MICROORGANISMS : F AND FOE
MICROORGANISMS : FRIENDYou have seen several kinds ofplants and animals. However,there are other living organismsaround us which we normally cannotsee. These are called microorganismsor microbes. For example, you mighthave observed that during the rainyseason moist bread gets spoilt and itssurface gets covered with greyish whitepatches. Observe these patches througha magnifying glass. You will see tiny,black rounded structures. Do you knowwhat these structures are and where dothese come from?2.1 MicroorganismsActivity 2.1Collect some moist soil from thefield in a beaker and add water toit. After the soil particles havesettled down, observe a drop ofwater from the beaker under amicroscope. What do you see ?Activity 2.2Take a few drops of water from apond. Spread on a glass slide andobserve through a microscope.Do you find tiny organisms movingaround?ANDFOEThese observations show that waterand soil are full of tiny organisms,though not all of them fall into thecategoryofmicrobes.Thesemicroorganisms or microbes are sosmall in size that they cannot be seenwith 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 helpof a microscope. That is why these arecalled microorganisms or microbes.Microorganisms are classified intofour major groups. These groups arebacteria, fungi, protozoa and somealgae. Some of these commonmicroorganisms are shown inFigs. 2.1 - 2.4.Viruses are also microscopic. They,however, reproduce only inside the cellsof the host organism, which may be abacterium, plant or animal. Some of theviruses are shown in Fig. 2.5. Commonailments like cold, influenza (flu) andmost coughs are caused by viruses.Serious diseases like polio and chickenpox are also caused by viruses.Diseases like dysentery and malariaare caused by protozoa(protozoans)whereas typhoid and tuberculosis (TB)are bacterial diseases.You have learnt about some ofthese microorganisms in Classes VIand VII.2015-16 (11-11-2014)
Spiral bacteriaRod-shaped bacteriaFig. 2.1: BacteriaAmoebaChlamydomonasSpirogyraParameciumFig. 2.3 : ProtozoaFig. 2.2 : AlgaeBread mouldPenicilliumAspergillusFig. 2.4 : Fungi18SCIENCE2015-16 (11-11-2014)
harmful and cause diseases. Let usstudy about them in detail.Friendly MicroorganismsMicroorganisms are used for variouspurposes. They are used in thepreparation of curd, bread and cake.Microorganisms have been used forthe production of alcohol since ages.Fig. 2.5 : Viruses2.2 Where do MicroorganismsLive?Microorganisms may be single-celledlike bacteria, some algae and protozoa,or multicellular, such as algae and fungi.They can survive under all types ofenvironment, ranging from ice coldclimate to hot springs and deserts tomarshy lands. They are also foundinside the bodies of animals includinghumans. Some microorganisms grow onother organisms while others existfreely. Microorganisms like amoeba canlive alone, while fungi and bacteria maylive in colonies.2.3 Microorganisms and UsMicroorganisms play an important rolein our lives. Some of them are beneficialin many ways whereas some others areMICROORGANISMS : FRIEND AND FOEThey are also used in cleaning upof the environment. For example, theorganic wastes (vegetable peels, remainsof animals, faeces, etc.) are brokendown into harmless and usablesubstances by bacteria. Recall thatbacteria are also used in thepreparation of medicines. In agriculturethey are used to increase soil fertilityby fixing nitrogen.Making of Curd and BreadYou have learnt in Class VII that milk isturned into curd by bacteria.I saw that my motheradded a little curd to warmmilk to set curd for thenext day. I wonder why?Curd contains several microorganisms. Of these, the bacterium,Lactobacillus promotes the formationof curd. It multiplies in milk and convertsit into curd. Bacteria are also involvedin the making of cheese, pickles andmany other food items. An importantingredient of rava (sooji ) idlis andbhaturas is curd. Can you guess why?192015-16 (11-11-2014)
