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MICROORGANISMS : FRIEND AND FOE Y ou have seen several kinds of These observations show that water plants and animals. However, and soil are full of tiny organisms, there are other living organisms though not all of them fall into the around us...

MICROORGANISMS : FRIEND AND FOE Y ou have seen several kinds of These observations show that water plants and animals. However, and soil are full of tiny organisms, there are other living organisms though not all of them fall into the around us which we normally cannot category of microbes. These see. These are called microorganisms microorganisms or microbes are so small in size that they cannot be seen or microbes. For example, you might with the unaided eye. Some of these, have observed that during the rainy such as the fungus that grows on bread, season moist bread gets spoilt and its can be seen with a magnifying glass. surface gets covered with greyish white Others cannot be seen without the help patches. Observe these patches through of a microscope. That is why these are a magnifying glass. You will see tiny, called microorganisms or microbes. black rounded structures. Do you know Microorganisms are classified into what these structures are and where do four major groups. These groups are these come from? bacteria, fungi, protozoa and some a l g a e. Some of these common 2.1 Microorganisms microorganisms are shown in Figs. 2.1 - 2.4. Activity 2.1 Viruses are also microscopic but are Collect some moist soil from the different from other microorganisms. field in a beaker and add water to They, however, reproduce only inside the it. After the soil particles have cells of the host organism, which may be a bacterium, plant or animal. Some of the settled down, observe a drop of viruses are shown in Fig. 2.5. Common water from the beaker under a ailments like cold, influenza (flu) and microscope. What do you see ? most coughs are caused by viruses. Serious diseases like polio and chicken Activity 2.2 pox are also caused by viruses. Diseases like dysentery and malaria Take a few drops of water from a are caused by protozoa(protozoans) pond. Spread on a glass slide and whereas typhoid and tuberculosis (TB) observe through a microscope. are bacterial diseases. You have lear nt about some of Do you find tiny organisms moving these microorganisms in Classes VI around? and VII. 2024-25  Fig. 2.1: Bacteria Amoeba Chlamydomonas Spirogyra Paramecium Fig. 2.2 : Algae Fig. 2.3 : Protozoa Bread mould Penicillium Aspergillus Fig. 2.4 : Fungi 18 SCIENCE 2024-25  Friendly Microorganisms Microorganisms are used for various purposes. They are used in the preparation of curd, bread and cake. Microorganisms have been used for the production of alcohol since ages. 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. Fig. 2.5 : Viruses Making of Curd and Bread You have learnt in Class VII that milk is 2.2 Where do Microorganisms turned into curd by bacteria. Live? Microorganisms may be single-celled like bacteria, some algae and protozoa, I saw that my mother or multicellular, such as many algae and added a little curd to warm fungi. They live in all types of milk to set curd for the environment, ranging from ice cold next day. I wonder why? climate to hot springs; and deserts to marshy lands. They are also found Curd contains several micro- inside the bodies of animals including organisms. Of these, the bacterium, humans. Some microorganisms Lactobacillus promotes the formation grow on other organisms while others of curd. It multiplies in milk and exist freely. converts it into curd. Bacteria are also involved in the making of cheese, 2.3 Microorganisms and Us pickles and many other food items. An Microorganisms play an important role important ingredient of rava (sooji ) in our lives. Some of them are beneficial idlis and bhaturas is curd. Can you in many ways whereas some others are guess why? Bacteria and yeast are also harmful and cause diseases. Let us helpful for fermentation of rice idlis study about them in detail. and dosa batter. MICROORGANISMS : FRIEND AND FOE 19 2024-25 Activity 2.3 spoon of yeast powder to the sugar Take ½ kg flour (atta or maida), solution. Keep it covered in a warm add some sugar and mix with place for 4-5 hours. Now smell the warm water. Add a small amount solution. Can you get a smell? of yeast powder and knead to This is the smell of alcohol as sugar make a soft dough. What do you has been converted into alcohol by yeast. observe after two hours? Did you This process of conversion of sugar into find the dough rising? alcohol is known as fermentation. Louis Pasteur discovered Maida with