NCERT Solutions for Class 12 Biology Chapter 8 Microbes in Human Welfare
NCERT Solutions for Class 12 Biology Chapter 8 Microbes in Human Welfare covers Household Products, Industrial Applications, Sewage Treatment, Biogas Production, Biocontrol Agents, and Biofertilizers.
Overview of Topics & Subtopics (Click to Jump)
1. Microbes in Household & Industrial Products
Short Note:
• Household Products:
- Curd: Lactobacillus / Lactic Acid Bacteria (LAB) converts milk sugar lactose into lactic acid, coagulating milk proteins and enriching Vitamin B12.
- Dough / Bread: Fermented using Baker's yeast (Saccharomyces cerevisiae). CO2 release gives puffy appearance.
- Swiss Cheese: Large holes created by CO2 produced by Propionibacterium shermanii.
• Industrial Chemicals & Enzymes:
- Citric acid: Aspergillus niger (Fungus)
- Acetic acid: Acetobacter aceti (Bacterium)
- Butyric acid: Clostridium butylicum (Bacterium)
- Lactic acid: Lactobacillus (Bacterium)
- Streptokinase: Produced by Streptococcus, acts as 'clot buster' in blood vessels.
- Cyclosporin A: Immunosuppressive agent produced by Trichoderma polysporum (Fungus).
- Statins: Blood-cholesterol lowering agent produced by Monascus purpureus (Yeast).
2. Microbes in Sewage Treatment & Biogas Production
Short Note:
• Sewage Treatment Process:
1. Primary Treatment (Physical): Sequential filtration and sedimentation to remove floating debris and grit.
2. Secondary Treatment (Biological): Primary effluent passed into aeration tanks. Aerobic microbes grow into 'flocs' (masses of bacteria associated with fungal filaments). Reduces BOD (Biochemical Oxygen Demand).
• Once BOD drops significantly, effluent passes into settling tank where flocs settle as activated sludge. Sludge goes to anaerobic sludge digesters where anaerobic methanogens produce biogas.
• Biogas Production: Biogas contains methane (CH4), CO2, and H2. Produced by anaerobic methanogenic bacteria like Methanobacterium operating on dung/organic waste.
3. Microbes as Biocontrol Agents & Biofertilizers
Short Note:
• Biocontrol Agents: Biological methods for controlling plant diseases and pests.
- Ladybird & Dragonflies: Control aphids and mosquitoes.
- Bacillus thuringiensis (Bt): Controls butterfly caterpillars.
- Trichoderma: Free-living fungus species effective against several plant pathogens in root ecosystems.
- Baculoviruses (Nucleopolyhedrovirus): Species-specific, narrow spectrum insecticidal applications with no negative impact on plants, mammals, or non-target insects.
• Biofertilizers: Organisms that enrich soil nutrient quality.
- Nitrogen Fixers: Symbiotic (Rhizobium with legumes; Mycorrhiza / Glomus with roots), Free-living (Azospirillum, Azotobacter), Cyanobacteria (Anabaena, Nostoc, Oscillatoria).
Intext & Conceptual Questions
Biochemical Oxygen Demand (BOD): It refers to the amount of oxygen that would be consumed if all the organic matter in one liter of water were oxidized by bacteria.
Relation to Water Pollution:
• Higher BOD indicates a greater amount of organic matter present in water, which means more aerobic bacteria are required to decompose it.
• Therefore, High BOD = Highly Polluted Water.
• As BOD decreases during sewage treatment, it indicates that water pollution has significantly reduced.
| Organism | Bioactive Molecule | Medical Application |
|---|---|---|
| Trichoderma polysporum (Fungus) | Cyclosporin A | Used as an immunosuppressive agent in organ-transplant patients. |
| Monascus purpureus (Yeast) | Statin | Used as a blood-cholesterol lowering agent by competitively inhibiting cholesterol-synthesizing enzymes. |
Textbook Chapter End Exercise Questions
• Primary Treatment: Microbes play no direct role in primary treatment, as it is a purely physical process involving filtration and sedimentation.
• Secondary Treatment (Biological Treatment):
1. Effluent is pumped into large aeration tanks where aerobic microbes grow rapidly into flocs (bacterial masses held together by fungal filaments).
2. These microbes consume organic matter in the effluent, significantly lowering the BOD.
3. The effluent is passed to a settling tank where flocs settle down to form activated sludge.
4. A major part of the sludge is pumped into anaerobic sludge digesters, where anaerobic bacteria (methanogens) digest the fungi and bacteria, producing biogas (methane, CO2, H2S).
Baculoviruses: They are pathogens (belonging to genus Nucleopolyhedrovirus) that attack insects and other arthropods.
Desirable features in IPM:
1. They act as species-specific, narrow-spectrum insecticidal agents.
2. They have no negative impact on plants, mammals, birds, fish, or non-target insects.
3. They are ideal when beneficial insects are being conserved or when ecologically sensitive areas are being treated.
1. Bacteria:
• Symbiotic: Rhizobium fixes atmospheric nitrogen in root nodules of leguminous plants.
• Free-living: Azospirillum and Azotobacter enrich soil nitrogen content.
2. Fungi (Mycorrhiza):
• Fungi of genus Glomus form symbiotic associations with plant roots. They absorb phosphorus from soil and pass it to the host plant.
3. Cyanobacteria (Blue-green algae):
• Anabaena, Nostoc, Oscillatoria fix atmospheric nitrogen and add organic matter to soil, especially in paddy fields.
Read More & Chapter Resources
These short notes are designed for quick revision. Read the main points once, then use the related material below to practise the same chapter. Revising a concept and checking it with questions can make your preparation more focused.