Activity 2.3Take ½ kg flour (atta or maida),add some sugar and mix withwarm water. Add a small amountof yeast powder and knead tomake a soft dough. What do youobserve after two hours? Did youfind the dough rising?Maida with yeast powderspoon of yeast powder to the sugarsolution. Keep it covered in a warmplace for 4-5 hours. Now smell thesolution. Can you get a smell?This is the smell of alcohol as sugarhas been converted into alcohol by yeast.This process of conversion of sugar intoalcohol is known as fermentation.Louis Pasteurdiscoveredfermentationin 1857.Medicinal Use of MicroorganismsRaised maidaFig. 2.6Yeast reproduces rapidly andproduces carbon dioxide duringrespiration. Bubbles of the gas fill thedough and increase its volume (Fig. 2.6).This is the basis of the use of yeast inthe baking industry for making breads,pastries and cakes.Commercial Use of MicroorganismsMicroorganisms are used for the large scaleproduction of alcohol, wine and acetic acid(vinegar). Yeast is used for commercialproduction of alcohol and wine. For thispurpose yeast is grown on natural sugarspresent in grains like barley, wheat, rice,crushed fruit juices, etc.Activity 2.4Take a 500 mL beaker filled upto¾ with water. Dissolve 2-3teaspoons of sugar in it. Add half a20Whenever you fall ill the doctor maygive you some antibiotic tablets,capsules or injections such as ofpenicillin. The source of thesemedicines is microorganisms. Thesemedicines kill or stop the growth of thedisease-causing microorganisms.Such medicines are called antibiotics.These days a number of antibiotics arebeing produced from bacteria andfungi. Streptomycin, tetracycline anderythromycin are some of theIn 1929, AlexanderFleming was workingon a culture of diseasecausingbacteria.Suddenly he found thespores of a little green mould in one ofhis culture plates. He observed thatthe presence of mould prevented thegrowth of bacteria. In fact, it also killedmany of these bacteria. From this themould penicillin was prepared.SCIENCE2015-16 (11-11-2014)
commonly known antibiotics which aremade from fungi and bacteria. Theantibiotics are manufactured bygrowing specific microorganisms andare used to cure a variety of diseases.Antibiotics are even mixed with thefeed of livestock and poultry to checkmicrobial infection in animals. They arealso used to control many plantdiseases.It is important to remember thatantibiotics should be taken only onthe advice of a qualified doctor. Alsoyou must complete the courseprescribed by the doctor. If you takeantibiotics when not needed or inwrong doses, it may make the drugless effective when you might needit in future. Also antibiotics takenunnecessarily may kill the beneficialbacteria in the body. Antibiotics,however, are not effective againstcold and flu as these are caused byviruses.VaccineWhy are children/infantsgiven vaccination?When a disease-carrying microbe entersour body, the body produces antibodiesto fight the invader. The body alsoremembers how to fight the microbe ifit enters again. So, if dead or weakenedmicrobes are introduced in a healthybody , the body fights and killsthem by producing suitable antibodies.The antibodies remain in the bodyand we are protected from theMICROORGANISMS : FRIEND AND FOEdisease-causing microbes. This is howa vaccine works. Several diseases,including cholera, tuberculosis,smallpox and hepatitis can be preventedby vaccination.Edward Jennerdiscovered thevaccine for smallpox in 1798.In your childhood, you must havebeen given injections to protect yourselfagainst several diseases. Can youprepare a list of these diseases? Youmay take help from your parents.It is essential to protect all childrenagainst these diseases. Necessaryvaccines are available in the nearbyhospitals. You might have seen theadvertisement on T.V. and newspapersregarding protection of children againstpolio under the Pulse Polio Programme.Polio drops given to children areactually a vaccine.A worldwide campaign againstsmallpox has finally led to its eradicationfrom most parts of the world.These days vaccines are made on alarge scale from microorganisms toprotect humans and other animals fromseveral diseases.Increasing Soil FertilitySome bacteria and blue green algae(Fig. 2.7) are able to fix nitrogen fromthe atmosphere to enrich soil withnitrogen and increase its fertility. Thesemicrobes are commonly calledbiological nitrogen fixers.212015-16 (11-11-2014)
