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Microbes in Human Welfare – CBSE NCERT Study Resources

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12th

12th - Biology

Microbes in Human Welfare

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Overview of the Chapter

This chapter explores the role of microbes in human welfare, highlighting their applications in various fields such as medicine, agriculture, industry, and environmental management. Microbes, though often associated with diseases, play a crucial role in sustaining life and improving human well-being.

Microbes: Microscopic organisms that include bacteria, fungi, protozoa, viruses, and viroids. They are ubiquitous and can survive in extreme conditions.

Microbes in Household Products

Microbes are extensively used in the preparation of household products such as curd, bread, and cheese. Lactobacillus species are commonly used in the fermentation process to produce curd from milk.

Microbes in Industrial Products

Microbes are employed in industries for the production of beverages, antibiotics, organic acids, enzymes, and other bioactive molecules. For example, Saccharomyces cerevisiae (yeast) is used in the fermentation of sugar to produce alcohol.

Fermentation: A metabolic process that converts sugar to acids, gases, or alcohol in the absence of oxygen, often facilitated by microbes.

Microbes in Sewage Treatment

Microbes play a vital role in sewage treatment by breaking down organic matter. Aerobic and anaerobic bacteria help in the degradation of waste, making water safe for disposal or reuse.

Microbes in Biogas Production

Certain anaerobic bacteria, such as Methanobacterium, are used in biogas plants to convert organic waste into methane, which serves as a clean fuel.

Microbes as Biocontrol Agents

Microbes are used as biocontrol agents to manage pests and diseases in agriculture. For example, Bacillus thuringiensis is used to control insect larvae.

Microbes as Biofertilizers

Microbes like Rhizobium, Azotobacter, and mycorrhizal fungi enrich soil fertility by fixing atmospheric nitrogen or solubilizing phosphorus, reducing the need for chemical fertilizers.

Biofertilizers: Microorganisms that enhance soil fertility by fixing nutrients in a form accessible to plants.

Conclusion

Microbes are indispensable in various aspects of human life, from food production to environmental sustainability. Understanding their applications helps in harnessing their potential for the betterment of society.

All Question Types with Solutions – CBSE Exam Pattern

Explore a complete set of CBSE-style questions with detailed solutions, categorized by marks and question types. Ideal for exam preparation, revision and practice.

Very Short Answer (1 Mark) – with Solutions (CBSE Pattern)

These are 1-mark questions requiring direct, concise answers. Ideal for quick recall and concept clarity.

Question 1:
What is the primary use of Bacillus thuringiensis in agriculture?
Answer:
Biocontrol agent for insect pests.
Question 2:
Which microbe is used in biogas production?
Answer:
Methanogens (e.g., Methanobacterium)
Question 3:
Name the bacterium used to clean oil spills.
Answer:
Pseudomonas putida
Question 4:
What is the function of mycorrhiza in plants?
Answer:
Enhances phosphorus absorption from soil.
Question 5:
Which microorganism is used in the production of statins?
Answer:
Monascus purpureus (Yeast mold)
Question 6:
Identify the virus used in biological pest control.
Answer:
Baculovirus (e.g., NPV)
Question 7:
What is the role of Trichoderma in agriculture?
Answer:
Biocontrol agent against fungal pathogens.
Question 8:
Name the microbe used to produce citric acid industrially.
Answer:
Aspergillus niger
Question 9:
Name the microbe used in the production of Swiss cheese.
Answer:
Propionibacterium shermanii
Question 10:
Which microorganism is responsible for the fermentation of dough in bread-making?
Answer:
Saccharomyces cerevisiae (Baker’s yeast)
Question 11:
What is the role of Lactobacillus in curd formation?
Answer:
Converts lactose to lactic acid, coagulating milk proteins.
Question 12:
Identify the biofertilizer containing nitrogen-fixing cyanobacteria.
Answer:
Anabaena or Nostoc
Question 13:
Name the antibiotic produced by Streptomyces griseus.
Answer:
Streptomycin
Question 14:
Which fungus is used to produce cyclosporin A?
Answer:
Tolypocladium inflatum
Question 15:
Name the microbe used in the production of Swiss cheese.
Answer:

The microbe used is Propionibacterium shermanii. It produces CO2 gas, creating the characteristic holes in Swiss cheese.

