PRINCIPLES OF

BIOLOGICAL SCIENCES
Yenukolu Aparna
Guest Lecturer in Zoology
GCM (A), Kadapa
UNIT-1 Branches of Biology
INTRODUCTION TO BIOLOGY: THE Biology is a broad field with many
STUDY OF LIFE specialized branches, including:
Biology is the scientific study of living Botany: The study of plants
organisms and their interactions with each
Zoology: The study of animals
other and their environment. It's a vast field
that encompasses everything from the Microbiology: The study of microorganisms
smallest single-celled bacteria to the largest
blue whale. Biochemistry: The study of the chemical
processes that occur in living organisms
Aristotle is regarded as the Father of
Biology. Genetics: Study of heredity and how traits
are passed from one generation to the next
He is also regarded as the Father of Zoology.
Ecology: The study of the interactions
He started classification with two kingdoms between organisms and their environment
Animalia and Plantae.
Physiology: The study of the functions of
Aristotle's theory of biology is known as living organisms
“Aristotle's Biology” which describes
metabolism, temperature regulation, and Anatomy: The study of the structure of
embryogenesis. living organisms

The world bio is derived from the Greek word BASIC PRINCIPLES OF BIOLOGY
which means ‘life and living organism'. Biology, the study of life, is guided by several
Biology is the study of life and its vital fundamental principles that form the
processes. foundation of our understanding of living
organisms. These principles include:
Key Concepts in Biology
1. Cell Theory
Cell Theory: All living things are made up
of cells, which are the basic units of life. All living organisms are composed of cells.
Cells are the basic unit of life.
Homeostasis: Organisms maintain a stable
internal environment, even when external All cells come from pre-existing cells.
conditions change.
2. Gene Theory
Evolution: Organisms change over time in
Traits are inherited through the transmission
response to their environment, leading to the
of genes.
diversity of life on Earth.
Genes are located on chromosomes and are
Genetics: The study of heredity and how
made of DNA.
traits are passed from one generation to the
next. 3. Homeostasis
Living organisms maintain a stable internal
environment.
They regulate their body temperature, pH, 2. Plantae: Multicellular organisms that
and other factors to ensure optimal function. cannot move and produce their own
food through photosynthesis.
4. Evolution
Living organisms change over time through
the process of evolution.
Evolution is driven by natural selection,
genetic variation, and genetic drift.
5. Laws of Thermodynamics
Living organisms follow the laws of
thermodynamics.
The first law states that energy cannot be
created or destroyed, only transformed.
Five-Kingdom Classification
The second law states that entropy (disorder)
increases over time.
This system, proposed by Robert Whittaker
6. Unity and Diversity of Life in 1969, divided living organisms into five
kingdoms based on their cellular
Despite their diversity, all living organisms organization, mode of nutrition, and body
share a common ancestry. organization:
This is evident in the similarities in their
1. Monera: Unicellular prokaryotes
genetic code, cellular structures, and (organisms without a nucleus) that
metabolic processes. reproduce asexually. Examples
These principles provide a framework for include bacteria and blue-green algae.
2. Protista: Unicellular eukaryotes
understanding the fundamental aspects of life
(organisms with a nucleus) that have
and serve as the basis for further exploration
a variety of modes of nutrition.
and research in biology. Examples include amoeba,
paramecium, and euglena.
3. Fungi: Multicellular eukaryotes that
BIOLOGICAL CLASSIFICATION – are heterotrophs (obtain food from
TWO KINGDOM AND FIVE KINGDOM others) and absorb nutrients from
decaying matter. Examples include
Two-Kingdom Classification mushrooms, molds, and yeasts.
4. Plantae: Multicellular eukaryotes
This system, proposed by Carolus Linnaeus that are autotrophs (produce their own
in the 18th century, divided all living food) through photosynthesis.
organisms into two kingdoms: Examples include plants, trees, and
algae.
1. Animalia: Multicellular organisms 5. Animalia: Multicellular eukaryotes
that can move and consume food. that are heterotrophs and ingest food.
 Examples include animals, humans, Unlike bacteria, which are living organisms,
and insects. viruses are considered non-living entities
because they cannot reproduce
independently. They require a host cell to
replicate, using the cell's machinery to make
copies of themselves.

