Introduction
You see animals and plants around you, but do you know that apart from these there are other living organisms which we cannot see with the naked eye. Such living organisms which we cannot see with the naked eye are called microorganisms or microbes. Various types of microorganisms are found around us, some of them are beneficial for us and some are harmful. During the rainy season you must have observed that the moist bread gets spoiled, and its surface gets covered with grayish white patches. In this chapter we will learn about various beneficial and harmful microorganisms.
Microorganisms
1. The size of microorganisms or microbes is so small that they cannot be seen
with the unaided eye.
2. Fungus can be seen with a magnifying glass.
3. Microorganisms other than fungus can't be seen without the help of microscope. That is why these are called microorganisms or microbes.
4. Microorganisms are classified into four major groups namely - bacteria, fungi, protozoa and some algae.
5. Viruses are different from other microorganisms. Though, viruses are microscopic.
6. Viruses reproduce only inside the cells of the host organism. The host organism may be a bacterium, plant or animal.
7. Protists comprise protozoa and algae.
8. Archaea have structure similar to bacteria, but they are distinct from bacteria. Initially, Archaea were classified as bacteria and called archaebacteria but now this term is not used.
9. Viruses cause ailments like polio, chicken pox, cold, influenza (flu) and
most coughs.
10. Protozoa(protozoans) cause diseases like dysentery and malaria.
11. Bacteria cause typhoid and tuberculosis (TB).
Living place of micro-organisms
1. Microorganisms maybe both single- celled and multicellular.
2. Bacteria are single- celled organisms.
3. Fungi may be both single-celled and multicellular.
4. Protozoa are single- celled organisms.
5. Algae may be both unicellular and multicellular.
6. Viruses are acellular i. e. neither unicellular nor multicellular and nor prokaryotic.
7. Microorganisms live in all types of environments such as ice-cold climate, hot springs, deserts and marshy lands.
8. Microorganisms also live inside the bodies of animals and humans.
9. Some microorganisms depend on other organisms for their growth while others exist freely.
We and Microorganisms
1. Some microorganisms are beneficial for us in many ways.
2. Some other microorganisms are harmful for us and cause many dreadful diseases
Beneficial microorganisms
1. Curd, bread, cake and alcohol are prepared with the help of microorganisms.
2. Microorganisms help us in cleaning our environment. For example, bacteria breakdown organic wastes into harmless and usable substances.
3. Medicines are prepared using bacteria.
4. Bacteria fixing nitrogen increase fertility of the soil.
5. The bacterium called Lactobacillus promotes the formation of curd.
6. An important ingredient of rava (sooji ), idlis and bhaturas is curd which is formed by bacterium Lactobacillus.
7. Making of cheese and pickles involve bacteria.
8. Formation of rice idlis and dosa batter involves bacteria.
9. Yeast produces carbon dioxide during respiration.
10. Yeast is used for making breads, pastries and cakes in the baking industry.
Commercial use of Microorganisms
1. The large-scale production of alcohol, wine and acetic acid (vinegar) is done with the help of microorganisms.
2. Grains like barley, wheat, rice and crushed fruit juices contain natural sugars.
3. Yeast is grown on natural sugar and is used for commercial production of alcohol and wine.
4. Yeast converts sugar into alcohol.
5. The process of conversion of sugar into alcohol is known as fermentation.
6. Fermentation was discovered by Louis Pasteur in 1857.
Medicinal use of Microorganisms
1. The source of antibiotics is microorganisms.
2. Antibiotics are medicines that kill or stop the growth of the disease-causing microorganisms.
3. Antibiotics are produced from bacteria and fungi.
4. Some of the commonly known antibiotics made from bacteria and fungi are Streptomycin, tetracycline and erythromycin.
5. Antibiotics are used to control many plant diseases and microbial infection in animals.
6. Antibiotics are not useful for controlling diseases caused by viruses.
7. Antibiotics should not be taken on unnecessarily as these may kill beneficial bacteria present in the body.
8. Mould penicillin was discovered by Alexander Fleming in 1929.
9. Penicillin is an antibiotic.
10. Penicillins are obtained from Penicillium moulds, principally P. chrysogenum and P. rubens.
Vaccine
1. Our body produces antibodies when an invader or a disease-carrying microbe enters the body.
2. Our body remembers how to fight microbe entering the body again.
3. Dead or weakened microbes are introduced into a healthy body, the body produces suitable antibodies and kills the invading bacteria.