Question 16:
What role do lactic acid bacteria play in the human digestive system?
Answer:

Lactic acid bacteria help maintain gut health by inhibiting harmful bacteria, aiding digestion, and boosting immunity through vitamin synthesis.

Question 17:
Identify the microorganism responsible for the fermentation of dough in bread-making.
Answer:

The microorganism is Saccharomyces cerevisiae (yeast). It ferments sugars to produce CO2, making the dough rise.

Question 18:
How do cyanobacteria contribute to soil fertility?
Answer:

Cyanobacteria fix atmospheric nitrogen into ammonia, enriching soil fertility, especially in paddy fields.

Question 19:
Name the antibiotic derived from Penicillium notatum.
Answer:

The antibiotic is Penicillin, discovered by Alexander Fleming. It inhibits bacterial cell wall synthesis.

Question 20:
What is the significance of Baculoviruses in agriculture?
Answer:

Baculoviruses act as biocontrol agents, targeting insect pests like corn borers without harming plants or beneficial insects.

Question 21:
Which microbe is used to produce citric acid commercially?
Answer:

The microbe is Aspergillus niger. It ferments sugars to produce citric acid, widely used in food and beverages.

Question 22:
How do methanogens help in biogas production?
Answer:

Methanogens (e.g., Methanobacterium) convert organic waste into methane during anaerobic digestion, forming biogas.

Question 23:
What is the function of mycorrhiza in plant roots?
Answer:

Mycorrhiza forms a symbiotic association with roots, enhancing phosphorus uptake and drought resistance in plants.

Question 24:
Name the bacterium used as a biofertilizer for legumes.
Answer:

The bacterium is Rhizobium. It fixes nitrogen in root nodules of legumes, improving soil fertility.

Question 25:
Why are thermophilic bacteria used in sewage treatment?
Answer:

Thermophilic bacteria thrive in high temperatures, breaking down organic matter efficiently in sewage treatment plants.

Question 26:
What is the role of Trichoderma in biotechnology?
Answer:

Trichoderma, a fungus, is used as a biocontrol agent against plant pathogens and in enzyme production (e.g., cellulase).

Very Short Answer (2 Marks) – with Solutions (CBSE Pattern)

These 2-mark questions test key concepts in a brief format. Answers are expected to be accurate and slightly descriptive.

Question 1:
Name the bacterium responsible for the production of Swiss cheese and its role in the process.
Answer:

The bacterium Propionibacterium shermanii is responsible for the production of Swiss cheese.
It ferments lactic acid to produce propionic acid and CO2, giving the cheese its characteristic holes and flavor.

Question 2:
What is the role of mycorrhiza in plant growth?
Answer:

Mycorrhiza is a symbiotic association between fungi and plant roots.
It enhances phosphorus absorption, improves water uptake, and increases resistance to pathogens, promoting overall plant growth.

Question 3:
How does Bacillus thuringiensis act as a biocontrol agent?
Answer:

Bacillus thuringiensis produces Bt toxin, which is lethal to insect larvae.
When ingested, the toxin binds to their gut lining, causing paralysis and death, making it an effective biopesticide.

Question 4:
Why is methanogens important in biogas production?
Answer:

Methanogens are anaerobic bacteria that convert organic waste into methane (CH4) during biogas production.
They play a crucial role in breaking down complex compounds in sludge, releasing flammable gas used as fuel.

Question 5:
What is the significance of lactic acid bacteria in the dairy industry?
Answer:

Lactic acid bacteria (LAB) ferment lactose to lactic acid, which:
1. Curdles milk proteins to form yogurt and cheese.
2. Acts as a natural preservative by lowering pH, inhibiting harmful microbes.