How Do Viruses Infect Cells?

Attachment: The virus attaches to specific

receptors on the surface of the host cell.

Penetration: The virus enters the cell, either

by fusing with the cell membrane or by being
engulfed by the cell.

Uncoating: The virus's protein coat is

removed, releasing its genetic material.

Replication: The virus's genetic material

takes control of the host cell's machinery to
produce new viral proteins and genetic
material.

Assembly: The newly produced viral

components are assembled into new virus
particles.

Release: The new virus particles are released

from the host cell, either by bursting the cell
or by budding off from the cell membrane.

This process can cause damage to host and

cause various diseases.
VIRUSES
Types of Viruses
Viruses are incredibly small, non-living
entities that require a host cell to replicate. Viruses can be classified based on their
They are composed of genetic material (DNA shape, size, and genetic material. Some
or RNA) surrounded by a protein coat. common types of viruses include:
Viruses are microscopic infectious agents
that are composed of a protein coat DNA viruses: Examples include
surrounding a genetic core of either DNA or herpesviruses, adenoviruses, and
RNA. papillomaviruses.
RNA viruses: Examples include influenza
viruses, HIV, and coronaviruses.

Bacteriophages: Viruses that infect bacteria.

Viruses are responsible for a wide range of

diseases, including:

Common cold
Influenza
HIV/AIDS
Ebola
Measles VIROIDS
Rabies
Polio Viroids are incredibly small, circular RNA
molecules that are capable of infecting plants.
Prevention and Treatment They are considered to be the simplest known
infectious agents, consisting solely of RNA
While there are no specific treatments for without a protein coat.
many viral infections, vaccines can help
prevent certain viral diseases. Antibiotics are Key Characteristics of Viroids:
ineffective against viruses, as they only target RNA-only: Viroids are composed entirely of
bacteria.
RNA, unlike viruses which have both RNA
or DNA and a protein coat.
Types of Viruses:
Circular: The RNA molecule is circular,
Viruses can infect a wide range of organisms, forming a loop.
including:
Small: Viroids are significantly smaller than
• Humans: Examples include the viruses.
common cold, influenza, HIV, and
COVID-19. Plant pathogens: Viroids exclusively infect
• Animals: Rabies, canine parvovirus, plants, causing various diseases.
and feline leukemia virus are How Viroids Infect Plants:
examples of viruses that affect
animals. Entry: Viroids enter plant cells through
• Plants: Tobacco mosaic virus and wounds or natural openings.
potato virus Y are examples of plant
viruses. Replication: The viroid RNA molecule uses
• Bacteria: Bacteriophages are viruses the host cell's machinery to replicate itself.
that infect bacteria.
Movement: The replicated viroids spread
throughout the plant.
Disease: The presence of viroids can disrupt
plant growth and development, leading to
disease symptoms such as stunted growth,
yellowing, and necrosis.
Examples of Viroid-Caused Diseases:
Potato spindle tuber viroid: Causes potato
tubers to become spindle-shaped and
deformed.
Citrus exocortis viroid: Causes rough, scaly
bark on citrus trees.
Coconut cadang-cadang viroid: A lethal Lichens can also be used for various
disease of coconut palms. purposes, including:

LICHENS: SYMBIOTIC ORGANISMS • Food: Some lichens are edible and

have been used as a food source for
Lichens are fascinating organisms that are centuries.
formed by a symbiotic relationship between a • Dyes: Lichens contain pigments that
fungus and a photosynthetic partner, which can be used to produce natural dyes
can be either an alga or a cyanobacterium. for textiles and other materials.
• Medicine: Certain lichens have
How Lichens Work: medicinal properties and have been
used in traditional medicine for
• Photosynthetic Partner: Provides various ailments.
food (carbohydrates) through • Perfumery: Lichens are used in the
photosynthesis. perfume industry to create unique
• Fungus: Absorbs water and minerals, fragrances.
protects the photosynthetic partner,
and anchors the lichen to a surface.

