Explain the basis for grouping organisms into five kingdoms.

Answer : Robert .H. Whittaker in 1959 proposed a five kingdom classification of living organisms on the basis of Linnaeus’ system of classification encorporating cell structure, mode and source of nutrition and body organisation as main features. The five kingdoms proposed by Whittaker are Monera, Protista, Fungi, Plantae, and Animalia

The basis for grouping organisms into five kingdoms is as follows :

(i) On the basis of the presence or absence of membrane-bound organelles, all living organisms  are divided into two broad categories of eukaryotes and prokaryotes. This division lead to the formation of kingdom Monera, which includes all prokaryotes.

(ii) Then, eukaryotes are divided as unicellular and multicellular, on the basis of cellularity. Unicellular eukaryotes form kingdom Protista, and multicellular eukaryotes form kingdom Fungi, Plantae, and Animalia.

(iii) Animals are then separated on the basis of the absence of a cell wall.

(iv) Since fungi and plants both contain a cell wall, they are separated into different kingdoms on the basis of their modes of nutrition. Fungi have saprophytic mode of nutrition, whereas plants have autotrophic mode of nutrition. This results in the formation of the five kingdoms

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How would you choose between two characteristics to be used for developing a hierarchy in classification?

For developing a hierarchy of classification, we choose the fundamental characteristic among several other characteristics. These fundamental characteristics are independent of any other characteristics in their effects on the form and function of the organism. The characteristics in the next level would be dependent on the previous one and would decide the variety in the next level. In this way, we can build up a whole hierarchy of mutually related characteristics to be used for classification. For example, plants differ from animals in many ways such as body design, photosynthesis, the absence of locomotion, chloroplasts, cell wall, etc. But, out of these, only locomotion is considered as the basic or fundamental feature that is used to distinguish between plants and animals. This is because the absence of locomotion in plants gave rise to many structural changes such as the presence of a cell wall for protection, and the presence of chloroplast for photosynthesis (as they cannot move around in search of food like animals). Thus, all these features are a result of locomotion. Therefore, locomotion is considered to be a fundamental characteristic. By choosing the basic or fundamental characteristic, we can make broad divisions in living organisms as the next level of characteristic is dependent on these. This goes on to form a hierarchy of characteristics.

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Chapter 7. Diversity in Living Organisms | CBSE Class 9th Science

What are the advantages of classifying organisms?

There are many advantages of classifying organisms which are given as below

1. Classifying organisms helps us in recognizing the basic arrangement of a hierarchical structure among diverse species.

2. It tells us about the resemblances and relationships between various organisms thus facilitating studies or research of wide variety associated with organisms effortlessly.

3. It helps in understanding the evolution of organisms, as it gives us most of the information permitting a reconstruction of phylogeny of life.

4. It has major role in  agriculture, public health and environmental biology. Exact identification of harmful pests, disease vectors    makes possible to control diseases much easier.

5. Several ornamental plants have been introduced by horticulturists due to proper identification and nomenclature.

6. It also gives us a fair idea about the vast number of life forms and we are able to understand diversity among living organisms in a much better way.

7. It helps in placement of different organisms in a definite taxonomic group which is the basic requirement of biological sciences.

8. It forms the basis for Taxonomy in biological sciences, which is a science of identifying, grouping, and naming organisms according to their established natural relationship.

9. Classification of organism has facilitated  science of  genetic engineering to a great extent

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Chapter 7. Diversity in Living Organisms | CBSE Class 9th Science