Diversity In Living Organisms: Classification, Kingdoms, Plants And Animals Explained

Living organisms show a huge variety in their structure, size, body organisation, nutrition and reproduction.

Some organisms are microscopic and unicellular, while others are large, complex and multicellular. To study this wide variety properly, scientists group organisms into categories. This process is called classification.

What Is Classification?

Classification is the process by which living organisms are grouped into convenient categories on the basis of easily observable characteristics.

Classification helps students and scientists study organisms in an organised way.

Aristotle’s Classification

The first scientific classification was given by Aristotle.

He classified organisms into two main groups:

• Plants
• Animals

Classification Of Plants By Aristotle

Aristotle classified plants into:

• Trees
• Shrubs
• Herbs

Classification Of Animals By Aristotle

Animals were classified on the basis of the presence of blood:

• Animals with red blood
• Animals without red blood

This classification was simple, but it was not fully scientific because it used only a few visible characters.

Two Kingdom Classification By Carolus Linnaeus

Carolus Linnaeus classified all organisms into two kingdoms:

• Plantae
• Animalia

This classification was given in his book Systema Naturae.

Carolus Linnaeus is known as the Father of Taxonomy.

What Is Taxonomy?

Taxonomy is the science of classification based on characteristics.

It includes:

• Identification
• Classification
• Nomenclature

Hierarchy Of Classification

The classification hierarchy arranges organisms from broad categories to specific categories.

The correct hierarchy is:

• Kingdom
• Phylum or Division
• Class
• Order
• Family
• Genus
• Species

For plants, the term Division is often used instead of Phylum.

Binomial Nomenclature

Binomial nomenclature was given by Carolus Linnaeus.

It is the scientific system of naming organisms.

Each scientific name has two parts:

• Generic name
• Specific epithet

Example

Mangifera indica

Here:

• Mangifera = Genus
• indica = Species

Rules Of Writing Scientific Names

• The genus name begins with a capital letter.
• The species name begins with a small letter.
• Both words are written in italics when typed.
• When handwritten, both words are underlined separately.

Example

Amoeba proteus

Five Kingdom Classification

The Five Kingdom Classification was proposed by R.H. Whittaker in 1969.

He classified organisms into five kingdoms:

• Monera
• Protista
• Fungi
• Plantae
• Animalia

This system is more scientific because it considers cell type, body organisation, mode of nutrition and other important features.

Comparison Of Five Kingdoms

Feature	Monera	Protista	Fungi	Plantae	Animalia
Cell Type	Prokaryotic	Eukaryotic	Eukaryotic	Eukaryotic	Eukaryotic
Cell Wall	Present, peptidoglycan	Present in some	Present, chitin	Present, cellulose	Absent
Nuclear Membrane	Absent	Present	Present	Present	Present
Nutrition	Autotrophic and heterotrophic	Autotrophic and heterotrophic	Heterotrophic	Autotrophic	Heterotrophic
Body Organisation	Cellular	Cellular	Mostly multicellular	Multicellular	Multicellular

Kingdom Monera

Kingdom Monera includes bacteria.

These organisms are unicellular and prokaryotic.

Features Of Monera

• They are unicellular.
• They are prokaryotic.
• A true nucleus is absent.
• Most have a cell wall.
• Cell wall is made of peptidoglycan.
• Mycoplasma lacks a cell wall.
• Heterotrophic bacteria are most abundant in nature.

Examples

• Bacteria
• Cyanobacteria
• Mycoplasma

Kingdom Protista

Kingdom Protista includes mostly unicellular eukaryotic organisms.

These organisms have a true nucleus.

Features Of Protista

• Mostly unicellular.
• Eukaryotic cells.
• Nuclear membrane is present.
• Some are autotrophic.
• Some are heterotrophic.
• Some have a cell wall, while others do not.

Examples

• Amoeba
• Paramecium
• Euglena
• Slime moulds

Amoeba, Paramecium and Euglena are unicellular protists.

Kingdom Fungi

Fungi are eukaryotic organisms with a cell wall made of chitin.

They are heterotrophic and usually absorb food from dead or decaying organic matter.

Features Of Fungi

• Eukaryotic.
• Mostly multicellular.
• Cell wall is made of chitin.
• Heterotrophic mode of nutrition.
• Do not contain chlorophyll.
• Many fungi act as decomposers.

