Microorganisms
Definition
The organisms which
cannot be observed with the naked eye and can be seen only through a microscope
are called microorganisms or microbes.
Food and water become
unsafe for consumption due to the presence of harmful organisms, commonly referred
to as germs. These germs are so small that they are invisible to the
naked eye, but can often cause dangerous diseases.
Since these organisms
can be seen only through a microscope, they are called microorganisms or
microbes.
When the body is
attacked by germs or pathogens, medicines called antibiotics are given.
Antibiotics act against the bacteria within the body, without harming the
person.
Microorganisms
Microorganisms are
present in the air, water, food and even inside our bodies. While a majority of
the microbes are harmless, some of them have the capability of causing
dangerous diseases.
Microorganisms
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Bacteria
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Algae
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Fungi
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Protozoa
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Viruses
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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 the large scale production of alcohol, wine and acetic acid (vinegar). Yeast is used for commercial production of alcohol and wine. For this purpose yeast is grown on natural sugars present in grains like barley, wheat, rice and crushed fruit juices, etc.
Whenever we fall ill the doctor may give us some antibiotic tablets, capsules or injections such as of penicillin. The source of these medicines is microorganisms. These 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. The antibiotics are manufactured by growing specific microorganisms and are used to cure a variety of diseases. 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.
When a disease-carrying microbe enters our body, the body produces antibodies to fight the invader. The body also remembers how to fight the microbe if it enters again. So, if dead or weakened microbes are introduced in a healthy body, the body fights and kills them by producing suitable antibodies. The antibodies remain in the body and we are protected from the disease causing microbes. This is how a vaccine works. Several diseases, including cholera, tuberculosis, smallpox and hepatitis can be prevented by vaccination.
Some microorganisms live inside our body. They help in certain functions of our bdoy systems. For example some bacteria in our gastrointestinal tract help in digestion. These type of organisms which reside in our body and are beneficial as well are called commensals.
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.
Pathogens enter our body through the air we breathe, the water we drink or the food we eat. They can also get transmitted by direct contact with an infected person or carried through an animal. Microbial diseases that can spread from an infected person to a healthy person through air, water, food or physical contact are called communicable diseases. Examples of such diseases include cholera, common cold, chicken pox and tuberculosis.
Disease— causing Microorganisms in Animals
Several microorganisms not only cause diseases in humans and plants, but also in other animals. For example, anthrax is a dangerous human and cattle disease caused by a bacterium. Foot and mouth disease of cattle is caused by a virus.
Several microorganisms cause diseases in plants like wheat, rice, potato, sugarcane, orange, apple and others. The diseases reduce the yield of crops. They can be controlled by the use of certain chemicals which kill the microbes.
Food poisoning could be due to the consumption of food spoilt by some microorganisms. Microorganisms that grow on our food sometimes produce toxic substances. These make the food poisonous causing serious illness and even death. So, it is very important that we preserve food to prevent it from being spoilt.
Microorganisms spoil our food. Spoiled food emits bad smell and has a bad taste and changed colour.
Chemical Method: Salts and edible oils are the common chemicals generally used to check the growth of microorganisms. Therefore they are called preservatives. We add salt or acid preservatives to pickles to prevent the attack of microbes. Sodium benzoate and sodium metabisulphite are common preservatives. These are also used in the jams and squashes to check their spoilage.
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. Certain bacteria and blue green algae present in the soil fix nitrogen from the atmosphere and convert 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 compounds.
Classification of
Microorganism
Microbes are mainly
classified into five major groups :
Bacteria :
Bacteria (singular:
bacterium) are single-called organisms that vary in shape and size. Some
bacteria are round or oval (coccus),
others are rod-shaped (bacillus) or spiral. Some bacteria are autotrophic as
they contain chlorophyll, but most of them are heterotrophic, showing
saprophytic or parasitic mode of nutrition.
Algae :
Autotrophic organisms
having undifferentiated plant bodies are called algae (singular: alga). Algae
occur abundantly, like grass in aquatic habitats and are also called 'grass
of water'.
