Microbes In Human Welfare

Class 12 | Pure Science — Zoology | Chapter 9

Class 12 Unit 9 Pure_Science

Unit 3 | Chapter 9

Microbes in Human Welfare

Saccharomyces cerevisiae, a species of yeast used in baking and brewing industry.

Chapter Outline

• 9.1 Microbes in household products
• 9.2 Microbes in industrial products
• 9.3 Microbes in sewage treatment and energy generation
• 9.4 Microbes in the production of biogas
• 9.5 Bioremediation

Learning Objectives

• Differentiates probiotics from pathogens.
• Understands the use of microbes in household products.
• Learns about antibiotic production and fermented beverages.
• Realizes the importance of microbes in sewage treatment and energy generation.
• Realizes the applications of microbes in bioremediation.

Microbes such as bacteria, fungi, protozoa, certain algae, viruses, viroids and prions are some of the major components of the biological system on Earth. Several microorganisms are beneficial and contribute to human welfare. Microbes are present everywhere in soil, water, air and within bodies of animals and plants. Microbes like bacteria and fungi can be grown on nutritive media to form colonies which can be visibly seen. Some of the microbes useful to human welfare are discussed here.

9.1 Microbes in Household Products

In every day life, microbes and their products are used in the preparation of idli, dosa, cheese, curd, yogurt, dough, bread, vinegar, etcetera. Bacteria like Lactobacillus acidophilus, L. lactis and Streptococcus lactis commonly called lactic acid bacteria (LAB) are probiotics which check the growth of pathogenic microbes in the stomach and other parts of the digestive tract. The Lactic Acid Bacteria grows in milk and convert it into curd, thereby digesting the milk protein casein. A small amount of curd added to fresh milk as a starter or inoculum contains millions of Lactobacilli, which under suitable temperature (less than or equal to 40°C) multiply and convert milk into curd. Curd is more nutritious than milk as it contains a number of organic acids and vitamins.

Do You Know?

Prebiotics are compounds in food (fibers) that induce the growth or activity of beneficial microorganisms. Probiotics are live microorganisms intended to provide health benefits when consumed, generally by improving or restoring the gut flora.

Yogurt is produced by bacterial fermentation of milk, and lactic acid is produced as a byproduct. Microorganisms such as Streptococcus thermophilus and Lactobacillus bulgaricus coagulate the milk protein and convert the lactose in the milk to lactic acid. The flavour in yogurt is due to acetaldehyde.

Cheese is a dairy product produced in a wide range of flavours, textures and is formed by coagulation of the milk protein, casein. During cheese production, milk is usually acidified and the enzyme rennet is added to cause coagulation. The solids are separated and pressed to form cheese. Most cheese are made with a starter bacteria Lactococcus, Lactobacillus or Streptococcus.

Paneer (cottage cheese) is fresh cheese common in South Asia, especially in India. It is made by curdling milk with lemon juice, vinegar and other edible acids.

Large holes in Swiss cheese is due to the production of large amount of carbon-di-oxide by the bacterium Propionibacterium shermanii.

The dough used in the preparation of idlis and dosas are fermented by the bacteria Leuconostoc mesenteroides whereas the dough used in bread making is fermented by Saccharomyces cerevisiae (Baker's Yeast). Fermentation of glucose mainly forms ethyl alcohol and carbon di oxide, which is responsible for leavening of dough. When leavened dough is baked, both carbon di oxide and ethyl alcohol evaporate making the bread porous and soft.

Single Cell Protein (SCP)

Single cell protein refers to edible unicellular microorganisms like Spirulina. Protein extracts from pure or mixed cultures of algae, yeasts, fungi or bacteria may be used as ingredient or as a substitute for protein rich foods and is suitable for human consumption or as animal feed.

9.2 Microbes in Industrial Products

Microbes are used to synthesize a number of products valuable to human beings. Products like beverages, antibiotics, organic acids, amino acids, vitamins, biofuels, single cell protein, enzymes, steroids, vaccines, pharmaceutical drugs, etcetera, are produced in industries. Production on a large scale requires growing microbes in very large vessels called fermentors. A fermentor (bioreactor) is a closed vessel with adequate arrangement for aeration, agitation, temperature, pH control and drain or overflow vent to remove the waste biomass of cultured microorganisms along-with their products.

