Microbes In Human Welfare Class 12 Biology Chapter Notes

Key Terms & Definitions

Lactic Acid Bacteria (LAB)

A group of bacteria (e.g., Lactobacillus) that convert lactose in milk into lactic acid, coagulating milk proteins to form curd and improving its nutritional value (e.g., Vitamin B12).

Biochemical Oxygen Demand (BOD)

The amount of oxygen consumed by microorganisms in decomposing organic matter present in a water sample. A higher BOD indicates greater pollution.

Primary Treatment (Sewage)

The initial physical removal of large and small particles from sewage through filtration and sedimentation processes, resulting in primary sludge and supernatant.

Secondary Treatment (Biological Treatment)

The biological process in sewage treatment where aerobic microbes consume organic matter in the effluent from primary treatment, significantly reducing BOD. This involves aeration tanks and activated sludge formation.

Biocontrol Agents

Biological methods of controlling plant diseases and pests using living organisms (e.g., bacteria, fungi, viruses, insects) instead of chemical pesticides.

Biofertilisers

Organisms that enrich the nutrient quality of the soil, such as bacteria (e.g., Rhizobium, Azotobacter) and fungi (e.g., Mycorrhiza) that help in nitrogen fixation or phosphorus solubilization.

Methanogens

A group of anaerobic bacteria (e.g., Methanobacterium) responsible for producing methane (biogas) through the decomposition of cellulosic material.

Statins

Bioactive molecules produced by the yeast Monascus purpureus, used as blood-cholesterol-lowering agents by competitively inhibiting the enzyme responsible for cholesterol synthesis.

Microbes in Industrial Production

Microorganisms play a pivotal role in large-scale industrial production of a variety of products, often grown in large vessels called fermenters. This industrial application leverages the metabolic activities of specific microbes for human benefit.

1. Fermented Beverages: Yeast, specifically Saccharomyces cerevisiae (also known as brewer's yeast), is central to the production of alcoholic beverages like wine, beer, whisky, brandy, and rum. The type of beverage depends on the raw material and the processing (with or without distillation). For instance, wine and beer are produced without distillation, while whisky, brandy, and rum require distillation of the fermented broth.

1. Antibiotics: These are chemical substances produced by some microbes that can kill or retard the growth of other (disease-causing) microbes. The first antibiotic, Penicillin, was discovered by Alexander Fleming from the mold Penicillium notatum. Its full potential was later explored by Ernst Chain and Howard Florey. Antibiotics have revolutionized medicine, treating diseases like plague, whooping cough, diphtheria, and leprosy.

1. Chemicals, Enzymes, and Bioactive Molecules: Microbes are exploited to produce a range of useful organic acids, alcohols, and enzymes.

• Organic Acids: Aspergillus niger (fungus) produces citric acid; Acetobacter aceti (bacterium) produces acetic acid; Clostridium butylicum (bacterium) produces butyric acid; and Lactobacillus (bacterium) produces lactic acid.
• Enzymes: Lipases are used in detergent formulations for removing oily stains. Pectinases and proteases are used to clarify bottled juices. Streptokinase, produced by the bacterium Streptococcus, is modified and used as a 'clot buster' for removing clots from blood vessels of patients who have undergone myocardial infarction.
• Bioactive Molecules: Cyclosporin A, produced by the fungus Trichoderma polysporum, is used as an immunosuppressive agent in organ transplant patients. Statins, produced by the yeast Monascus purpureus, are used as blood-cholesterol-lowering agents by competitively inhibiting the enzyme responsible for cholesterol synthesis.

Sewage Treatment Process (Wastewater Treatment)

1. — Involves physical removal of large and small particles from sewage through sequential filtration and sedimentation. - Filtration: Removes floating debris. - Grit Removal: Sedimentation of sand and small pebbles. - Sedimentation: Solids (settleable solids) settle down to form primary sludge, while the supernatant forms the effluent.
2. — The primary effluent is transferred to large aeration tanks, where it is constantly agitated mechanically and air is pumped into it. - Aeration: Promotes vigorous growth of useful aerobic microbes (flocs – masses of bacteria associated with fungal filaments). - BOD Reduction: These microbes consume the major part of the organic matter in the effluent, significantly reducing its BOD. The greater the BOD, the more polluting the water. - Settling Tank: Once BOD is reduced, the effluent is passed into a settling tank where the bacterial flocs settle, forming activated sludge. - Anaerobic Sludge Digester: A small part of the activated sludge is pumped back into the aeration tank as an inoculum, while the remaining major part is pumped into anaerobic sludge digesters. Here, anaerobic bacteria (methanogens) digest the bacteria and fungi in the sludge, producing biogas (methane, H2S, CO2). - Discharge: The effluent from the secondary treatment plant is generally released into natural water bodies.

