We have seen and learn several kinds of plants and animals. However, there are other living organisms around us which we normally cannot see. These are called microorganisms or microbes.
Some of these, such as the fungus that grows on bread, can be seen with a magnifying glass. Others 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.
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.
Diseases like dysentery and malaria are caused by protozoa(protozoans) whereas typhoid and tuberculosis (TB) are bacterial diseases.
Microorganisms may be single-celled like bacteria, some algae and protozoa, or multicellular, such as many algae and fungi. They live in all types of environment, ranging from ice cold climate to hot springs; and deserts to marshy lands. Some microorganisms grow on other organisms while others exist freely.
Microorganisms play an important role in our lives. Some of them are beneficial in many ways whereas some others are harmful and cause diseases. Microorganisms are used for various purposes. They are used in the preparation of curd, bread and cake.
Curd contains several microorganisms. Of these, the bacterium, Lactobacillus promotes the formation of curd. It multiplies in milk and converts it into curd. Bacteria are also involved in the making of cheese, pickles and many other food items.
Microorganisms are used for the large scale production of alcohol, wine and acetic acid.
Some of medicines kill or stop the growth of the disease-causing microorganisms. Such medicines are called antibiotics. These days a number of antibiotics are being produced from bacteria and fungi. Streptomycin, tetracycline and erythromycin are some of the commonly known antibiotics which are made from fungi and bacteria. Antibiotics are even mixed with the feed of livestock and poultry to check microbial infection in animals. They are also used to control many plant diseases.
Some bacteria are able to fix nitrogen from the atmosphere to enrich soil with nitrogen and increase its fertility. These microbes are commonly called biological nitrogen fixers.
Microorganisms are harmful in many ways. Some of the microorganisms cause diseases in human beings, plants and animals. Such disease-causing microorganisms are called pathogens. Some microorganisms spoil food, clothing and leather.
Microbial diseases that can spread from an infected person to a healthy person through air, water, food or physical contact are called communicable diseases.
Some of the microorganisms are very helpful for us that prevent the food. Like Salts and edible oils are the common chemicals generally used to check the growth of microorganisms. Therefore they are called preservatives.
Common salt has been used to preserve meat and fish for ages. Meat and fish are covered with dry salt to check the growth of bacteria.
We have learnt about the bacterium Rhizobium in previous classes. It is involved in the fixation of nitrogen in leguminous plants (pulses). Sometimes nitrogen gets fixed through the action of lightning. But we know that the amount of nitrogen in the atmosphere remains constant.
In 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. 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. Nitrogen is then used for the synthesis of plant proteins and other compounds.
When 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.