Types of Lichens Based on Appearance: DIVERSITY IN LIVING WORLD

• Crustose Lichens: Flat, tightly Diversity in the living world refers to the vast
adhered to the substrate, often array of life forms that exist on Earth. It
difficult to remove. encompasses the incredible variety of
• Foliose Lichens: Leaf-like, loosely species, their genetic makeup, and the
attached to the substrate. ecosystems they inhabit. This diversity is a
• Fruticose Lichens: Shrub-like or result of millions of years of evolution,
hair-like, often branching. adaptation, and natural selection.

Lichens as Environmental Indicators: Key aspects of biodiversity:

Lichens are sensitive to air pollution, so their 1. Species diversity: This refers to the
presence or absence can be used as an number and variety of species within
indicator of air quality. They can also be used a given ecosystem or region. For
to determine the age of rocks and other example, a rainforest typically has
surfaces.
 much higher species diversity than a importance of biodiversity and to support
desert. conservation efforts.
2. Genetic diversity: This refers to the
variation in genetic material within a Biodiversity in Seshachalam Hills
species. It is essential for the survival
of a species as it allows individuals to Seshachalam Hills are a prominent range in
adapt to changing environmental the Eastern Ghats of Andhra Pradesh, India.
conditions. Known for their rich biodiversity, these hills
3. Ecosystem diversity: This refers to are home to a wide variety of flora and fauna.
the variety of ecosystems within a
region. Different ecosystems support Flora
different species and provide unique
ecological services. • Tropical evergreen forests: These
dense forests are characterized by tall,
Threats to biodiversity: broad-leaved trees like teak,
rosewood, and sandalwood.
• Habitat loss: The destruction of • Tropical deciduous forests: These
natural habitats due to human forests shed their leaves during the
activities such as deforestation, dry season. Trees like sal, tamarind,
urbanization, and agriculture is the and banyan are common.
primary threat to biodiversity. • Scrub forests: These are
• Climate change: Climate change is characterized by thorny shrubs and
altering ecosystems and affecting the small trees, often found in drier
distribution and survival of many regions.
species. • Grasslands: Open grasslands are
• Pollution: Pollution can contaminate found in some areas, supporting
water, air, and soil, leading to the various grasses and herbaceous
decline of biodiversity. plants.
• Overexploitation: Overfishing,
overhunting, and illegal wildlife trade Fauna
are major threats to biodiversity.
• Invasive species: Invasive species • Mammals: Seshachalam Hills are
can outcompete native species and home to a diverse range of mammals,
disrupt ecosystems. including leopards, tigers, elephants,
wild boars, deer, monkeys, and
Conservation efforts: various small mammals.
• Birds: The hills are a birdwatcher's
To protect biodiversity, it is essential to take paradise, with over 400 species
steps to conserve and restore natural habitats, recorded. Key species include
reduce pollution, and control invasive peacocks, hornbills, kingfishers, and
species. International agreements such as the migratory birds.
Convention on Biological Diversity (CBD) • Reptiles: A variety of reptiles,
have been established to promote including snakes, lizards, and turtles,
biodiversity conservation. Additionally, can be found in the hills.
many organizations and individuals are
working to raise awareness about the
 • Amphibians: The hills support a
diverse amphibian fauna, including
frogs, toads, and salamanders.

Conservation Efforts:

Due to the rich biodiversity and ecological

significance of Seshachalam Hills, several
conservation efforts have been undertaken:

• Sri Venkateswara National Park: Domain

This national park covers a significant
portion of the Seshachalam Hills and The broadest category, grouping organisms
protects the region's biodiversity. based on fundamental cellular differences.
• Community-based conservation:
Local communities are involved in o Eukarya: Organisms with eukaryotic
conservation efforts through cells (cells containing a nucleus)
initiatives like afforestation, wildlife o Bacteria: Prokaryotic organisms (cells
monitoring, and eco-tourism. without a nucleus)
• Research and education: Research o Archaea: Prokaryotic organisms with
institutions and NGOs are working to unique cellular features
study and conserve the biodiversity of
the hills. Kingdom
While Seshachalam Hills have faced threats A major grouping within a domain.
like deforestation and poaching, these
conservation efforts have helped to protect o Animalia: Animals
their unique ecosystems and the species that o Plantae: Plants
inhabit them. o Fungi: Fungi
o Protista: Single-celled organisms
(diverse group)
TAXONOMIC CATEGORIES o Monera: Prokaryotes (now often divided
into Bacteria and Archaea)
Taxonomic categories are the hierarchical
levels used to classify organisms based on Phylum (or Division in plants)
their shared characteristics. They form a
system that helps scientists organize and A grouping of organisms with similar body
understand the diversity of life on Earth. Each plans or characteristics.
category, referred to as a unit of
classification, in fact, represents a rank and is o Chordata: Animals with a notochord,
commonly termed as taxon (pl.: taxa). Here dorsal nerve cord, and pharyngeal
are the main taxonomic categories, from slits
broadest to narrowest: o Arthropoda: Animals with jointed
appendages and exoskeletons
Class • Kingdom: Animalia
• Phylum: Chordata
A grouping of organisms within a phylum • Class: Mammalia
that share more specific characteristics. • Order: Primates
• Family: Hominidae
o Mammalia: Mammals • Genus: Homo
o Insecta: Insects • Species: Homo sapiens

Order

A grouping of organisms within a class that

share more specific characteristics.

o Carnivora: Carnivorous mammals

o Primates: Primates

Family

A grouping of organisms within an order that TAXONOMIC AIDS

share more specific characteristics.
Taxonomic aids are tools and techniques used
o Felidae: Cats by scientists to identify, classify, and study
o Hominidae: Great apes organisms. These aids help in understanding
the relationships between different species
Genus and their evolutionary history. Here are some
common taxonomic aids:
A grouping of organisms within a family that
are closely related and share many
characteristics.

o Panthera: Big cats (lions, tigers,

leopards)
o Homo: Humans

Species

The most specific category, representing a

group of organisms that can interbreed and
produce fertile offspring.

o Homo sapiens: Humans 1. Herbarium:

Example: A human would be classified as • A collection of dried plants, pressed

follows: and mounted on sheets, arranged
systematically.
• Domain: Eukarya
 • Each specimen is labeled with 3. Botanical Garden:
information about its collection
location, date, and collector. • A cultivated collection of plants
• Used for studying plant morphology, arranged according to their taxonomic
taxonomy, and distribution. classification.
• Provides a living environment for
plants and allows for studying their
growth, reproduction, and
interactions with other organisms.

2. Museum:

• A collection of preserved specimens 4. Zoological Park:

of animals, plants, and other
organisms. • A collection of live animals exhibited
• Specimens can be preserved in in enclosures that mimic their natural
various ways, such as taxidermy, habitats.
skeletons, or preserved in alcohol. • Used for studying animal behavior,
• Used for studying animal ecology, and conservation.
morphology, taxonomy, and
distribution.