yeast powder fermentation in 1857. Medicinal Use of Microorganisms Raised maida Whenever you fall ill the doctor may Fig. 2.6 give you some antibiotic tablets, Yeast r eproduces rapidly and capsules or injections such as of produces carbon dioxide during penicillin. The source of these respiration. Bubbles of the gas fill the medicines is microorganisms. These dough and increase its volume (Fig. 2.6). medicines kill or stop the growth of the This is the basis of the use of yeast in disease-causing microorganisms. Such the baking industry for making breads, medicines are called antibiotics. These pastries and cakes. days a number of antibiotics are being produced from bacteria and fungi. Commercial Use of Microorganisms Streptomycin, tetracycline and Microorganisms are used for the large scale erythromycin are some of the production of alcohol, wine and acetic acid (vinegar). Yeast is used for commercial production of alcohol and wine. For this In 1929, Alexander Fleming was working purpose yeast is grown on natural sugars on a culture of disease- present in grains like barley, wheat, rice, causing bacteria. crushed fruit juices, etc. Suddenly he found the spores of a little green mould in one of Activity 2.4 his culture plates. He observed that the presence of mould prevented the Take a 500 mL beaker filled upto growth of bacteria. In fact, it also killed ¾ with water. Dissolve 2-3 many of these bacteria. From this the teaspoons of sugar in it. Add half a mould penicillin was prepared. 20 SCIENCE 2024-25 commonly known antibiotics which are from the disease-causing microbes for made from fungi and bacteria. The ever. This is how a vaccine works. antibiotics are manufactured by Several diseases, including cholera, growing specific microorganisms and tuberculosis, smallpox and hepatitis can are used to cure a variety of diseases. be prevented by vaccination. Antibiotics are even mixed with the feed of livestock and poultry to check microbial infection in animals. They are Edward Jenner also used to control many plant discovered the vaccine for small- diseases. pox in 1798. It is important to remember that antibiotics should be taken only on the advice of a qualified doctor. Also In your childhood, you must have you must complete the course been given injections to protect prescribed by the doctor. If you take yourself against several diseases. antibiotics when not needed or in Can you prepare a list of these wrong doses, it may make the drug diseases? You may take help from less effective when you might need your parents. it in future. Also antibiotics taken unnecessarily may kill the beneficial It is essential to protect all children bacteria in the body. Antibiotics, against these diseases. Necessary however, are not effective against vaccines are available in the nearby cold and flu as these are caused by hospitals. You might have seen the viruses. advertisement on TV and newspapers regarding protection of children against Vaccine polio under the Pulse Polio Programme. Polio drops given to children are actually a vaccine. A worldwide campaign against Why are children/infants smallpox has finally led to its eradication given vaccination? from most parts of the world. These days vaccines are made on a When a disease-carrying microbe enters large scale from microorganisms to our body, the body produces antibodies protect humans and other animals from to fight the invader. The body also several diseases. remembers how to fight the microbe if it enters again. If dead or weakened Increasing Soil Fertility microbes are introduced into a healthy Some bacteria (Fig. 2.7) are able to fix body, the body fights and kills nitrogen from the atmosphere to enrich the invading bacteria by producing soil with nitrogen and increase its suitable antibodies. The antibodies fertility. These microbes are commonly remain in the body and we are protected called biological nitrogen fixers. MICROORGANISMS : FRIEND AND FOE 21 2024-25  Fig. 2.7 : The Nitrogen fixing cyanobacteria (blue green algae) Cleaning the Environment released in the process can be used by Boojho and Paheli had observed the the plants again. school gardener making manure. Along Did you notice that in pot B, the with their friends, they collected wastes polythene bags, empty glasses, bottles of plants, vegetables and fruits from and broken toy parts did not undergo nearby houses and gardens. They put any such change? The microbes could them in a pit meant for waste disposal. not ‘act’ on them and convert them into After some time, it decomposed and got manure. converted to manure. Boojho and You often see large amounts of Paheli wanted to know how this had