9.2.1 Antibiotic Production

Antibiotics are chemical substances produced by microorganisms which can kill or retard the growth of other disease-causing microbes even in low concentration. Antibiotic means "against life". Antibiotics are used to treat diseases such as plague, meningitis, diphtheria, syphilis, leprosy, tuberculosis etcetera. Selman Waksman discovered Streptomycin and was the first to use the term "antibiotic" in 1943.

While working on Staphylococci bacteria, Alexander Fleming observed a green mould growing in one of his unwashed culture plates around which Staphylococci could not grow. He found that it was due to a chemical produced by the mould and he named it as penicillin, which was the first antibiotic discovered by Alexander Fleming in 1926.

Penicillin is produced by the fungi Penicillium notatum and Penicillium chrysogenum. It is bactericidal (antibiotics that kill bacteria) in action and inhibits the synthesis of the bacterial cell wall. Penicillin is also referred as the "queen of drugs" and its full potential as an effective antibiotic was established much later by Earnest Chain and Howard Florey when they treated the wounded soldiers in World War 2 with penicillin. Fleming, Chain and Florey were awarded the Nobel prize in 1945 for the discovery of penicillin.

Key Terms

• Antibiosis is the property of antibiotics to kill microorganisms.
• Broad spectrum antibiotics act against a wide range of disease causing bacteria.
• Narrow spectrum antibiotics are active against a selected group of bacterial types.

Do You Know?

Hypersensitivity reaction is a major problem with the use of penicillin, resulting in nausea, vomiting, wheezing and ultimately cardiovascular collapse. To check the sensitivity reaction, doctors use a needle to prick the forearm of the patients to give a weak dose of penicillin. An itchy red region in the forearm is an indication that the patient is allergic to penicillin. This test is important before administration of penicillin to a patient.

Tetracycline is a broad-spectrum bacteriostatic antibiotic (antibiotics that limit the growth of bacteria) that inhibits microbial protein synthesis. Chlortetracycline is the first antibiotic of this group, isolated from the cultures of Streptomyces aureofaciens.

Streptomycin is a broad-spectrum antibiotic isolated from the actinomycetes, Streptomyces griseus. It is bactericidal against both gram positive and gram-negative bacteria, especially against Mycobacterium tuberculosis.

Antibiotics, such as erythromycin, chloromycetin, griseofulvin, neomycin, kenamycin, bacitracin, etcetera, are also isolated as microbial products.

Antibiotic Resistance

Antibiotic resistance occurs when bacteria develop the ability to defeat the drug designed to kill or inhibit their growth. It is one of the most acute threats to public health. Antibiotic resistance is accelerated by the misuse and over use of antibiotics, as well as poor infection prevention control. Antibiotics should be used only when prescribed by a certified health professional. When the bacteria become resistant, antibiotics cannot fight against them and the bacteria multiply. Narrow spectrum antibiotics are preferred over broad-spectrum antibiotics. They effectively and accurately target specific pathogenic organisms and are less likely to cause resistance. "Superbug" is a term used to describe strains of bacteria that are resistant to the majority of antibiotics commonly used today.

9.2.2 Fermented Beverages

Microbes especially yeast is being used from time immemorial for the production of beverages like wine, beer, whisky, brandy and rum. Wine is among the oldest alcoholic beverages known and is produced by fermentation of fruit juice by yeast. Zymology is an applied science which deals with the biochemical process of fermentation and its practical uses. Saccharomyces cerevisiae commonly called brewer's yeast is used for fermenting malted cereals and fruit juices to produce various alcoholic beverages. Wine and beer are produced without distillation, whereas whisky, brandy and rum are obtained by fermentation and distillation.

Do You Know?

The Pasteur effect is the inhibiting effect of oxygen on the fermentation process. Oenology is the science and study of wine and wine making.

Wine is made from the fermentation of grape juice. Grape juice is fermented by various strains of Saccharomyces cerevisiae into alcohol. Grape wine is of two types, red wine and white wine. For red wine, black grapes are used including skins and sometimes the stems also are used. In contrast white wine is produced only from the juice of either white or red grapes without their skin and stems.