Fig. 2.7 : The Nitrogen fixing blue green algaeCleaning the EnvironmentBoojho and Paheli had observed theschool gardener making manure. Alongwith their friends, they collected wastesof plants, vegetables and fruits fromnearby houses and gardens. They putthem in a pit meant for waste disposal.After some time, it decomposed and gotconverted to manure. Boojho andPaheli wanted to know how this hadhappened.Activity 2.5Take two pots and fill each pot halfwith soil. Mark them A and B. Putplant waste in pot A and things likepolythene bags, empty glass bottlesand broken plastic toys in pot B.Put the pots aside. Observe themafter 3-4 weeks.Do you find any difference in thecontents of the two pots? If so, what isthe difference? You will find that plantwaste in pot A, has been decomposed.How did this happen? The plant wastehas been converted into manure by theaction of microbes. The nutrients22released in the process can be used bythe plants again.Did you notice that in pot B, thepolythene bags, empty glasses, bottlesand broken toy parts did not undergoany such change? The microbes couldnot ‘act’ on them and convert them intomanure.You often see large amounts ofdead organic matter in the form ofdecaying plants and sometimes deadanimals on the ground. You findthat they disappear after some time.This is because the microorganismsdecompose dead organic waste of plantsand animals converting them intosimple substances. These substancesare again used by other plants andanimals. Thus, microorganisms canbe used to degrade the harmful andsmelly substances and thereby cleanup the environment.2.4 Harmful MicroorganismsMicroorganisms are harmful in manyways. Some of the microorganismscause diseases in human beings, plantsand animals. Such disease-causingSCIENCE2015-16 (11-11-2014)
microorganisms are called pathogens.Some microorganisms spoil food,clothing and leather. Let us study moreabout their harmful activities.Disease causing Microorganismsin HumansPathogens enter our body through theair we breathe, the water we drink orthe food we eat. They can also gettransmitted by direct contact with aninfected person or carried through ananimal. Microbial diseases that canspread from an infected person to ahealthy person through air, water, foodor physical contact are calledcommunicable diseases. Examples ofsuch diseases include cholera, commoncold, chicken pox and tuberculosis.When a person suffering fromcommon cold sneezes, fine droplets ofmoisture carrying thousands of virusesare spread in the air. The virus may enterthe body of a healthy person whilebreathing.Then how do youprevent the spread ofcommunicablediseases?We should keep ahandkerchief on thenose and mouth whilesneezing. It is better tokeep a distance frominfected persons.MICROORGANISMS : FRIEND AND FOEThere are some insects and animalswhich act as carriers of diseasecausing microbes. Housefly is one suchcarrier. The flies sit on the garbage andanimal excreta. Pathogens stick to theirbodies. When these flies sit on uncoveredfood they may transfer the pathogens.Whoever eats the contaminated food islikely to get sick. So, it is advisable toalways keep food covered. Avoidconsuming uncovered items of food.Another example of a carrier is thefemale Anopheles mosquito (Fig. 2.8),which carries the parasite of malaria.Female Aedes mosquito acts as carrierof dengue virus. How can we control thespread of malaria or dengue?Fig. 2.8 : Female Anopheles mosquitoWhy does the teacherkeep telling us notto let water collectanywhere in theneighbourhood?All mosquitoes breed in water. Hence,one should not let water collectanywhere, in coolers, tyres, flower pot,etc. By keeping the surroundings cleanand dry we can prevent mosquitoes frombreeding. Try to make a list of measureswhich help to avoid the spread ofmalaria.232015-16 (11-11-2014)
Table 2.1: Some Common Human Diseases caused by MicroorganismsHuman DiseaseCausativeMode ofMicroorganism Chicken riaWater/FoodTyphoidBacteriaWaterHepatitis AVirusWaterMalariaProtozoaMosquitoSome of the common diseasesaffecting humans, their mode oftransmission and few general methodsof prevention are shown in Table 2.1.Disease causing Microorganismsin AnimalsSeveral microorganisms not only causediseases in humans and plants, but alsoRobert Köch (1876)discovered the bacterium(Bacillus anthracis) whichcauses anthrax disease.24Preventive Measures(General)Keep the patient in completeisolation. Keep the personalbelongings of the patient awayfrom those of the others.Vaccination to be given atsuitable age.Maintain personal hygieneand good sanitary habits.Consume properly cooked foodand boiled drinking water.Vaccination.Drink boiled drinking water.Vaccination.Use mosquito net andrepellents. Spray insecticidesand control breeding ofmosquitoes by not allowingwater to collect in thesurroundings.in other animals. For example, anthraxis a dangerous human and cattledisease caused by a bacterium. Footand mouth disease of cattle is causedby a virus.Disease causing Microorganismsin PlantsSeveralmicroorganismscausediseases in plants like wheat, rice, potato,sugarcane, orange, apple and others.The diseases reduce the yield of crops.See Table 2.2 for some such plantdiseases. They can be controlled by theSCIENCE2015-16 (11-11-2014)
