CHAPTER 1 THE LIVING WORLD

Topic Covered ✏

1.1 Diversity in the Living World 

1.2 Taxonomic Categories

1.1 Diversity in the Living World 

• Each different kind of plant, animal or organism that you see, represents a species. 

• The number of species that are known and described range between 1.7-1.8 million. This refers to biodiversity or the number and types of organisms present on earth.

    Nomenclature

• Naming of living organisms such that a particular organism is known by the same name all over the world.

• Nomenclature or naming is only possible when the organism is described correctly and we know to what organism the name is attached to. This is identification.

Number of scientists have established procedures to assign a scientific name to each known organism

• For plants - International Code for Botanical Nomenclature (ICBN). 
• For Animal - International Code of Zoological Nomenclature (ICZN).

    Binomial nomenclature 

• Given by Carolus Linnaeus 

• Universal rules of nomenclature are as follows:-

1. Biological names are generally in Latin and written in italics. They are Latinised or derived from Latin irrespective of their origin.
2. The first word in a biological name represents the genus while the second component denotes the specific epithet.
3. Both the words in a biological name, when handwritten, are separately underlined, or printed in italics to indicate their Latin origin. 
4. The first word denoting the genus starts with a capital letter while the specific epithet starts with a small letter. 

e.g. - Mangifera indica. 

    Classification 

• Classification is the process by which anything is grouped into convenient categories based on some easily observable characters.
• It is nearly impossible to study all the living organisms, hence need classification.
• All these - ‘Dogs’, ‘Cats’, ‘Mammals’, ‘Wheat’, ‘Rice’, ‘Plants’, ‘Animals’, etc., are convenient categories.
• The scientific term for these categories is taxa.

    Taxonomy

• Based on characteristics, all living organisms can be classified into different taxa. This process of classification is taxonomy.
• Basis of modern taxonomic studies :

1. External and internal structure
2. Structure of cell
3. Development process and 
4. Ecological information of organisms

• Hence, characterisation, identification, classification and nomenclature are the processes that are basic to taxonomy.

In early days, human beings needed to find sources for their basic needs of food, clothing and shelter. Hence, the earliest classifications were based on the ‘uses’ of various organisms.

    Systematics 

• The word systematics is derived from the Latin word ‘systema’ which means systematic arrangement of organisms.
• Systematics =Taxonomy + evolutionary relationships between organisms.  
• Linnaeus used Systema Naturae as the title of his publication.

 

1.2 TAXONOMIC CATEGORIES

• Classification is not a single step process but involves hierarchy of steps in which each step represents a rank or category.  
• Since the category is a part of overall taxonomic arrangement, it is called the taxonomic category and all categories together constitute the taxonomic hierarchy. 
• Each category, referred to as a unit of classification, in fact, represents a rank and is commonly termed as taxon (pl.: taxa).
• Taxonomical studies of all known organisms have led to the development of common categories such as kingdom, phylum or division (for plants), class, order, family, genus and species.

1.2.1 Species 

• A group of individual organisms with fundamental similarities as a species.
• One species distinguish from the other closely related species based on the distinct morphological differences.

1.2.2 Genus 

• Genus comprises a group of related species which has more characters in common in comparison to species of other genera. 
• Genera are aggregates of closely related species.

1.2.3 Family 

• Family, has a group of related genera with still less number of similarities as compared to genus and species. 
• Families are characterised on the basis of both vegetative and reproductive features of plant species. 

1.2.4 Order

• It is the assemblage of families which exhibit a few similar characters. 
• The similar characters are less in number as compared to different genera included in a family.

1.2.5 Class 

• This category includes related orders. 

1.2.6 Phylum

• Animal - Phylum
• Plant - Division

1.2.7 Kingdom 

• Highest category

• Taxonomists have also developed sub-categories in this hierarchy to facilitate more sound and scientific placement of various taxa.
• As we go higher from species to kingdom, the number of common characteristics goes on decreasing. 
• Lower the taxa, more are the characteristics that the members within the taxon share. 
• Higher the category, greater is the difficulty of determining the relationship to other taxa at the same level. Hence, the problem of classification becomes more complex. 
• Categories like species, genus and families are based on a number of similar characters.   
• Generally, order and other higher taxonomic categories are identified based on the aggregates of characters.

TABLE 1.1 Organisms with their Taxonomic Categories