Introduction to Diversity in Living Organisms
Life exists in different forms on Earth. When it comes to the question of the number of living organisms found on the earth, the answer is unimaginable. This is so because of the large diversity of organisms continuously evolving into a different variety ever since the origin of life had taken place. Diversity is present at different levels like genetic diversity, species diversity, and ecological diversity. Mango alone has around 10,000 varieties in India. This alone example indicates how large and diverse are the living organisms. Gaining knowledge about this large diversity is impossible without classifying them. Thus classification becomes an important step towards the study of different organisms found on the earth.
The process of putting all the organisms in certain groups on the basis of certain similarities and differences is known as Classification
Various characteristics are taken into account in order to classify an organism. Some of them are-
The type of cell present whether the organism is having a eukaryotic cell or a prokaryotic cell.
The number of cells whether the organism is unicellular or multicellular.
Body organization whether the organization is cellular, tissue-level, or organ level.
The nutrition of organisms whether it's autotrophic or heterotrophic.
Morphological features of the organisms.
Anatomical features of the organism etc.
All these features including many others are taken into consideration during classification
Various scientists have proposed their own model of classifying organisms. Some of these are given below.
Two Kingdom Classification
Carolus Linnaeus gave the 2-kingdom system of classification and divided all the organisms into two groups as Plantae and Animalia. This kind of classification brought all the organisms which had a cell wall together within their cell in one group called the Plantae and rest all were placed in the other group known as Animalia. Plantae got comprised of bacteria, fungi with plants. All were very different from each other but still were kept together under two-kingdom classification. There was no distinction between the prokaryotes as well as eukaryotes. Thus this system of classification was not right but surely helped in evolving a better classification system.
Five Kingdom Classification
R.H Whittaker proposed a five-kingdom classification. This classification is accepted and corrects worldwide. A number of criteria were considered for making this model like the cell type, cell number, cell organization, nutrition, etc.
It consists of 5 groups /kingdoms
Characteristics of 5 Kingdom
This kingdom has organisms that are unicellular and have a prokaryotic cell.
It includes bacteria, cyanobacteria, etc.
Their cell usually has a cell wall.
They can be autotrophic or either heterotrophic.
This kingdom includes organisms that are also unicellular but have a eukaryotic cell.
They may be photosynthetic or heterotrophic.
They may possess structures like flagella and cilia.
Examples are amoeba, euglena, paramecium, etc.
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This is the first kingdom with multicellular organisms.
They exhibit a heterotrophic mode of nutrition more specifically saprotrophic mode of nutrition.
They have a eukaryotic cell with a cell wall which is made up of chitin.
Example - yeast, mushroom
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All organisms are eukaryotic and multicellular.
The body can be seen as differentiated into higher groups.
They are photosynthetic and exhibit an autotrophic mode of nutrition. Some members are partially heterotrophic.
Their cell has a cell wall made up of cellulose.
Examples-mango tree, red algae, etc.
All members are eukaryotic and multicellular.
Their cells lack a cell wall.
They are heterotrophs.
Examples-lion, dog, fish, etc.
The broadest group Kingdom is further divided into small groups to reach a point of maximum similarity in one group of organisms. Thus a hierarchy of classification is developed when the small groups are arranged from the lowest to the highest order. Each category in the hierarchy is known as Taxon.
Following is the Hierarchy of Classification.
Phylum / Division
Species are the basic unit of classification.
Yeast is the only unicellular fungus.
Lichens are organisms in which algae and fungi live together and exhibit symbiotic relationship.
1. Comment on the Relation Between Classification and Evolution.
As we take a closer look at the classification of organisms and how the kingdoms and phyla are arranged one after the other, depicting a change from simple to complex forms, it actually indicates the pattern of evolution that has taken place on the earth in the past years. Classification and its hierarchy is the direct evidence of evolution. Higher groups are evolved from the lower groups from gradual evolution and these groups are placed accordingly in the hierarchy. Thus Classification is interrelated to evolution though were developed and studied independently.
2. Define the Artificial System of Classification.
Organisms were also classified on the basis of habitat and feeding habits are known as an artificial system of classification.
Some groups on the basis of habitats are mentioned below :
Aquatic - Organisms that live in water are considered aquatic organisms. It has many other subgroups like Benthos (bottom-dwelling), sedentary (fixed in water), etc.
Terrestrial - Organisms that live on land are known as terrestrial. They can be scansorial (wall climbers), arboreal (tree climbers), cursorial (fast-moving ), etc. Example- ants, monkey, etc.
Amphibious- They type of organisms can live both on land and water. Example- Frog and Crocodile.