Biological Classification

Monera is a kingdom which is known to contain prokaryotic unicellular organisms.

Fungi have eukaryotic organisms which may be unicellular or multicellular.

Bacteria comes under the kingdom Monera.

He divided organisms into five kingdoms:

a) Monera

b) Protista

c) Fungi

d) Plantae

e) Animalia

C.Linnaeus proposed two kingdom classification. He divided organisms into plantae and animalia.

Vichrow proposed theory of cell lineage.

These organisms are capable of thriving in extreme saline condition.

Commonly called the saprophytic fungus; grows on decaying vegetation.

It lacks cell wall. [ But cellulosic cell wall do exist in spore stage.]

Fungi belonging to this group have multinucleate protoplast.

It is a symbiotic association, which helps in nutrient absorption especially phosphorus absorption and in return mycorrhiza gets shelter.

Lichen is symbiosis between algae and fungi.

Fern belongs to pteridophytes.

Blue green algae remain in association with the roots of higher plants to form coralloid roots. It helps in nitrogen fixation.

Dikaryon means the stage when two nuclei are present within a cell.

This stage arises when after plasmogamy, karyogamy doesn’t take place immediately.

In 1898 M.W. Beijerinek called the living infectious fluid as contagium vivum fluidum, i.e. extract isolated from infected tobacco plant can cause infection in healthy tobacco plant.

Symbiotic association of algae and fungi is called the lichen. Algal component is called the phycobionts. Fungal partners are known as the mycobiont.

Structurally viruses have envelope, capsids and nucleoid.

Envelope and capsid is composed of protein and some amount of lipid and carbohydrate.

Sequence of sexual cycle:

a) Plasmogamy: two fungal hyphae comes in contact and anastomise[fusion of protoplasm].

b) Karyogamy: fusion between two nuclei.

c) Meiosis: reductional division takes place in order to maintain the ploidy level.

Viruses are regarded as the intermediate between non living entities and living organisms.

Hence their kingdom is still unspecified.

Phycomycetes is divided into two subclasses :

a) Oomyctes- also called aquatic fungi. Due to aquatic habitat. Also lives as an obligate parasites on plants.

b) Zygomycetes- members belonging to this group are found on decaying wood in moist and damp places.

• Cyanobacteria are capable of fixing nitrogen with the help of specialised cells called the heterocyst.

• They enrich the soil fertility. Hence BGA’s are used in agricultural fields. E.g. Colonies of Nostoc and Anabena grows in Paddy field.

According to the listed features the organism must be a dinoflagellate. All the eukaryotic unicellular organism belong to the kingdom Protista.

• The two kingdom classification didn’t distinguish between eukaryotes and prokaryotes.

• There were few organisms like Chlamydomonas, Euglena and the slime mould which have been claimed by both zoologists and botanist.

• When the five kingdom classification was proposed it was able to settle all these issues of anomalies by introducing three more kingdoms.

Polluted water bodies are rich in nutrients especially in nitrogen content which provides favourable condition to algae like Nostoc and Oscillotoria to bloom in the water bodies.

Chemosynthetic bacteria are autotrophic in nature. They obtain energy for the food synthesis by oxidising inorganic substances.

• In different countries, Pea is known by different names.

• In order to avoid remembering many names, worldwide standardization of name is set up.

• Hence scientific names are used.

Following are the characters which resemble a non living entity:

• Viruses have no complete cellular structure.

• Don’t show growth, division, metabolism and lack respiration.

• High specific gravity

• Don’t follow Robert Koch’s postulate

• Cannot be grown under “in vitro” condition.

Out of five kingdoms, four kingdoms have eukaryotic organisms- a) Protista b) Fungi c) Plantae d)Animalia.

Eukaryotes are the organisms whose nucleus and cell is bounded by membrane.

Diatoms are majorly phytoplankton’s which are the chief producers of ocean. Hence known as “pearls of oceans”.

Fairy rings are the annular rings, at the periphery visible fruiting body i.e. the basidiocarp are produced. Network of mycelia are produced underground, when it gets moist condition it produces visible basidiocarp on the ground. Initially basidiocarps are produced in clusters in form of disc. But as it grows diameter increases and due to exhaustion of nutrients in the central region this disc like structure changes to the annulus or a ring.

