow in
size. While growth in a non-living thing happens because of accumulation of
matter from outside, growth in living beings happens because of internal
processes, i.e. due to formation of new cells. While plants usually show
indeterminate growth, the animals show definite growth. Growth of an
animal stops after a certain size.
Reproduction: Reproduction if an important feature of living beings. This is
the process by which a living being produces its own kind. Reproduction
helps in continuing the lineage of a species. There are two types of
reproduction, viz. sexual reproduction and asexual reproduction.

Metabolism: Various biological processes are called metabolism.
Metabolism involves continuous change in the chemicals within a living
organism. Metabolism is composed of two processes, viz. anabolism and
catabolism.
a. Anabolism: The process of synthesis of any substance is called
anabolism, e.g. photosynthesis.
b. Catabolism: The process of breaking up of a substance is called
catabolism, e.g. respiration.
Response to External Stimuli: All living organisms respond to external
stimuli. Light, heat, chemicals, other organisms, etc. are examples of
external stimuli. Response to external stimuli is important for the survival of
an organism. Let us take the example of an animal when it sees its food.
Food is external stimulus and the organism’s response is to take up the food.
Since nutrition is essential for survival hence response to the sight of food is
essential for survival of an organism.
Nomenclature and Identification:
An organism is known by different names in different languages. It would be
impossible for any person to remember the names of an organism in all the

2. The Living world (Topic)
Class-11th Sub-Biology
Balbeer Kour 2
languages. Hence, there is need for a uniform system of nomenclature of
organisms. A uniform system of nomenclature and identification helps the
scientists in systematic study of living beings. ICBN (International Code for
Botanical Nomenclature) applies to the plants and ICZN (International Code
for Zoological Nomenclature) applies to the animals.
General Rules for Nomenclature:
 Biological names are usually written in Latin. They are written in
italics.
 A biological name usually contains two terms. The first term shows the
genus, while the second term shows the species.
 Biological name is underlined, when it is handwritten.
 The first term of the biological name begins with a capital letter. The
second and the subsequent terms begin with the small letter.

Taxonomic Categories
Various steps of the classification hierarchy are called taxonomic
categories. Each category represents a particular rank and is usually called
the taxon.
Species: A group of individuals in which the individuals can interbreed
among themselves is called species. Members of a species have a large
number of similar characters. For example; all the tigers are called
Panthera tigris. Since all of them can interbreed hence, they are kept under
one species.
Genus: A group of closely related species is called genus. Example; Lion
(Panthera leo), leopard (Panthera pardus) and tiger (Panthera tigris) are
members of the genus Panthera. Similarly, potato, tomato and brinjal belong
to the genus Solanum.
Family: A group of closely related genera is called a family. For example;
potato and chili belong the family Solanaceae. Similarly, the genus Panthera
and the genus Felis belong to the family Felidae.

3. The Living world (Topic)
Class-11th Sub-Biology
Balbeer Kour 3
Order: A group of closely related families is called order. For example;
Convolvulaceae and Solanaceae are plant families which belong to the
order Polymoniales. Similarly, Felidae and Concidae belong the order
Carnivora.
Class: The group of closely related orders is called class. For example;
orders Primata and Carnivora belong to the class Mammalia.
Phylum: A group of closely related classes is called phylum. In the Plant
Kingdom; the term phylum has been replaced with division. For example;
pisces, amphibia, reptilia, aves and mammalia belong to the Phylum
Chordata. All members of chordate have notochord at some stage of life.
Kingdom: The group of all the related phyla is called the Kingdom. For
example; all autotrophic organisms which are eukaryotic and contain
chloroplast are kept under the Plant Kingdom. Similarly, all heterotrophic
organisms which are eukaryotic and lack a cell wall are kept under Animal
Kingdom.