Examples

• Mushroom
• Penicillium
• Yeast
• Mould

The antibiotic penicillin is obtained from fungi such as Penicillium notatum or Penicillium chrysogenum.

Lichens

Lichens are symbiotic associations of algae and fungi.

In lichens:

• Algae prepare food by photosynthesis.
• Fungi provide shelter, water and minerals.

Kingdom Plantae

Kingdom Plantae includes multicellular, eukaryotic and mostly autotrophic organisms.

They contain chlorophyll and prepare their own food by photosynthesis.

Features Of Plantae

• Eukaryotic.
• Multicellular.
• Cell wall made of cellulose.
• Autotrophic nutrition.
• Chlorophyll is present.
• Store food mainly as starch.

Classification Of Plant Kingdom

Kingdom Plantae is divided into five main groups:

• Thallophyta
• Bryophyta
• Pteridophyta
• Gymnosperms
• Angiosperms

Thallophyta

Thallophytes have a simple plant body.

The body is not clearly differentiated into root, stem and leaves.

Features Of Thallophyta

• Simple body structure.
• Body is thallus-like.
• No true root, stem and leaves.
• Mostly aquatic.

Examples

• Algae
• Spirogyra

Bryophyta

Bryophytes are known as the amphibians of the plant kingdom because they need water for reproduction.

They do not have true vascular tissues.

Features Of Bryophyta

• Small plants.
• Lack true roots, stems and leaves.
• Lack xylem and phloem.
• Need water for reproduction.

Example

• Marchantia

Marchantia is a bryophyte and does not possess specialized conducting tissues like xylem and phloem.

Pteridophyta

Pteridophytes are the first vascular cryptogams.

They have vascular tissues but do not produce seeds.

Features Of Pteridophyta

• Have xylem and phloem.
• Have true roots, stems and leaves.
• Do not produce seeds.
• Reproduce through spores.

Examples

• Fern
• Marsilea
• Horsetail

Marsilea, ferns and horsetails are examples of pteridophytes.

Gymnosperms

Gymnosperms are seed-producing plants, but their seeds are naked.

This means seeds are not enclosed inside fruits.

Features Of Gymnosperms

• Seeds are naked.
• Vascular tissues are present.
• Usually woody plants.
• Do not produce fruits.

Example

• Cycas

Angiosperms

Angiosperms are flowering plants.

Their seeds are enclosed inside fruits.

Features Of Angiosperms

• Flowering plants.
• Seeds enclosed inside fruits.
• Well-developed vascular tissues.
• Most advanced plant group.

Examples

• Mango
• Wheat
• Mustard

Kingdom Animalia

Kingdom Animalia includes multicellular, eukaryotic and heterotrophic organisms.

Animals do not have a cell wall.

Features Of Animalia

• Multicellular.
• Eukaryotic.
• Cell wall absent.
• Heterotrophic nutrition.
• Mostly show movement.
• Highly organised body systems in advanced animals.

Basis Of Animal Classification

Animals are classified on the basis of several important features.

1. Level Of Organisation

Animal body organisation may be:

• Cellular level
• Tissue level
• Organ level
• Organ system level

Cellular Level

Cells are arranged as loose cell aggregates.

Example:

• Porifera

Tissue Level

Cells performing similar functions are arranged into tissues.

Example:

• Cnidaria

Organ Level

Different tissues combine to form organs.

Example:

• Platyhelminthes

Organ System Level

Organs work together to form organ systems.

This is found in higher animals.

Example:

• From Aschelminthes to Chordata

2. Germ Layers

Animals may be diploblastic or triploblastic.

Diploblastic Animals

They have two germ layers.

• Ectoderm
• Endoderm

Examples:

• Cnidaria
• Ctenophora

Triploblastic Animals

They have three germ layers.

• Ectoderm
• Mesoderm
• Endoderm

Examples:

• Platyhelminthes onwards

3. Symmetry

Symmetry refers to body arrangement.

Asymmetrical Animals

The body cannot be divided into equal halves.

Example:

• Porifera

Radial Symmetry

The body can be divided into equal halves through many planes passing through the centre.

Example:

• Cnidaria

Bilateral Symmetry

The body can be divided into two equal halves only through one plane.

Example:

• Nereis

Nereis shows bilateral symmetry.

4. Coelom

Coelom is the body cavity present between the body wall and the gut wall.

Acoelomate Animals

Body cavity is absent.

