Diversity In Living Organisms: An Overview of Classification

The diversity in living organisms may be seen all across the world. The earth's warm and humid regions are rich in biodiversity and are known as the "region of mega biodiversity". When we compare human beings to different species, such as a horse or a fish, we can see that we are very different in practically every way, but when a horse is compared to a zebra, we can only see a few distinctions. 

• There are various living organisms on earth with different shapes, sizes, habitats, nutrition and reproduction.
• Cells are one of the most significant aspects of living things since they are the building blocks of life. 
• They are biological structural units that perform certain activities.

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Introduction to Diversity in Living Organisms

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A variety of living organisms exist on Earth in various shapes and sizes. More than half of the world's biodiversity is concentrated in only 12 countries, India being one of them. The basic functional and structural unit of life that contributes to the diversity in living organisms is called the cell.

• Animals live in a variety of settings, such as water, land, deserts, woods, grasslands, and ice. 
• With the discovery of genetics and various laws supporting evolution, diversity in living organisms appears to date back millions of years.
• For better understanding, the living organisms present in the ecosystem are classified on the basis of their habitat and physical characteristics.

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Classification System of Living Organisms

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Classification is the defined arrangement of living organisms in different groups on the basis of similarities and dissimilarities. The number of living organisms that are found on Earth is uncountable. 

• This is because a large diversity of organisms are continuously evolving into a different form ever since their origin.
• Morphology and phylogeny (evolution history) are the basis of classification.
• This is also done to retain data about organisms, study their diversity and establish relationships among them.
• It also explains means of discussion relating to specific organisms.

Classification System

In class 9, as we know that there are two types of classification systems, but in higher classes, we will learn about other types of classification systems that help in understanding diversity in living organisms. The two important classification systems are as follows: 

Two Kingdom System

Carolus Linnaeus proposed the two-kingdom classification system, which divided organisms into two types: plants and animals. The classification is done on the basis of nutrition and locomotion. 

• Linnaeus is popular with the name of the father of taxonomy.
• They can ingest food in either liquid or solid state.
• According to binomial nomenclature, species will have two names, their genus name and species name. 

Five Kingdom System

CH. Whittaker proposed the Five-Kingdom Classification, which classified creatures into five different classes: Monera, Protista, Fungi, Plantae and Animalia.

• This is considered the most accepted system of classification.
• This diversity of living organisms is divided into unicellular and multicellular organisms.
• They are divided into the categories of producers (plantae), decomposers (fungi), and consumers (animalia).

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Basis of Classification

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We've seen a lot of variation in living things over time. From ape-like creatures to Homo sapiens, we've come a long way. We look for commonalities between species so that we may classify them and analyze them as a whole.

• To do so, we must first settle on essential traits that will serve as the foundation for classification.
• The factors used for the basis of classification are as follows:

1. Presence of Nucleus

Prokaryotes are creatures with cells that lack a well-defined nucleus. Eukaryotes are organisms that have cells with a well-defined nucleus. The presence of a nucleus and membrane-bound organelles improves cell efficiency.

2. Number of Cells

Unicellular organisms are those that only have a single cell that is in charge of performing all of the processes required to keep life going. Multicellular organisms have more than one cell, and some division of labour can be done to increase efficiency.

3. Production of Food

Autotrophs are green plants that are capable of making their own food with the help of a pigment (chlorophyll) that aids photosynthesis.

• Heterotrophs are organisms that are dependent on either plants or animals.
• This category includes all mammals, fungi, and some bacteria and protozoa.

4. Level of structure

In small multicellular creatures like hydra, a certain group of cells is assigned a specific purpose. Tissues, on the other hand, gather together to create an organ, which then forms an organ system in bigger creatures.

• Humans, for example, have various systems for completing different jobs.
• Plants and animals have different body designs, so these characteristics can vary.

As a result, these prominent designs and distinguishing characteristics can be used to create subgroups rather than a broad classifications. 

Basis of Classification 

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Hierarchy of Classification

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At several levels, Carolus Linnaeus classified the species into different taxonomic categories. From the highest, groups are:

Kingdom

A kingdom is the highest level of classification, consisting of a group of related phyla or divisions (in the case of plants).

Phylum

A phylum/division is a classification level that consists of several classes with similar characteristics.

Class

A class is a level of classification that includes a group of orders that have comparable qualities.

Order

An order is a classification level that includes a group of families with comparable traits.

