class 12 notes

Class 12 Biology Notes Chapter 10 (Microbes in Human Welfare) – Examplar Problems Book

Philoid

Philoid

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Examplar Problems
Alright class, let's delve into Chapter 10: Microbes in Human Welfare. This is a crucial chapter, not just for your board exams but also for various competitive government exams, as it highlights the immensely beneficial roles microbes play, often overlooked. We'll focus on the key aspects relevant for objective-type questions.

Chapter 10: Microbes in Human Welfare - Detailed Notes

Introduction:
Microbes (bacteria, fungi, protozoa, viruses, viroids, prions) are omnipresent. While many are pathogenic, a vast majority are useful to humans in diverse ways. This chapter explores these positive contributions.

1. Microbes in Household Products:

  • Curd Production:
    • Microbe: Lactic Acid Bacteria (LAB), primarily Lactobacillus.
    • Process: LAB grow in milk, fermenting lactose into lactic acid.
    • Benefits: Lactic acid coagulates and partially digests milk proteins (casein). Increases nutritional value by increasing Vitamin B12. Checks the growth of disease-causing microbes in the stomach.
    • Inoculum/Starter: A small amount of curd containing millions of LAB is added to fresh milk.
  • Dough Fermentation:
    • Microbes: Bacteria and Fungi (Yeasts).
    • Products: Dosa, Idli (fermented by bacteria, puffiness due to CO2 production). Bread (fermented by Baker's Yeast - Saccharomyces cerevisiae).
    • Process: Fermentation releases CO2, causing the dough to rise ('leavening').
  • Toddy:
    • Traditional drink in Southern India.
    • Process: Fermentation of sap from palms by naturally occurring yeasts.
  • Cheese:
    • One of the oldest microbially processed foods.
    • Process: Concentration of milk fat and casein. Different varieties depend on the specific microbes used for ripening.
    • Examples:
      • Swiss Cheese: Characterized by large holes due to the production of large amounts of CO2 by the bacterium Propionibacterium shermanii.
      • Roquefort Cheese: Ripened by growing a specific fungus, Penicillium roqueforti, on it, giving a characteristic flavour.

2. Microbes in Industrial Products:

Large-scale production requires growing microbes in very large vessels called fermenters.

  • Fermented Beverages:
    • Microbe: Saccharomyces cerevisiae (Brewer's Yeast). Also used for bread-making.
    • Process: Ferments malted cereals and fruit juices to produce ethanol (alcohol).
    • Types:
      • Without distillation: Wine, Beer (lower alcohol content).
      • With distillation: Whisky, Brandy, Rum, Gin, Vodka (higher alcohol content). Distillation increases alcohol concentration.
  • Antibiotics:
    • Definition: Chemical substances produced by some microbes that can kill or retard the growth of other (disease-causing) microbes.
    • Discovery: Penicillin was the first antibiotic discovered by Alexander Fleming (working on Staphylococcus bacteria, observed inhibition by Penicillium notatum mould). Its full potential was established later by Ernest Chain and Howard Florey. Fleming, Chain, and Florey were awarded the Nobel Prize in 1945.
    • Significance: Revolutionized medicine, treating deadly diseases like plague, whooping cough, diphtheria, leprosy.
  • Chemicals, Enzymes, and Other Bioactive Molecules:
    • Organic Acids:
      • Aspergillus niger (fungus): Citric acid
      • Acetobacter aceti (bacterium): Acetic acid
      • Clostridium butylicum (bacterium): Butyric acid
      • Lactobacillus (bacterium): Lactic acid
    • Ethanol: Saccharomyces cerevisiae (yeast) - commercial production.
    • Enzymes:
      • Lipases: Used in detergent formulations (oil stain removal), laundry.
      • 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 in myocardial infarction (heart attack) patients.
    • Bioactive Molecules:
      • Cyclosporin A: Produced by the fungus Trichoderma polysporum. Used as an immunosuppressive agent in organ transplant patients.
      • Statins: Produced by the yeast Monascus purpureus. Used as blood-cholesterol lowering agents. They act by competitively inhibiting the enzyme responsible for cholesterol synthesis.

3. Microbes in Sewage Treatment:

  • Sewage: Municipal wastewater containing large amounts of organic matter and pathogenic microbes. Cannot be discharged directly into natural water bodies.
  • Sewage Treatment Plants (STPs): Treatment is done in two stages:
    • Primary Treatment (Physical):
      • Removal of large and small particles through filtration (removing floating debris) and sedimentation (grit/soil settles).
      • Solids that settle form primary sludge. The supernatant forms the effluent.
    • Secondary Treatment (Biological):
      • Primary effluent is passed into large aeration tanks. Air is pumped in, allowing vigorous growth of useful aerobic microbes into flocs (masses of bacteria associated with fungal filaments forming mesh-like structures).
      • Microbes consume the major part of the organic matter in the effluent, significantly reducing the BOD (Biochemical Oxygen Demand). BOD is a measure of the organic matter present; higher BOD means more pollution potential.
      • Effluent is then passed into a settling tank where bacterial flocs sediment. This sediment is called activated sludge.
      • A small part of activated sludge is pumped back into the aeration tank as inoculum.
      • The 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).
      • The effluent from the secondary treatment plant is generally released into natural water bodies.
  • Ministry of Environment & Forests: Initiated Ganga Action Plan & Yamuna Action Plan to save major rivers from pollution, involving building more STPs.

