TNPSC BIOLOGY (ENGLISH)
WHAT ARE THE CLASSIFICATION OF LIVING ORGANISMS?
All living organisms are classified into groups based on very basic, shared characteristics. Organisms within each group are then further divided into smaller groups. These smaller groups are based on more detailed similarities within each larger group.
Need for Classification
It is not possible for anyone to study all the organisms. But if they are grouped in some convention way, the study would become easier. Classification allows us to understand diversity better
Necessity for classification
Classification helps us to identify the living organisms easily. It helps us to learn about different kinds of plants and animals, their features, similarities and differences. It enables us to understand how complex organisms evolve from simple ones.
Aristotle was the earliest to attempt a more scientific basis for classification. He used simple morphological characters to classify plants into trees, shrubs and herbs. He also divided animals into two groups, those which had red blood and those that did not.
In Linnaeus time (1758), a two kingdom system of classification with plantae and Animalia kingdoms was developed that included all plants and animals, respectively.
R_H. Whittaker (1920 - 1980) was an American plant ecologist. In 1969 he classified the organisms into five kingdoms. This classification has been accepted by all scientists.
About 9,000 species are identified under Kingdom Monera. The number of species in Kingdom Protista is about 59,950. The number of species under Fungi is about 100,000. The number of species identified under the Kingdom Plantae is about 289,640. The total number of species identified under Animalia is about 1,170,000.
The Five Kindoms are Monera, Protista, Fungi, Plantae and Animalia.
Kingdom of Monera
✦ The kingdom Monera comprises all the bacteria and the cyanobactreia.
✦ They are Primitive unicellular or filamentous prokaryotes, single celled organisms.
✦ Their mode of nutrition is autotrophic or heterotrophic.
✦ They cause diseases like diphtheria, pneumonia, tuberculosis, leprosy etc.
✦ They are also used in manufacture of antibiotics to cure many diseases.
✦ Reproduce by vegetative, asexual and sexual methods.
Kingdom of Protista
✦ The kingdom Protista includes unicellular eukaryotes.
✦ Animals and plants of protista live in sea as well as in fresh water. Some are parasites. Through they are single celled, they have the capacity of performing all the body activities
✦ They have nucleus enclosed by a nuclear membrane (eukaryotic).
✦ Locomotory structure may be cilia, flagella, pseudopodia or absent.
✦ Some of them posses chloroplast and make their food by photosynthesis. e.g. Euglena
✦ Reproduce by sexual and asexual methods.
There are two main groups of protista.
✦ Plant like protista called photosynthetic and are commonly known as Micro-algae. They can be seen only under microscope. They occur as single cells or filaments or colonies. eg. Chlamydomonas, Volvox etc.
✦ Algae are autotrophs. `
✦ Animal like protista are often called protozoans. Protozoans include Amoeba and Paramecium like animals.
✦ The Paramecium, which consists of cilia, belongs to class ciliate. Amoeba which consists of pseudopodia belongs to class Sarcodina.
✦ All unicellular plants are collectively called phytoplanktons and unicellular animals as zooplanktons_
✦ Euglena, a protozoan possesses chloroplast and makes their food by photosynthesis. It has two modes of nutrition. In the presence of sunlightit is heterotrophic. This mode of nutrition is known as myxotrophic and hence they form a border line between plants and animals.
Kingdom of Fungi
✦ This kingdom Fungi includes Yeast, moulds, mushrooms (Kaalaan), toadstools, puffballs and Penicillium
✦ Fungi are eukaryotic and mostly multicellular eukaryotes.
✦ Their mode of nutrition is heterotrophic (obtain their nutrients from other organisms). Since they lack the green pigment chlorophyll.
✦ They have cell walls, made of a tough complex sugar called chitin. Fungi act either as decomposers (decay-causing organisms) or as parasites (live in other organisms) in nature.
✦ Mould fungi grow stale bread, cheese, fruit or other food.
✦ Penicillium is a fungus. Penicillin is also known as "the queen of drugs".
The kingdom fungi is classified into two divisions,
Myxomycophyta and Eumycophyta.
Kingdom of Plantae
✦ It includes all multi - cellular plants of land and water, autotrophic eukaryotes. The kingdom plantae contains about 300000 different species plants of plants. Among the five kingdoms, kingdom plantae is very important, as they are the source of food for all other living creatures present on planet earth, which depends on plants to survive.
Based on their classification, plants are divided into the four main groups. These classification was based on
⋆The presence of vascular tissue
⋆The absence of vascular tissue
⋆The presence of seeds
⋆The absence of seeds
⋆Kingdom Plantae includes.
eg. Larninaria, spirogyra, chara
eg. Riccia, moss
(iii)Pteridophytes: eg. Ferns
eg. Cycas, pinus
eg. Grass, coconut mango, neem (veppamaram)
✦ Plantae are multicellular eukaryotes.
✦The plant cells have an outside cell wall that contain cellulose.
