📝 Chapter Notes & Revision

Microbes in Human Welfare

🏫 MP BoardClass 12Biology

📐 Formula & Cheat Sheet (English)

Quick Revision Notes: Class 12 Biology

Chapter: Microbes in Human Welfare (मानव कल्याण में सूक्ष्मजीव)

### 1. Introduction to Microbes in Human Welfare

Microbes (सूक्ष्मजीव) are major components of biological systems on Earth. While many cause diseases, a majority of them are extremely useful to humans.

  • Categories: Bacteria, Fungi, Protozoa, and some microscopic plants/viruses (like bacteriophages).
  • Habit: They can live in extreme environments like geysers (thermal vents), deep in the soil, under snow, etc.

### 2. Microbes in Household Products

Microbes are commonly used to convert simple food items into more nutritious and palatable forms.

  • Curd (दही):
    • Produced by Lactic Acid Bacteria (LAB) such as Lactobacillus.
    • LAB grow in milk and convert it to curd by producing acids that coagulate and partially digest milk proteins (casein).
    • Nutritional Benefit: Improves Vitamin B12 content in curd.
  • Dough Fermentation (खमीर उठाना):
    • Dough used for making foods like dosa and idli is fermented by bacteria.
    • The puffy appearance of dough is due to the production of Carbon Dioxide ($\text{CO}_2$) gas by respiration.
  • Bread Making:
    • Baker's yeast ($Saccharomyces\ cerevisiae$) is used to ferment dough for bread.
  • Traditional Drinks/Foods:
    • Toddy: A traditional drink of southern India made by fermenting sap from palms.
    • Swiss Cheese: Large holes in Swiss cheese are due to the production of a large amount of $\text{CO}_2$ by the bacterium Propionibacterium sharmanii.
    • Roquefort Cheese: Ripened by growing a specific fungi on them, giving them a particular flavor.

### 3. Microbes in Industrial Products

For industrial scale production, microbes are grown in large vessels called Fermenters (किण्वित्र).

  • Fermented Beverages:
    • Yeast (Saccharomyces cerevisiae / Brewer's yeast) is used for fermenting malted cereals and fruit juices to produce ethanol.
    • Wine and Beer are produced without distillation.
    • Whisky, Brandy, and Rum are produced by distillation of the fermented broth.
  • Antibiotics (प्रतिजैविक):
    • Chemical substances produced by some microbes that can kill or retard the growth of other (pathogenic) microbes.
    • First Antibiotic Discovered: Penicillin (by Alexander Fleming from Penicillium notatum).
    • Its full potential as an effective antibiotic was established by Ernest Chain and Howard Florey.
    • Other examples: Streptomycin, Erythromycin, Tetracycline.
  • Chemicals, Enzymes, and other Bioactive Molecules:
    • Organic Acids:
      • Aspergillus niger (Fungus) $\rightarrow$ Citric acid
      • Acetobacter acetic (Bacterium) $\rightarrow$ Acetic acid
      • Butyribacterium (Bacterium) $\rightarrow$ Butyric acid
      • Lactobacillus (Bacterium) $\rightarrow$ Lactic acid
    • Alcohols:
      • Saccharomyces cerevisiae $\rightarrow$ Ethanol
    • Enzymes:
      • Lipases: Used in detergent formulations to remove oily stains from laundry.
      • Pectinases and Proteases: Used for clearing bottled fruit juices.
      • Streptokinase: Produced by the bacterium Streptococcus and modified by genetic engineering; used as a "clot buster" for removing clots from the blood vessels of patients who have undergone myocardial infarction (heart attack).
    • 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 by competitively inhibiting the enzyme responsible for synthesis of cholesterol.

### 4. Microbes in Sewage Treatment (वाहित मल उपचार)

Sewage contains large amounts of organic matter and microbes. It cannot be discharged directly into natural water bodies without treatment done in Sewage Treatment Plants (STPs).

  • Primary Treatment (Physical Treatment):
    • Involves physical removal of particles (large and small) through filtration and sedimentation.
    • Floating debris is removed by sequential filtration.
    • Grit (soil and small pebbles) is removed by sedimentation.
    • The effluent from primary settling is taken for secondary treatment.
  • Secondary Treatment (Biological Treatment):
    • Primary effluent is passed into large aeration tanks and constantly agitated mechanically, and air is pumped into it.
    • This allows rapid growth of useful aerobic microbes into flocs (masses of bacteria associated with fungal filaments to form mesh-like structures).
    • While growing, these microbes consume the major part of the organic matter in the effluent.
    • This significantly reduces the BOD (Biochemical Oxygen Demand) of the effluent.
    • BOD (जैविक ऑक्सीजन मांग): The amount of oxygen that would be consumed if all the organic matter in one liter of water were oxidized by bacteria. Higher BOD = More polluted water.
    • Once BOD is reduced, the effluent is passed into a settling tank where the bacterial flocs are allowed to sediment. This sediment is called activated sludge.
    • A small part of the activated sludge is pumped back into the aeration tank to serve as the 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 a mixture of gases such as Methane ($\text{CH}_4$), Hydrogen Sulphide ($\text{H}_2\text{S}$), and Carbon Dioxide ($\text{CO}_2$)—commonly known as Biogas.

### 5. Microbes as Biofertilisers (जैव उर्वरक)

Biofertilisers are organisms that enrich the nutrient quality of the soil. The main sources of biofertilisers are bacteria, fungi, and cyanobacteria.

  • Rhizobium (Bacteria): Forms symbiotic associations with the root nodules of leguminous plants and fixes atmospheric nitrogen into organic forms.
  • Free-living Nitrogen Fixers (in soil): Azospirillum and Azotobacter enrich the nitrogen content of the soil.
  • Mycorrhiza (Fungi): Symbiotic association between fungi and roots of higher plants (e.g., Glomus genus).
    • Benefits: Fungal symbiont absorbs phosphorus from soil and passes it to the plant. Provides resistance to root-borne pathogens, tolerance to salinity and drought, and overall plant growth.
  • Cyanobacteria (Blue-Green Algae): Autotrophic microbes widely distributed in aquatic and terrestrial environments, many of which can fix atmospheric nitrogen (e.g., Anabaena, Nostoc, Oscillatoria).
    • Example: In paddy fields, Blue-Green Algae serve as an important biofertiliser. Anabaena enriches soil fertility by adding organic matter.

### 6. Microbes as Biopesticides (जैव-पीड़कनाशियों के रूप में सूक्ष्मजीव)

Biopesticides are biological agents used to control plant pests and diseases, offering an eco-friendly alternative to toxic chemical pesticides.

  • Bt Cotton / Bacillus thuringiensis:
    • The bacterium Bacillus thuringiensis (Bt) produces crystal proteins containing toxic insecticidal proteins.
    • These crystals kill specific insect pests (like lepidopterans, coleopterans, dipterans).
    • The toxin is inactive in the bacteria as protoxins, but once ingested by the insect, the alkaline gut of the insect solubilizes the crystals, turning it into an active form that creates pores in the gut cells, causing death.
  • Nucleopolyhedrovirus (NPV):
    • Viruses that attack insects and other arthropods.
    • Most NPVs used as biological control agents are in the genus Nucleopolyhedrovirus.
    • They are excellent candidates for Species-specific, narrow-spectrum insecticidal applications. They have no negative impacts on plants, mammals, birds, fish, or even non-target insects (ideal for Integrated Pest Management - IPM).
  • Trichoderma:
    • Free-living fungi that are very common in root ecosystems.
    • They are effective biocontrol agents of several plant pathogens.