Introduction
The nature is a boon to us. The part of earth in which living and non-living organisms exist is called the biosphere. It contains a huge variety of species living in it that interdepends on each other. The interrelationship of the species and their relationship with the environment to support life is called biological diversity.
This community of organisms interacting with each other and their physical environment is called ecosystem.
Biosphere
Ecosystem
Classification and Evolution
Organizing the living organisms into groups according to a certain set of characteristics is called classification.
The features belonging to a particular organism is called characteristics.
We need classification due to following reasons:
- It is not possible to study about each existing living organism in details.
- Classifying organisms into groups makes it easier to know about the different life forms.
- It helps us to understand the evolution of all life forms to a large extent.
- It also forms the basis for the giving scientific names to the living organisms in order to universalize their names so that people around the world can recognize the organism irrespective of their local word for the organism.
Organisms can be classified on the basis of their characteristics:
- Size: The size of the organisms.
- Cellularity: Whether the organism is multicellular or unicellular.
- Habitat: This classification is done on the basis of whether the organism lives on land, air or water.
- Body organization: The way in which the cells are organized in the body of organisms.
Aristotle classified the organism on the basis of their habitat.
- The animals living on land were called terrestrial animals.
- The animals living in water were called aquatic animals.
- The animals living on air were called aerial animals.
But this strategy couldn’t work because the plants weren’t considered here.
Some animals except one characteristic did not share any other characteristics in common. For example, fish and octopus both are aquatic animals but except living in water they don’t share any other common characteristics.
The process of development of complex organisms from simpler one with time is called evolution.
Fig. Evolution in Human beings
The Hierarchy of Classification-Groups
Ernst Haeckel (1894), Robert Whittaker (1959) and Carl Woese (1977) classified the organisms into wider classes called kingdoms.
Robert Whittaker used the following points to categorize the organisms:
- Cell structure
- Body organization
- Mode and source of nutrition
All living organisms were broadly categorized into following 5 categories called kingdoms:
- Monera
- Protista
- Fungi,
- Plantae
- Animalia
The structure of a kingdom is as follows:
Monera
Monera do not have a defined nucleus or organelles.
They do not show multi-cellular body designs.
Some organisms belonging to this group have cell walls.
The organisms belonging to this group are either autotrophs (produce their own food) or heterotrophs (Consume the food from the environment).
Examples of organisms belonging to this group are bacteria, blue-green algae or cyanobacteria, and mycoplasma.
Protista
- The unicellular eukaryotic organisms belong to this group.
- The organisms belonging to this group makes use of appendages, such as hair-like cilia or whip-like flagella for their movement.
- The organisms belonging to this group are either autotrophs (produce their own food) or heterotrophs (Consume the food from the environment).
- Examples of organisms belonging to this group are unicellular algae, diatoms and protozoans.
Fig. Paramecium
Fig :Amoeba
Fungi
The organisms belonging to this group are heterotrophic (Consume the food from the environment) eukaryotic organisms.
The organisms belonging to this group consume decaying organic material as food. Therefore they are called saprophytes.
These organisms can become multicellular organisms at specific stages of their lives.
The cell-walls of these organisms are made of a tough complex sugar called chitin.
Examples of organisms belonging to this group are yeast and mushrooms.
Some fungal species live are found to live in long-lasting mutually dependent relationships with blue-green algae (or cyanobacteria) and hence are said to be in a symbiotic relation.
Plantae
Plantae are multicellular eukaryotes having cell walls.
The organisms belonging to this group are autotrophs and makes use of chlorophyll for photosynthesis in order to produce food for themselves.
The following chart shows the classification of organisms in this group.
Thallophyta
The organisms belonging to this group do not have well-differentiated body design.
These organisms have naked embryos called spores.
Examples of organisms belonging to this group are algae, Spirogyra, Ulothrix, Cladophora and Chara
Bryophyta
The organisms belonging to this group are called the amphibians of the plant kingdom.