✦They show various modes of nutrition them are autotrophs sincethey have chlorophyll.
Some plants are heterotrophs
eg. Cuscuta is a parasite
✦ Nepenthes and Drosera are insectivorous plants.
More to Know
✦Kingdom Plan includes
✦Bryophyia - 24,000 species
✦Pteridophyta - 10,000 species
✦Gymnosperms - 640 species
✦Angiosperms - 255,000 species
Kingdom of Animalia
✦ This kingdom includes all multicellular eukaryotic animals.
✦All animals show heterotrophic mode of nutrition. They directly or indirectly depend on plants for their basic requirements particularly they form the consumers of an ecosystem.
✦The cells are without cell wall. They have contractibility of the muscle cells. They have well-developed control and coordination mechanisms. They can transmit impulses due to the presence of nerve cells.
✦Some groups of animals are parasites e.g. tapeworms and roundworms.
✦Most members of can move from place to place. However ,some animals such as adult sponges and corals are permanently attached to a surface
✦Kingdom Animalia includes the following phyla.
They are primitive organisms; most of them are salt water spomges. They do not have organs or nerve cells or muscle cells. Approximately, 8000 species exists today. Eg., Sycon, Euspongia, Spongilla.
Phylum Coelenterata: This group is composed of Jelly fish and other lower aquatic animals. Approximately, 15,000 species exist today. Eg., Aurelia, Adamsia.
Phylum Plathyhelminthes: This group consists of flat worms.they inhabitat both marine and fresh water habitats and they are mostly endoparasites found in animals. Eg., Taenia, Fascicola.
Phylum Aschelmeinthes: It is a group of round worms, most of them are parasites. This phylum consists of about 80,000 parasitic worms.
Phylum Annelida: They are present in aquatic, terrestrial and are free living or parasitic in nature. This phylum comprises of segmented worms. Eg., Earthworm, Leech, etc.,
Hirudin is a naturally occurring protein in the salivary glands of Leeches that has a blood anticoagulant property. Hence blood fails to clot ensuring continuous flow of blood. This property is widely used in the field of medicine
Phylum Arthropoda: This is the largest phylum which consists of insects. There are over 1 million species of insectsexisting today. Eg., Locustus, Butterfly, Scorpion, Prawn.
Phylum Mollusca: It is the second largest phylum. They are terrestrial and aquatic. Eg., Pila, Octopus.
Phylum Echinodermata: This consists of sea stars and sea urchins. There are about 6000 species. Eg., Asteria, Ophuria.
Phylum Chordata: Animals of this phylum have a characteristic feature of presence of notochord, a dorsal hollow nerve cord and paired pharyngeal gill slits. All animals in the chordate phylum have backbones. They are also called “Vertebrates”. The chordate phylum is split into classes. Several classes are listed below.
Mammal Class: These animals usually have hair/fur. They give birth to live young ones and feed their young with milk. Mammals are warm blooded. Includes: Rodents, Hoofed animals, Marsupials, Bats, Rabbits, Weasels, Raccoons, Bears, Dogs and Cats.
Bird Class: This class is also called “Aves”. Birds are warm blooded. They have hollow bones and feathers. Most can fly atleast short distances. Birds are born from hard shelled eggs. Includes: Raptors, Gulls, Songbirds and Fowl.
Amphibian Class: Those animals have smooth skin, and most spend atleast part of their life in water. Amphibians are cold blooded. They usually have three life stages: egg, larva and adult. Includes: Frogs, Toads, Salamanders and Newts.
Reptile Class: These animals have dry, scaly skin. They are cold blooded. Most reptiles lay soft shelled legs, but some bear live young. Includes: Lizards, Snakes, Turtles and Crocodiles.
Bony Fish Class: This class is also called “Osteichthyes”. It includes almost all fish. Skeletons are made of mostly bone. Includes: Sunfish, Catfish, Minnows, Perch, Goldfish and most others.
✦The slowest reptile - Giant tortoises of Galapagos Islands
✦The fastest reptile Spiny tailed Iguana of Costa Rica
✦World's fastest snake - The black mamba of Africa
✦The World's longest snake A reticulated phthon
✦Largest poisonous snake - King Cobra
✦Smallest reptile - Gecko
✦Largest reptile –Komodo dragon
History of classification ,
✦Aristotle categorized organisms into plants and animals
✦Hippocrates, the Father of Medicine, listed organisms with medicinal value.
✦Joh Ray introduced the term species
✦Carolus Linnaeus (1707-1778) organized a simple naming system for plants. So, he is known as Father of Taxonomy. He invented the modern system of Binomial nomenclature. Prior to the adoption of the modern binomial system of naming species, a scientific name consisted of a generic name combined with a specific name that was from one to several words long.
Levels of classification
Linnaeus classified organisms into kingdom, phylum, class, order, family, genus and species.
Basic Principles of Binomial Nomenclature
✦Scientific names must be either Latin or Latinized
✦The name of the genus must 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, name should be underlined