5. Keys:

• Dichotomous keys are a series of

paired statements that are used to
 identify organisms based on their PLANT ORGANIZATION: FORM,
characteristics. STRUCTURE, AND FUNCTION
• Each statement presents two
contrasting options, and the user Plants are multicellular organisms that
chooses the one that best describes the exhibit a complex organization, allowing
organism. them to perform various essential functions.
This organization is characterized by the
6. Flora and Fauna: presence of specialized tissues and organs,
each with specific roles.
• Flora refers to the plants of a region,
while fauna refers to the animals. Basic Plant Structure
• Flora and fauna books provide
descriptions, illustrations, and keys A typical plant consists of the following main
for identifying plants and animals in a parts:
specific region.
• Roots: These are usually
7. Monographs: underground structures that anchor
the plant, absorb water and minerals
• Detailed studies of a single taxon from the soil, and store nutrients.
(e.g., a genus, species, or family). • Stems: The above-ground structures
• Monographs provide comprehensive that support the plant, transport water,
information on the morphology, minerals, and sugars, and contain
taxonomy, distribution, and biology buds that develop into leaves and
of a particular group of organisms. flowers.
• Leaves: The primary organs of
8. Taxonomic Databases: photosynthesis, where plants convert
sunlight into energy. They also help
• Electronic databases that store in transpiration and gas exchange.
information about the classification, • Flowers: Reproductive organs that
distribution, and other characteristics produce seeds and fruits.
of organisms. • Fruits: The ripened ovaries that
• Examples include NCBI (National contain seeds and protect them.
Center for Biotechnology
Information) and GBIF (Global Plant Organs and Their Functions
Biodiversity Information Facility).
• Roots:
These taxonomic aids are essential for o Anchor the plant to the ground
scientists and researchers in various fields, o Absorb water and minerals
such as biology, ecology, and conservation. from the soil
They help in understanding the diversity of o Store nutrients
life on Earth and preserving it for future o Some roots can specialize in
generations functions like aerial
respiration (e.g., mangroves)
or nitrogen fixation (e.g.,
legumes).
• Stems:
 o Support the plant Vegetative Organs
o Transport water, minerals,
and sugars Vegetative organs are those that are involved
o Contain buds that develop in the growth and maintenance of the plant.
into leaves and flowers They include:
o Some stems can be modified
for storage (e.g., tubers) or • Roots:
climbing (e.g., tendrils). o Anchor the plant to the soil
• Leaves: o Absorb water and minerals
o Photosynthesis: Convert o Store nutrients
sunlight, water, and carbon o Some roots can be modified
dioxide into glucose and for specialized functions, such
oxygen. as aerial roots for respiration
o Transpiration: Lose water (e.g., mangroves) or storage
through tiny pores called (e.g., sweet potatoes).
stomata, which helps in • Stems:
cooling the plant and o Support the plant
transporting water and o Transport water, minerals,
minerals. and sugars
o Gas exchange: Exchange o Contain buds that develop
carbon dioxide and oxygen into leaves and flowers
with the atmosphere. o Can be modified for storage
• Flowers: (e.g., tubers) or climbing (e.g.,
o Reproduction: Contain male tendrils).
(stamens) and female (pistils) • Leaves:
reproductive organs. o Photosynthesis: Convert
o Pollination: Attract sunlight into energy
pollinators (e.g., bees, o Transpiration: Lose water to
butterflies) to transfer pollen help regulate temperature
from the stamens to the pistils. o Gas exchange: Exchange
• Fruits: carbon dioxide and oxygen
o Protect and disperse seeds o Can be modified for
o Attract animals to consume specialized functions, such as
and disperse the seeds. tendrils for climbing or spines
for defense.
This organization allows plants to adapt to
various environments and perform essential
functions, such as growth, reproduction, and
survival.

Plant Organization: Vegetative and

Reproductive Organs

Plants are organized into two main types of

organs: vegetative and reproductive.
 Relationship between Vegetative and
Reproductive Organs:

• Nutrient Supply: Vegetative organs,

especially leaves, provide the
nutrients necessary for the
development of reproductive organs.
• Support: The stem provides support
•
for the flowers and fruits.
• Resource Allocation: Plants often
Reproductive Organs allocate resources to reproductive
organs at the expense of vegetative
Reproductive organs are those involved in the growth, especially in harsh
reproduction of the plant. They include: environments.

• Flowers: Specialized Structures:

