e-Content ClassVIII
Class 8th PPT on
CHAPTER 02
MICROORGANISMS : FRIEND AND FOE
INTRODUCTION
The microorganisms or microbes are so small in size that they cannot be seen with the unaided eye. 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
microorganisms
Microorganisms
are called or microbes. are classified
into four major groups.
groups are bacteria,
These fungi,
protozoa and some algae.
ACTIVITY - 1
Collect some moist soil from the field in a beaker and add water to it. After soil particles have settled, observe a drop of water from the beaker under a microscope. What do you see ?
ACTIVITY - 2
Take a few drops of water from a pond. Spread on a glass slide and observe through a microscope.
Do you find tiny organisms moving around?
OBSERVATIONS
Those small things you observe through the microscope are called a microorganisms. Some of the pictorial example are given in the next section.
THESE ARE TYPES OF BACTERIA.
THESE ARE TYPES OF ALGAE.
THESE ARE TYPES OF PARAMECIUM.
THESE ARE TYPES OF FUNGI.
THESE ARE TYPES OF VIRUS.
WHERE DO MICROORGANISMS LIVE?
Microorganisms may be single-celled like bacteria, some algae and protozoa, or multicellular, such as algae and fungi. They can survive under all types of environment, ranging from ice cold climate to hot springs and deserts to marshy lands. They are also found inside the bodies of animals including humans. Some microorganisms grow on other organisms while others exist freely. Microorganisms like amoeba can live alone, while fungi and bacteria may live in colonies.
FRIENDLY MICROORGANISMS
Microorganisms are used for various purposes. They are used in the preparation of curd, bread and cake.
They are also used in cleaning up of the environment. For example, the organic wastes (vegetable peels, remains of animals, faeces, etc.) are broken down into harmless and usable substances by bacteria. Recall that bacteria are also used in the preparation of medicines. In agriculture they are used to increase soil fertility by fixing nitrogen.
MAKING OF CURD
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,
many other food
important ingredient of
pickles and items. An rava
(sooji), idlis and bhaturas is curd.
MAKING OF BREAD
Yeast reproduces rapidly and produces carbon dioxide during respiration. Bubbles of the gas fill the dough and increase its volume. This is the basis of the use of yeast in the baking industry for making breads, pastries and cakes.
ACTIVITY - 3
Take ½ kg flour (Atta or Maida), add some sugar and mix with warm water. Add a small amount of yeast powder and knead to make a soft dough. What do you observe after two hours? Did you find the dough rising?
OBSERVATION
Yeast reproduces rapidly and produces carbon dioxide during respiration. Bubbles of the gas fill the dough and increase its volume . This is the basis of the use of yeast in the baking industry for making breads, pastries and cakes.
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. The process of conversion of sugar into alcohol is known as fermentation.
ACTIVITY - 4
Take a 500 ml beaker filled up to
¾ with water. Dissolve 2-3 teaspoons of sugar in it. Add half a spoon of yeast powder to the sugar solution. Keep it covered in a warm place for 4-5 hours. Now smell the solution. Could you get a smell ?
OBSERVATION
This is the smell of alcohol as sugar has been converted into alcohol by yeast. This process of conversion of sugar into alcohol is known as FERMENTATION.
MEDICINAL USE OF MICROORGANISMS
Whenever you fall ill the doctor may give you 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.
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MEDICINAL USE OF MICROORGANISMS
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.
ALEXANDER FLEMING AND PENICILLIN.
In 1929, Alexander Fleming was working on a culture of disease-causing bacteria. Suddenly he found the spores of a little green mould in one of his culture plates. He observed that the presence of mould prevented the growth of bacteria. In fact, it also killed many of these bacteria. From this the mould penicillin was prepared.
EDWARD JENNER AND SMALL-POX VACCINE
It is important to remember that antibiotics should be taken only on the advice of a qualified doctor. Also you must finish the course prescribed by the doctor. If you take antibiotics when not needed or in wrong doses, it may make the drug
less effective when you might antibiotics taken unnecessarily
need it in future. Also may kill the beneficial
bacteria in the body. Antibiotics, however, are not effective against cold and flu as these are caused by viruses.
WHY ARE CHILDREN AND INFANTS GIVEN VACCINATION?
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
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WHY ARE CHILDREN AND INFANTS GIVEN VACCINATION?