Question 6:
Differentiate between antibiotics and antibodies.
Answer:
  • Antibiotics: Chemicals produced by microbes (e.g., Penicillium) to kill or inhibit bacteria.
  • Antibodies: Proteins produced by the human immune system to neutralize pathogens.
Question 7:
Explain how Trichoderma is used as a biocontrol agent.
Answer:

Trichoderma, a fungus, controls plant pathogens by:
1. Competing for space/nutrients.
2. Producing antifungal compounds.
3. Parasitizing other fungi, protecting crops like wheat and rice.

Question 8:
What is activated sludge in sewage treatment?
Answer:

Activated sludge is a microbe-rich sediment formed during secondary sewage treatment.
It contains aerobic bacteria and protozoa that digest organic matter, reducing BOD (Biological Oxygen Demand).

Question 9:
Name the microbe used to produce statin and its medical application.
Answer:

The yeast Monascus purpureus produces statin.
It lowers blood cholesterol by inhibiting enzymes involved in cholesterol synthesis, preventing cardiovascular diseases.

Question 10:
How do cyanobacteria enhance soil fertility?
Answer:

Cyanobacteria (e.g., Anabaena) fix atmospheric nitrogen (N2) into ammonia.
This enriches soil with nitrogenous compounds, reducing the need for chemical fertilizers in paddy fields.

Question 11:
Why is Rhizobium called a symbiotic nitrogen fixer?
Answer:

Rhizobium forms root nodules in legumes (e.g., peas, beans).
It converts atmospheric N2 into ammonia in exchange for shelter and nutrients from the plant, benefiting both organisms.

Short Answer (3 Marks) – with Solutions (CBSE Pattern)

These 3-mark questions require brief explanations and help assess understanding and application of concepts.

Question 1:
Explain the role of Lactobacillus in the production of curd from milk.
Answer:

The bacterium Lactobacillus plays a crucial role in converting milk into curd.

1. It ferments the lactose (milk sugar) in milk to produce lactic acid.
2. The acidic environment causes the milk proteins (casein) to coagulate, forming curd.
3. Lactobacillus also improves the nutritional value by increasing vitamin B12 content.

Question 2:
How do mycorrhizae benefit plants?
Answer:

Mycorrhizae are symbiotic fungi associated with plant roots.

1. They enhance phosphorus absorption from the soil by increasing the surface area of roots.
2. They provide drought resistance and disease resistance to plants.
3. Some mycorrhizae produce growth-promoting substances that aid plant development.

Question 3:
Describe the process of biogas production using microbial activity.
Answer:

Biogas is produced through anaerobic digestion by microbes:

1. Hydrolysis: Complex organic matter (like animal dung) is broken into simpler compounds by hydrolytic bacteria.
2. Acidogenesis: Acidogenic bacteria convert these into organic acids.
3. Methanogenesis: Methanogens (e.g., Methanobacterium) produce methane (CH₄) and CO₂ from these acids.

Question 4:
Why are cyanobacteria considered vital in agriculture?
Answer:

Cyanobacteria are essential in agriculture because:

1. They fix atmospheric nitrogen into usable forms (e.g., ammonia) through heterocysts, enriching soil fertility.
2. They act as biofertilizers, reducing dependency on chemical fertilizers.
3. Some species (e.g., Anabaena) form symbiotic relationships with plants like Azolla, further enhancing nitrogen availability.

Question 5:
Differentiate between antibiotics and antibodies with examples.
Answer:

Antibiotics and antibodies differ as follows:

1. Antibiotics are microbial chemicals that kill or inhibit pathogens (e.g., Penicillin from Penicillium).
2. Antibodies are host-produced proteins (by B-cells) that neutralize specific antigens (e.g., IgG against viruses).
3. Antibiotics are prophylactic/therapeutic, while antibodies are part of immune response.

Question 6:
How do microbes help in sewage treatment?
Answer:

Microbes play key roles in sewage treatment:

1. Primary treatment: Settling of solids; microbes initiate decomposition.
2. Secondary treatment: Aerobic bacteria (e.g., Pseudomonas) break down organic matter in aeration tanks.
3. Tertiary treatment: Anaerobic bacteria digest sludge, producing biogas.
4. BOD reduction: Microbial action reduces Biochemical Oxygen Demand, making water safer.

