WBCS Preliminary( Biology): Microorganism

1. Microorganisms or microbes are too small and are not visible to the unaided eye. They may be unicellular or multicellular.

   • Microorganisms include bacteria, fungi, protozoa and some algae. Viruses, though different from the above mentioned living organisms, are considered microbes. Viruses are quite different from other microorganisms. They reproduce only inside the host organism; bacterium, plant or animal cell.
   • They can live in all kinds of environment, ranging from ice cold climate to hot springs and deserts to marshy lands. Microorganisms are found in air, water and in the bodies of plants and animals.
   • Some microorganisms are useful for commercial production of medicines and alcohol. In agriculture they are used to increase soil fertility by fixing nitrogen.
2. Virus:
   • A complete virus particle, known as a virion , is little more than a gene transporter, consisting of nucleic acid either deoxyribonucleic acid (DNA) or ribonucleic acid (RNA) surrounded by a protective coat of protein called a capsid. A capsid is composed of proteins encoded by the viral genome and its shape serves as the basis for morphological distinction. Virally coded protein units called protomers will self-assemble to form the capsid, requiring no input from the virus genome - however, a few viruses code for proteins which assist in the construction of their capsid. Proteins associated with nucleic acid are known as nucleoproteins, and the association of viral capsid proteins with viral nucleic acid is called a nucleocapsid.
   • Viruses are dead outside the cells multiply only inside living cells and moves along blood or Phloem sap in animals and plants respectively. The nucleic acid of the virus enters the cell and control the host cell to produce identical virus nucleic acid and protein coat and thus it multiplies. Continuous multiplication of virus, exhaust the protoplasmic contents and it finally the cell ruptures and realises virus. This process is known as lysis of the host cell. The new viruses repeat the entire multiplication process.
3. Bacteria:
   • Bacteria are microorganisms that lack a nucleus and have a cell wall composed of peptidoglycan, a protein-sugar molecule. Bacteria are the most common organisms on earth and are intimately connected to the lives of all organisms. The common structural forms are:
     1. Spherical or ovoid (coccus )
     2. rod shaped or cylindrical (bacillus )
     3. spiral or screw (spirillum) Many forms of bacteria are not capable of independent movement,. Some Bacteria which live in liquid often have thread like projections called flagella (e.g Salmonella bacterium)
   • Reproduction in bacteria is largely by binary fission i.e. it splits into two. In some case due to some extreme environmental conditions, they form tiny structures is called Spores. It is formed by condensation of protoplasm into a spherical or egg shaped body and they germinate under favourable conditions. Some bacteria exhibit a type of sexual reproduction.
   • Vaccination or Immunization or inoculation is a method of stimulating resistance in the human body to specific diseases using microorganisms -bacteria or viruses-that have been modified or killed. These vaccines do not cause diseases but stimulates the production of antibodies in its blood. It build a defense mechanism that continuously guards against the disease.
   • Serum is a preparation from blood of an animal that has been inoculated with bacteria. This contains antibodies that formed as a consequence of the disease. The important antibodies produced with the help of bacteria are streptomycin, Aureomycin, Terramycin.
4. Fungi: The fungi (singular fungus) are a kingdom of eukaryotic organisms. Fungi lack chlorophyll; consequently they cannot synthesize their own food. In order to feed fungi release digestive enzymes that break down food outside their bodies. The fungus then absorbs the dissolved food through their cell walls. It is a simple plant body that has no roots, stems, flowers and seeds. It includes mushrooms, molds, yeasts, truffles etc. The branch of biology involving the study of fungi is known as mycology.
5. Algae: These are chiefly plant like organisms found usually in water bodies and moist environments that are not subjected to direct sunlight. They make their own food by photosynthesis but they lack roots, leaves and other structures typical of true plants. They capture more of sun’s energy than all plants combined and form the foundation of most aquatic food webs.