Biological Classification Test - 1

Mycoplasma or mollicutes are the simplest and the smallest of the free living prokaryotes classified under kingdom Monera. They were discovered in pleural fluid of cattle suffering from pleuropneumonial (Nocard and Roux, 1898). The size ranges from 0.1-0.15 μm. A cell wall is absent. Plasma membrane forms the outer boundary of the cell. They mostly produce pleuropneumonia in domestic animals, a typical pneumonia and mycoplasmal urethritis in humans, little leaf disease of brinjal and witche, broom in plants. Mycoplasma can survive without O₂.

Pathogen of cholera is Vibrio choleras bacterium. Cholera is transmitted by contaminated water. Typhoid  or enteric fever spreads through contaminated water in which bacterium Salmonella typhi is present. Citrus canker and crown gall are bacterial diseases of plants caused by Xanthomonas cilri and Agrobacterium tumetaciens respectively.

Bacteria are grouped under four categories based on their shapes: the spherical coccus (pl.: coccl), the rod-shaped bacillus (pi.: bacilli), the comma-shaped vibrium (pl.: vibrio) and the spiral spirillum (pl.: spirilla).

Methanogens are a type of archaebacteria which a restrictan aerobes. Nutritionally they are autotrophs which obtain both energy and carbon from decomposition products. They occur in marshy areas where they convert formic acid and carbon dioxide into methane with the help of hydrogen. This capability is commercially exploited in the production of methane and fuel gas inside gobar gas plants
Example: Methanobacterium, Methanococcus.

Nostoc occurs in both aquatic and subaerial habitats. A dense mucilage covering (labelled as B in the given figure) is present on the outside. Each trichome is beaded, S-shaped and consists of a large number of vegetative cells, a few term in a land intercalary large pale coloured heterocysts - (labelled as A in the given figure) and thick-walled resting cells called akinetes. Heterocysts are specialised to perform nitrogen fixation.

In a bacterial cell, membrane bound cell organelles as found in eukaryotes are absent. Various structures present in the cytoplasm of a prokaryotic cell include mesosomes, 70S ribosomes, nucleoid, plasmids, gas vacuoles, food reserve, etc.

Reproduction in bacteria occurs by three methods - binary fission, sporulation and sexual reproduction. Binary fission is the most common method of bacterial multiplication under favourable conditions, in which a mature bacterium divides into two equal daughter cells.

Cyano bacteria or blue-green algae are Gram + photosynthetic prokaryotes which perform oxygenic photo- synthesis. Photosynthetic pigments include chlorophyll a, carotenoids  and phycobilins. Cyanobacteria are classified under kingdom Monera. Cyanobacterial cell structure is  typically prokaryotic - one envelope organisation with peptidoglycan wall, naked DNA, 70S ribosomes and absence of membrane bound structures like endoplasmic reticulum, mltochondria, Golgi bodies, plastids, lysosomes, sap vacuoles. The outer part of the protoplast, called chromoplasm, contains a number of photosynthetic thylakoids.

Chemoautotrophic bacteria or chemosynthetic  autotrophic bacteria are able to manufacture their organic food from inorganic raw materials with the help of energy derived from exergonic chemical reactions Involving oxidation of an inorganic substance present in the external medium. The chemical energy obtained from oxidation reaction is trapped in ATP molecules. This energy is then used in carbon assimilation with the help of hydrogen brought from sources other than water. There are several types of chemoautotrophic bacteria but the well known examples are nitrifying bacteria, sulphur oxidising bacteria and iron bacteria.

Bacterial plasma membrane or plasmalemma has a structure similar to that of a typical membrane. It is made of a phospholipid bilayer with proteins of various types (extrinsic, integral, transmembrane). Archaebacteria are a group of most primitive prokaryotes which are able te survive in extremely hostile conditions. Their cell membranes are different from eubacteria and are characterized by the presence of a monolayer of branched chain lipids.

Saprophytic bacteria are free living bacteria which obtain their food from organic remains, e.g., corpses, animal excreta, fallen leaves, vegetables, fruits, meat, jams, jellies, bread and other products of plant and animal origin. Aerobic breakdown of organic compounds is known as decay. In nature saprophytic bacteria alongwith saprotrophic fungi are the decomposers of organic remains.

Several cyanobacteria have the ability of nitrogen fixation. The filamentous forms possess special large pale cells or heterocysts for this. Some of the fixed nitrogen comes out as excretion. After death of cyanobacteria the substratum becomes rich in nitrogen. Such nitrogen fixing cyanobacteria are now regularly inoculated in the rice fields This saves application of nitrogen fertilizers.

Heterocyst is a large-sized pale coloured thick-walled cell which occurs in terminal, intercalary or lateral position in filamentous cyanobacteria, e.g., Nostoc. The thick wall impermeable to oxygen but permeable to nitrogen. Mucilage sheath is absent. Photosystem II is absent. Thylakoids laid phycobilisomes. Therefore, photosynthesis is absent but cyclic photophosphorylation occurs. Heterocyst is dependent for its nourishment on adjacent vegetative cells. It has enzyme nitrogenase and so, it is specialised to perform nitrogen fixation.

Monera kingdom includes prokaryotes - mycoplasma bacteria, actinomycetes and cyanobacteria or blue greet algae. Alongwith fungi, they are decomposers and mineralisers of the biosphere.

Antibiotics are substances produced by microorganisms which in low concentration are antagonistic then the growth of other micro-organisms (Waksman, 1942 medicinally antibiotics are those organic secretions which destroy or check the growth of different pathogens without hanning the host. Maximum number of antibotics are produced by mucelial bactera known as Actinomycetes.
Example: Streptomucin-Streptomyces groseus, Chloromycetin or chloramphenicol-Streptomyces venezuelae and S.Lavendulae.