Classification of organisms

➢ Classification: Classification is the process of grouping the living beings into various groups and sub-groups on the basis of similar and dissimilar characteristics.

➢ Importance of classification: Classification makes the study of plants and animals easier and more systematic. A large group of organisms having similar characteristics can be studied at the same time. It helps to understand the relation among various groups of plants and animals. It gives us an idea about the evolution of plants and animals.

➢ Genus: A genus is a group of closely related species. For example, all true cats like a lion, tiger and domestic cat are kept in the genus 'Panthera' or 'Felis'.

➢ Species: A species is a group of closely related organisms having almost all similar characteristics which can interbreed freely and produce healthy offspring. For example, all types of human beings throughout the world are kept in the same species 'sapiens'.

➢ Five kingdom system of classification: This system of classification was introduced by American taxonomist Robert H. Whittaker in 1669 AD. According to this system of classification, living beings are classified as follows:

1. Kingdom Monera: This kingdom includes unicellular prokaryotic microscopic organisms. Their cell contains DNA as a nucleus. They may be autotrophs or parasites. Examples: Bacteria, Azotobacter, Blue-green algae, etc.

2. Kingdom Protista: This kingdom includes eukaryotic unicellular organisms. Their cells contain a well-developed nucleus. Examples: Amoeba, Paramecium, Euglena, etc.

3. Kingdom Fungi: This kingdom includes unicellular and multi-cellular non-green plants. Their body is thalloid. They derive their food from dead and decaying organic matter. Examples: Mushroom, Yeast, Mucor, etc.

4. Kingdom Plantae: This kingdom includes different types of non-flowering and flowering plants. This kingdom is divided into three divisions. They are: (i) Algae (ii) Bryophyta (iii) Tracheophyta

5. Kingdom Animalia: This kingdom includes different types of invertebrates and vertebrates. This kingdom is divided into 9 phyla. They are as follows:

(i) Porifera (ii) Coelenterata (iii) Platyhelminthes (iv) Nemathelminthe (v) Annelida (vi) Arthropoda (vii) Mollusca (viii) Echinodermata and (ix) Chordata.

➢ Division Algae

(i) The plants of this division may be unicellular or multicellular.

(ii) They can prepare their own food due to the presence of chlorophyll. Examples: Spirogyra, Chlamydomonas, Fucus, Volvox, Ulothrix, etc.

➢ Division Bryophyta

(i) All the plants of this division are multicellular and green.

(ii) They are found in moist places and absorb water and minerals by means rhizoids. They need water for reproduction.

Examples: Moss, Riccia, Marchantia, etc.

➢ Division Tracheophyta

This division includes developed non-flowering and flowering plants having vascular tissues. This division is divided into the following three sub-division.

1. Pteridophyta

2. Gymnosperms

3. Angiosperms

➢ Sub-division Pteridophyte

(i) Plants belonging to this division bear distinct roots, stem and feather-like leaves They have well developed complex tissues like the xylem and phloem.

(ii) Their life cycle completes into two stages, viz. sporophyte and gametophyte Examples: Fern, Horsetail, Lycopodium, Fiddle head fern, selaginella, Teris, etc.

➢ Sub-division Gymnosperms

(i)Cones are present instead of true flowers. Male cones and female cones are separated.

(ii) Seeds are not enclosed in fruit.

(iii) Needle-shaped leaves are present.

Examples: Pine, cedar (deodar), Juniper, Himalayan yew, cycas, etc.

➢ Sub-division Angiosperms

(i) They are flowering plants whose seeds are enclosed in a fruit.

(ii)The reproductive organs are aggregated in a flower.

(iii) Most of the plants are bisexual but some of them are unisexual. 

Examples: Pea, maize, rice, mango, bean, sugarcane, rose, turmeric, barley banana, etc.

➢ Porifera

(i) The animals belonging to this phylum bear numerous pores in their bodies. 

(ii) Their body remains attached to the substratum in fresh water or marine water Examples: Sponge, Sycon, Spongilla, Leucosolenia, Hylonema, Cliona, etc.

➢ Coelenterata

(i) The animals belonging to this phylum have a hollow body cavity, i.e. coelenteron.

(ii) They move and catch their food with the help of tentacles. Examples: Hydra Obelia, Coral, Jellyfish, etc.

➢ Platyhelminthes

(i) The animals belonging to this phylum have leaf-like or ribbon-like flat body.

(ii) They have suckers. Examples: Tapeworm, Liver fluke, Planaria, Bloodfluke, Diplozoon, Atoplana, etc.

➢ Nemathelminthes

(i)The animals belonging to this phylum have elongated and round bodies having pointed ends.

(ii)Sexes are separate. Examples: Ascaris, Hookworm, Pinworm, etc.

➢ Annelida

(i) The animals belonging to this phylum have elongated and cylindrical bodies having numerous segmented rings.

(ii) They have moist skin and well-developed alimentary canal.

Examples: Earthworm, Leech, Nereis, etc.

➢ Arthropoda

(i) The animals belonging to this phylum have jointed appendages.

(ii) Their body can be divided into three parts (i.e., head, thorax and abdomen) or two parts (i.e. cephalothorax and abdomen).

Examples: Butterfly, Crab, Scorpion, Spider, Centipede, etc.

➢ Mollusca

(i) The soft body of mollusks remains covered with a hard protective shell made up of calcium carbonate.

(ii) They move with the help of the muscular feet.

Examples: Slug, Octopus, Snail, Cuttle fish, Unio, etc.

➢ Echinodermata

(i) The body of echinoderms remains covered with spiny skin. (ii) They move with the help of tube feet.

Examples: Starfish, Sea urchin, Sea cucumber, etc.

➢ Characteristics of Phylum Chordata

(i)Notochord is present at some stage of the life history.

(ii)Dorsal hollow nerve cord is present, lying just above the notochord.

(iii) They have a closed blood system.

Examples: Amphioxus, fish, bat, human, etc.

➢ Characteristics of Sub-phylum Vertebrata

(i) In vertebrates, the notochord is replaced by the vertebral column.

(ii) The dorsal tubular nerve cord is present which is divided into the brain and spinal cord.

(iii) Body is well developed having a head, trunk and paired fins or limbs.

Examples: Fish, frog, snake, bird, cow, etc.

➢ Cold-blooded animals: The animals whose body temperature changes according to the temperature of the surrounding are called cold-blooded or poikilothermic animals. Examples: Fish, frog, snake, lizard, etc.

➢ Warm-blooded animals: The animals whose body temperature remains constant and does not change according to the temperature of the surrounding are called warm- blooded animals.

➢ Pisces: The animals having streamlined body that breathe through gills and swim by fins are called Pisces. Examples: fish, shark, sea horse, rohu, etc.

➢ Amphibians: Amphibians are cold-blood vertebrates adapted to live on both land and in water. Examples: Frog, salamander, toad, etc.

➢ Reptiles: The crawling animals which breathe through lungs and have hard, dry and horny scales in the body are called reptiles. Examples: Snake, lizard, crocodile, tortoise, wall lizard, etc.

➢ Aves: The flying vertebrates having feathers and wings are called aves. Examples: Crow, pigeon, peacock, eagle, etc.

➢ Mammals: The animals which directly give birth to their babies and suckle them are called mammals. Their body is covered with hair. Examples: Human, cow, elephant. dolphin, bat, whale, squirrel, etc.