Beer is produced from germinated barley malt grain by Saccharomyces carlsbergensis or Saccharomyces cerevisiae.

Rum is made from fermented sugarcane or molasses or directly from sugarcane juice by Saccharomyces cerevisiae.

Whisky is a type of distilled alcoholic beverage made from fermented grain mash by Saccharomyces cerevisiae.

Alcohol Content in Various Beverages

• Beer contains 3 to 5 percent
• Wine contains 9 to 14 percent
• Wine coolers 4 to 6 percent
• Whiskey, gin, scotch and vodka 35 to 50 percent

In some parts of South India, a traditional drink called pathaneer is obtained from fermenting sap of palms and coconut trees. A common source is tapping of unopened spadices of coconut. It is a refreshing drink, which on boiling produces jaggery or palm sugar. When pathaneer is left undisturbed for few hours it gets fermented to form toddy with the help of naturally occurring yeast, to form a beverage that contains 4 percent alcohol. After 24 hours toddy becomes unpalatable and is used for the production of vinegar.

Saccharomyces cerevisiae is the major producer of ethanol (C₂H₅OH). It is used for industrial, laboratory and fuel purposes so ethanol is referred to as industrial alcohol. Bacteria such as Zymomonas mobilis and Sarcina ventriculi are also involved in ethanol production. The principal substrates for the commercial production of industrial alcohol include molasses or corn, potatoes and wood wastes. The process of ethanol production starts by milling a feed stock followed by the addition of dilute or fungal amylase (enzyme) from Aspergillus to break down the starch into fermentable sugars. Yeast is then added to convert the sugars to ethanol which is then distilled off to obtain ethanol which is upto 96 percent in concentration.

The two most common type of biofuels in use today are ethanol and biodiesel, both of them represent the first generation of biofuel technology. Ethanol is often used as a fuel, mainly as a biofuel additive for gasoline.

Biodiesel

Biodiesel is a fuel made from vegetable oils, fats or greases. Biodiesel fuel can be used in diesel engines without altering the engine. Pure biodiesel is non-toxic, biodegradable and produces lower level of air pollutants than petroleum-based diesel fuel. The Government of India approved the National Policy on Biofuels in December 2009 and identified Jatropha curcas as the most suitable oilseed for biodiesel production. Pongamia species is also a suitable choice for production of biodiesel.

Do You Know?

World biofuel day is observed every year on 10th August to create awareness about the importance of renewable bio-fuels as an alternative to conventional non-renewable fossil fuels. This day also highlights the various efforts taken by the Government in the biofuel sector.

9.2.3 Chemicals, Enzymes and Other Bioactive Molecules

Microbes are not only used for commercial and industrial production of alcohol, but also used for production of chemicals like organic acids and enzymes.

Examples of Organic Acid Producers

• Aspergillus niger — Citric acid
• Acetobacter aceti — Acetic acid
• Rhizopus oryzae — Fumaric acid
• Clostridium butyricum — Butyric acid
• Lactobacillus — Lactic acid

Yeast (Saccharomyces cerevisiae) and bacteria are used for commercial production of enzymes. Lipases are used in detergent formulations and are used for removing oily stains from the laundry. Bottled juices are clarified by the use of pectinase, protease and cellulase. Rennet can also be used to separate milk into solid curds for cheese making.

Streptokinase produced by the bacterium Streptococcus and genetically engineered Streptococci are used as "clot buster" for removing clots from the blood vessels of patients who have undergone myocardial infarction.

Cyclosporin A, an immunosuppressant used in organ transplantation is produced from the fungus Trichoderma polysporum. It is also used for its anti-inflammatory, antifungal and anti-parasitic properties.

Statins produced by the yeast Monascus purpureus have been used to lower blood cholesterol levels. It acts by competitively inhibiting the enzyme responsible for the synthesis of cholesterol.

Recombinant human insulin has been produced predominantly using Escherichia coli and Saccharomyces cerevisiae for therapeutic use in human.

