Hierarchy :- Hierachy is a system of classification into which taxonomic categories are arranged in descending order.
Category :- Plants and animals are ranked in an arrangement of known categories. Such as Kingdom, Phylum (for animals) or Division (for plants), Class, Order, Family, Genus and Species.
Taxon :- Taxon is defined as a unit of classification of organisms which can be recognised to a definite category at any level of classification e.g. fishes, insects etc.
Kingdom → Largest Group
Phylum (for animals) / Division (for plants)
Classification and Evolution
Charles Darwin first described the idea of evolution in 1859 in his book, "The Origin of Species".
Darwin suggested that organisms are related to each other by descent. They had common ancestors from which they gradually evolved into their present form.
The ancestral forms were simple and are called 'primitive' and primitive organisms have evolved into advanced orgamisms which are more complex.
This process of gradual change from simple life forms to complex life forms is called 'Evolution'.
Nomenclature : (The naming of organisms)
Binomial Nomenclature : Binomial nomenclature was proposed by Carolus Linnaeus. According to his the name of any organism consists of two words.
The first word denoting the name of 'genus' and second word denoting 'species'.
First letter of generic name must be written in capital lettter whereas species name is started with small letter.
Scientific name is generally derived from Greek or Latin words.
The binomial names are printed in italics and underlined separately when written.
Potato - Solanumtuberosum
Tiger - Panthera tigris
Do you know ?
Carolus Linnaeus proposed scientific name of plants in his book "Species Plantarum" (1753).
Kingdom Systems :
1. Two Kingdom Classification :
First suggested by Carolus Linnaeus in 1758.
Living organisms have been divided into two kingdoms.
Three Kingdom Classification: Proposed by Ernst Haeckel in 1886. He suggested a third Kingdom - Protista for unicellular organisms.
(i) Kingdom Plantae - All the plants constitute kingdom planate. The kingdom includes bacteria, lichens, fungi, algae, bryophytes, ferns, gymnosperms and angiosperms.
(ii) Kingdom Animalia - All the animals constitute kingdom animalia. The kingdom animalia includes protozoans, sponges, Hydra, Jelly Fish, worms, insects, spiders, octopus, star fish, fishes, frogs, salamanders, lizards, snakes, birds and mammals.
Drawbacks in two kingdom classification :-
Certain organisms did not strictly fit either under plant or animal kingdom like :Euglena and Viruses.
Five kingdom classification :
This concept was propounded by Robert H. Whittaker in 1969.
On the basis of cell structure, complexity in organisms and type of nutrition, he divided living organisms into 5 kingdoms.(i) Monera, (ii) Protista, (iii) Fungi, (iv) Plantae, (v) Animalia.
Carl Woese (1977, 1994) has divided the kingdom monera into archaebacteria (= archea) and eubacteria (or bacteria). All other kingdom are included in his superkingdom of eukarya.
Characteristic of five kingdoms
1. Kingdom - Monera :
Prokaryotic Nature : The genetic material is not organised into a nucleus. It lies directly inside the cytoplasm and is called nucleoid.
Membrane Bound Cell Organelles. Membrane bound
cell organelles like mitochondria, Golgi apparatus, plastids, lysosomes, are absent.
Unicellular Nature : Monerans are basically unicellular.
In filaments and colonies the cells are similar and independent.
Mode of nutrition is either autotrophic (Blue-green algae) or heterotrophic(Mycoplasma and most bacteria).
Some organisms have cell wall (in bacteria) while other lacking (in Mycoplasma)
Blue Green Algae (Cyanobacteria) Anabaena, Nostoc.
Bacteria (Vibrio cholerae, Clostridium botulinum, Escherichia coli)
Mycoplasma (Produces diseases in humans, animals and plants).
2. Kingdom - Protista :
Organisms are unicellular, eukaryotic organization.
There is a true nucleus and membrane bound other cell organelles.
Cell wall : Some protists are covered with cell wall (most photosynthetic protists) while others do not possess it (e.g., protozoan protists).
Mode of nutrition is either autotrophic (algae and diatomes) or heterotrophic(protozoans).
Some organisms have cilia (e.g. Paramecium) ; flagellum (e.g. Euglena) andpseudopodia (e.g. Amoeba) for locomation.
Sexual reporduction is present but an embryo stage is absent.
Examples : Unicellular algae Chlamydomonas, Chlorella
Diatoms Pinnularia, Navicula
Dinoflagellates Gonyaulax, Noctiluca
Protozoa Amoeba, Plasmodium, Euglena, Paramecium
Photosynthetic nutrition occurs in unicellular algae (e.g., dinoflagellates, diatoms) and Euglena like organisms. They are the major producers of aquatic systems.
Euglena and its relatives perform photosynthesis in light. In dark and in the presence of organic matter, they switch over to saprophytic nutrition. Such a dual nutrition is called mixotrophic nutrition.
3. Kingdom - Fungi
These are non-green (lacking chlorophyll)eukaryotic, organisms.
They may be unicelluar (e.g. Yeast) or Multicellular (most fungi).
The body of a multicellular and filamentous fungus is called mycelium and is composed of several thread like structures termed as hyphae.
Heterotrophic mode of nutrition is found.
Fungi are heterotrophic with absorptive nutrition. Most of them are decomposers (hence kingdom of
Food is gained by either saprophytically (from dead organic matter) or parasitically (from other living tissues).
Cell Wall contain - Chitin.
Reserve food material - Glycogen.
Examples : Yeast, Rhizopus (Bread mould), Penicillium, Mucor, Mushroom (Agaricus) ; Smut (Ustilago).
4. Kingdom - Plantae
Plants are multicellular, eukaryotes with cellulosic cell wall.
They are autotrophs i.e. prepare own food by photosynthesis.
5. Kingdom - Animalia
Animals are multicellular, eukaryotes without Cell Walls.
They are heterotrophic.