Aristotle first attempted the biological classification of plants and animals. He classified the plants into Herbs, shrubs, and trees. He also classified animals into red blood-containing animals, called ENAIMA, and which do not have red blood called ANAIMA.
Two kingdom system of classification was put forth by Carolus Linnaeus. He also classified living organisms into KINGDOM PLANT AND ANIMAL. This classification was based on the presence and absence of cell wall. All organisms possessing cell walls were included in the PLANT KINGDOM like plants, fungi, and bacteria. Organisms which do not have cell wall were included in ANIMAL KINGDOM like Animals, Amoeba, Paramecium, etc. But this classification was found inadequate because this placed prokaryotes and eukaryotes in the same group and did not differentiate between unicellular and multicellular organisms or photosynthetic and non-photosynthetic organisms. For example. Prokaryotes like bacteria and eukaryotes like fungi and plants are placed in one group PLANTAE.
Classification systems have undergone several changes over time. R.H. Whittaker proposed a FIVE KINGDOM SYSTEM OF CLASSIFICATION. These five kingdoms were MONERA, PROTISTA, FUNGI, PLANTAE, AND ANIMALIA.
The main criteria used for classification were cell structure, body organization, mode of nutrition, reproduction, and phylogenetic relationships.
1. KINGDOM MONERA:
Unicellular Prokaryotes- BACTERIA are included in this group.
Bacteria can be spherical ( coccus ), rod-shaped ( bacillus), comma-shaped ( vibrio ), and spiral ( spirillum) in shape.
These organisms show extensive metabolic diversity. Some of the bacteria can be photo-autotrophic or chemoautotrophic. The majority of them are heterotrophic. This kingdom includes archaebacteria and eubacteria
1.1. ARCHAEBACTERIA:
These are EXTREMOPHILES, found in the most extreme habitats of the earth. HALOPHILES found at extreme salty areas, METHANOGENS at marshy places, and THERMOPHILES OR THERMOACIDOPHILES at hot springs.
1.2. EUBACTERIA:
These are called TRUE BACTERIA. These include PHOTOAUTOTROPHS like Cyanobacteria ( BGA ), which have chlorophyll a, like green plants, and a specialized structure called HETEROCYST for nitrogen fixation. eg. Nostoc, Anabaena.
CHEMOAUTOTROPHS or CHEMOSYNTHETIC AUTOTROPHS oxidizes inorganic substances like nitrates, nitrites, ammonia, and the released energy is used for ATP production. They play an important role in the recycling of nitrogen, iron, phosphorous, and sulfur.
HETEROTROPHIC bacteria can be saprophytic or decomposers and used for antibiotic production, fermentation, nitrogen fixation. Some can be pathogenic to plants and animals.
Bacteria divide asexually by BINARY FISSION but can transfer their DNA by CONJUGATION process from one cell to another via SEX PILUS OR CONJUGATION TUBE.
MYCOPLASMA are the smallest living cell without cell wall and can survive in anaerobic conditions.
2. KINGDOM PROTISTA:
This kingdom includes all single-celled eukaryotes. PROTISTA forms a link between monera and all other kingdoms like plants, fungi, and animals.
This kingdom includes PLANT LIKE PROTISTS, FUNGI LIKE PROTISTS, and ANIMAL LIKE PROTISTS.
2.1. PLANT-LIKE PROTISTS - CHRYSOPHYTES:
Diatoms and golden algae ( desmids) are included in this group. These are microscopic, photosynthetic and float passively in water ( plankton).
Diatoms are soap case like in appearance and chief producers in the oceans. Diatomaceous earth is formed by cell wall deposits of diatoms, and it is used for polishing, filtration of oils and syrups.
2.2. DINOFLAGELLATES:
These are mostly marine, photosynthetic organisms with two flagella ( one longitudinal and another transverse). Stiff cellulosic plates are observed on the outer surface. These can be red, green, yellow, brown, or blue in color.