9.3 Microbes in Sewage Treatment and Energy Generation

Sewage is the waste generated every day in cities and towns containing human excreta. It contains large amounts of organic matter and microbes, which are pathogenic to humans and are biodegradable pollutants. Domestic waste consists of approximately 99 percent water, suspended solids and other soluble organic and inorganic substances. Sewage should not be discharged directly into natural water bodies like rivers and streams. Before disposal, sewage should be treated in sewage treatment plants to make it less polluting. Microbes (mass of bacteria floc) are allowed to grow in aerated water (secondary treatment). They consume major part of organic matter in the effluent and reduce the Biochemical Oxygen Demand in the waste water (The details on waste water treatment are discussed in chapter 13).

9.3.1 Microbial Fuel Cell (MFC)

A microbial fuel cell is a bio-electrochemical system that drives an electric current by using bacteria and mimicking bacterial interaction found in nature. Microbial fuel cells work by allowing bacteria to oxidize and reduce organic molecules. Bacterial respiration is basically one big redox reaction in which electrons are being moved around. A Microbial Fuel Cell consists of an anode and a cathode separated by a proton exchange membrane. Microbes at the anode oxidize the organic fuel generating protons which pass through the membrane to the cathode and the electrons pass through the anode to the external circuit to generate current.

9.4 Microbes in the Production of Biogas

Biogas is a mixture of different gases produced by the breakdown of organic matter in the absence of oxygen. Biogas can be produced from raw materials such as agricultural wastes, manure, municipal wastes, plant material, sewage, food waste, etcetera. Biogas is produced under anaerobic condition, when the organic materials are converted through microbiological reactions into gas and organic fertilizer. Biogas primarily consists of methane (63 percent), along with carbon di oxide and hydrogen. Methane producing bacteria are called methanogens and one such common bacterium is Methanobacterium. Biogas is devoid of smell and burns with a blue flame without smoke.

The Methanogens are also present in anaerobic sludge and rumen of cattle. In rumen, these bacteria help in the breakdown of cellulose. The excreta of cattle called dung is commonly called "Gobar". Gobar gas is generated by the anaerobic decomposition of cattle dung. It consists of methane, carbon di oxide with some hydrogen, nitrogen and other gases in trace amounts.

In a biogas plant, anaerobic digestion is carried out in an air tight cylindrical tank known as digester. It is made up of concrete bricks and cement or steel. Bio-wastes are collected and slurry of dung is fed into this digester. It has a side opening into which organic materials for digestion are incorporated for microbial activity. Anaerobic digestion is accomplished in three stages: solubilisation, acidogenesis and methanogenesis. The outlet is connected to a pipe to supply biogas. The slurry is drained through another outlet and is used as fertilizer. Biogas is used for cooking and lighting.

The technology of biogas production was developed in India mainly due to the efforts of Indian Agricultural Research Institute (IARI) and Khadi and Village Industries Commission (KVIC).

9.5 Bioremediation

The use of naturally occurring or genetically engineered microorganisms to reduce or degrade pollutants is called bioremediation. Bioremediation is less expensive and more sustainable than other remediations available. It is grouped into in situ bioremediation (treatment of contaminated soil or water in the site) and ex situ bioremediation (treatment of contaminated soil or water that is removed from the site and treated).

9.5.1 Microorganisms Involved in Bioremediation

Aerobic microbes degrade the pollutants in the presence of oxygen. They mainly degrade pesticides and hydrocarbons. Pseudomonas putida is a genetically engineered microorganism (GEM). Ananda Mohan Chakrabarty obtained patent for this recombinant bacterial strain. It is multi-plasmid hydrocarbon-degrading bacterium which can digest the hydrocarbons in the oil spills.

Nitrosomonas europaea is also capable of degrading benzene and a variety of halogenated organic compounds including trichloroethylene and vinyl chloride.

Ideonella sakaiensis is currently tried for recycling of PET plastics. These bacteria use PETase and MHETase enzymes to breakdown PET plastic into terephthalic acid and ethylene glycol.

Anaerobic microbes degrade the pollutants in the absence of oxygen. Dechloromonas aromatica has the ability to degrade benzene anaerobically and to oxidize toluene and xylene.

Phanerochaete chrysosporium an anaerobic fungus exhibits strong potential for bioremediation of pesticides, polyaromatic hydrocarbons, dyes, trinitrotoluene, cyanides, carbon tetrachloride, etcetera.

Dehalococcoides species are responsible for anaerobic bioremediation of toxic trichloroethene to non-toxic ethane.