In your childhood, you must have been given injections to protect yourself against several diseases. Can you prepare a list of these diseases? You may take help from your parents. It is essential
to protect Necessary
all children against these diseases. vaccines are available in the nearby
hospitals. You might have seen the advertisement on T.V. and newspapers regarding protection of children against polio under Pulse Polio Program.
WHY ARE CHILDREN AND INFANTS GIVEN VACCINATION?
Polio drops given to children are actually a vaccine. A worldwide campaign against smallpox has finally led to its eradication from most parts of the world. These days vaccines are made on a large scale from microorganisms to protect humans and other animals from several diseases.
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.
THESE ARE THE NITROGEN FIXING BLUE GREEN ALGAE.
ACTIVITY - 5
Take two pots and fill each pot half with soil. Mark them A and B. Put plant waste in pot A and things like polythene bags, empty glass bottles and broken plastic toys in pot B. Put the pots aside. Observe them after 3-4 weeks. Do you find any difference in the contents of the two pots? If so, what is the difference?
OBSERVATION
You will find that plant waste in pot A, has been decomposed. How could this happen? The plant waste has been converted into manure by the action of microbes. The nutrients released in the process could be used by the plants again. Did you notice that in pot B, the polythene bags, empty glasses, bottles and broken toy parts did not undergo any such change? The microbes could not ‘act’ on them and convert them into manure.
HARMFUL MICROORGANISMS
Microorganisms are harmful in many ways. Some of the
microorganisms
diseases in plants and
human animals.
cause beings, Such
disease-causing microorganisms pathogens. microorganisms
spoil
are called Some 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 communicable diseases.
contact Examples
are called of such
diseases include cholera, common cold, chicken pox and tuberculosis.
DISEASE- CAUSING MICROORGANISMS IN HUMANS
suffering
from
common
cold
When a person sneezes,
fine droplets of moisture carrying
thousands of viruses are spread in the air. The virus may enter the body of a healthy person while breathing.
SMALL INSECTS OF DISEASE
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. So, it is
advisable to always keep food covered. Avoid consuming
uncovered
items of food.
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.
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SMALL INSECTS OF DISEASE
All mosquitoes breed in water. Hence, one should not let water collect anywhere, in coolers, tyres, flower pot etc. By keeping the surroundings clean and dry we can prevent mosquitoes from breeding. Try to make a list of measures which help to avoid the spread of malaria.
FEMALE
ANOPHELES
MOSQUITO
SOME COMMON HUMAN DISEASES CAUSED BY MICROORGANISMS
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
SOME COMMON PLANT DISEASES CAUSED BY MICROORGANISMS
CHEMICAL METHOD
Salts and edible oils are the common chemicals
generally used microorganisms.
to check Therefore
the growth of they are called
preservatives. We add salt or acid preservatives to pickles to prevent the attack of microbes. Sodium benzoate and sodium meta bisulphite 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 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.
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.
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.
LOUIS PASTEUR AND PASTEURIZATION
Louis Pasteur was a French biologist, microbiologist and chemist renowned for his discoveries of the principles of
microbial
and
vaccination, fermentation pasteurization.
He is
remembered for his remarkable breakthroughs in the causes and prevention of diseases, and his discoveries have saved many lives ever since.
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LOUIS PASTEUR AND PASTEURIZATION
bacteriology, together Ferdinand Cohn and
with Robert
Koch, and is popularly known as the
“FATHER OF MICROBIOLOGY".
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LOUIS PASTEUR AND PASTEURIZATION
Pasteurized milk can be consumed without boiling as it is free from harmful microbes. The milk is heated to about 700 C for 15 to 30 seconds and then suddenly chilled and stored. By doing so, it prevents the growth of microbes. This process was also 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
You have learnt about the bacterium Rhizobium in Classes VI and VII. It is involved in the fixation of nitrogen in leguminous plants (pulses). Recall that Rhizobium lives in the root nodules of leguminous plants , such as beans and peas, with which it has a symbiotic relationship. Sometimes nitrogen gets fixed through the action of lightning. But you know that the amount of nitrogen in the atmosphere remains constant. You may wonder how? Let us understand this in the next section.
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. 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 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.
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NITROGEN CYCLE
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.
Diagram continued in next page…
NITROGEN CYCLE
KEYWORDS
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