o Contain male (stamens) and
female (pistils) reproductive Both vegetative and reproductive organs can
organs be modified for specific functions. For
o Attract pollinators (e.g., bees, example:
butterflies) to transfer pollen
• Fruits: • Modified Roots: Storage roots (e.g.,
o Develop from the ovary of a carrots), adventitious roots (e.g.,
flower aerial roots of mangroves), and
o Contain seeds and protect contractile roots (e.g., bulbs).
them • Modified Stems: Rhizomes
o Disperse seeds to new (underground stems), tubers (storage
locations stems), stolons (horizontal stems),
and cladodes (flattened stems).
• Modified Leaves: Tendrils (for
climbing), spines (for defense), and
scales (for protection).
• Modified Flowers: Incomplete
flowers (lacking one or more floral
 parts), unisexual flowers (only male
or female parts), and inflorescences Characteristics of Kingdom Plantae
(clusters of flowers).
The plant kingdom has the following
Understanding the form, structure, and characteristic features:
function of both vegetative and reproductive
organs is crucial for understanding the life 1. They are non-motile.
cycle and adaptations of plants. 2. They make their own food and hence
are called autotrophs.
3. They reproduce asexually by
vegetative propagation or sexually.
4. These are multicellular eukaryotes.
The plant cell contains the outer cell
wall and a large central vacuole.
5. Plants contain photosynthetic
pigments called chlorophyll present
in the plastids.
6. They have different organelles for
anchorage, reproduction, support and
photosynthesis.

A plant kingdom is further classified into

subgroups. Classification is based on the
following criteria:

1. Plant body: Presence or absence of a

well-differentiated plant body. E.g.
Root, Stem and Leaves.
2. Vascular system: Presence or
absence of a vascular system for the
transportation of water and other
CLASSIFICATION OF THE PLANT substances. E.g. Phloem and Xylem.
KINGDOM 3. Seed formation: Presence or absence
Kingdom Plantae includes all the plants. of flowers and seeds and if the seeds
are naked or enclosed in a fruit.
They are eukaryotic, multicellular and
autotrophic organisms. The plant cell
contains a rigid cell wall. Plants have
chloroplast and chlorophyll pigment, which
is required for photosynthesis.
 branched or unbranched. Examples include
green algae, red algae and brown algae.
Common examples are Volvox, Fucus,
Spirogyra, Chara, Polysiphonia, Ulothrix,
etc.

Plants are classified into two main groups

Cryptogams – Non-flowering and non-seed

bearing plants. E.g. Thallophyta, Bryophyta,
Pteridophyta

Phanerogams – Flowering and seed-bearing

plants. E.g. Gymnosperms, Angiosperms
Bryophyta
These are further divided based on the
presence or absence of vascular system. Bryophytes do not have vascular tissues. The
plant body has root-like, stem-like and leaf-
The plant kingdom has been classified into
like structures. Bryophytes are terrestrial
five subgroups according to the above-
plants but are known as “amphibians of the
mentioned criteria:
plant kingdom” as they require water for
1. Thallophyta sexual reproduction. They are present in
2. Bryophyta moist and shady places. Bryophyta includes
3. Pteridophyta mosses, hornworts and liverworts. Some of
4. Gymnosperms the common examples are Marchantia,
5. Angiosperms Funaria, Sphagnum, Antheoceros, etc.

Thallophyta

Thallophytes lack a well-differentiated body

structure and the plant body is thallus like.

Thallophyta includes plants with primitive

and simple body structures. The plant body is
thallus, they may be filamentous, colonial,
 Angiosperms
Pteridophyta
Angiosperms are seed-bearing vascular
Pteridophytes have a well-differentiated plant plants with a well-differentiated plant
body into root, stem and leaves. They have a body. The seeds of angiosperms are enclosed
vascular system for the conduction of water within the fruits. Angiosperms are widely
and other substances. Some of the common distributed and vary greatly in size, e.g.
Wolffia is small measuring about 0.1 cm and
examples are Selaginella, Equisetum, Pteris,
Eucalyptus trees are around 100 m tall.
etc. Angiosperms are further divided into
monocotyledons and dicotyledons according
to the number of cotyledons present in the
seeds. Some of the common examples are
mango, rose, tomato, onion, wheat, maize,
etc.
Further divided into two classes based on the
number of cotyledons (seed leaves) in their
embryos:

• Monocotyledons (Monocots): Have

one cotyledon. Examples: grasses,
lilies, orchids
• Dicotyledons (Dicots): Have two
cotyledons. Examples: roses, daisies,
oak trees
Gymnosperms

Gymnosperms have a well-differentiated

plant body and vascular tissues. They bear
naked seeds, i.e. seeds are not enclosed
within a fruit. Some of the common examples
of gymnosperms are Cycas, Pinus, Ephedra,
etc.
BASIS FOR ANIMAL 6. Embryonic Development:
CLASSIFICATION
• The pattern of embryonic
Animals are classified based on various development, such as protostome or
shared characteristics, including: deuterostome development.

