Class 12 Biology Notes Chapter 10 (Microbes in human welfare) – Biology Book
Detailed Notes with MCQs of Chapter 10: Microbes in Human Welfare. This chapter is crucial because it shifts our perspective from microbes solely as disease-causing agents to their immensely beneficial roles in our daily lives, industries, and environment. For your government exams, pay close attention to the specific microbes, their products, and the processes involved.
Microbes in Human Welfare: Detailed Notes
1. Introduction:
- Microbes (bacteria, fungi, protozoa, viruses, viroids, prions) are diverse and ubiquitous.
- While many cause diseases, a vast majority are beneficial to humans directly or indirectly.
2. Microbes in Household Products:
- Curd Production:
- Microbe: Lactic Acid Bacteria (LAB), e.g., Lactobacillus.
- Process: LAB grow in milk, ferment lactose into lactic acid.
- Benefits: Acid coagulates and partially digests milk proteins. Increases nutritional value by increasing Vitamin B12. LAB checks disease-causing microbes in the stomach.
- Inoculum/Starter: A small amount of curd containing millions of LAB is added to fresh milk.
- Dough Fermentation:
- Microbe: Baker's Yeast (Saccharomyces cerevisiae).
- Process: Fermentation of sugars produces CO2, causing dough to rise (leavening).
- Uses: Bread making.
- Other Fermented Foods: Dosa, Idli (fermented by bacteria, CO2 production causes puffing), Toddy (traditional South Indian drink made by fermenting sap from palms).
- Cheese Production:
- Process: Concentrated milk fat and protein. Different varieties depend on specific microbes used, texture, flavour, and ripening process.
- Examples:
- Swiss Cheese: Large holes due to CO2 production by Propionibacterium shermanii.
- Roquefort Cheese: Ripened by growing a specific fungus (Penicillium roqueforti) on it, giving a characteristic flavour.
3. Microbes in Industrial Products:
- Large-scale production requires growing microbes in very large vessels called fermentors.
- Fermented Beverages:
- Microbe: Brewer's Yeast (Saccharomyces cerevisiae) used for fermenting malted cereals and fruit juices.
- Products:
- Without Distillation: Wine, Beer (lower alcohol content).
- With Distillation: Whisky, Brandy, Rum (higher alcohol content). Distillation increases the concentration of alcohol.
- Antibiotics:
- Definition: Chemical substances produced by some microbes that can kill or retard the growth of other (disease-causing) microbes.
- Discovery: Alexander Fleming observed Penicillium notatum inhibiting Staphylococcus bacteria. The antibiotic was named Penicillin.
- Full Potential: Established later by Ernest Chain and Howard Florey. Fleming, Chain, and Florey awarded Nobel Prize in 1945.
- Significance: Revolutionized medicine, treating deadly diseases like plague, whooping cough, diphtheria, leprosy.
- Other Examples: Streptomycin, Tetracycline etc. (derived from other bacteria/fungi).
- Chemicals, Enzymes, and Bioactive Molecules:
- Organic Acids:
- Citric Acid: Aspergillus niger (fungus)
- Acetic Acid: Acetobacter aceti (bacterium)
- Butyric Acid: Clostridium butylicum (bacterium)
- Lactic Acid: Lactobacillus (bacterium)
- Ethanol: Saccharomyces cerevisiae (yeast) - large scale industrial production.
- Enzymes:
- Lipases: Used in detergents (oil stain removal), produced by microbes.
- Pectinases & Proteases: Used for clarifying bottled fruit juices.
- Streptokinase: Produced by Streptococcus bacteria. Genetically engineered. Used as a 'clot buster' for removing clots from blood vessels of heart attack patients (myocardial infarction).
- Bioactive Molecules:
- Cyclosporin A: Produced by Trichoderma polysporum (fungus). Used as an immunosuppressive agent in organ transplant patients.
- Statins: Produced by Monascus purpureus (yeast). Used as blood-cholesterol lowering agents. They act by competitively inhibiting the enzyme responsible for cholesterol synthesis.