Pestalotiopsis microspora is a species of endophytic fungus capable of breaking down and digesting polyurethane. This makes the fungus a potential candidate for bioremediation projects involving large quantities of plastics.

Summary

• All microbes are not pathogenic, many of them are beneficial to human beings.
• We use microbes and their derived products almost every day.
• Lactic acid bacteria convert milk into curd.
• Saccharomyces cerevisiae (yeast) is used in bread making.
• Idly and dosa are made from dough fermented by microbes.
• Bacteria and fungi are used in cheese making.
• Industrial products like lactic acid, acetic acid and alcohol are produced by microbes.
• Antibiotics are produced from useful microbes to kill the disease-causing harmful microbes.
• For more than a hundred years, microbes are being used to treat sewage by the process of activated sludge formation.
• Bio gas produced by microbes is used as a source of energy in rural areas.
• In bioremediation naturally occurring or genetically engineered microorganisms are used to reduce or degrade pollutants.

Evaluation

Exercise MCQ — Choose the Correct Answer

1. Which of the following microorganism is used for production of citric acid in industries?

a) Lactobacillus bulgaris b) Penicillium citrinum c) Aspergillus niger d) Rhizopus nigricans

2. Which of the following pair is correctly matched for the product produced by them?

a) Acetobacter aceti – Antibiotics b) Methanobacterium – Lactic acid c) Penicillium notatum – Acetic acid d) Saccharomyces cerevisiae – Ethanol

3. The most common substrate used in distilleries for the production of ethanol is ___

a) Soyameal b) Groundgram c) Molasses d) Corn meal

4. Cyclosporin A is an immunosuppressive drug produced from ___

a) Aspergillus niger b) Monascus purpureus c) Penicillium notatum d) Trichoderma polysporum

5. Carbon di oxide is not released during ___

a) Alcoholic fermentation b) Lactate fermentation c) Aerobic respiration in animals d) Aerobic respiration in plants

6. The purpose of biological treatment of waste water is to ___

a) Reduce Biochemical Oxygen Demand b) Increase Biochemical Oxygen Demand c) Reduce sedimentation d) Increase sedimentation

7. The gases produced in anaerobic sludge digesters are ___

a) Methane, oxygen and hydrogen sulphide. b) Hydrogen sulphide, methane and sulphur dioxide. c) Hydrogen sulphide, nitrogen and methane. d) Methane, hydrogen sulphide and carbon di oxide. Exercise 8. Short Answer

8. How is milk converted into curd? Explain the process of curd formation.

Exercise 9. Short Answer

9. Give any two bioactive molecules produced by microbes and state their uses.

Exercise 10. Define the Following Terms

a) Antibiotics

b) Zymology

c) Superbug

Exercise 11. Write Short Notes on the Following

a) Brewer's yeast

b) Ideonella sakaiensis

c) Microbial fuel cells

Exercise 12. Short Answer

12. List the advantages of biogas plants in rural areas.

Exercise 13. Short Answer

13. When does antibiotic resistance develop?

Exercise 14. Long Answer

14. What is referred to as industrial alcohol? Briefly describe its preparation.

Exercise 15. Short Answer

15. What is bioremediation?

ICT Corner — Microbes in Human Welfare

Procedure:

• Step 1: Type the URL or scan the QR code to open the activity page and click "START" to begin the fermentation experiment.
• Step 2: Click "next" for all the flasks combination.
• Step 3: When the "Matching Game" starts to know the result, "Drag and place" the combination perfectly to their respective flasks.
• Step 4: Go on through the other tests, explanations and the principle involved in the fermentation process.

URL: http://www.bch.cuhk.edu.hk/vlab2/animation/fermentation/

*Pictures are indicative only. *Allow flash player

Book-back Exercises — Questions & Answers

Answers generated strictly from the Samacheer Kalvi textbook content. Attempt each question first, then click "Show Answer" to check.

I. Choose the Correct Answer

1. Which of the following microorganism is used for production of citric acid in industries?

a) Lactobacillus bulgaris b) Penicillium citrinum c) Aspergillus niger d) Rhizopus nigricans

Answer: c) Aspergillus niger

Explanation: According to the chapter, Aspergillus niger is an example of an organic acid producer used for production of citric acid in industries.