Table 2.2: Some Common Plant Diseases caused by MicroorganismsPlantDiseasesMicroorganismMode ofTransmissionCitruscankerBacteriaAirRust ofwheatFungiAir,seedsYellow veinmosaic ofbhindi (Okra)VirusInsectuse of certain chemicals which kill themicrobes.Food PoisoningBoojho was invited by his friend to aparty and he ate a variety of foodstuff.On reaching home he started vomitingand had to be taken to a hospital. Thedoctor said that this condition could bedue to food poisoning.Paheli wonders howfood can become a‘poison’.Food poisoning could be due to theconsumption of food spoilt by somemicroorganisms. Microorganismsthat grow on our food sometimesproduce toxic substances. TheseMICROORGANISMS : FRIEND AND FOEFiguresmake the food poisonous causingserious illness and even death. So, itis very important that we preservefood to prevent it from being spoilt.2.5 Food PreservationIn Chapter 1, we have learnt about themethods used to preserve and store foodgrains. How do we preserve cooked foodat home? You know that bread leftunused under moist conditions isattacked by fungus. Microorganismsspoil our food. Spoiled food emits badsmell and has a bad taste and colourchange. Is spoiling of food a chemicalreaction?Paheli bought some mangoes but shecould not eat them for a few days. Latershe found that they were spoilt androtten. But she knows that the mangopickle her grandmother makes does notspoil for a long time. She is confused.252015-16 (11-11-2014)
Let us study the common methodsof preserving food in our homes. Wehave to save it from the attack ofmicroorganisms.Similarly, we keep our food in therefrigerator. Low temperature inhibitsthe growth of microbes.Chemical MethodSalts and edible oils are the commonchemicals generally used to check thegrowth of microorganisms. Thereforethey are called preservatives. We addsalt or acid preservatives to pickles toprevent the attack of microbes. Sodiumbenzoate and sodium metabisulphite arecommon preservatives. These are alsoused in the jams and squashes to checktheir spoilage.Preservation by Common SaltCommon salt has been used to preservemeat and fish for ages. Meat and fishare covered with dry salt to checkthe growth of bacteria. Salting is alsoused to preserve amla, raw mangoes,tamarind, etc.Preservation by SugarJams, jellies and squashes are preservedby sugar. Sugar reduces the moisturecontent which inhibits the growth ofbacteria which spoil food.Preservation by Oil and VinegarUse of oil and vinegar prevents spoilageof pickles because bacteria cannot livein such an environment. Vegetables,fruits, fish and meat are often preservedby this method.Heat and Cold TreatmentsYou must have observed your motherboiling milk before it is stored or used.Boiling kills many microorganisms.26Why does the milk thatcomes in packets not spoil?My mother told me that themilk is ‘pasteurised’. Whatis pasteurisation?Pasteurised milk can be consumedwithout boiling as it is free from harmfulmicrobes. The milk is heated to about700 C for 15 to 30 seconds and thensuddenly chilled and stored. By doingso, it prevents the growth of microbes.This process was discovered by LouisPasteur. It is called pasteurisation.Storage and PackingThese days dry fruits and evenvegetables are sold in sealed air tightpackets to prevent the attack ofmicrobes.2.6 Nitrogen FixationYou have learnt about the bacteriumRhizobium in Classes VI and VII. It isinvolved in the fixation of nitrogen inleguminous plants (pulses). Recall thatRhizobium lives in the root nodules ofleguminous plants (Fig. 2.9), such asbeans and peas, with which it has asymbiotic relationship. Sometimesnitrogen gets fixed through the actionof lightning. But you know that theamount of nitrogen in the atmosphereremains constant. You may wonderhow ? Let us understand this in the nextsection.SCIENCE2015-16 (11-11-2014)
