Systems of Classification and Evolution


 
 
Concept Explanation
 

Systems of Classification and Evolution

To begin with, Linnaeus (1758) divided all organisms into two kingdoms—plants (Plantae) and animals (Animalia).

Plants and animals seemed so obviously different that this appeared to be a very logical way of classifying organisms. Plants can prepare their own food with the help of chlorophyll. Animals do not have chlorophyll, so they cannot manufacture food. Plant cells have a cell wall, while animal cells do not.

A third kingdom called Protista was created by Ernst Haeckel (1866), a German zoologist. All unicellular animals were placed in this kingdom. Then two superkingdoms were created. One for prokaryotes, or unicellular organisms lacking a true nucleus. And the other for eukaryotes, or all organisms (unicellular and multicellular) with a true nucleus.

The prefixes ‘super’ and ‘sub’ are often used to divide or join the groups (kingdom, phylum, etc.) under the system of classification we have already discussed. The super kingdoms Prokaryota include bacteria and cyanobacteria. It has only one kingdom under it. This kingdom of bacteria and cyanobacteria is called Monera.

Cyanobacteria are prokaryotic like bacteria, but can photosynthesize like plants.The creation of the kingdom “Monera” did not solve all the problems with classifying organisms.

Fungi created the next problem. Like bacteria, they cannot photosynthesize, but they are eukaryotic. They could neither be placed in Monera, nor in Protista, which now includes photosynthesizing algae.

A new kingdom was then created for fungi. Robert Whittaker (1969) is credited with the creation of the kingdoms Monera and Fungi.

The five kingdoms of Monera, Protista, Fungi, Plantae and Animalia include all organisms except viruses. Viruses cannot really be called living organisms because they are noncellular. A virus is just a bit of DNA or RNA inside a covering of protein. The kingdom Monera falls under the super kingdom Prokaryota. The other four kingdoms fall under the super kingdom Eukaryota.                                               

Sample Questions
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Question : 1

In  the five kingdom classification the unicellular eukaryotes are placed under _________________ kingdom.

Right Option : B
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Question : 2

Which of the following characteristics is not taken into consideration while classifying organisms?

Right Option : B
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Question : 3

Aristotle classified organisms on the basis of similarity in their ______________

Right Option : C
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