2. Which of the following pair is correctly matched for the product produced by them?

a) Acetobacter aceti – Antibiotics b) Methanobacterium – Lactic acid c) Penicillium notatum – Acetic acid d) Saccharomyces cerevisiae – Ethanol

Answer: d) Saccharomyces cerevisiae – Ethanol

Explanation: Saccharomyces cerevisiae is the major producer of ethanol (C₂H₅OH), used for industrial, laboratory and fuel purposes.

3. The most common substrate used in distilleries for the production of ethanol is –

a) Soyameal b) Groundgram c) Molasses d) Corn meal

Answer: c) Molasses

Explanation: The principal substrates for the commercial production of industrial alcohol include molasses or corn, potatoes and wood wastes. Molasses is the most common substrate used in distilleries.

4. Cyclosporin A is an immunosuppressive drug produced from –

a) Aspergillus niger b) Monascus purpureus c) Penicillium notatum d) Trichoderma polysporum

Answer: d) Trichoderma polysporum

Explanation: Cyclosporin A, an immunosuppressant used in organ transplantation, is produced from the fungus Trichoderma polysporum.

5. Carbon dioxide is not released during –

a) Alcoholic fermentation b) Lactate fermentation c) Aerobic respiration in animals d) Aerobic respiration in plants

Answer: b) Lactate fermentation

Explanation: During lactate fermentation, lactic acid is produced as a byproduct without the release of carbon dioxide, unlike alcoholic fermentation where CO₂ is released.

6. The purpose of biological treatment of waste water is to –

a) Reduce Bio chemical Oxygen Demand b) Increase Bio chemical Oxygen Demand c) Reduce sedimentation d) Increase sedimentation

Answer: a) Reduce Bio chemical Oxygen Demand

Explanation: Microbes (mass of bacteria floc) are allowed to grow in aerated water during secondary treatment. They consume the major part of organic matter in the effluent and reduce the Biochemical Oxygen Demand in the waste water.

7. The gases produced in anaerobic sludge digesters are –

a) Methane, oxygen and hydrogen sulphide b) Hydrogen sulphide, methane and sulphur dioxide c) Hydrogen sulphide, nitrogen and methane d) Methane, hydrogen sulphide and Carbon dioxide

Answer: d) Methane, hydrogen sulphide and Carbon dioxide

Explanation: Biogas primarily consists of methane (63%), along with carbon dioxide and hydrogen. Gobar gas consists of methane, carbon dioxide with some hydrogen, nitrogen and other gases in trace amounts, including hydrogen sulphide.

II. Answer Briefly

8. How is milk converted into curd? Explain the process of curd formation.

Answer: Lactic Acid Bacteria (LAB) such as Lactobacillus acidophilus, L. lactis and Streptococcus lactis grow in milk and convert it into curd by digesting the milk protein casein. A small amount of curd added to fresh milk as a starter or inoculum contains millions of Lactobacilli, which under suitable temperature (less than or equal to 40°C) multiply and convert milk into curd. Curd is more nutritious than milk as it contains a number of organic acids and vitamins.

9. Give any two bioactive molecules produced by microbes and state their uses.

Answer: 1. Cyclosporin A – produced by the fungus Trichoderma polysporum; it is an immunosuppressant used in organ transplantation and also has anti-inflammatory, antifungal and anti-parasitic properties. 2. Statins – produced by the yeast Monascus purpureus; they are used to lower blood cholesterol levels by competitively inhibiting the enzyme responsible for synthesis of cholesterol.

10. Define the following terms: a) Antibiotics b) Zymology c) Superbug

Answer:
a) Antibiotics: Antibiotics are chemical substances produced by microorganisms which can kill or retard the growth of other disease-causing microbes even in low concentration. The term "antibiotic" means "against life."
b) Zymology: Zymology is an applied science which deals with the biochemical process of fermentation and its practical uses.
c) Superbug: "Superbug" is a term used to describe strains of bacteria that are resistant to the majority of antibiotics commonly used today.

