- Those living organisms around us which we cannot be seen with naked eyes are called microorganisms or microbes.
- Some of these can be seen with a magnifying glass while some cannot be seen without the help of a microscope. That is why these are called microorganisms or microbes.
- Microorganisms are classified into four major groups. These groups are bacteria, fungi, protozoa and some algae.
Classification of microorganisms
- Single-celled organisms
- Found in wide range of habitats ranging from glaciers to deserts and hot springs
- For example: curd bacteria (Lactobacillus)
- Multicellular, heterotrophic organisms
- Lack chlorophyll and are generally found in colonies
- For example: Penicillium, Aspergillus
- Unicellular or multicellular microorganisms
- Usually found in water
- For example: Amoeba and Paramecium
- Unicellular or multicellular autotrophic organisms
- Contain chlorophyll pigment and carry out photosynthesis
- For example: Chlamydomonas and Spirogyra
- Viruses are also microscopic which reproduce only inside the cells of the host organism, which may be a bacterium, plant or animal.
- Ultramicroscopic organisms
- Require host cells to reproduce and complete their life cycle.
- For example: Influenza virus, polio virus.
- Process of preventing the spoilage of food items by the action of microbes is called food preservation.
- Microorganisms act on food items and spoil them.
Methods of food preservation
(i) Chemical methods
- The chemicals that controls the growth of microorganisms on food are called preservatives.
- For example: sodium benzoate, sodium metabisulphite, salts and edible oil.
- Common salt is used as preservative in pickles. It is also used to preserve meat and fish.
- Sugar is used as preservative in jams and jellies.
- Oil and vinegar are used as preservatives in pickles and vegetables.
(ii) Heat and cold treatments
- Boiling the milk helps in killing microorganisms present in it.
- Pasteurization is a technique of preserving milk in which it is boiled to about 70°C for 15 to 30 seconds and then suddenly chilled and stored.
(iii) Storage and packing
- Dry fruits and vegetables are stored in sealed air tight packets to prevent microbial attack.
Importance of microorganisms
(i) In food industry
- Lactobacillus bacteria promote the conversion of milk into curd.
- Yeast is used in preparation of breads, pastries and cakes.
(ii) In beverage industry
- Yeast is used for commercial production of alcohol, wine and vinegar (acetic acid).
- Yeast acts on sugar and converts it into alcohol by the process of fermentation. Louis Pasteur discovered fermentation.
(iii) In medicine production
- Medicines produced by certain microorganisms to kill or stop the growth of other disease-causing microorganisms are called antibiotics.
- Antibiotics are obtained from bacteria and fungi.
- Commonly used antibiotics are streptomycin, tetracycline, and erythromycin.
- First antibiotic penicillin was prepared by Alexander Fleming
(iv) In vaccine production
- Protection of the body from the attack of various disease-causing microorganisms through vaccines is known as vaccination.
- Vaccine includes dead or weakened microbes that trigger the production of antibodies in the body.
- These antibodies help in preventing the attack from disease-causing microorganisms.
- Vaccination helps in controlling diseases such as cholera, polio, small pox, hepatitis etc.
- Vaccine for small pox was discovered by Edward Jenner.
(v) In increasing soil fertility
- Blue green algae and Rhizobium bacteria are called biological nitrogen fixers.
- They fix free atmospheric nitrogen to enhance soil fertility.
(vi) In cleaning the environment
- Microorganisms (decomposers) help in converting dead waste of plants and animals into simpler substances by the process of decomposition.
- It involves circulation of nitrogen through living and non-living components of nature.
- Nitrogen gas comprises 78% of the atmosphere.
- First process of nitrogen cycle is fixation of nitrogen gas into nitrogenous compounds caused by bacterium Rhizobium and lightning.
- Nitrogen compounds in soil are taken up by the plants through roots and used up in synthesis of plant proteins. Animals obtain nitrogen by feeding on plants.
- Waste of plants and animals are converted to nitrogenous compounds by the action of bacteria and fungi in the soil.
- Some bacteria convert nitrogenous compounds back to nitrogen to maintain atmospheric levels of nitrogen.
- Disease-causing microorganisms are called pathogens.
- Diseases in humans caused by microorganisms
- Diseases caused by microorganisms that spread from an infected person to a healthy person through air, water, or food are called communicable diseases.
- The example includes cholera, chicken pox, and tuberculosis.
- The organisms that transmit diseases from one place to the other are called carriers.
Example of carriers
- Housefly spreads diseases such as cholera, dysentery, and typhoid.
- Female Anopheles mosquito spreads malarial parasites.
- Female Aedes mosquito spreads dengue virus.
Examples of human diseases caused by bacteria
Examples of human diseases caused by virus
- Chicken pox
Examples of human diseases caused by protozoa
Diseases in animals caused by microorganisms
- Anthrax is caused by bacteria
- Foot and mouth disease in cattle is caused by virus
Diseases in plants caused by microorganisms
- Citrus canker disease is caused by bacteria
- Rust of wheat is caused by fungi
- Yellow vein mosaic of Bhindi (Okra) is caused by virus