Fungi :
Fungi (singular:
fungus) are a group of plant-like organisms exhibiting heterophic (saprophytic
or parasitic) nutrition. They are commonly found on bread, leather, cotton,
paper, etc. Fungi grow vigorously in damp, warm, dark places, Yeast, moulds and
mushrooms are forms of fungi. Yeast, moulds and mushrooms are forms of fungi.
Yeast is commonly used for baking breaed, cakes, etc. The yeast ferments sugar
present in the wheat and converts it to carbon dioxide and alcohol. The gas
expands, so that the dough (kneaded atta) rises, giving shape and flavour to
the preparation.
Protozoa :
Unicellular organisms
that exhibit animal-like characteristics are called protozoa (singular:
protozoan). The word protozoan literally means 'the first animal'. Most
protozoa are heterotrophic.
Viruses :
A virus is a
microorganism which exhibits characteristics of living as well as non-living
things. Viruses exhibit a variety of shapes, having simple structure.
Reproducing only inside a living organism, viruses can cause many diseases.
Useful
Microorganisms
Humans have many
microorganism in their in their digestive system that contribute to overall
health. The microbial community in humans not only protects us from disease,
but also provides necessary vitamins.
Bacteria also help in
nitrogen fixation in production of antibiotics, etc. Algae are also useful in a
number of industries. Therefore, even through microbes are responsible for food
spoilage and many diseases, they can also be very helpful.
Yoghurt or curd (dahi)
is the commonest example of beneficial use of microbes. Youghurt is a part of our
daily diet and we eat it in various forms, with different flavour. This dahi is
made from milk by the action of a bacterium called lactobacillus or latic acid
bacteria. It converts the sugar in milk (lactose) to lactic acid, giving curd
its sour taste. This process was initially used as a way to preserved milk.
Lactose ------Lactobacillus----------> Lactic Acid (Yoghurt)
Curdling of milk takes
places naturally, due to heat (specially in summer).
Curding of milk also
takes place due to addition of any of the acid products such as sour curd,
lemon juice and even tomato juice.
Microorganisms and weMicroorganisms play an important role in our lives. Some of them are beneficial in many ways whereas some others are harmful and cause diseases.
Commercial Use of Microorganisms
Microorganisms are used for the large scale production of alcohol, wine and acetic acid (vinegar). Yeast is used for commercial production of alcohol and wine. For this purpose yeast is grown on natural sugars present in grains like barley, wheat, rice and crushed fruit juices, etc.
Medicinal Use of Microorganisms
Whenever we fall ill the doctor may give us some antibiotic tablets, capsules or injections such as of penicillin. The source of these medicines is microorganisms. These 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. The antibiotics are manufactured by growing specific microorganisms and are used to cure a variety of diseases. 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.
Vaccine
When a disease-carrying microbe enters our body, the body produces antibodies to fight the invader. The body also remembers how to fight the microbe if it enters again. So, if dead or weakened microbes are introduced in a healthy body, the body fights and kills them by producing suitable antibodies. The antibodies remain in the body and we are protected from the disease causing microbes. This is how a vaccine works. Several diseases, including cholera, tuberculosis, smallpox and hepatitis can be prevented by vaccination.
Increasing Soil Fertility
Some bacteria and blue green algae 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.
Commensals:
Some microorganisms live inside our body. They help in certain functions of our bdoy systems. For example some bacteria in our gastrointestinal tract help in digestion. These type of organisms which reside in our body and are beneficial as well are called commensals.
Apart from them certain food like curd, contain beneficial bacteria.
Harmful Microorganisms
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.
Disease— causing Microorganisms in Humans
Pathogens enter our body through the air we breathe, the water we drink or the food we eat. They can also get transmitted by direct contact with an infected person or carried through an animal. Microbial diseases that can spread from an infected person to a healthy person through air, water, food or physical contact are called communicable diseases. Examples of such diseases include cholera, common cold, chicken pox and tuberculosis.