- Organic Acids:
4. Microbes in Sewage Treatment:
- Sewage: Municipal wastewater containing large amounts of human excreta and organic matter. Pathogenic microbes are often present.
- Treatment Aim: Reduce organic matter and kill pathogens before discharge into natural water bodies. Carried out in Sewage Treatment Plants (STPs).
- Primary Treatment (Physical):
- Removal of large and small particles through filtration (removing floating debris) and sedimentation (grit/soil removal).
- Solids that settle form primary sludge. Supernatant forms the primary effluent.
- Secondary Treatment (Biological):
- Primary effluent passed into large aeration tanks.
- Air is pumped, and it's mechanically agitated. Allows vigorous growth of useful aerobic microbes into flocs (masses of bacteria associated with fungal filaments to form mesh-like structures).
- Microbes consume the major part of the organic matter in the effluent, significantly reducing the BOD (Biochemical Oxygen Demand).
- BOD: Amount of oxygen consumed by bacteria to oxidize all organic matter in 1 litre of water. High BOD indicates high pollution potential.
- Effluent passed to a settling tank. Bacterial flocs sediment, forming activated sludge.
- A small part of activated sludge is pumped back into the aeration tank as inoculum.
- Remaining major part of the sludge is pumped into large tanks called anaerobic sludge digesters.
- Here, anaerobic bacteria digest the bacteria and fungi in the sludge, producing biogas (mixture of methane, H2S, CO2).
- Effluent from the secondary treatment plant is generally released into natural water bodies.
- Government Initiatives: Ministry of Environment & Forests initiated Ganga Action Plan and Yamuna Action Plan to save major rivers from sewage pollution by building more STPs.
5. Microbes in Production of Biogas:
- Biogas: Mixture of gases (predominantly methane) produced by microbial activity. Used as fuel.
- Microbes: Methanogens (e.g., Methanobacterium). These are anaerobic bacteria.
- Substrate: Grow on cellulosic material.
- Location: Found in anaerobic sludge (sewage treatment), rumen of cattle (help digest cellulose), marshy areas.
- Composition: Methane (CH4), Carbon Dioxide (CO2), Hydrogen Sulfide (H2S). Methane is flammable.
- Source Material: Cattle dung (gobar), agricultural waste, sewage.
- Biogas Plant:
- Concrete tank (10-15 feet deep).
- Slurry of dung and water is fed.
- A floating cover rises as gas is produced.
- Outlet pipe connected to supply biogas.
- Spent slurry removed through another outlet, used as fertilizer.
- Technology Development: Indian Agricultural Research Institute (IARI) and Khadi and Village Industries Commission (KVIC). Common in rural areas.
6. Microbes as Biocontrol Agents:
- Biocontrol: Use of biological methods for controlling plant diseases and pests. Reduces reliance on toxic chemical pesticides and insecticides.
- Principle: Natural predation and parasitism.
- Examples:
- Ladybird beetle (insect) controls Aphids (pest).
- Dragonflies (insect) control Mosquitoes.
- Bacillus thuringiensis (Bt) (bacterium):
- Available as dried spores (sachets), mixed with water and sprayed onto vulnerable plants (e.g., brassicas, fruit trees).
- Eaten by insect larvae (e.g., butterfly caterpillars).
- In the alkaline gut of the larva, the toxin (Bt toxin) is released and activated.
- Toxin binds to epithelial cells, creates pores, causes swelling, lysis, and death of the larva.
- Specific Bt toxin genes introduced into plants (e.g., Bt cotton) make them resistant to insect pests.
- Trichoderma (fungus):
- Free-living fungi, common in root ecosystems.
- Effective biocontrol agents for several soil-borne plant pathogens.
- Baculoviruses:
- Pathogens that attack insects and other arthropods.
- Majority belong to the genus Nucleopolyhedrovirus (NPV).
- Species-specific, narrow spectrum insecticidal applications. No negative impact on plants, mammals, birds, fish, or non-target insects.
- Desirable for Integrated Pest Management (IPM) programs or when conserving beneficial insects.
