Five kingdom classification
Rahul went for morning walk with his younger brother. They stopped for rest in a nearby garden.
Rahul’s younger brother saw something near the bench they were sitting on and excitedly said, “Brother, see, a white plant.”
Rahul replied, “It is not a plant brother, it is a type of fungus.”
“'A fungus? But it looks like a plant”, said Rahul’s brother.
Rahul answered, “Our world has living things that are not just plants and animals. We have many microorganisms like bacteria, fungi, etc. around us".
Wide variety of organisms are present on the Earth, it is not possible to study each of them. So, there is a need to group them.
We have classified all the living organisms into different kingdoms. But Five Kingdom Classification is the most accepted one.
R.H. Whittaker was the scientist who divided all living organisms into five kingdoms.
The classification is based on different criteria.
Let us see the criteria used for the five-kingdom classification.
All living organisms are made up of cells, which are the basic units of life.
Hence, the first criterion is based on the complex structure of cells, whether they have a well-defined nucleus and other complex organelles or not.
Organisms with no well-defined nucleus and lack of cell organelles except ribosomes are called prokaryotes and those with a well-defined nucleus and cell organelles are called eukaryotes.
After that, we see whether the organism is made up of a single cell (unicellular) or many cells (multicellular).
Also, all cells need energy for survival and organisms get it from food.
The manner in which organisms take the food is known as mode of nutrition, which is the next criterion for classification.
Some organisms like plants make their own food by photosynthesis and this mode of nutrition is known as autotrophic mode of nutrition.
Some other organisms depend on other organisms for their food and this is known as heterotrophic mode of nutrition.
Some of these heterotrophic organisms take food by mouth and digest it to get energy which is called holozoic nutrition.
Many of the heterotrophic organisms obtain nutrients from dead and decaying organic matter. Such a type of nutrition is called saprotrophic nutrition.
When organisms show more than one mode of nutrition, this is known as mixotrophic nutrition.
All modes of nutrition ultimately provide energy to organisms.
Mode of utilisation of energy is used as the next criterion for classification.
Producers like green plants utilise energy by producing their own food.
Consumers utilise energy by eating these producers or another consumer.
Decomposers utilise energy by decomposing dead plants and animals into simple inorganic compounds.
After considering the mode of utilisation of energy, organisms can be classified on the basis of evolutionary history.
Relating organisms based on evolutionary history is known as phylogenetic relationship which is the last criteria for classification.
Based on these criteria we classify organisms into five kingdom.
Monera, Protista, Fungi, Plantae and Animalia are the five kingdoms.
Monera includes unicellular, prokaryotic organisms with simple cell structure.
Protista has evolved from prokaryotes. They are unicellular organisms but with a well-defined nucleus and organelles (eukaryotes).
Fungi, Plantae and Animalia include multicellular eukaryotic organisms that evolved from Protista.
Fungi are either unicellular or multicellular eukaryotes showing a Saprotrophic mode of nutrition. They have cell wall but they lack chlorophyll.
Yeast is an exceptional fungi which is unicellular.
Kingdom Plantae includes eukaryotic, multicellular and autotrophic organisms having cell wall and chlorophyll.
Animalia includes multicellular eukaryotes, without chlorophyll and they show a holozoic mode of nutrition.
Our world is full of living organisms that differ from each other in many aspects.
R.H. Whittaker proposed a system of classification for these organisms known as five kingdom classification.
This classification is based on criteria such as complexity of cell structure, the complexity of organisms body, mode of nutrition as well as energy utilisation and phylogenetic relationship.
Based on these criteria, organisms are divided into five kingdoms: Monera, Protista, Fungi, Plantae and Animalia.