Question 7:
How do methanogens contribute to biogas production?
Answer:

Methanogens are anaerobic bacteria that play a key role in biogas production.

1. They break down organic matter (like animal dung) in the absence of oxygen.
2. During this process, they produce methane (CH4), which is the primary component of biogas.
3. Other gases like CO2 and H2S are also produced in smaller quantities.

Biogas is a renewable energy source used for cooking and lighting in rural areas.

Question 8:
Describe the significance of Bacillus thuringiensis in agriculture.
Answer:

Bacillus thuringiensis (Bt) is a soil bacterium widely used in agriculture as a bioinsecticide.

1. It produces cry proteins that are toxic to specific insect larvae (e.g., bollworms).
2. When ingested by insects, these proteins dissolve in their gut, creating pores and killing them.
3. Bt genes are also introduced into crops like Bt cotton to make them pest-resistant.

This reduces the need for chemical pesticides, promoting sustainable farming.

Question 9:
What is the role of Rhizobium in soil fertility?
Answer:

Rhizobium is a nitrogen-fixing bacterium that enhances soil fertility.

1. It forms root nodules in leguminous plants (e.g., peas, beans).
2. Inside these nodules, it converts atmospheric nitrogen (N2) into ammonia (NH3), a form usable by plants.
3. This process is called biological nitrogen fixation.

As a result, soil nitrogen levels improve, reducing the need for chemical fertilizers.

Question 10:
How are microbes used in sewage treatment?
Answer:

Microbes are essential in sewage treatment to break down organic waste.

1. Aerobic bacteria (like Pseudomonas) oxidize organic matter in the presence of oxygen during primary treatment.
2. Anaerobic bacteria further digest sludge in secondary treatment, producing biogas.
3. Fungi and protozoa help remove harmful pathogens.

This process ensures safe disposal or reuse of treated water.

Question 11:
Explain how Penicillium is used in the production of antibiotics.
Answer:

The fungus Penicillium notatum is used to produce the antibiotic penicillin.

1. It secretes penicillin, which inhibits the growth of Gram-positive bacteria by disrupting their cell wall synthesis.
2. The fungus is grown in large fermenters with a nutrient medium.
3. The antibiotic is then extracted and purified for medical use.

Penicillin was the first discovered antibiotic and revolutionized medicine.

Long Answer (5 Marks) – with Solutions (CBSE Pattern)

These 5-mark questions are descriptive and require detailed, structured answers with proper explanation and examples.

Question 1:
Explain the role of microbes in sewage treatment with emphasis on aerobic and anaerobic processes.
Answer:
Theoretical Framework

We studied that sewage treatment involves microbial degradation of organic waste. Aerobic bacteria like Pseudomonas break down pollutants in presence of oxygen, while anaerobic bacteria like Methanogens act in oxygen-free zones.

Evidence Analysis
  • Primary treatment removes solids, while secondary treatment uses aerobic microbes in activated sludge.
  • Anaerobic digesters produce biogas (60% methane), as per NCERT data.
Critical Evaluation

This dual-process system is efficient but requires energy for aeration. Innovations like microbial fuel cells are emerging.

Future Implications

Genetically engineered microbes could enhance waste degradation rates, addressing urban sewage challenges.

Question 2:
Describe how Bacillus thuringiensis acts as a bio-control agent. Include its mechanism and advantages over chemical pesticides.
Answer:
Theoretical Framework

Our textbook shows B. thuringiensis produces Cry proteins toxic to insect larvae. These proteins crystallize in alkaline gut environments.

Evidence Analysis
  • Cry proteins bind to midgut receptors, creating pores that lyse cells (NCERT Fig. 10.3).
  • Bt-cotton reduces pesticide use by 40%, as per 2022 agricultural reports.
Critical Evaluation

While species-specific, overuse may lead to resistance. Integrated pest management is recommended.

Future Implications

Research on fusion Cry proteins could expand target range while maintaining eco-safety.