This naturally occurring ring or arch of mushrooms, occurring as a common turf disease, is identified as large dead rings or arch of grass in lawns during the spring or summer and is known as a ‘fairy rings’.

Due to following reasons Neurospora is used as a genetic tool :

• Fastest growing in vitro, can be grown in minimal media.

• Due to its haploid nature it can express both dominant as well as recessive traits.

• Analysis of genetic combination is facilitated by the ordered sequence of the products in the form of eight ascospores [result of meiosis and mitosis].

• Release of ascospores per ascus takes place systematically i.e. one by one, so that single ascospores in an orderly sequence can be isolated in successive single spore culture.

• All the seven chromosomes of Nuerospora are either telocentric and achrocentric. Hence genes can be easily mapped.

• Nutritionally, cyanobacteria and heterotrophic bacteria differ greatly. Cynobacteria are autotrophic, they synthesise their own food. Whereas heterotrophic bacteria depends on other organisms for food.

• But due to unicellular and prokaryotic nature of the organisms, both Cynobacteria and heterotrophic bacteria are categorised under Eubacteria of kingdom Monera.

• Hence the classification according to the cellular structure is justified.

Ascocarp i.e. the fruiting body present in the ascomycetes are divided into three types i.e apothecium, perithecium and cleistothecium. This division is based on the difference in shapes of the fruiting body and presence and absence of the opening lid called the ostiole.

• Apothecium: It’s a saucer or cup shaped, open fruiting body.

• Perithecium: Flask shaped fruiting body. With an opening lid called the ostiole.

• Cleistothecium: It’s a closed spherical structure. Ostiole is absent.

Due to following characters:

• Trypansoma is a unicellular eukaryotic organism.

• Locomotion is facilitated by flagella.

• Method of reproduction is asexual.

• The reserve food material is present in form of granules.

Role of Fungi-

• As food: Agaricus bisporus (mushrooms), Morchella, Truffles etc.

• As single cell proteins: Sacchromyces sp. (yeast) is used to produce tons of protein.

• Used in brewery and baking industry: Sacchromyces cerivesea is used. Under anaerobic conditions process of fermentation takes place which releases ethanol and CO_2.

The release of CO₂ helps the dough to rise up.

• Also used as biological control agents: Soil inhabiting fungus Trichoderma kills Pythium fungus known to cause root rot.

Some of the asexual spores produced by algae are:

• Zoospore: a) structure: thin walled spores, motile flagellated.

a) It is produced under favourable conditions

• Aplanospores: a) Structure: thin walled, non motile spores [lacks flagella].

B) It is produced under unfavourable conditions.

• Hypnospores: a) Structure: these are the thick walled spores.

b) It helps to tide over unfavourable conditions.

• Akinites : a) Structure: these are from the vegetative cells, thick cell wall.

b) formed under unfavourable condition.

• Hormogonia: a) Structure: these are the fragments of filaments formed due to breakage of thallus due to the formation of mucilaginous filled necridia.

b) formed under unfavourable condition.

• Peat is formed from the wetland vegetation especially from the Sphagnum (bog moss).

• Sphagnum likes to grow in acidic nature in the bog, due the acidity the complete degradation of cell could not takes place due to presence of less number of bacteria.

• Sphagnum uptakes water from the dead hyaline pores and holds a great amount of water.

• Due to fossilization of Sphagnum, Peat is formed.

Yes, biological classification is an ever evolving phenomenon.

• In the starting C. Linnaeus divided organisms into two kingdoms- Plantae and Animalia. This classification was based on the morphological characters.

• But later on it was realised that only two kingdoms were not sufficient because there were certain organisms which were claimed by both botanists and zoologists.

• This problem vanished when R.H. Whittaker proposed five kingdom classification system. Euglena and slime moulds were given place under kingdom Protista. Blue green algae and bacteria were been placed under Monera.

• In 1977 Carl Woese proposed six kingdom classification. In this classification the Kingdom Monera was splitted into two more domains i.e. Eubacteria and Archebacteria this was done on the basis of some major differences in cell wall.

Still the classification system is not complete because there are many organisms like viruse, virioids and prions which have not been classified under any kingdom. And many of the organisms are still waiting to be discovered and classified. Hence it can be said that the biological classification is ever evolving phenomenon.