Red dinoflagellate Gonyaulax undergoes rapid division and causes seawater to appear red ( RED TIDE). Toxins released by them can kill marine animals.
2.3. EUGLENOIDS:
These are photosynthetic in presence of light and heterotrophs in absence of light. eg. Euglena. The majority of them are freshwater organisms. Instead of cell wall, they have a protein-rich layer pellicle. Pigments of euglenoids are identical to higher plants.
2.4. FUNGI LIKE PROTISTS-SLIME MOULDS:
These are saprophytic protists or Fungi-like protists. Spores possess true walls and are dispersed by air current. Spores germinate under favorable conditions to form unicellular eukaryotic slime molds. These unicellular structures are united under favorable conditions to form PLASMODIUM. Plasmodium can spread and move along the decaying twigs and logs engulfing organic material.
2.5. ANIMAL-LIKE PROTISTS-PROTOZOANS:
These are heterotrophic organisms living as predators or parasites.
FOUR MAJOR GROUPS OF PROTOZOANS ARE,
I. AMOEBOID PROTOZOANS: These organisms use PSEUDOPODIA for locomotion and capturing their prey. eg. Entamoeba and Amoeba.
II. FLAGELLTED PROTOZOANS: These are free-living or parasitic forms, possessing flagella.
eg. Trypanosoma causes sleeping sickness.
III. CILIATED PROTOZOANS: Organisms like Paramoecium are included in this group. Locomotion occurs by cilia.
IV. SPOROZOANS: These protozoans show an infectious spore-like stage in their life cycle. eg. Plasmodium
3. KINGDOM- FUNGI-
These are heterotrophic organisms and can be saprophytes, degrading organic material or can be parasites on living plants and animals. These can live in symbiotic association with algae to form lichen and with roots of plants as mycorrhiza.
KINGDOM FUNGI IS DIVIDED INTO FOUR GROUPS BASED ON MORPHOLOGY OF MYCELIUM, TYPES OF FRUITING BODIES, and SPORE FORMATION.
I. PHYCOMYCETES:
These fungi are found at moist places hence called algal fungi. Mycelium is aseptate and coenocytic. Asexual reproduction occurs by endogenously produced motile zoospores and non-motile aplanospores. Zygospore is a sexually produced spore. Gametes produced are isogamous i.e similar in morphology or can be anisogamous i.e. dissimilar in morphology or oogamous i.e. female gamete is larger in size than male gamete.
eg. Mucor, Rhizopus ( bread mold), Albugo ( parasitic fungi on mustard )
II. ASCOMYCETES:
These are sac fungi. Hyphae is septate and branched. Asexual spores called conidia are produced exogenously on conidiophores.
ASCOSPORES are sexual spores produced inside a sac-like structure called ascus ( plural. Asci).
Asci are produced over fruiting body ASCOCARP.
eg. Multicellular ascomycetes- Aspergillus, Claviceps, Penicillium, and Neurospora
Unicellular ascomycetes- Yeast
Neurospora is used for biochemical and genetic studies.
Morels and Truffles are used as edible ascomycetes.
III. BASIDIOMYCETES:
Members of this group are also called shelf fungi/bracket fungi, or puffballs. Mycelium is branched and septate.
Asexual spores are not found but vegetative reproduction occurs, by fragmentation.
Basidiospores are sexual spores produced exogenously, on a basidium. Basidia are arranged in fruiting bodies called BASDIOCARPS.
eg. Agaricus ( Mushroom), Ustilago ( smut ). Puccinia ( rust )
III. DEUTEROMYCETES:
These fungi reproduce only vegetatively and asexually, so-called Fungi Imperfectii or Imperfect fungi. Mycelium is septate and branched. Asexual spores produced are Conidia.
Large members are decomposers of litter and organic matter and are involved in mineral cycling.
eg. Alternaria, Colletotrichum, Trichoderma.
RELATED LINKS:
BIOLOGICAL CLASSIFICATION AND TAXONOMIC CATEGORIES
No comments:
Post a Comment