dead organic matter in the form of happened. decaying plants and sometimes dead animals on the ground. You find Activity 2.5 that they disappear after some time. This is because the microorganisms Take two pots and fill each pot half decompose dead organic waste of plants with soil. Mark them A and B. Put plant waste in pot A and things like and animals converting them into polythene bags, empty glass bottles simple substances. These substances and broken plastic toys in pot B. are again used by other plants and Put the pots aside. Observe them animals. Thus, microorganisms can after 3-4 weeks. be used to degrade the harmful and smelly substances and thereby clean Do you find any difference in the up the environment. contents of the two pots? If so, what is the difference? You will find that plant 2.4 Harmful Microorganisms waste in pot A, has been decomposed. Microorganisms are harmful in many How did this happen? The plant waste ways. Some of the microorganisms has been converted into manure by the cause diseases in human beings, plants action of microbes. The nutrients and animals. Such disease-causing 22 SCIENCE 2024-25 microorganisms are called pathogens. There are some insects and animals Some microorganisms spoil food, which act as carriers of disease- clothing and leather. Let us study more causing microbes. Housefly is one such about their harmful activities. carrier. The flies sit on the garbage and animal excreta. Pathogens stick to their Disease causing Microorganisms bodies. When these flies sit on uncovered in Humans food they may transfer the pathogens. Pathogens enter our body through the Whoever eats the contaminated food is air we breathe, the water we drink or likely to get sick. So, it is advisable to the food we eat. They can also get always keep food covered. Avoid transmitted by direct contact with an consuming uncovered items of food. infected person or carried by an animal. Another example of a carrier is the Microbial diseases that can spread from female Anopheles mosquito (Fig. 2.8), an infected person to a healthy person which carries the parasite of malaria through air, water, food or physical (Plasmodium). Female Aedes mosquito contact are called communicable acts as carrier of dengue virus. diseases. Examples of such diseases How can we control the spread of malaria include cholera, common cold, chicken or dengue? pox and tuberculosis. When a person suffering from common cold 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 and cause infection. Fig. 2.8 : Female Anopheles mosquito Then how do you prevent the spread of Why does the teacher communicable keep telling us not diseases? to let water collect anywhere in the neighbourhood? All mosquitoes breed in water. Hence, one should not let water collect We should keep a anywhere, in coolers, tyres, flower pot, handkerchief on the etc. By keeping the surroundings clean nose and mouth while and dry we can prevent mosquitoes from sneezing. It is better to breeding. Try to make a list of measures keep a distance from which help to avoid the spread of infected persons. malaria. MICROORGANISMS : FRIEND AND FOE 23 2024-25  Table 2.1: Some Common Human Diseases caused by Microorganisms Human Disease Causative Mode of Preventive Measures Microorganism Transmission (General) Tuberculosis Bacteria Air Keep the patient in complete isolation. Keep the personal Measles Virus Air belongings of the patient away from those of the others. Chicken Pox Virus Air/Contact Vaccination to be given at Polio Virus Air/Water suitable age. Cholera Bacteria Water/Food Maintain personal hygiene and good sanitary habits. Typhoid Bacteria Water Consume properly cooked food and boiled drinking water. Vaccination. Hepatitis A Virus Water Drink boiled drinking water. Vaccination. Use mosquito net and Malaria Protozoa Mosquito repellents. Spray insecticides and control breeding of mosquitoes by not allowing water to collect in the surroundings. Some of the common diseases in other animals. For example, anthrax affecting humans, their mode of is a dangerous human and cattle transmission and few general methods disease caused by a bacterium. Foot of prevention are shown in Table 2.1. and mouth disease of cattle is caused by a virus. Disease causing Microorganisms in Animals Disease causing Microorganisms Several microorganisms not only cause in Plants diseases in humans and plants, but also Several microorganisms cause diseases in plants like wheat, rice, potato, Robert Köch (1876) sugarcane, orange, apple and others. discovered the bacterium The diseases reduce the yield of crops. (Bacillus anthracis) which See Table 2.2 for some such plant causes anthrax disease. diseases. They can be controlled by the 24 SCIENCE 2024-25  Table 2.2: Some Common Plant Diseases caused by Microorganisms Plant Micro- Mode of Diseases organism Transmission Citrus Bacteria Air canker Rust of Fungi Air, wheat seeds Yellow vein Virus Insect mosaic of bhindi (Okra) use of certain chemicals which kill the make the food poisonous causing microbes. serious illness and even death. So, it is very important that we preserve Food Poisoning food to prevent it from being spoilt. Boojho was invited by his friend to a party and he ate a variety of foodstuff. 