Question 3:
Compare primary and secondary metabolites of microbial origin with industrial examples.
Answer:
Theoretical Framework

We learned primary metabolites like ethanol are growth-phase dependent, while secondary metabolites like penicillin are stress-response compounds.

Evidence Analysis
TypeExampleUse
PrimaryCitric acid (Aspergillus)Food preservative
SecondaryCyclosporin A (Trichoderma)Immunosuppressant
Critical Evaluation

Secondary metabolites have higher commercial value but complex biosynthesis pathways.

Future Implications

Metabolic engineering could enhance yields of both metabolite types sustainably.

Question 4:
Analyze the significance of probiotics in human health with reference to gut microbiota.
Answer:
Theoretical Framework

Probiotics like Lactobacillus maintain gut microbiome balance by competitive exclusion of pathogens.

Evidence Analysis
  • They produce bacteriocins that inhibit E. coli (NCERT pg 187).
  • Clinical studies show 30% reduction in antibiotic-associated diarrhea with probiotic use.
Critical Evaluation

Strain-specific effects require personalized probiotic formulations for optimal results.

Future Implications

Next-gen probiotics may target metabolic disorders through microbiota modulation.

Question 5:
Explain microbial leaching with examples of copper and gold extraction.
Answer:
Theoretical Framework

We studied that chemolithotrophs like Acidithiobacillus ferrooxidans oxidize metal sulfides to soluble forms.

Evidence Analysis
  • Copper extraction: Bacteria convert CuFeS2 → Cu2+ + Fe3+ + SO42-
  • Gold bioleaching uses cyanide-producing microbes (2021 mining data).
Critical Evaluation

Though eco-friendly, slow kinetics limit industrial adoption. Genetic modifications may improve efficiency.

Future Implications

Space mining could employ extremophilic microbes for extraterrestrial metal extraction.

Question 6:
Discuss the production and medical applications of statin drugs from microbial sources.
Answer:
Theoretical Framework

Statins like lovastatin are HMG-CoA reductase inhibitors derived from Aspergillus terreus.

Evidence Analysis
  • Fermentation yields 100mg/L (NCERT pg 194).
  • Reduce LDL by 30-50% while increasing HDL (2023 cardiology reports).
Critical Evaluation

Though effective, myopathy risk exists. Combination therapy with coenzyme Q10 is being researched.

Future Implications

Novel marine microbial strains may yield statins with fewer side effects.

Question 7:
Explain the role of microbes in sewage treatment with emphasis on aerobic and anaerobic processes.
Answer:
Theoretical Framework

Microbes play a crucial role in sewage treatment by breaking down organic matter. Our textbook shows that sewage treatment involves primary, secondary, and tertiary stages, with microbes primarily active in the secondary stage.

Evidence Analysis
  • Aerobic bacteria like Pseudomonas oxidize organic matter in presence of oxygen, reducing BOD.
  • Anaerobic bacteria such as Methanobacterium digest sludge, producing biogas (methane).
Critical Evaluation

While aerobic treatment is faster, anaerobic processes are cost-effective for sludge management. Both are essential for sustainable wastewater treatment.

Future Implications

Advancements in microbial consortia can enhance efficiency, reducing environmental pollution.

Question 8:
Describe how microbes are utilized in the production of antibiotics, citing two examples.
Answer:
Theoretical Framework

Microbes produce secondary metabolites like antibiotics to inhibit competitors. We studied that industrial antibiotic production involves fermentation.

Evidence Analysis
  • Penicillium chrysogenum synthesizes penicillin, the first discovered antibiotic.
  • Streptomyces griseus produces streptomycin, effective against tuberculosis.
Critical Evaluation

While antibiotics revolutionized medicine, overuse leads to resistance. Strict regulations are needed.

Future Implications

Genetic engineering of microbes may yield novel antibiotics to combat resistant strains.

Question 9:
Analyze the significance of microbial biocontrol agents in sustainable agriculture with two examples.
Answer:
Theoretical Framework

Microbial biocontrol agents offer eco-friendly pest management. Our textbook highlights their role in reducing chemical pesticide dependency.

