Chapter : 2 MICROORGANISMS : FRIEND AND FOE During the rainy season one may have observed that moist bread gets spoilt and its surface gets covered with greyish white patches. When these patches are observed through a magnifying glass we see tiny, black rounded structures. These structures are called Microbes or Microorganisms.Microorganisms are tiny microscopic organisms that are not visible to the naked eye.They may be unicellular or multicellular.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.Microorganisms are classified into four major groups: Fig: Bacteria Fig:Algae Fig: Protozoa Fig: Fungi Viruses are also microscopic but are different from other microorganisms.They, however, reproduce only inside the cells of the host organism, which may be a bacterium, plant or animal.Common ailments like cold, influenza (flu) and most coughs are caused by viruses.Serious diseases like polio and chicken pox are also caused by viruses. Fig: viruses Microorganisms Uses Beneficial Microorganisms They are used in: The preparation of curd (Lactobacillus), bread and cake. Some microorganisms decompose the organic waste and dead plants and animals into simple substances and clean up the environment. The preparation of medicines- penicillin, antibiotics (Streptomycin, tetracycline and erythromycin ). The manufacture of vaccines (substance which is used to stimulate the production of antibodies, thereby providing immunity against certain diseases.) In agriculture they are used to increase soil fertility by fixing nitrogen (Cyanobacteria-blus green algae). Harmful Microorganisms Disease causing Microorganisms in Humans Some insects and animals which act as carriers of disease- causing microbes. Ex: Housefly – carrier of harmful pathogens Anopheles mosquito -carries the parasite of malaria (Plasmodium). Female Aedes mosquito – carrier of dengue virus. Disease causing Microorganisms in Animalsanthrax – caused by a bacterium.Foot and mouth disease- caused by a virus. Food poisoningWhen food contaminated with pathogens or toxins are consumed, it causes food poisoning.The most common symptom is a pain in the stomach.In severe cases, food poisoning can also cause death. Food preservation Chemical methodsChemical preservatives are used in food preservations by major food industries as they are harmless to humans.Salts and edible oils -common chemicals generally used to check the growth of microorganisms.Sodium meta-bisulphate and sodium benzoate are commonly used chemical preservatives. Preservation by common saltCommon salt (sodium chloride) is used as a preserve meat and fish, amla, raw mangoes, tamarind, etc. Preservation by SugarSugar is used for the preservation of jams, jellies and squashes.Sugar reduces the moisture content which inhibits the growth of bacteria which spoil food. Preservation by oil and VinegarMany food preparations like pickles are preserved by adding either oil or vinegar to them.Bacteria cannot grow in such medium.Vegetables, fruits, fish and meat can also be preserved. PasteurizationPasteurization is a process of superheating and cooling the beverages.This prevents the growth of microbes. Storage and PackingDry fruits and many vegetables are preserved in airtight/air sealed containers.The absence of air prevents the growth of bacteria or fungi. Nitrogen cycle Our atmosphere has 78% nitrogen gas.Nitrogen is one of the essential constituents of all living organisms as part of proteins, chlorophyll, nucleic acids and vitamins.PROCESS Fig: Nitrogen Cycle The atmospheric nitrogen cannot be taken directly by plants and animals.Certain bacteria and blue green algae present in the soil fix nitrogen from the atmosphere and convert it into compounds of nitrogen.Once nitrogen is converted into these usable compounds, it can be utilised by plants from the soil through their root system.Nitrogen is then used for the synthesis of plant proteins and other compounds.Animals feeding on plants get these proteins and other nitrogen compoundsWhen plants and animals die, bacteria and fungi present in the soil convert the nitrogenous wastes into nitrogenous compounds to be used by plants again.Certain other bacteria convert some part of them to nitrogen gas which goes back into the atmosphere.This ensures that the percentage of nitrogen in the atmosphere remains more or less constant.