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CLASS VIIICHAPTER 02

MICROORGANISMS : FRIEND AND FOE

INTRODUCTION

The microorganisms or microbesare so small in size that theycannot be seen with the unaidedeye. Some of these, such as thefungus that grows on bread, canbe seen with a magnifying glass.Others cannot be seen withoutthe help of a microscope. That iswhy thesemicroorganismsMicroorganisms

are called ormicrobes. areclassified

into four major groups.groups are bacteria,

These fungi,

protozoa and some algae.

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.

Microorganisms may be single-celled like bacteria,some algae and protozoa, or multicellular, such asalgae and fungi. They can survive under all types ofenvironment, ranging from ice cold climate to hotsprings and deserts to marshy lands. They are alsofound inside the bodies of animals including humans.Some microorganisms grow on other organismswhile others exist freely. Microorganisms likeamoeba can live alone, while fungi and bacteria maylive in colonies.

WHERE DO MICROORGANISMS LIVE?

FRIENDLY MICROORGANISMS

Microorganisms are used for various purposes.They are used in the preparation of curd, bread andcake.They are also used in cleaning up of theenvironment. For example, the organic wastes(vegetable peels, remains of animals, faeces, etc.)are broken down into harmless and usablesubstances by bacteria. Recall that bacteria arealso used in the preparation of medicines. Inagriculture they are used to increase soil fertility byfixing nitrogen.

MAKING OF CURD

Curd contains severalmicroorganisms. Of these, thebacterium Lactobacillus promotesthe formation of curd. It multipliesin milk and converts it into curd.Bacteria are also involved in themaking of cheese,many other foodimportant ingredient of

pickles and items. An

rava(sooji), idlis and bhaturas is curd.

Yeast reproduces rapidlyand produces carbon dioxideduring respiration. Bubblesof the gas fill the dough andincrease its volume. This isthe basis of the use of yeastin the baking industry formaking breads, pastries andcakes.

MAKING OF BREAD

COMMERCIAL USE OF MICROORGANISMS

Microorganisms are used for the large scaleproduction of alcohol, wine and acetic acid(vinegar). Yeast is used for commercial productionof alcohol and wine. For this purpose yeast isgrown on natural sugars present in grains likebarley, wheat, rice and crushed fruit juices, etc.The process of conversion of sugar into alcohol isknown as fermentation.

ACTIVITY

Take a 500 ml beaker filled up to¾ with water. Dissolve 2-3teaspoons of sugar in it. Add halfa spoon of yeast powder to thesugar solution. Keep it coveredin a warm place for 4-5 hours.Now smell the solution. Couldyou get a smell ?

OBSERVATION

This is the smell of alcohol as sugarhas been converted into alcohol byyeast. This process of conversion ofsugar into alcohol is known asFERMENTATION.

MEDICINAL USE OF MICROORGANISMS

Whenever you fall ill the doctor may give you someantibiotic tablets, capsules or injections such as ofpenicillin. The source of these medicines ismicroorganisms. These medicines kill or stop thegrowth of the disease-causing microorganisms.Such medicines are called antibiotics. These daysa number of antibiotics are being produced frombacteria and fungi. Streptomycin, tetracycline anderythromycin are some of the commonly knownantibiotics which are made from fungi and bacteria.

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MEDICINAL USE OF MICROORGANISMS

The antibiotics are manufactured by growingspecific microorganisms and are used to cure avariety of diseases. Antibiotics are even mixedwith the feed of livestock and poultry to checkmicrobial infection in animals. They are alsoused to control many plant diseases.

In 1929, Alexander Fleming was working on aculture of disease-causing bacteria. Suddenly hefound the spores of a little green mould in one of hisculture plates. He observed that the presence ofmould prevented the growth of bacteria. In fact, italso killed many of these bacteria. From this themould penicillin was prepared.

ALEXANDER FLEMING AND PENICILLIN.

EDWARD JENNER AND SMALL-POX VACCINE

It is important to remember that antibiotics should be takenonly on the advice of a qualified doctor. Also you must finishthe course prescribed by the doctor. If you take antibioticswhen not needed or in wrong doses, it may make the drugless 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.

Some bacteria and blue green algae are able to fixnitrogen from the atmosphere to enrich soil withnitrogen and increase its fertility. These microbesare commonly called biological nitrogen fixers.

INCREASING SOIL FERTILITY

THESE ARE THE NITROGEN FIXING BLUE GREEN ALGAE.

Microorganisms are harmful in many ways. Some of themicroorganismsdiseases in plants and

human animals.

cause beings,

Suchdisease-causing microorganisms pathogens. microorganisms spoil

are calledSomefood,

clothing and leather.

HARMFUL MICROORGANISMS

Pathogens enter our body through the air webreathe, the water we drink or the food we eat.They can also get transmitted by direct contactwith an infected person or carried through ananimal. Microbial diseases that can spread froman 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 coldWhen a person sneezes, fine droplets of moisture carryingthousands of viruses are spread in the air. Thevirus may enter the body of a healthy person whilebreathing.

DISEASE- CAUSING MICROORGANISMS IN HUMANS

There are some insects and animals which act ascarriers of disease-causing microbes. Housefly isone such carrier. The flies sit on the garbage andanimal excreta. Pathogens stick to their bodies.When these flies sit on uncovered food they maytransfer the pathogens. Whoever eats thecontaminated food is likely to get sick. So, it isadvisable to always keep food covered. Avoid consuming uncovered items of food. Anotherexample of a carrier is the female Anophelesmosquito, which carries the parasite of malaria.Female Aedes mosquito acts as carrier of denguevirus.

SMALL INSECTS OF DISEASE

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All mosquitoes breed in water. Hence, one shouldnot let water collect anywhere, in coolers, tyres,flower pot etc. By keeping the surroundings cleanand dry we can prevent mosquitoes from breeding.Try to make a list of measures which help to avoidthe spread of malaria.

FEMALE ANOPHELES MOSQUITO

SMALL INSECTS OF DISEASE

SOME COMMON HUMAN DISEASES CAUSED BY MICROORGANISMS

SOME COMMON PLANT DISEASES CAUSED BY MICROORGANISMS

bacterial contamination, aprocess now calledpasteurization. He is regarded asone of the three main founders ofbacteriology, together Ferdinand Cohn and

with Robert

LOUIS PASTEUR AND PASTEURIZATION

Koch, and is popularly known as the

“FATHER OF MICROBIOLOGY".

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Pasteurized milk can be consumed without boiling as itis free from harmful microbes. The milk is heated toabout 700 C for 15 to 30 seconds and then suddenlychilled and stored. By doing so, it prevents the growthof microbes. This process was also discovered byLouis Pasteur. It is called pasteurization.

STORAGE AND PACKING

These days dry fruits and even vegetables are soldin sealed air tight packets to prevent the attack ofmicrobes.

LOUIS PASTEUR AND PASTEURIZATION

NITROGEN CYCLE