There are some insects and animals which act as carriers of disease causing microbes. Housefly is one such carrier. The flies sit on the garbage and animal excreta. Pathogens stick to their bodies. When these flies sit on uncovered food they may transfer the pathogens. Whoever eats the contaminated food is likely to get sick. Another example of a carrier is the female Anopheles mosquito, which carries the parasite of malaria. Female Aedes mosquito acts as carrier of dengue virus.
Some Common Human Diseases caused by Microorganisms
Disease— causing Microorganisms in Animals
Several microorganisms not only cause diseases in humans and plants, but also in other animals. For example, anthrax is a dangerous human and cattle disease caused by a bacterium. Foot and mouth disease of cattle is caused by a virus.
Disease— causing Microorganisms in Plants
Several microorganisms cause diseases in plants like wheat, rice, potato, sugarcane, orange, apple and others. The diseases reduce the yield of crops. They can be controlled by the use of certain chemicals which kill the microbes.
Food Poisoning
Food poisoning could be due to the consumption of food spoilt by some microorganisms. Microorganisms that grow on our food sometimes produce toxic substances. These make the food poisonous causing serious illness and even death. So, it is very important that we preserve food to prevent it from being spoilt.
Food Preservation
Microorganisms spoil our food. Spoiled food emits bad smell and has a bad taste and changed colour.
Common methods to preserve food in our homes.
Chemical Method: Salts and edible oils are the common chemicals generally used to check the growth of microorganisms. Therefore they are called preservatives. We add salt or acid preservatives to pickles to prevent the attack of microbes. Sodium benzoate and sodium metabisulphite are common preservatives. These are also used in the jams and squashes to check their spoilage.
Preservation by Common Salt: 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. Salting is also used to preserve amla, raw mangoes, tamarind, etc.
Preservation by Sugar: Jams, jellies and squashes are preserved by sugar. Sugar reduces the moisture content which inhibits the growth of bacteria which spoil food.
Preservation by Oil and Vinegar: Use of oil and vinegar prevents spoilage of pickles because bacteria cannot live in such an environment. Vegetables, fruits, fish and meat are often preserved by this method.
Heat and Cold Treatments: You must have observed your mother boiling milk before it is stored or used. Boiling kills many microorganisms.
Similarly, we keep our food in the refrigerator. Low temperature inhibits the growth of microbes. Pasteurized milk can be consumed without boiling as it is free from harmful microbes. The milk is heated to about 700C for 15 to 30 seconds and then suddenly chilled and stored. By doing so, it prevents the growth of microbes. This process was discovered by Louis Pasteur. It is called pasteurization.
Storage and Packing: These days dry fruits and even vegetables are sold in sealed air tight packets to prevent the attack of microbes.
Nitrogen Fixation: Rhizobium is involved in the fixation of nitrogen in leguminous plants (pulses). Sometimes nitrogen gets fixed through the action of lightning. But the amount of nitrogen in the atmosphere remains constant.
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. Certain bacteria and blue green algae present in the soil fix nitrogen from the atmosphere and convert 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 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. As a result, the percentage of nitrogen in the atmosphere remains more or less constant.
Steps Involved in Nitrogen Cycle
The atomspheric nitrogen is fixed into nitrogen compounds like nitrates hy Rhizobium bacteria, bluegreen
algae, lightning or industrial method.
The plants absorb nitrate compounds from the soil and water and convert them into plant proteins.
The plants are eaten up by animals and thus plant protiens are used for making animal proteins.
When the plants and animals die, the putrefying bacteria and fungi present in the soil decompose the
protiens of dead plants and animal into ammonia. This process is called ammonification.
Ammonia thus formed is converted first into nitrites and then into nitrates by the action of Nitrosomonas
and Nitrobacter bacteria respectively. The process is called nitrification. These nitrates are again
absorbed by plants and the cycle is repreated.
The soil contians denirifying bacteria called Pseudomonas which convert nitrate form of nitrogen into
free nitrogen which goes back into the atmosphere. The process is called denitrification.
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