7. Microbes as Biofertilizers:
- Biofertilizers: Organisms that enrich the nutrient quality (mainly nitrogen, phosphorus) of the soil. Reduce dependence on chemical fertilizers.
- Sources: Bacteria, fungi, cyanobacteria.
- Bacteria:
- Rhizobium: Symbiotic association with root nodules of leguminous plants (e.g., peas, beans). Fix atmospheric nitrogen (N2) into organic forms usable by the plant.
- Azospirillum & Azotobacter: Free-living bacteria in the soil. Fix atmospheric nitrogen, enriching soil nitrogen content.
- Fungi:
- Mycorrhiza: Symbiotic association between fungi and roots of higher plants.
- Fungal partner (e.g., genus Glomus) forms a network around/within the roots.
- Benefits to Plant:
- Absorbs phosphorus from the soil and passes it to the plant.
- Increases tolerance to salinity and drought.
- Provides resistance to root-borne pathogens.
- Overall increase in plant growth and development.
- Cyanobacteria (Blue-Green Algae):
- Autotrophic microbes, widely distributed.
- Examples: Anabaena, Nostoc, Oscillatoria.
- Fix atmospheric nitrogen.
- Important biofertilizers, especially in paddy fields (rice).
- Also add organic matter to the soil, increasing its fertility.
Conclusion:
Microbes are integral components of life on Earth and play vital, often unseen, roles in environmental balance, agriculture, industry, and human health. Understanding their beneficial activities is essential.
Multiple Choice Questions (MCQs):
-
Which bacterium is responsible for the large holes seen in Swiss cheese?
a) Lactobacillus
b) Propionibacterium shermanii
c) Penicillium roqueforti
d) Acetobacter aceti -
Statins, used for lowering blood-cholesterol levels, are obtained from:
a) Streptococcus
b) Trichoderma polysporum
c) Monascus purpureus
d) Aspergillus niger -
During secondary treatment of sewage, flocs are allowed to sediment in a settling tank. This sediment is called:
a) Primary sludge
b) Activated sludge
c) Anaerobic sludge
d) Primary effluent -
Which of the following is NOT a primary component of biogas produced by methanogens?
a) Methane (CH4)
b) Carbon Dioxide (CO2)
c) Oxygen (O2)
d) Hydrogen Sulfide (H2S) -
Bacillus thuringiensis (Bt) is used as a biocontrol agent against:
a) Aphids
b) Mosquito larvae
c) Butterfly caterpillars
d) Plant pathogenic fungi -
Cyclosporin A, an immunosuppressive agent, is produced by the fungus:
a) Penicillium notatum
b) Trichoderma polysporum
c) Saccharomyces cerevisiae
d) Monascus purpureus -
Which group of organisms forms mycorrhizal associations with plant roots, primarily aiding in phosphorus absorption?
a) Bacteria like Rhizobium
b) Cyanobacteria like Nostoc
c) Fungi like Glomus
d) Baculoviruses -
The BOD (Biochemical Oxygen Demand) of wastewater is reduced significantly during which stage of sewage treatment?
a) Primary treatment (Sedimentation)
b) Secondary treatment (Aeration tank)
c) Anaerobic sludge digestion
d) Filtration -
Which of the following microbes is used for producing citric acid commercially?
a) Acetobacter aceti
b) Lactobacillus
c) Aspergillus niger
d) Clostridium butylicum -
Baculoviruses, particularly Nucleopolyhedrovirus (NPV), are considered excellent biocontrol agents because they are:
a) Broad-spectrum pesticides
b) Effective against fungi
c) Species-specific and safe for non-target organisms
d) Producers of antibiotics
Answer Key for MCQs:
- b) Propionibacterium shermanii
- c) Monascus purpureus
- b) Activated sludge
- c) Oxygen (O2)
- c) Butterfly caterpillars
- b) Trichoderma polysporum
- c) Fungi like Glomus
- b) Secondary treatment (Aeration tank)
- c) Aspergillus niger
- c) Species-specific and safe for non-target organisms
Make sure you revise these specific examples and processes thoroughly. Good luck with your preparation!