1. Body Structure: 7. Phylogeny:

• Symmetry: Animals can be classified • The evolutionary relationships

based on their body symmetry: between different animal groups,
o Radial symmetry: Body parts radiate based on shared characteristics and
from a central point. genetic data.
o Bilateral symmetry: The body can
be divided into two equal halves. These are just some of the criteria used to
• Body cavities: The presence or absence of classify animals. The specific characteristics
body cavities (coelom) is another used may vary depending on the taxonomic
important characteristic. level being considered.
o Acoelomate: No body cavity
o Pseudocoelomate: False body cavity
o Coelomate: True body cavity
ANIMAL KINGDOM
2. Tissue Organization: CLASSIFICATION

• Diploblastic: Animals with two germ

layers (ectoderm and endoderm).
• Triploblastic: Animals with three
germ layers (ectoderm, mesoderm,
and endoderm).

3. Segmentation:

• The presence or absence of body

segments (metameres).

4. Presence or Absence of Notochord:

• A notochord is a flexible rod-shapedThe science of classifying organisms is called

structure found in the dorsal part of
taxonomy. Every species discovered so far are
the embryo. classified into five kingdoms – one among them is
• Animals with a notochord are Kingdom Animalia or Animal kingdom. The members
classified as chordates. of kingdom Animalia are further classified into
different Phyla, Class, Order,
5. Mode of Reproduction: Family, and Genus based on certain identifiable
characteristic features.
• Sexual or asexual reproduction.
 small group of worm-like, marine species
with an organ-system level of organization.

Members of phylum Porifera, Coelenterata,

Ctenophora, Platyhelminthes,
Aschelminthes, Annelida, Arthropoda,
Mollusca, Echinodermata and Hemichordata
fall under Non-chordates.

The general characteristic features of Non-

Chordates are:
One of the most fundamental forms of • They are cylindrical, triploblastic,
classification of animals is the presence or coelomate, or pseudocoelomate
absence of the notochord. Hence, two major animals.
groups exist, namely: Chordates and Non- • Respiration in these animals takes
place through gills, trachea or body
chordates. surface.
• Most of the times, sexes cannot be
Non-chordates and the Chordates distinguished among the members.
• Modes of reproduction involve sexual
The notochord is a flexible rod made out of a and asexual
material similar to cartilage. If an animal has • Fertilization is external, though
a notochord during any stage of its life, it is internal fertilization also occurs in
classified as a chordate. Contrary to popular some species.
• The body of non-chordates generally
belief, chordates do not exclusively include
includes an open type of circulatory
vertebrates. system.