4. Microbes in Production of Biogas:

  • Biogas: Mixture of gases (predominantly methane - CH4) produced by microbial activity. Used as fuel.
  • Microbes: Methanogens (e.g., Methanobacterium). These are anaerobic bacteria.
  • Substrate: Cellulose-rich materials (e.g., cattle dung - gobar, plant waste). Methanogens are also present in the rumen of cattle, helping digest cellulose.
  • Process: Occurs in a biogas plant (concrete tank with slurry inlet, digester, gas outlet, gas holder, slurry outlet).
    • Slurry of dung and water is fed.
    • Anaerobic digestion by methanogens produces biogas (CH4, CO2, H2, H2S).
    • Gas is collected and used for cooking and lighting.
    • Spent slurry is removed and used as fertilizer.
  • Technology Development: In India, mainly due to efforts of IARI (Indian Agricultural Research Institute) and KVIC (Khadi and Village Industries Commission). Particularly beneficial in rural areas.

5. Microbes as Biocontrol Agents:

  • Biocontrol: Use of biological methods for controlling plant diseases and pests. Reduces reliance on chemical pesticides and insecticides.
  • Principle: Based on natural predation or host-pathogen relationships.
  • Examples:
    • Ladybird beetle (Red & black markings) controls Aphids.
    • Dragonflies control Mosquitoes.
    • Bacillus thuringiensis (Bt):
      • Bacterium whose dried spores are mixed with water and sprayed onto vulnerable plants (e.g., brassicas, fruit trees).
      • Eaten by insect larvae (caterpillars). In the alkaline gut of the larva, the toxin (Bt toxin - Cry protein) is released and activated, causing pores in the gut lining, leading to death.
      • Specific to the target insect group.
      • Genes encoding Bt toxin have been introduced into plants (e.g., Bt Cotton) making them pest-resistant.
    • Trichoderma species:
      • 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.

6. Microbes as Biofertilizers:

  • Biofertilizers: Organisms that enrich the nutrient quality (mainly nitrogen and phosphorus) of the soil. Reduce dependence on chemical fertilizers.
  • Main Sources: Bacteria, Fungi, Cyanobacteria.
  • Examples:
    • 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.
      • Free-living N-fixing bacteria: Azospirillum and Azotobacter. Enrich nitrogen content of the soil.
    • Fungi:
      • Mycorrhiza: Symbiotic association between fungi and roots of higher plants.
        • Fungal symbiont (e.g., genus Glomus) absorbs phosphorus from the soil and passes it to the plant.
        • Also provides benefits like resistance to root-borne pathogens, tolerance to salinity and drought.
    • Cyanobacteria (Blue-Green Algae):
      • Autotrophic microbes, widely distributed.
      • Examples: Anabaena, Nostoc, Oscillatoria.
      • Fix atmospheric nitrogen (often in specialized cells called heterocysts).
      • Important biofertilizers, especially in paddy fields (rice).
      • Also add organic matter to the soil, increasing fertility.

Conclusion:
Microbes are integral components of life on Earth and play critical, beneficial roles in ecological balance and human welfare, from food production and medicine to waste management and agriculture. Understanding these roles is essential.

Multiple Choice Questions (MCQs):

  1. The large holes in Swiss cheese are due to the production of a large amount of CO2 by which microbe?
    a) Lactobacillus
    b) Saccharomyces cerevisiae
    c) Propionibacterium shermanii
    d) Penicillium roqueforti

  2. Which of the following is produced without distillation?
    a) Whisky
    b) Brandy
    c) Rum
    d) Wine

  3. Statins, used for lowering blood-cholesterol levels, are produced by:
    a) Streptococcus
    b) Monascus purpureus
    c) Trichoderma polysporum
    d) Aspergillus niger

  4. During secondary treatment of sewage, bacterial flocs are allowed to sediment in a settling tank. This sediment is called:
    a) Primary sludge
    b) Activated sludge
    c) Effluent
    d) Flocculated biomass

  5. The primary gas produced in a biogas plant by methanogens is:
    a) Carbon dioxide (CO2)
    b) Methane (CH4)
    c) Hydrogen sulfide (H2S)
    d) Oxygen (O2)

  6. Bacillus thuringiensis (Bt) is used as a biocontrol agent against:
    a) Aphids
    b) Mosquitoes
    c) Insect larvae (caterpillars)
    d) Plant pathogenic fungi

  7. Cyclosporin A, an immunosuppressive agent, is obtained from:
    a) Monascus purpureus (Yeast)
    b) Aspergillus niger (Fungus)
    c) Trichoderma polysporum (Fungus)
    d) Penicillium notatum (Fungus)

  8. Which of the following is a free-living nitrogen-fixing bacterium found in the soil?
    a) Rhizobium
    b) Glomus
    c) Azotobacter
    d) Nostoc

  9. Mycorrhiza represents a symbiotic association between:
    a) Bacteria and roots of higher plants
    b) Fungi and roots of higher plants
    c) Algae and fungi (Lichens)
    d) Cyanobacteria and roots of cycads

  10. BOD (Biochemical Oxygen Demand) is a measure of:
    a) Industrial pollution only
    b) Dissolved oxygen needed by aerobic microbes to oxidise organic matter
    c) The amount of carbon dioxide produced during fermentation
    d) The activity of anaerobic bacteria in sludge digesters

Answer Key:

  1. c
  2. d
  3. b
  4. b
  5. b
  6. c
  7. c
  8. c
  9. b
  10. b

Study these notes thoroughly. Pay close attention to the specific names of microbes and their products or functions. Good luck with your preparation!

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