4. We are protected as the antibodies produced remain in the body and kill disease-causing microbes entering again.
5. Cholera, tuberculosis, smallpox and hepatitis can be prevented by vaccination.
6. The vaccine for smallpox was discovered by Edward Jenner in 1798.
7. Polio drops are actually a vaccine.
8. Vaccines are made on a large scale from microorganisms.
9. Vaccination is essential for both animals and humans for protection from several diseases.
Harmful Microorganisms
1. Disease -causing microorganisms are called pathogens.
2. Pathogens cause diseases in human beings, plants and animals.
3. Some microorganisms spoil food, clothing and leather.
4. Pathogens can enter our body through air, water and food.
5. Pathogens can be transmitted by direct contact with an infected person.
6. Pathogens can be carried by animals.
7. Microbial diseases that spread from an infected person to a healthy person are called communicable diseases. Mode of transmission of pathogens can be air, water, food physical contact.
8. Cholera, common cold, chicken pox and tuberculosis are examples of communicable diseases.
9. Housefly is a carrier of disease- causing microbes.
10. The female Anopheles mosquito is a carrier of the parasite of malaria (Plasmodium).
11. Female Aedes mosquito is a carrier of dengue virus.
12. Tuberculosis (TB) is caused by bacteria and its mode of transmission is air.
13. Measles is caused by virus and its mode of transmission is air
14. Chicken pox is caused by virus and its modes of transmission are air and contact.
15. Polio is caused by virus and its modes of transmission are air and water.
16. Cholera is caused by bacteria and its modes of transmission are water and food.
17. Typhoid is caused by bacteria and its mode of transmission is water.
18. Hepatitis A is caused by virus and its mode of transmission is water.
19. Malaria is caused by protozoa and its mode of transmission is mosquito.
20. Foot and mouth disease of cattle is caused by a virus.
21. Anthrax is a disease caused by a bacterium which is dangerous for humans and cattles.
22. Citrus canker is a plant disease; it is caused by bacteria and its mode of transmission is air.
23. Rust of wheat is a plant disease; it is caused by fungi and its modes of transmission are air and seeds.
24. Yellow vein mosaic of bhindi (Okra) is a plant disease, it is caused by virus and its mode of transmission is insect.
25. Microorganisms that grow on our food sometimes produce toxic substances that cause food poisoning.
Food Preservation
1. Salts and edible oils are called preservatives because they check the growth of microorganisms.
2. Sodium benzoate and sodium metabisulphite are common preservatives which are used in jams and squashes to check their spoilage.
3. Salt or acid preservatives are added to pickles to prevent the attack of microbes.
4. Common salt is used to preserve meat and fish. Common salt checks the growth of bacteria.
5. To preserve amla, raw mangoes and tamarind salting is used.
6. Sugar inhibits the growth of bacteria which spoil food by reducing the moisture content.
7. Pickles, vegetables, fruits, fish and meat are preserved by oil and vinegar as bacteria cannot live in such an environment.
8. Boiling and cooling kill many microorganisms and food is preserved.
9. Pasteurization was discovered by Louis Pasteur.
10. In the process of pasteurization, the milk is heated to about 70 °C for 15 to 30 seconds and then suddenly chilled and stored.
Nitrogen Fixation
1. Rhizobium is a nitrogen fixing bacterium.
2. Pulses plants such as beans and peas are leguminous plants.
3. Rhizobium lives in the root nodules of leguminous plants, and it has a symbiotic relationship.
4. Sometimes lighting fixes nitrogen.
Nitrogen cycle
1. There is 78% nitrogen gas in the atmosphere.
2. Nitrogen is a major component of chlorophyll which is essential for photosynthesis.
3. Nitrogen is an essential element of proteins, nucleic acids and vitamins.
4. Humans and animals cannot utilize atmospheric nitrogen directly.
5. Atmospheric nitrogen is fixed and converted into usable compounds by certain bacteria and
blue green algae present in the soil.
6. Plants absorb nitrogen compound from the soil through their roots.
7. Animals absorb nitrogen by consuming plants and other animals.
8. Humans absorb nitrogen by consuming plants and animals that contain nitrogen.
9. Nitrogenous wastes (dead plants and animals) are converted into nitrogenous compounds by bacteria and fungi present in the soil.
10. Nitrogenous compounds obtained from nitrogenous wastes are used by plants again.
11. Certain other bacteria convert some part of nitrogenous compounds to nitrogen gas which goes back into the atmosphere. Thus, the percentage of nitrogen in the atmosphere remains almost constant.
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