Key Points to Remember

• LAB (Lactobacillus) in milk converts lactose to lactic acid, coagulating milk protein to form curd and increasing its Vitamin B12 content.
• Brewer's yeast (Saccharomyces cerevisiae) is used for fermenting malted cereals and fruit juices to produce ethanol in alcoholic beverages.
• Antibiotics are microbial products that inhibit or kill other microbes. Penicillin (Penicillium notatum) was the first discovered antibiotic.
• BOD is a measure of the organic pollutant amount in water; higher BOD indicates more pollution requiring more oxygen for decomposition.
• Activated sludge is the bacterial floc that settles in the secondary treatment of sewage; it contains aerobic microbes.
• Biogas is a mixture of gases (primarily methane) produced by anaerobic breakdown of organic matter by methanogens (e.g., Methanobacterium).
• Bacillus thuringiensis (Bt) is a commonly used biocontrol agent for insect pests, producing a toxin that kills larvae.
• The fungus Trichoderma is a free-living fungus effective as a biocontrol agent against several plant pathogens.
• Nucleopolyhedrovirus (NPV) is a genus of viruses used as biocontrol agents, species-specific and not harmful to other organisms.
• Biofertilisers include bacteria (Rhizobium, Azotobacter), cyanobacteria (Anabaena, Nostoc), and fungi (mycorrhiza) that enrich soil fertility.

Examples of Microbial Applications

• {"title":"Microbes in Biogas Production","description":"Methanogens, a group of anaerobic bacteria like Methanobacterium, are found in the anaerobic sludge digesters during sewage treatment and in the rumen of cattle. They break down cellulosic material to produce biogas, a mixture primarily of methane (CH4), carbon dioxide (CO2), and hydrogen (H2). This biogas is a valuable fuel source."}
• {"title":"Microbes as Biocontrol Agents","description":"Bacillus thuringiensis (Bt) is widely used to control insect pests. Spores of Bt are mixed with water and sprayed onto vulnerable plants. When larvae ingest these spores, the toxin produced by the bacteria becomes active in their gut, killing them. Genetically engineered Bt cotton produces this toxin directly."}
• {"title":"Microbes as Biofertilisers","description":"Rhizobium bacteria live symbiotically in the root nodules of leguminous plants. They fix atmospheric nitrogen into organic forms that plants can readily use, thereby increasing soil fertility and reducing the need for chemical nitrogen fertilizers."}

Exam Tip for Microbes in Human Welfare

To score well in this chapter, memorize specific microbial names along with their exact products and functions. For instance, know that Aspergillus niger yields citric acid, not acetic acid. Be precise about where each microbe operates (e.g., anaerobic sludge digester for methanogens, aeration tank for aerobic flocs). Pay special attention to the sequential steps of sewage treatment and the significance of BOD. Practice drawing diagrams of a typical biogas plant if asked. Distinguish clearly between biocontrol agents and biofertilisers, providing relevant examples for each. Board examiners often look for correct scientific names (underline them!) and the specific roles these microbes play.

Practice Questions with Solutions

• Q: What is the primary role of Lactic Acid Bacteria (LAB) in the production of curd from milk? A: LAB converts lactose sugar in milk into lactic acid. This lactic acid coagulates the milk proteins, making curd, and also increases its nutritional value by enhancing Vitamin B12 content.
• Q: Briefly explain the term 'BOD' and its significance in wastewater treatment. A: BOD stands for Biochemical Oxygen Demand, which is the amount of oxygen consumed by microorganisms to decompose organic matter in a given volume of water. A higher BOD value indicates greater organic pollution in the water, and effective wastewater treatment aims to reduce BOD significantly.
• Q: Name one microbe used as a biocontrol agent and mention the pest it targets. A: Bacillus thuringiensis (Bt) is a biocontrol agent that targets various insect larvae, including butterfly caterpillars and beetle larvae.
• Q: What is the main gas produced by methanogens during anaerobic digestion, and what is its use? A: The main gas produced by methanogens is methane (CH4). It is the primary component of biogas, which is used as a fuel for cooking, lighting, and generating electricity.

Frequently Asked Questions