Fig. 2.9 : Roots of a leguminous plant with rootnodules2.7 Nitrogen cycleOur atmosphere has 78% nitrogen gas.Nitrogen is one of the essentialconstituents of all living organisms aspart of proteins, chlorophyll, nucleicacids and vitamins. The atmosphericnitrogen cannot be taken directly byplants and animals. Certain bacteria andblue green algae present in the soil fixnitrogen from the atmosphere andconvert it into compounds of nitrogen.Once nitrogen is converted into theseusable compounds, it can be utilised byplants from the soil through their rootsystem. Nitrogen is then used for thesynthesis of plant proteins and othercompounds. Animals feeding on plantsget these proteins and other nitrogencompounds (Fig. 2.10).When plants and animals die,bacteria and fungi present in the soilconvert the nitrogenous wastes intonitrogenous compounds to be used byplants again. Certain other bacteriaconvert some part of them to nitrogengas which goes back into theatmosphere. As a result, the percentageof nitrogen in the atmosphere remainsmore or less constant.Fig. 2.10 : Nitrogen cycleMICROORGANISMS : FRIEND AND FOE272015-16 (11-11-2014)
KEYWORDSALGAEWHAT YOU HAVE LEARNTÜMicroorganisms are too small and are notvisible to the unaided eye.ANTIBIOTICSÜThey can live in all kinds of environment,ANTIBODIESranging from ice cold climate to hot springsBACTERIAand deserts to marshy lands.ÜCARRIERCOMMUNICABLEDISEASESin the bodies of plants and animals.ÜThey may be unicellular or multicellular.ÜMicroorganisms include bacteria, fungi,protozoa and some algae. Viruses, thoughdifferent from the above mentioned livingFERMENTATIONFUNGIorganisms, are considered microbes.ÜLACTOBACILLUSViruses are quite different from othermicroorganisms. They reproduce only insidethe host organism: bacterium, plant or ani-MICROORGANISMNITROGEN CYCLEMicroorganisms are found in air, water andmal cell.ÜSome microorganisms are useful forcommercial production of medicines andNITROGEN FIXATIONPASTEURISATIONalcohol.ÜSome microorganisms decompose the organicwaste and dead plants and animals into ces and clean up the environment.Üdysentery and malaria.ÜSome of the microorganisms grow on our foodand cause food poisoning.ÜVACCINESome microorganisms reside in the rootnodules of leguminous plants. They can fixnitrogen from air into soil and increase theVIRUSYEASTProtozoans cause serious diseases likesoil fertility.ÜSome bacteria and blue green algae presentin the soil fix nitrogen from the atmosphereand convert into nitrogenous compounds.ÜCertain bacteria convert compounds ofnitrogen present in the soil into nitrogen gaswhich is released to the atmosphere.28SCIENCE2015-16 (11-11-2014)
Exercises1.2.Fill in the blanks.(a)Microorganisms can be seen with the help of a .(b)Blue green algae fix directly from air to enhance fertilityof soil.(c)Alcohol is produced with the help of .(d)Cholera is caused by .Tick the correct answer.(a)Yeast is used in the production of(i) sugar(b)(ii) alcohol(iii) hydrochloric acidThe following is an antibiotic(i) Sodium bicarbonate(c)(ii) Streptomycin(ii) houseflycockroachbutterfly(iii) dragonfly(iv) spiderThe bread or idli dough rises because of(i) heat(f)(iv) YeastThe most common carrier of communicable diseases is(i) ant(e)(iii) AlcoholCarrier of malaria-causing protozoan is(i) female Anopheles mosquito (ii)(iii) housefly(iv)(d)(iv) oxygen(ii) grinding(iii) growth of yeast cells (iv) kneadingThe process of conversion of sugar into alcohol is called(i) nitrogen fixation (ii) moulding (iii) fermentation (iv) infection3.Match the organisms in Column A with their action inColumn B.AB(i) Bacteria(a) Fixing nitrogen(ii) Rhizobium(b) Setting of curd(iii) Lactobacillus(c) Baking of bread(iv) Yeast(d) Causing malaria(v) A protozoan(e) Causing cholera(vi) A virus(f) Causing AIDS(g) Producing antibodies4.Can microorganisms be seen with the naked eye? If not, how can they beseen?MICROORGANISMS : FRIEND AND FOE292015-16 (11-11-2014)