The body of the plant gets differentiated that leads to the formation of stem and leaf-like
The organisms belonging to this group has naked embryos that are called spores.
These organisms have no specialized tissue for conduction of water and other substances from one part of the body of plant to other.
Examples of organisms belonging to this group are moss (Funaria) and Marchantia.
Pteridophyta
The bodies of the plants belonging to this group are differentiated into roots, stem and leaves.
These organisms have naked embryos called spores.
They have specialized tissue that conducts water and other essential substances from one part of the body of plant to other.
Examples of organisms belonging to this group are Marsilea, ferns and horse-tails.
This group of plants is again divided into two broad categories gymnosperms and angiosperms. The classification is based upon the following facts:
- Naked seeds
- Seeds enclosed in fruits.
Gymnosperms
The term gymnosperm is derived from two different words. They are
- gymno– means naked and
- sperma– means seed.
The plants belonging to this group have naked seeds.
The plants of this group are generally perennial, evergreen and woody.
Examples of plants belonging to this group are pines and cycas.
Angiosperms
The term angiosperm is derived from two different words. They are
- Angio- means covered and
- Sperma – means seed.
The seeds develop inside the organs of the plants that get modified into fruit. They are therefore called flowering plants.
The plant embryos present in the seeds have certain structures. They are called cotyledons or seed leaves.
These structures emerge and become green during the germination of the seed.
Plants whose seeds have a single cotyledon are called monocotyledonous or monocots.
Plants whose seeds have two cotyledons are called dicots.
Fig: Ipomoea
Animalia
The organisms like multicellular eukaryotes belong to this group.
They do not have cell walls
The organisms belonging to this group are heterotrophs (Consume the food from the environment).
Most animals of this group are movable.
Porifera
The organisms belonging to this group have holes.
The animals of this group are non- motile and are attached to some rigid support.
The organisms belonging to this group have pores throughout their body.
They have a canal system circulates the water throughout the body of these organisms to transport the food and oxygen.
These organisms are covered with a hard external layer or skeleton.
Examples of animals belonging to this group are Euplectelea, Sycon, Spongilla.
Coelenterata (cnidaria)
The animals living in water belong to this group.
The organisms belonging to this group possesses more body design differentiation.
They also have cavity in their body.
The body of these organisms has 2 layers of cells.
- One type of layer makes up cells on the outside of the body.
- The second type of layer composes the inner lining of the body.
The organisms of this group live either in colonies (corals) or have a solitary like–span (Hydra).
Examples of animals belonging to this group are Jellyfish and sea anemones
Platyhelminthes
The organisms belonging to this group are complexly designed.
The body of these organisms has bilaterally symmetrical shape. This means that the design of the left and the right halves of the body are alike.
These organisms have three layers of cells that makes up differentiated tissues due to which such animals are called triploblastic.
These organisms have no true internal body cavity or coelom.
The body of these organisms is flattened dorsiventrally which means from top to bottom due to which these animals are also called flatworms.
These organisms are either freely existing or parasitic.
Examples of animals belonging to this group are planarians, or parasitic animals like liverflukes.
Fig. Planaria (left) and Liverflukes (right)
Nematoda
The bodies of the organisms belonging to this group are bilaterally symmetrical and triploblastic.
The body of these organisms is cylindrical.
These organisms have tissues but no real organs.
They have body cavity or a pseudocoelom in their body.
Examples of animals belonging to this group are Ascaris, Wuchereria.
Annelida
The organisms belonging to this group are bilaterally symmetrical and triploblastic.
These organisms have a true body cavity so that the true organs are enveloped within the body structure.
The differentiation occurs in a segmental fashion, with the segments lined up one after
the other from head to tail.
An organism of this group lives in variety of habitats like fresh water, marine water and land.
Examples of organisms belonging to this group are Earthworms and leeches are familiar examples
Arthropoda
This is the largest group of animals
The bodies of the organisms belonging to this group are bilaterally symmetrical and segmented.