Family

A family is a level of classification that includes several Genus that share similar characteristics.

Genus

A genus is a level of categorization that includes a group of species that share comparable traits.

Species

A species is a level of classification that includes a group of creatures that have similar traits and may breed to produce fertile offspring.

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Nomenclature

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Carolus Linnaeus, popularly known as the "Father of Taxonomy," is a Swedish botanist and physician. He established the Binomial nomenclature and established the foundation rules for the current taxonomy. 

Binomial Nomenclature:

Linnaeus established Binomial Nomenclature as a means of naming organisms in taxonomy. It is divided into two sections. The Genus name, which is printed in capital letters, is the first part. The species name, which is not capitalised, is the second part. For example, the scientific name of mango fruit is Mangifera indica. Now according to binomial nomenclature, the first part which is "Manginifera" is the name of the genus, while "indica", the second part is the name of the species.

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Characteristics of Five Kingdom

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R.H. Whittaker's five Kingdom categorization is the most widely acknowledged system of classification. This classification resolved the majority of taxonomic difficulties about the location of bacteria and fungus. Monera, Protista, Fungi, Plantae, and Animalia are the five kingdoms.

Monera

Monera are prokaryotes with only one cell. This Kingdom is home to all prokaryotic creatures. It is made up of bacteria and archaebacteria, an ancient cousin of bacteria.

• Monera doesn't have a true nucleus.
• A cell wall may be present or absent.
• They can be either heterotrophic or autotrophic.

Protista

Protista organisms are unicellular and eukaryotic. They eat in either an autotrophic or heterotrophic manner.

• For motility, they have pseudopodia, cilia, and flagella.
• Except for the yeast, all eukaryotic unicellular organisms belong to the kingdom Protista.

Fungi

Fungi organisms are multicellular and eukaryotic. They consume food in a saprophytic manner. Chitin makes up the cell wall.

• They coexist with blue-green algae in a symbiotic interaction.
• It is the only Kingdom in the world that contains both multicellular and unicellular species.

​Plantae

Plantae organisms are multicellular and eukaryotic. The cellulose of these organisms is made up of cell walls. They prepare their food by photosynthesis.

• Thallophyta, Bryophyta, Pteridophyta, Gymnosperms, and Angiosperms are the sub-divisions of the kingdom Plantae.
• This kingdom encompasses all the plants and trees we see around us.
• They're all autotrophic and have chloroplasts in their cells.

Animalia

Animalia are eukaryotic multicellular creatures without a cell wall. They're called heterotrophs because they eat both plants and animals.

• Animalia has both simple and complex organisms.
• They come from a wide range of genetic backgrounds.
• They are organised at the organ-system level.

Porifera, Coelenterata, Echinodermata, Chordata, and other phyla are subdivided into them. They are either herbivores or carnivores, and their mode of sustenance is holozoic.

• The majority of animals are mobile, meaning they can move around on their own in search of food, shelter, or a mate.
• Animals are made up of a variety of organ systems that work together to perform essential functions for the organism's existence.
• The majority of animals are bilaterally symmetrical, except primitive animals.
• Primitive animals are asymmetrical, and cnidarians and echinoderms are radially symmetrical.

 Classification of Five Kingdom

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Classification and Evolution

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The diversity of living organisms is also done on the basis of evolution. Evolution is defined as the study of the growth and the change in the characteristics of a species as it moves from generation to generation. 

• The concept helps us understand the concept of heredity.
• Charles Darwin, along with Alfred Russel Wallace, proposed the theory of evolution.
• It also explains the concept of biodiversity.
• The theory helps us study the spread of alleles, variants, trait values, or character states.
• Lower organisms, also known as primitive organisms, have ancient types of bodies.
• Higher organisms, also known as advanced organisms, have particular body designs.

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Things to Remember

• The diversity of living organisms is one of the fundamental concepts of NCERT Class 9 Biology.
• Factors for the classification of organisms include the presence of a nucleus, the number of cells, and the level of body structure.
• Carolus Linnaeus proposed the theory of a two-kingdom classification system, which divided organisms into plants and animals.
• H. Whittaker laid the foundation of the five-kingdom classification.
• The five systems of classification divide organisms into monera, protista, fungi, plantae, and animalia.
• Carolus Linnaeus divided the species into different taxonomic categories. 
• From top to bottom, the groups are Kingdom, phylum, class, order, family, genus and species.