Example:

• Platyhelminthes

Pseudocoelomate Animals

False body cavity is present.

Example:

• Aschelminthes

Coelomate Animals

True body cavity is present.

Examples:

• Annelida
• Arthropoda
• Mollusca
• Echinodermata
• Chordata

5. Notochord

The notochord is a rod-like structure present along the dorsal side of the body during embryonic development.

It provides support and attachment for muscles.

Based On Notochord

Animals are divided into:

• Chordates
• Non-chordates

Chordates

Notochord is present at least during some stage of life.

Non-Chordates

Notochord is absent.

Example:

• Porifera

Major Animal Phyla

Porifera

Porifera includes simple aquatic animals.

Features

• Cellular level of organisation.
• Mostly asymmetrical.
• Body has pores.
• Notochord absent.

Example

• Sycon

Cnidaria

Cnidarians are aquatic animals with stinging cells.

Features

• Tissue level of organisation.
• Diploblastic.
• Radial symmetry.
• Acoelomate.

Example

• Jellyfish or Aurelia

Ctenophora

Ctenophores are marine animals.

Features

• Diploblastic.
• Radial symmetry.
• Acoelomate.

Platyhelminthes

Platyhelminthes are flatworms.

Features

• Organ level of organisation.
• Triploblastic.
• Bilateral symmetry.
• Acoelomate.

Aschelminthes Or Nematoda

These are roundworms.

Features

• Organ system level of organisation.
• Triploblastic.
• Bilateral symmetry.
• Pseudocoelomate.

Examples

• Ascaris
• Wuchereria bancrofti
• Enterobius

Annelida

Annelids are segmented worms.

Features

• Bilateral symmetry.
• True coelom present.
• Segmented body.

Example

• Nereis

Nereis moves with the help of parapodia.

Arthropoda

Arthropoda is one of the largest animal groups.

Features

• Jointed legs.
• Bilateral symmetry.
• True coelom.
• Hard exoskeleton.

Examples

• Insects
• Spider
• Scorpion
• Crab

Insects have three pairs of legs, while spiders and scorpions have four pairs of legs.

Mollusca

Molluscs are soft-bodied animals.

Features

• Soft body.
• Usually protected by shell.
• True coelom present.

Examples

• Snail
• Cuttlefish

Pearls are made of calcium carbonate secreted by the mantle of molluscs.

Echinodermata

Echinoderms are marine animals.

Features

• True coelom.
• Spiny skin.
• Mostly radial symmetry in adults.

Chordata

Chordates possess a notochord at some stage of life.

Features

• Notochord present.
• Dorsal nerve cord present.
• Organ system level of organisation.

Vertebrate Groups

Chordates include vertebrates such as fishes, amphibians, reptiles, birds and mammals.

Pisces

Pisces are true fishes.

Example:

• Flying fish

Silverfish and cuttlefish are not true fishes.

Amphibia

Amphibians live both on land and in water.

Most amphibians have a three-chambered heart.

Reptilia

Reptiles are cold-blooded animals.

Most reptiles have a three-chambered heart, except crocodiles.

Aves

Birds are warm-blooded animals.

Example:

• Peacock

Mammalia

Mammals are warm-blooded animals.

Examples:

• Ape
• Camel
• Blue whale

The blue whale gives birth to the largest baby among animals.

Viruses

Viruses are non-cellular organisms.

They need living cells to reproduce.

Features Of Viruses

• Acellular.
• Cannot reproduce outside living cells.
• Act as parasites.
• Do not perform photosynthesis.
• Outside the host, they behave like chemical substances.

Most plant viruses are RNA viruses, while many animal viruses are DNA viruses.

Key Takeaways

• Classification helps in the systematic study of living organisms.
• Taxonomy includes identification, classification and nomenclature.
• Binomial nomenclature gives every organism a two-part scientific name.
• Whittaker’s Five Kingdom Classification includes Monera, Protista, Fungi, Plantae and Animalia.
• Monera includes prokaryotic organisms.
• Protista includes mostly unicellular eukaryotes.
• Fungi are heterotrophic organisms with chitin cell walls.
• Plantae includes autotrophic organisms with cellulose cell walls.
• Animalia includes multicellular heterotrophic organisms without cell walls.
• Plants are classified into thallophytes, bryophytes, pteridophytes, gymnosperms and angiosperms.
• Animals are classified on the basis of body organisation, germ layers, symmetry, coelom and notochord.

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