EXERCISES5.What are the major groups of microorganisms?6.Name the microorganisms which can fix atmospheric nitrogen in the soil.7.Write 10 lines on the usefulness of microorganisms in our lives.8.Write a short paragraph on the harms caused by microorganisms.9.What are antibiotics? What precautions must be taken while takingantibiotics?Extended Learning — Activities and Projects1.Pull out a gram or bean plant from the field. Observe its roots. Youwill find round structures called root nodules on the roots. Draw adiagram of the root and show the root nodules.2.Collect the labels from the bottles of jams and jellies. Write downthe list of contents printed on the labels.3.Visit a doctor. Find out why antibiotics should not be overused.Prepare a short report.4.Project : Requirements – 2 test tubes, marker pen, sugar, yeastpowder, 2 balloons and lime water.Take two test tubes and mark them A and B. Clamp these tubes ina stand and fill them with water leaving some space at the top. Puttwo spoonfuls of sugar in eachof the test tubes. Add a spoonfulof yeast in test tube B. Inflate thetwo balloons incompletely. Nowtie the balloons on the mouthsof each test tube. Keep them ina warm place, away fromsunlight. Watch the setup everyBAday for next 3-4 days. Recordyour observations and think ofan explanation.Now take another test tubefilled 1/4 with lime water.Remove the balloon from testtube B in such a manner thatgas inside the balloon does notescape. Fit the balloon on thetest tube and shake well.Observe and explain.30SCIENCE2015-16 (11-11-2014)
Did You Know?Bacteria have lived on the earth for much longer than human beings.They are such hardy organisms that they can live under extreme conditions.They have been found living in boiling mudpots and extremly cold icy waters.They have been found in lakes of caustic soda and in pools of concentratedsulphuric acid. They can survive at depths of several kilometres. Theyprobably can survive in space, too. A kind of bacterium was recoveredfrom a camera which stood on the moon for two years.There is probably noenvironment in which bacteria cannot survive.MICROORGANISMS : FRIEND AND FOE312015-16 (11-11-2014)
MICROORGANISMS: FRIEND AND FOE 19 2.2Where do Microorganisms Live? Microorganisms may be single-celled like bacteria, some algae and protozoa, or multicellular , such as algae and fungi.
Asepsis Asepsis is the freedom from disease-causing microorganisms and its spores Medical asepsis: all practices intended to confine a specific microorganism to a specific area, limiting the number of microorganisms, growth and transmission. - Clean objects: absence of almost all microorganisms.-Dirty (Soiled, Contaminated) : have microorganisms,
of trillions of different cells). Different species of microorganisms vary in size, shape, appearance, and way of surviving. The largest microorganisms are most fungi and many species of protozoa. Viruses are . by far the smallest of all microorganisms. If a virus was the size of a baseball, an average bacterium would be the size of a pitcher’s
In the previous lesson, you learned that there are microorganisms living on and in the human body. You also compared the sizes of microorganisms to other tiny things. In this lesson, you will think very carefully about the small sizes of these microorganisms. Unit Question
Tests Test Canvas : Brock Biology of Microorganisms 14th Edition Test Canvas: Brock Biology of Microorganisms 14th Edition Description Instructions Total Questions 147 Total Points 1,155 Select: All None Select by Type: - Question Type - Delete Points UpdateUpdate Hide Question Details 1. Multiple Choice: A Pasteur flask has a(n)
a hands-on approach to observing microorganisms from soil samples or pond water. This learning unit was . opportunity to observe microorganisms under a microscope. Fig. 1. Student responses based on their preconceptions about microorganisms. . with seeing through the eyepiece, focusing
OBSERVING MICROORGANISMS THROUGH A MICROSCOPE By: . Microorganisms are too small to be seen by nacked eye, SO: Microscope Must be used to see those microorganisms . There are several types of microscopes but which used in lab is called : Microscope
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current trends and techniques in the fi eld of analytical chemistry. Written for undergraduate and postgraduate students of chemistry, this revised and updated edition treats each concept and principle systematically to make the subject comprehensible to beginners as well as advanced learners. FEATURES Updated nomenclature Addition of tests for metals based on fl ame atomic emission .
