1. Five Kingdom Classification:
(i) Aristotle was a pioneer in the classification system in a more scientific manner.
(ii) He divided animals into two groups:
(a) Having red blood cells and
(b) Do not have red blood cells.
(iii) R.H. Whittaker's classification is phylogenetic and is called five kingdom system of classification.
(a) He divided organisms into five kingdoms, Monera, Protista, Fungi, Animalia and Plantae.
(iv) The following are the bases of his classification:
(a) Cell structure (Prokaryotic or Eukaryotic)
(b) Life form (Unicellular or Multicellular)
(c) Mode of Nutrition (Autotrophic or Heterotrophic)
(d) Ecological role (Consumer or Decomposer)
(e) Phylogenetic or evolutionary relationship
2. In brief, the characteristic features of all five kingdoms are furnished:
Monera | Protista | Fungi | Plantae | Animalia | |
Cell type | Prokaryotic | Eukaryotic | Eukaryotic | Eukaryotic | Eukaryotic |
Cell wall | Non-cellulosic (Polysaccharide + amino acid) | Present in some | Present (without cellulose) | Present (cellulose) | Absent |
Nuclear membrane | Absent | Present | Present | Present | Present |
Body Organization | Cellular | Cellular | Multicellular/ loose tissue | Tissue/organ | Tissue/organ/ organ system |
Mode of nutrition | Autotrophic (chemosynthetic and photosynthetic) and Heterotrophic (saprophytic/parasite) | Autotrophic (Photosynthetic) and Heterotrophic | Heterotrophic (Saprophytic Parasitic) | Autotrophic (Photosynthetic) | Heterotrophic (Holozoic etc.) |
(i) His system of classification could not classify the viruses properly.
3. History Of Classification And Taxonomy:
(i) Linnaeus gave the first proper classification of organisms into two Kingdoms, Plantae and Animalia.
(ii) This is called the Two Kingdom system of classification.
(iii) The major criteria used by him was locomotion, presence or absence of cell wall, mode of nutrition, response to external stimuli, and contractile vacuoles.
(iv) The salient features of the two kingdoms are presented in the following table:
1. Cell wall | Present | Absent |
2. Locomotion | Absent | Absent |
3. Mode of nutrition | Do not eat/ autotrophic. | Feed on others/ heterotrophic. |
4. Response to external stimulus | Slow | Fast |
5. Contractile system | Absent | Present |
6. Organisms | Bacteria, algae, fungi, bryophytes, pteridophytes, gymnosperms, angiosperms | Protozoa, vertebrates, invertebrates |
(a) One of the major drawbacks of this system was that it could not justify the inclusion of fungi in Plantae and that it could not classify some organisms with intermediate features.
(v) Haeckel proposed the Three Kingdom system of classification, which proposed Protista, Plantae and Animalia kingdoms.
(a) The Protista members were separated based on many exclusive features present in them.
(vi) Copeland proposed the Four Kingdom system of classification, which included Monera, Protozoa, Metaphyta (equivalent to Plantae) and Metazoa (equivalent to Animalia).
(a) Unicellular forms which show overlapping features were separated out as protozoa.
(vii) R. H. Whittaker proposed the Five Kingdom system of classification.
4. Kingdom Animalia:
(i) Salient features of this kingdom include:
(a) The organisms lack a cell wall.
(b) They are directly or indirectly dependent on other living organisms for food, so they are called heterotrophs.
(c) They follow definite growth pattern.
(d) Their nutrition is called holozoic.
(e) Higher forms possess an elaborate sensory mechanism.
5. Kingdom Fungi:
(i) They are the most diverse group of organisms.
(ii) Organisms possess cell wall made up of chitin (and not cellulose or peptidoglycan).
(iii) They lack chloroplast and thus are not autotrophic.
(iv) Their body is like a thread, called hypha, which forms a web-like mass called Mycelia.
(v) They may be parasitic (Puccinia graminis ver. tritichi), or saprohytic (Ganoderma).
(vi) They produce different types of asexual spores during reproduction, like zoospores, chlamydospores, conidia, sporangiospores, etc.
(vii) Sexual reproduction is complex involving plasmogamy, karyogamy and meiosis.
(viii) They are classified into four main classes:
(ix) Phycomycetes or Zygomycetes are lower fungi, like Rhizopus, Albugo, etc.
(x) Ascomycetes are called sac fungi, which produce ascospores (a type of sexual spore). Examples Neurospora, Claviceps, Morels, Truffles, etc.
(xi) Basidiomycetes are called club fungi, which produces basidiospores (a type of sexual spore). Example Agaricus, stinkhorns, Puccinia, etc.
(xii) Deuteromycetes are called Fungi Imperfecti, as sexual stages are absent or not detected in them. Example Alternaria.
(xiii) Most fungi are harmful and cause diseases in plants and animals.
6. Kingdom Protista:
(i) The organisms are always unicellular and eukaryotic.
(ii) They show plant-like features, animal-like features or fungus-like features.
(iii) Plant-like protists have the following features:
(a) They have a cell wall (except Euglenophyta members).
(b) They have chloroplast and chlorophyll-a.