These organisms have an open circulatory system. Therefore the blood does not flow in a well-defined blood vessel.
The coelomic cavity of these organisms is blood-filled.
These organisms have jointed legs.
Examples of organisms belonging to this group are prawns, butterflies,
houseflies, spiders, scorpions and crabs.
Mollusca
The organisms belonging to this group are bilaterally symmetrical.
The coelomic cavity is reduced in these organisms.
There is little segmentation.
They have an open circulatory system.
They have kidney-like organs for excretion.
There is a foot that helps for movement.
Examples of animals belonging to this group are snails and mussels, pila, unio.
Echinodermata
The organism that belongs to this group are spiny skinned organisms.
They are free-existing marine animals.
They are triploblastic.
They have a coelomic cavity.
These organisms use an irregular water-driven cylindrical system for movement.
They have hard calcium carbonate structures which is their skeleton.
Examples of organisms belonging to this group are starfish and sea urchins.
Protochordata
Protochordates are generally marine animals.
The organisms belonging to this group are bilaterally symmetrical.
They are triploblastic and have a coelom.
They have a long rod-like support structure called notochord at certain stages during their lives. The notochord is a runs along the back of the animal and separates the nervous tissue from the gut that gives a place for the muscles to attach for an easy and comfortable movement.
Examples of organisms belonging to this group are Balanoglossus, Herdmania and Amphioxus
Vertebrata
The animals belonging to this group possesses a true vertebral column.
These organisms have internal skeleton which allows a completely different distribution of muscle attachment points required for movement.
Animals belonging to this group are bilaterally symmetrical.
They are triploblastic, coelomic and segmented.
They have a notochord, dorsal nerve cord and paired gill pouches.
They also have a complex differentiation of body tissues and organs.
This group of animals can be further divided into following categories:
Pisces
The fishes belong to this group.
This group contains the aquatic animals.
This group of animals has skin covered with scales.
They absorb the oxygen dissolved in water by using gills to meet their requirements for their survival.
They have streamlined body and a muscular tail which helps them to move.
They are cold-blooded.
They have two chambered heart.
They lay eggs to give birth to their young ones.
Some aquatic species have a skeletons made entirely of cartilage. For example, sharks.
Whereas some species have a skeleton made of both bone and cartilage. For example, fishes like tuna or rohu.
Amphibia
The animals belonging to this group do not have scales.
They have a three-chambered heart.
These organisms respire either through their gills or lungs.
They lay eggs to give birth to their young ones.
These animals are found both in water and on land.
Examples of animals belonging to this group are Frogs, toads and salamanders
Reptilia
These animals belonging to this group are cold-blooded.
These animals have scales in their body.
They breathe through their lungs.
Most of the animals of this group have a three-chambered heart but crocodiles have four chambered heart.
They lay eggs with tough coverings to give birth to their young ones.
They do not need to lay their eggs in water, unlike amphibians.
Examples of animals belonging to this group are Snakes, turtles, lizards and crocodiles.
Aves
The animals belonging to this group are warm-blooded.
They have a four-chambered heart.
They breathe through lungs.
They lay eggs to give birth to their young ones.
These animals have an outside layer of feathers.
They also characterized by two forelimbs, toothless beaked jaws, and are adapted to fly.
Birds belong to this group.
Mammalia
The animals belonging to this group are warm-blooded.
They have a four-chambered heart.
They are characterized by mammary gland that produces milk to nourish their young, hairy skin, sweat and oil glands.
All the animals and human beings giving birth to their young ones are called mammals.
Nomenclature
The process of classification led to the creation of scientific names of the animals.
Certain rules have to be followed to write the scientific names of animals:
- The name of the genus begins with a capital letter.
- The name of the species begins with a small letter.
- When printed, the scientific name is given in italics.
- When written by hand, the genus name and the species name have to be underlined separately.
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