Diversity in Living Organisms 9th Class Full Chapter

Our Earth is crowded with many kinds of organisms. Some are very large while Others are so small that can not be seen by the naked eye. All organisms depend on each other for food, shelter, and clothing. Some Organisms provide company, amusement, aesthetics, pleasure, and joy while others give pain, irritation, and even cause death. Therefore identification or recognition of useful and harmful organisms among the huge biodiversity is a basic need of man.


Biodiversity refers to the huge variety of living organisms on this earth. More than 1.7 million species of organisms have been identified so far. This number is increasing by about 15000 new species every year. According to an estimate, the number of species on the earth ranges between 5 to 30 million. Oceans and tropical rainforests support the rich biodiversity.

Classification and Its Needs

Due to huge Biodiversity, the study of each and every organism is not possible. We therefore categorize or classify organisms based on their similarity and dissimilarity.

For Example, imagine a group that contains 100 organisms. It is not possible to Study all 100 organisms of the group. But if we know the basic characters of the group, we can have an idea about the basic characters of all the organisms of this group.

The significance of Classification can be recognized by another example. In a Big library, where books are not classified and arranged systematically, the search of a particular book is almost an impossible task. Further, a new title in such a library can not be added in a meaningful way. But if Books are Classified, then search for a particular title becomes very easy.

Similarly, biological classification helps us to identify and recognize organisms. The science of classification is known as taxonomy. The Father of Taxonomy is Carolus Linnaeus

What is the Basis of Classification

Every Classification requires some criteria. When we classify living beings, we have to consider some characteristics. These are used as criteria to classify living beings.

Since, we follow a classification system, based on a hierarchy, we first take the criteria/ characters which are very broad. This helps us to divide the organisms at the broadest level. Then we have to pick the next set of characteristics for making subgroups within these divisions. This process of classification within each group can then continue using new characteristics each time.

The Choice of Characteristics in the Next Level depends on the previous one. We can understand this with the help of an example. Suppose we want to construct a stone wall. The Stones that are used can have different shapes and sizes. The stones at the top of the wall do not influence the choice of stones at the lower level. But opposite to it, the Shape and size of stones at the lower level would definitely influence the shape and size of the stones at the upper levels

Common Criteria used for Classification of Living Organisms

In the present time, where knowledge is coming from every corner, we focus on the interrelated characteristics of organisms. Some important such characteristics have been discussed below

Nature of the Cell: Cells may be prokaryotic and eukaryotic. A eukaryotic cell has membrane-bound organelles, including a nucleus. In prokaryotic cells such membrane-bound organelles and nucleus is absent

Cellular Composition: Organisms may be single-celled (unicellular), or may be composed of many cells (multicellular. A single-celled organism is overburdened, whereas a multicellular one has a greater efficiency of work due to the division of labour. It can carry out some specialized functions also. In multicellular organisms, all cells are not of the same type. They have certain differences according to their functions.

Autotroph and Heterotroph: Some organisms such as green plants are able to produce their food by their own efforts, using sunlight. These are called autotrophs. For this, they have well-developed machinery inside their cells. On the Other hand, heterotrophs are those which have lacked this machinery and can not produce their own food.

Body Organisation: Some organisms are very simple in their organization. They are neither made up of just a single cell or a few cells. They have no special structures in them. On the Other hand, some organisms are very complex. They have a large number of special organs.

All These Features form the criteria for the Classification of organisms at a broader level. As we move down through hierarchy, the choice if characters becomes more complex.

Five Kingdom Classification

In all earlier taxonomic attempts, living beings were classified into two kingdoms РAnimals and Plants. Carolus Linnaeus also recognized two kingdoms Plantae and Animalia, including respectively the plants and animals.

But, after the discovery of micro-organisms, the need of one more kingdom was felt. German zoologist, E.H. Haeckel proposed a third kingdom Protista for unicellular micro-organisms.

Laterron, After the discovery of more complex life forms and emerging objections, and shortcomings in the two-kingdom system, a Five-Kingdom system of classification was proposed by Robert H. Whittaker (an American taxonomist). It is the most widely accepted system of classification. Whittaker classified all living organisms and placed them in 5 large kingdoms. These kingdoms are Monera, Protista, Fungi, Plantae, and Animalia.

Five Basis of Kindom Classification

The Five kingdoms proposed by Whittaker were found based on the structure and nature of the cell. Eukaryotic or prokaryotic, cellular organization (Unicellular or multicellular), source of nutrition (autotrophic or heterotrophic), and presence and nature of cell wall

Schematic outlines of this classification are seen in the following table

Five Kindom Classification at a glance
Kingdoms Striking Characters
Monera Prokaryotic Organisms
Protista Unicellular but Eukaryotic
Fungi Multicellular (Except Years Etc.), Cell wall present. known chlorophyllous, heterotrophs
Plantae Multicellular, Chlorophylius, cellulosic cell wall, reserve food starch
Animalia Multicellular, No Chlorophyll, No cell wall, Active locomotion present


Kingdom Monera

Monera (mono=single), Includes prokaryotic organisms such as bacteria, cyanobacteria, and mycoplasma Etc.

The following features characterize it:

  • These are Strictly prokaryotic organisms
  • They are Unicellular, but they may be found in multicellular, aggregation
  • Except mycoplasma group, all organisms of this kingdom have reset cell wall. The cell wall is not composed of cellulose.
  • Almost all of the nutrition is present. Some Organisms (such as cyanobacteria are autotrophic i.e., they can synthesize their own food by using sunlight). Other Organisms are heterotrophic
  • Cell has no Nucleus.
  • Cell organelles like mitochondria, Golgi bodies, Endoplasmic Reticulum Etc. are absent
  • DNA is naked and freely present in the Cytoplasm
  • Main mode of reproduction is asexual. It is through budding, binary fission, or by Spore formation.
  • Examples of bacteria, cyanobacteria, mycoplasma Etc.


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