2.5 Food Preservation On reaching home he started vomiting In Chapter 1, we have learnt about the and had to be taken to a hospital. The methods used to preserve and store food doctor said that this condition could be grains. How do we preserve cooked food due to food poisoning. at home? You know that bread left unused under moist conditions is attacked by fungus. Microorganisms spoil our food. Spoiled food emits bad Paheli wonders how smell and has a bad taste and changed food can become a colour. Is spoiling of food a chemical ‘poison’. reaction? Paheli bought some mangoes but she Food poisoning could be due to the could not eat them for a few days. Later consumption of food spoilt by some she found that they were spoilt and microorganisms. Microorganisms rotten. But she knows that the mango that grow on our food sometimes pickle her grandmother makes does not produce toxic substances. These spoil for a long time. She is confused. MICROORGANISMS : FRIEND AND FOE 25 2024-25  Let us study the common methods Similarly, we keep our food in the of preserving food in our homes. We refrigerator. Low temperature inhibits have to save it from the attack of the growth of microbes. microorganisms. Chemical Method Salts and edible oils are the common Why does the milk that chemicals generally used to check the comes in packets not spoil? growth of microorganisms. Therefore My mother told me that the they are called preservatives. We add milk is ‘pasteurised’. What salt or acid preservatives to pickles to is pasteurisation? prevent the attack of microbes. Sodium benzoate and sodium metabisulphite are Pasteurised milk can be consumed common preservatives. These are also without boiling as it is free from harmful used in jams and squashes to check microbes. The milk is heated to about their spoilage. 700C for 15 to 30 seconds and then suddenly chilled and stored. By doing Preservation by Common Salt so, it prevents the growth of microbes. Common salt has been used to preserve This process was discovered by Louis meat and fish for ages. Meat and fish Pasteur. It is called pasteurisation. are covered with dry salt to check the growth of bacteria. Salting is also Storage and Packing used to preserve amla, raw mangoes, These days dry fruits and even tamarind, etc. vegetables are sold in sealed air tight packets to prevent the attack of Preservation by Sugar microbes. Jams, jellies and squashes are preserved by sugar. Sugar reduces the moisture 2.6 Nitrogen Fixation content which inhibits the growth of You have learnt about the bacterium bacteria which spoil food. Rhizobium in Classes VI and VII. It is involved in the fixation of nitrogen in Preservation by Oil and Vinegar leguminous plants (pulses). Recall that Use of oil and vinegar prevents spoilage Rhizobium lives in the root nodules of of pickles because bacteria cannot live leguminous plants (Fig. 2.9), such as in such an environment. Vegetables, beans and peas, with which it has a fruits, fish and meat are often preserved symbiotic relationship. Sometimes by this method. nitrogen gets fixed through the action of lightning. But you know that the Heat and Cold Treatments amount of nitrogen in the atmosphere You must have observed your mother remains constant. You may wonder boiling milk before it is stored or used. how? Let us understand this in the next Boiling kills many microorganisms. section. 26 SCIENCE 2024-25  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 it 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 (Fig. 2.10). When plants and animals die, Fig. 2.9 : Roots of a leguminous plant with root bacteria and fungi present in the soil nodules convert the nitrogenous wastes into nitrogenous compounds to be used by 2.7 Nitrogen cycle plants again. Certain other bacteria Our atmosphere has 78% nitrogen gas. convert some part of them to nitrogen Nitrogen is one of the essential gas which goes back into the constituents of all living organisms as atmosphere. As a result, the percentage part of proteins, chlorophyll, nucleic of nitrogen in the atmosphere remains acids and