There are invertebrates that possess a

Chordates
notochord during some point in their lives
and hence, are classified as chordates. Thus Chordates are animals characterized by the
all vertebrates are chordates but not all presence of notochord at some stage during
chordates are vertebrates. their development. Members possess a
hollow nerve cord and pharyngeal gill slits.
Non-chordates The other general characteristic features of
Chordates are as follows:
Non-chordates are animals without a
notochord – the rod-like elastic structure that • They are bilaterally symmetrical,
supports the body. This phylum consists of a triploblastic, and coelomate with the
organ-system level of organization.
 • They hold a post-anal tail Subphylum – Vertebrata
• The body includes a closed
circulatory system. In this subphylum, the notochord is present in
• In some members of Phylum the embryonic stages and is replaced by a
Chordata, the notochord is present vertebral column in the adult. They have 2, 3
only in the larval tail, and in some, it
is present throughout their life from or 4 chambered heart, paired appendages for
head to tail region. locomotion and kidneys for excretion or
• Chordates have many sub-divisions osmoregulation.
and Protochordates are one of the
earliest to evolve.
Vertebrates Classification
Phylum Chordata is divided into three
subphyla: Urochordata, Cephalochordata, The subphylum Vertebrata is divided into
and Vertebrata. five classes of vertebrates. These five classes
of vertebrates comprise of all the species of
Subphylum – Urochordata animals and have developed vertebral
column as well as an internal skeleton.
It is also referred to as Tunicata which are
marine animals. The body of these animals is There are over 66,000 species of vertebrates
surrounded by a leathery covering (similar to identified under phylum Chordata till date.
a tunic, hence the name). Larvae are free- The defining feature of vertebrates is that
swimming, the notochord is present only in their bodies are bilaterally symmetrical,
the tail of larvae and after settling on the coelomic, triploblastic, and with complex
seabed, they get transformed into sessile differentiation of body tissues and organs.
adults. They are generally hermaphrodites.
Other characteristic features of
Examples include – Ascidians, Doliolum, vertebrates are:
Oikopleura, etc.
• Presence of a true vertebral column
Subphylum – Cephalochordata and internal skeleton with muscle
attachment points for body
It mainly consists of small, fish-like marine movement.
animals in which the notochord is extended • A front-side muscular heart with two,
along the entire body. The animals also have three or four chambers.
• Kidneys for excretion and
pharynx, which is large with numerous gill-
osmoregulation
slits. Members of this subphylum have
• A paired appendages which may be
separate sexes. fins or limbs.
• Possess notochord during the
Example include – Amphioxus or lancelet. embryonic stage.
 • Vertebrates are the only chordates to are mainly characterized by the two pairs of
possess a brain as a part of the central
nervous system. limbs, smooth and moist skin for respiration.
They also possess protruding eyes which are
Classification of Vertebrates protected by usually more than one pair of
eyelids. (Frogs have 3).
• Pisces
• Amphibia Examples of Class Amphibia are frog, toad,
• Reptilia and salamander.
• Aves
• Mammalia Class Reptilia

Class Reptilia comprises those organisms

which are ectothermic in nature (cold-
blooded). They are characterized
by osteoderms which form scales, bony
Class Pisces (Fishes) plates or scutes on the skin. Reptiles also
They are aquatic animals, having a lack an external ear and some reptiles such as
streamlined body and a pair of fins which are snakes are actually “deaf” and instead, pick
used for propulsion and movement. up vibrations through the ground. Another
Furthermore, fish are cold-blooded, but the amazing sense that only snakes possess is
discovery of a new species in 2015 has Thermoception. This means that snakes can
changed this perception. The opah or the see infrared radiation emitted by objects or
moon-fish is a fully warm-blooded fish prey.
capable of regulating its body temperature.
Examples of Class Reptilia are Tortoise, Wall
Endoskeleton may be cartilaginous or bony lizard, Snake, etc.
and respiration occurs through gills. They do
not possess eyelids because the surface of the Class Aves (Birds)
eye is to be kept moist all the time. Most members have a streamlined body
specially designed to offer low air resistance
Examples of Class Pisces includes dogfish
during flight. In such birds, the forelimbs are
and Rohu.
modified into wings, with the power coming
from breast muscles. Feathers play important
Class Amphibia
roles, from flight, thermal insulation to water-
They usually comprise those organisms proofing. All members of this class are
which are cold-blooded and require an
aquatic habitat to lay eggs. These organisms
warm-blooded and are able to regulate their
body temperature.

Aves have beaks, which are used for various

functions such as preening and feeding.
Furthermore, birds are considered to be the
living relatives of dinosaurs (evolved from a
group of meat-eating dinosaurs called the
theropods).

Examples of Class Aves are Parrot, Pigeon,

Duck, etc.

Class Mammalia

These organisms are distinguished by the

presence of mammary glands. They have two
pairs of limb for walking, grasping,
swimming, flying, etc. Digits are provided
with claws, nails or hooves. Skin is covered
by hair and they have an external ear called
pinnae. They are warm-blooded animals.

Examples of Class Mammalia include

monkeys, lions, bats, squirrels and humans.