Classification of Living Things                                                             

•    Classification presented by Aristotle – He classified animals on the basis of their habitats – land, water and air.
•    But it can be easily observed that the animals that live at a particular habitat say land are still so different from each other.
•    Therefore, it was decided to classify the living organisms on the basis of a hierarchy.
•    This hierarchical classification was based on the similarities and dissimilarities in the characteristics of the living organisms.
•    Organisms having similar characteristics were placed in a similar category.

  Why do we need to classify organisms?
1. If we classify organisms into several categories, it will be easier for us to study them.
2. It will help us in understanding how did these organisms evolve.
3. We can also understand how different organisms are related to each other.
4. We can learn why different organisms are found at distinct geographical conditions.

Hierarchy Classification - Formation of Kingdoms
Biologists categorized different organisms into several kingdoms.

Classification

Proposed by

Type of organisms

 

Two kingdom classification

Carolus Linnaeus in 1758

1. Plants 

 

2. Animals

 

Five Kingdom classification

Robert Whittaker in 1959

1. Monera

 

2. Protista 

 

3. Fungi

 

4. Plantae

 

5. Animalia

 

Carl Woese in 1977 

1. Monera

 

(i) Archaea

 

(ii) Eubacteria

 

2. Protista 

 

3. Fungi

 

4. Plantae

 

5. Animalia

 

 

 

 

 
 

 The order of Classification

1. Kingdom
2. Phylum / Division
3. Class
4. Order
5. Family
6. Genus
7. Species
Species is called as the Basic Unit of Classification. Species is a group of organism which can interbreed with each other. The picture below explains how humans are classified in a hierarchical order.


Hierarchical Order of Classifying Humans

Five Kingdom Classifications

 

                                                                                      Five Kingdom Classification

  • The organization inside the cells
    • Prokaryotic Cells – Cells with no definite nucleus
    • Eukaryotic Cells – Cells with a definite nucleus
  • The organization of cells in the body

 

    • Unicellular – Single-celled organisms
    • Multicellular – Multi-cell organisms
  • organisms obtain their food

 

    • Autotrophs – Produce their food on their own 
    • Heterotrophs – Depend on other organisms for their food

 

                                                          Classification of Organisms       

Classification of Organisms

 

Monera 

Protista

Fungi

Plantae

Animalia 

Organization inside the cells

Consists of Prokaryotes.

Eukaryotes – some of them use appendages to move around such as flagella (whip-like structure) and Cilia (hair-like structure)

Eukaryotes

Eukaryotes

Eukaryotes

Organization of cells in the body

Unicellular 

Unicellular 

Initially unicellular. Can become multicellular in later stages of life 

Multicellular

Multicellular

Organisms obtain their food 

Some of them are autotrophs like blue green algae while others are heterotrophs

Both autotrophs and heterotrophs 

Heterotrophs. Most of them are decomposers or may be parasitic.

Autotrophs

Heterotrophs

Presence of cell wall

Some lack a cell wall while others have a cell wall 

Only some have cell wall 

Have cell walls. They are made up of complex sugar called chitin.

Have cell walls made of cellulose.

No cell walls

Example

Blue-green algae, Bacteria, Mycoplasma

Protozoan, Diatoms and Golden algae

Yeast and Mushroom ( Agaricus), Rhizopus ( Bread mould), Pencillium

Flowering plants, moss 

Insects, reptiles 

Archea Kingdom

    The monera kingdom is further classified as Archaea.
    These are microbes (bacteria) that can live in harsh conditions. Since they can live in extreme temperatures, they are also called Extremophiles
    These organisms lack a cell wall. 
    Their cell membrane is made up of lipids.
They are further classified into three categories, based on their habitat:

Halophiles

Thermophiles

Methanogens

These are salt loving bacteria. They live in extremely salty water.

They live in boiling water such as hot springs and volcanoes.

They are found in the guts of animals like cow and sheep. They produce methane gas from their dung. 

 

Who are Saprophytes?
Fungi also called as Saprophytes because they grow over the organic material and survive on them.
What are Symbiotic relationships?
Some species of fungi live in permanent mutually dependent relations with blue-green algae. They are said to have a symbiotic relationship. For Example, Lichens are often found on the bark of the trees.