vitamins. The atmospheric more or less constant. Fig. 2.10 : Nitrogen cycle MICROORGANISMS : FRIEND AND FOE 27 2024-25 KEYWORDS WHA WHAT OU HA YOU T Y VE LEARNT HAVE ALGAE Ü Microorganisms are too small and are not ANTIBIOTICS visible to the unaided eye. Ü They can live in all kinds of environment, ANTIBODIES ranging from ice cold climate to hot springs BACTERIA and deserts to marshy lands. Ü Microorganisms are found in air, water and CARRIER in the bodies of plants and animals. Ü They may be unicellular or multicellular. COMMUNICABLE Ü Microorganisms include bacteria, fungi, DISEASES protozoa and some algae. Viruses, though FERMENTATION different from the above mentioned living organisms, are considered microbes. FUNGI Ü Viruses are quite different from other LACTOBACILLUS microorganisms. They reproduce only inside the host organism: bacterium, plant or ani- MICROORGANISM mal cell. NITROGEN CYCLE Ü Some microorganisms are useful for commercial production of medicines and NITROGEN FIXATION alcohol. PASTEURISATION Ü Some microorganisms decompose the organic waste and dead plants and animals into simple PATHOGEN substances and clean up the environment. Ü Protozoans cause serious diseases like PRESERVATION dysentery and malaria. PROTOZOA Ü Some of the microorganisms grow on our food and cause food poisoning. RHIZOBIUM Ü Some microorganisms reside in the root VACCINE nodules of leguminous plants. They can fix nitrogen from air into soil and increase the VIRUS soil fertility. YEAST Ü Some bacteria present in the soil fix nitrogen from the atmosphere and convert into nitrogenous compounds. Ü Certain bacteria convert compounds of nitro- gen present in the soil into nitrogen gas which is released to the atmosphere. 28 SCIENCE 2024-25  Exercises 1. Fill in the blanks. (a) Microorganisms can be seen with the help of a ____________. (b) Blue green algae fix __________ directly from air and enhance fertility of soil. (c) Alcohol is produced with the help of __________. (d) Cholera is caused by __________. 2. Tick the correct answer. (a) Yeast is used in the production of (i) sugar (ii) alcohol (iii) hydrochloric acid (iv) oxygen (b) The following is an antibiotic (i) Sodium bicarbonate (ii) Streptomycin (iii) Alcohol (iv) Yeast (c) Carrier of malaria-causing protozoan is (i) female Anopheles mosquito (ii) cockroach (iii) housefly (iv) butterfly (d) The most common carrier of communicable diseases is (i) ant (ii) housefly (iii) dragonfly (iv) spider (e) The bread or idli dough rises because of (i) heat (ii) grinding (iii) growth of yeast cells (iv) kneading (f) The process of conversion of sugar into alcohol is called (i) nitrogen fixation (ii) moulding (iii) fermentation (iv) infection 3. Match the organisms in Column A with their action in Column B. A B (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 antibodies 4. Can microorganisms be seen with the naked eye? If not, how can they be seen? MICROORGANISMS : FRIEND AND FOE 29 2024-25  5. What are the major groups of microorganisms? EXERCISES 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 harmful effects of microorganisms. 9. What are antibiotics? What precautions must be taken while taking antibiotics? Extended Learning — Activities and Projects 1. Pull out a gram or bean plant from the field. Observe its roots. You will find round structures called root nodules on the roots. Draw a diagram of the root and show the root nodules. 2. Collect the labels from the bottles of jams and jellies. Write down the 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, yeast powder, 2 balloons and lime water. Take two test tubes and mark them A and B. Clamp these tubes in a stand and fill them with water leaving some space at the top. Put two spoonfuls of sugar in each of the test tubes. Add a spoonful of yeast in test tube B. Inflate the two balloons incompletely. Now tie the balloons on the mouths of each test tube. Keep them in a warm place, away from sunlight. Watch the setup every day for next 3-4 days. Record A B your observations and think of an explanation. Now take another test tube filled 1/4 with lime water. Remove the balloon from test tube B in such a manner that gas inside the balloon does not escape. Fit the balloon on the test tube and shake well. Observe and explain. 30 SCIENCE 2024-25  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 concentrated sulphuric acid. They can survive at depths of several kilometres. They probably can survive in space, too. A kind of bacterium was recovered from a camera which stood on the moon for two years.There is probably no environment in which bacteria cannot survive. MICROORGANISMS : FRIEND AND FOE 31 2024-25