Classification Systems of Organisms
There are three classification systems of organisms. These are following
- Two kingdom classification system
- Three kingdom classification system
- Five kingdom classification system
Two kingdom classification systems
- It is the oldest system of classification
- It divides organisms into two kingdoms, planate, and Animalia.
- Plants are autotrophs because they can prepare food from simple organic materials.
- Animalia is heterotrophs because they cannot prepare their food and depend upon other organisms.
- Bacteria, fungi, and algae were included in the kingdom Plantae.
Drawbacks of the two-kingdom classification system
- It does not explain euglena-like organisms because it is plant-like as well as animal-like.
- It ignores the difference between prokaryotes and eukaryotes.
Three kingdom classification systems
- It divides organisms into three kingdoms, Plantae, Animalia, and Protista.
- Kingdom Protista was proposed by Ernst Hackel in 1866.
- Protista includes those organisms that do not fit into Plantae or Animalia i.e. Euglena
Drawbacks of three kingdom classification system
- It ignores the difference between prokaryotes and eukaryotes.
- It places fungi in the kingdom Plantae, which is wrong.
Differences of fungi from plants and animals
- It has cellulose in its cell wall.
- It gets food by absorption.
Five kingdom classification systems
- It was introduced by Robert Whittaker in 1967.
- It is based on levels of cellular organization and principal modes of nutrition.
- It divides organisms into five kingdoms, Plantae, Animalia, Protista, fungi, and Monera.
- Kingdom monera have prokaryotic cells. Kingdom Protista, Fungi, Plantae, and Animalia have eukaryotic cell
Kingdom Monera
- It includes organisms formed by prokaryotic cells i.e bacteria and cyanobacteria.
- Prokaryotic cells may be unicellular or form chains, clusters, or colonies.
- Prokaryotic cells are different from eukaryotic cells.
Kingdom Protista
- It includes eukaryotic unicellular or multicellular organisms.
- There are three types of protists.
- Algae: These are plant-like protists. These have cell walls and chlorophyll. These are unicellular, colonial, or multicellular.
- Protozoans: These are animal-like protists.
- Fungus like protists
Importance of kingdom Protista
Biologists believe that plants, animals, and fungi are evolved from Protista. Protists are evolved from monera.
Kingdom fungi
- It includes eukaryotic multicellular, heterotrophic organisms which get food by absorption.
- They live on organic matter and mostly are decomposers.
- Its example is mushrooms.
Kingdom Plantae
- It includes eukaryotic, multicellular, autotrophic organisms. e.g mosses, flowering plants, etc.
- Plants can make their own food by photosynthesis.
- These have multicellular sex organs and form embryos.
Kingdom Animalia
- It includes eukaryotic, multicellular, consumers. e.g. cow, earthworm, etc.
- Animals ingest food and digest it in body cavities.
- They show movements.