11. Write short notes on the following: a) Brewer's yeast b) Ideonella sakaiensis c) Microbial fuel cells

Answer:
a) Brewer's yeast: Saccharomyces cerevisiae, commonly called brewer's yeast, is used for fermenting malted cereals and fruit juices to produce various alcoholic beverages such as wine, beer, whisky, brandy and rum.
b) Ideonella sakaiensis: It is currently being tried for recycling of PET plastics. These bacteria use PETase and MHETase enzymes to break down PET plastic into terephthalic acid and ethylene glycol.
c) Microbial fuel cells: A microbial fuel cell is a bio-electrochemical system that drives an electric current by using bacteria. It consists of an anode and cathode separated by a proton exchange membrane. Microbes at the anode oxidize organic fuel, generating protons that pass through the membrane to the cathode, while electrons pass through the external circuit to generate current.

12. List the advantages of biogas plants in rural areas.

Answer: The advantages of biogas plants in rural areas are: (i) Biogas is devoid of smell and burns with a blue flame without smoke, making it a clean fuel. (ii) Biogas is used for cooking and lighting. (iii) The slurry drained from the biogas plant is used as fertilizer, enriching the soil. (iv) Bio-wastes such as agricultural wastes, manure and municipal wastes are effectively utilized. (v) Biogas is produced under anaerobic conditions, converting organic materials through microbiological reactions into gas and organic fertilizer.

13. When does antibiotic resistance develop?

Answer: Antibiotic resistance occurs when bacteria develop the ability to defeat the drug designed to kill or inhibit their growth. It is accelerated by the misuse and overuse of antibiotics, as well as poor infection prevention and control. When bacteria become resistant, antibiotics cannot fight against them and the bacteria multiply.

III. Answer in Detail

14. What is referred to as industrial alcohol? Briefly describe its preparation.

Answer: Saccharomyces cerevisiae is the major producer of ethanol (C₂H₅OH). Since it is used for industrial, laboratory and fuel purposes, ethanol is referred to as industrial alcohol. Bacteria such as Zymomonas mobilis and Sarcina ventriculi are also involved in ethanol production.

Preparation: The principal substrates for commercial production include molasses or corn, potatoes and wood wastes. The process starts by milling a feedstock, followed by the addition of dilute or fungal amylase (enzyme from Aspergillus) to break down the starch into fermentable sugars. Yeast is then added to convert the sugars to ethanol, which is then distilled off to obtain ethanol up to 96% concentration. Ethanol is often used as a fuel, mainly as a biofuel additive for gasoline.

15. What is bioremediation?

Answer: The use of naturally occurring or genetically engineered microorganisms to reduce or degrade pollutants is called bioremediation. It is less expensive and more sustainable than other remediations available. It is grouped into in situ bioremediation (treatment of contaminated soil or water at the site) and ex situ bioremediation (treatment of contaminated soil or water that is removed from the site and treated). Aerobic microbes degrade pesticides and hydrocarbons in the presence of oxygen, while anaerobic microbes degrade pollutants in the absence of oxygen. Examples include Pseudomonas putida (a genetically engineered microorganism) which degrades hydrocarbons in oil spills, Ideonella sakaiensis which breaks down PET plastic, and Pestalotiopsis microspora which digests polyurethane.

📝 Summary

1. Microbes such as bacteria, fungi, protozoa, algae, viruses, viroids, and prions are major components of the biological system on Earth and are present everywhere — in soil, water, air, and within bodies of animals and plants — contributing significantly to human welfare.
2. Lactic Acid Bacteria (LAB) such as Lactobacillus acidophilus, L. lactis, and Streptococcus lactis act as probiotics, checking the growth of pathogenic microbes in the digestive tract and converting milk into curd by digesting the milk protein casein under suitable temperatures (≤40°C).
3. Common household food products like yogurt, cheese, idli, dosa, and bread are all produced with the help of specific microorganisms — for example, Streptococcus thermophilus and Lactobacillus bulgaricus for yogurt, and Saccharomyces cerevisiae (Baker's Yeast) for bread-making dough fermentation.
4. During bread making, fermentation of glucose by Saccharomyces cerevisiae produces ethyl alcohol and carbon dioxide, which leaven the dough; when baked, both gases evaporate, making the bread porous and soft.
5. Single Cell Protein (SCP) refers to edible unicellular microorganisms like Spirulina; protein extracts from algae, yeasts, fungi, or bacteria can serve as a substitute for protein-rich foods suitable for human consumption or as animal feed.