Classification and Diversity of Life
Why classify
Classification groups organisms by similarity. Carolus Linnaeus (Father of Taxonomy) gave the binomial nomenclature system: every organism has a genus name (capitalised) and a species name (small), e.g. Homo sapiens, Mangifera indica (mango), Panthera leo (lion).
- Hierarchy: Kingdom, Phylum (Division in plants), Class, Order, Family, Genus, Species.
- Five-kingdom classification (R. H. Whittaker, 1969): Monera, Protista, Fungi, Plantae, Animalia.
- Carl Woese proposed three domains (Bacteria, Archaea, Eukarya).
| Kingdom | Features | Examples |
|---|---|---|
| Monera | Prokaryotes, unicellular | Bacteria, cyanobacteria |
| Protista | Unicellular eukaryotes | Amoeba, paramecium, euglena, diatoms |
| Fungi | Heterotrophs, cell walls of chitin, decompose and absorb | Yeast, mushroom, penicillium, mould |
| Plantae | Autotrophs, cell wall of cellulose | All plants |
| Animalia | Heterotrophs, no cell wall, multicellular | All animals |
Plant kingdom
| Group | Features | Examples |
|---|---|---|
| Thallophyta (algae) | No differentiated body; mostly aquatic | Spirogyra, Ulothrix, Chara |
| Bryophyta | Amphibians of the plant kingdom; moist places; no vascular tissue | Moss (Funaria), liverwort (Marchantia) |
| Pteridophyta | Vascular tissue, no seeds or flowers | Ferns, Marsilea, horsetails |
| Gymnosperms | Naked seeds, no fruits; cones | Pine, deodar, cycas, spruce |
| Angiosperms | Flowering, seeds enclosed in fruits | Mango, wheat, rose |
Angiosperms are of two types:
| Monocot | Dicot |
|---|---|
| One cotyledon | Two cotyledons |
| Parallel venation, fibrous roots | Reticulate venation, tap roots |
| Wheat, rice, maize, grass, onion | Pea, gram, mango, mustard |
| Flower parts in threes | In fours or fives |
Animal kingdom
| Phylum / group | Features | Examples |
|---|---|---|
| Porifera | Pore-bearing, sessile, cellular level | Sponges (Sycon) |
| Coelenterata (Cnidaria) | Stinging cells, tentacles, radial symmetry | Hydra, jellyfish, sea anemone, coral |
| Platyhelminthes | Flatworms, no body cavity | Tapeworm, liver fluke, planaria |
| Nematoda | Roundworms | Ascaris, filaria, hookworm |
| Annelida | Segmented body | Earthworm, leech, nereis |
| Arthropoda | Largest phylum; jointed legs, chitin exoskeleton | Insects, spiders, prawn, crab, scorpion, centipede |
| Mollusca | Soft body, usually a shell | Snail, octopus, squid, pearl oyster |
| Echinodermata | Spiny skin, marine | Starfish, sea urchin |
| Chordata | Notochord, dorsal nerve cord, gill slits | Vertebrates |
Vertebrates (backbone):
| Class | Features | Examples |
|---|---|---|
| Pisces (fishes) | Gills, cold-blooded, 2-chambered heart, scales | Shark, rohu, seahorse, torpedo |
| Amphibia | Live on land and water; 3-chambered heart; moist skin | Frog, toad, salamander |
| Reptilia | Dry scaly skin, lay eggs on land; most have 3-chambered heart (crocodile has 4) | Snake, lizard, turtle, crocodile |
| Aves (birds) | Warm-blooded, feathers, 4-chambered heart, hollow bones, lay eggs | Crow, ostrich, penguin, kiwi |
| Mammalia | Warm-blooded, mammary glands, hair, 4-chambered heart, mostly bear young | Humans, bat, whale, dolphin |
- Egg-laying mammals: platypus and echidna. Marsupials carry young in a pouch (kangaroo). Bats are the only flying mammals; whales and dolphins are aquatic mammals.
- Cold-blooded (poikilotherms): fishes, amphibians, reptiles. Warm-blooded (homeotherms): birds and mammals.
Microorganisms
- Bacteria, viruses, fungi, protozoa and algae are microorganisms. Viruses are non-cellular, living only inside host cells; bacteriophages attack bacteria.
- Useful uses: curd (Lactobacillus), bread, cakes, alcohol and fermentation (yeast), antibiotics (penicillin from Penicillium), vaccines, nitrogen fixation (Rhizobium in legume roots; Azotobacter; blue-green algae), decomposers, sewage treatment.
- Harmful: diseases, food spoilage, crop diseases.
- Edward Jenner (smallpox vaccine, 1796); Louis Pasteur (germ theory, rabies vaccine); Robert Koch (TB and cholera bacteria, Koch's postulates); Alexander Fleming (penicillin); Ronald Ross (malaria parasite in mosquito).
Keep practising
Notes are only half the work. Test yourself with questions and discuss doubts with other aspirants.
Prepared for exam revision from the NCERT Science textbooks for Classes 6 to 10 and standard sources. Space missions, awards and records change, so check official sources for recent facts. Found a mistake? Tell us.