(c) They are classified as Chrysophyta, Dinoflagellates and Euglenophyta.
(iv) Animal-like protists have the following features:
(a) They do not have a cell wall and are called protozoa.
(b) They are heterotrophs, parasites or predators.
(c) They may be amoeboid protozoan, flagellated protozoan, ciliated protozoan or sporozoan.
(v) Fungus-like protists have the following features:
(a) They are called Slime moulds.
(b) They have no cell wall in their vegetative phase.
(c) Cell wall is present only in their spores.
(d) They are decomposers Protista members
7. Kingdom Plantae:
(i) They are essentially autotrophic, chlorophyll-containing organisms.
(ii) They possess a cell wall, made up of Cellulose, Hemicellulose, Pectin, etc.
(iii) Some forms may be partially heterotrophic (like insectivorous plants).
(iv) They are further divided into Thallophyta (Algae), Bryophyta (Moss), Pteridophyta (Ferns), Gymnosperms and Angiosperms.
8. Kingdom Monera
(i) They are the only Prokaryotic organisms (commonly called bacteria).
(ii) The cell has no membrane-bound organelles.
(iii) The genetic material is single, double-stranded, circular, naked DNA (called Nucleoid or Genophore).
(iv) Ribosome is present which is of 70S type.
(v) They produce endospores, one of the types of asexual spores.
(vi) Sexual reproduction involves the exchange of genetic material via other bacteria (transformation), virus (transduction) or animal cells (transfection).
(vii) They are further divided into the following categories:
(a) Archaebacteria are called evolutionary relicts or extremophiles.
(b) Cyanobacteria are called Blue-green algae, due to the presence of c-phycoerythrin and c-phycocyanin.
- Some of them help in nitrogen fixation and possess heterocysts.
(c) Eubacteria includes true bacteria.
(d) Mycoplasma are the smallest living cellular organisms.
- They are mostly known to produce various types of diseases.
Group | Main Habitats | Cell Wall | Representatives |
Spirochetes | Live in tissues of marine invertebrates. | Gram-negative | Prochloron |
Purple or green bacteria | Generally anaerobic and reside on sediments of lakes and ponds. | Gram-negative | Rhodospirillum and Chlorobium |
Some Heterotrophic Bacteria | |||
Spirochetes | Aquatic habitats, parasites of animals | Gram-negative | Spirochaeta and Treponema. |
Aerobic rods andcocci | Soil, aquatic habitats, parasites of animals and plants | Gram-negative | Pseudomonas, Neisseria, Nitrobacter, Azotobacter and Agrobacterium |
Facultative anaerobic rods (enterobacteria) | Soil, plants, animal gut | Gram-negative | Salmonella, Shigella, Proteus, Escherichia and Photobacterium |
Sulphur and sulphate reducing bacteria | Anaerobic muds, sediments (as in bogs, marshes) | Gram-negative | Desulfovibrio |
Myxobacteria | Decaying plant and animal matter, bark of living trees | Gram-negative | Myxococcus and Chondromyces |
9. Lichens:
(i) They are composite organisms, made up of an Alga (phycobionts) and a fungus (mycobiont).
(ii) They are excellent pollution indicators, as they cannot grow in polluted areas and are sensitive to oxides of sulphur.
(iii) They yield various dyes, chemicals.
10. Virus, Viroids, Prions:
(i) Viruses are in the borderline between living and non-living.
(ii) They are obligatory intracellular parasites.
(iii) They are smaller than bacteria (20-200 nm in size range).
(iv) The name virus which means poisonous fluid was Dmitri Ivanowskyundefined.
(a) He recognized that the mosaic disease caused in tobacco was by some microbes which can pass through the bacterial filter.
(v) Beijerinck in1898 showed that the extract of the infected plants of tobacco could cause infection in healthy plants.
(a) He called the fluid Contagium vivum fluidum (infectious living fluid)
(vi) Stanley in undefined first time crystallized TMV, which was largely made up of proteins only.
(vii) They are simple structures:
(a) A protein coat called Capsid.
(b) A genetic material, which is either DNA or RNA (never both).
(viii) The genetic material may be of various types:
(a)ssDNA
(b)dsDNS
(c)ssRNA
(d)dsRNA
(ix) Most plant viruses are with RNA genome, while most animal viruses have DNA genome.
(x) Bacteriophages, the viruses which infects the bacteria generally containdsDNA.
(xi) Common symptoms of viral attack in plants include mosaic formation, leaf rolling and curling, yellowing and vein clearing, dwarf structure and stunted growth.
(xii) Viroids are smaller than viruses, made up of naked, single-stranded RNA.
(a) They do not have protein coats and have low molecular weight.
(xiii) They were discovered by T. O. Diener.
(a) They cause disease like potato spindle tuber disease.
(b) They are capsid-free infectious RNA particles.
(xiv) Prions are misfolded and infectious proteins that can auto-replicate.
(a) They cause disease (like Kuru, Scrapie, mad cow disease in cattle).
(b) They can convert normal proteins into infective proteins.
(c) Most notable form of these prions causes bovine spongiform encephalopathy BSE.
(xv) Prions were discovered by Stanley B. Prusiner.