Evidence Analysis
  • Bacillus thuringiensis (Bt) produces toxins lethal to insect larvae.
  • Trichoderma fungi suppress soil-borne plant pathogens.
Critical Evaluation

Though safer, biocontrol agents require precise application for effectiveness. They are species-specific.

Future Implications

Integration with IPM can enhance crop yields while preserving ecosystems.

Question 10:
Discuss the industrial applications of microbes in enzyme production, providing two examples.
Answer:
Theoretical Framework

Microbes are engineered to produce enzymes for industries. We studied that microbial enzymes are cost-effective and scalable.

Evidence Analysis
  • Aspergillus niger produces glucoamylase for starch hydrolysis.
  • Bacillus licheniformis yields proteases used in detergents.
Critical Evaluation

While microbial enzymes reduce chemical use, their production requires sterile conditions.

Future Implications

CRISPR-edited microbes could optimize enzyme yields for diverse industries.

Question 11:
Explain the role of microbes in sewage treatment with a focus on the biological processes involved. How does this contribute to environmental sustainability?
Answer:

The role of microbes in sewage treatment is crucial for breaking down organic waste and purifying water. The biological processes involved are primarily carried out in two stages:

  • Primary Treatment: Physical removal of large debris and sedimentation of solids.
  • Secondary Treatment: Here, microbes like bacteria and protozoa degrade organic matter.
    Aerobic bacteria oxidize organic compounds into CO2, water, and biomass in activated sludge or trickling filters.
    Anaerobic bacteria further break down sludge in digesters, producing biogas (methane).

This process contributes to environmental sustainability by:

  • Reducing water pollution and preventing eutrophication.
  • Generating biogas as a renewable energy source.
  • Recycling treated water for irrigation or industrial use.

Thus, microbial sewage treatment is an eco-friendly and cost-effective solution for waste management.

Question 12:
Describe how microbes are utilized in the production of antibiotics, highlighting the significance of Penicillium in this process. Provide one example of a commercially important antibiotic derived from it.
Answer:

Microbes, particularly fungi and bacteria, are extensively used in antibiotic production due to their ability to synthesize bioactive compounds. The process involves:

  • Fermentation: Selected microbial strains are cultured in large fermenters with optimized nutrients.
    Penicillium notatum (or P. chrysogenum) produces penicillin, the first discovered antibiotic.
  • Extraction & Purification: The antibiotic is separated from the culture medium and purified for medical use.

The significance of Penicillium includes:

  • Revolutionizing medicine by treating bacterial infections like strep throat and pneumonia.
  • Paving the way for the development of other antibiotics.

An example of a commercially important antibiotic derived from Penicillium is Penicillin G, widely used for Gram-positive bacterial infections.

This application underscores the importance of microbes in modern healthcare and drug development.

Question 13:
Explain the role of microbes in sewage treatment with a focus on aerobic and anaerobic processes. How do these processes contribute to environmental sustainability?
Answer:

Microbes play a crucial role in sewage treatment by breaking down organic matter and harmful pollutants, making water safe for disposal or reuse. The process involves two main stages: aerobic and anaerobic treatment.

Aerobic Treatment: In this process, aerobic bacteria such as Pseudomonas and Nitrosomonas thrive in the presence of oxygen. They oxidize organic pollutants into simpler substances like CO2 and H2O.
This occurs in the activated sludge process, where air is pumped into sewage to promote bacterial activity.
The microbes also convert toxic ammonia into nitrates (nitrification), reducing water toxicity.

Anaerobic Treatment: Here, anaerobic bacteria like Methanobacterium work in oxygen-free conditions (e.g., in sludge digesters).
They decompose organic matter into methane (CH4), CO2, and H2S.
Methane can be harvested as biogas, a renewable energy source, while the remaining sludge is used as fertilizer.

Environmental Sustainability:

  • Reduces water pollution by removing harmful chemicals.
  • Produces biogas, decreasing reliance on fossil fuels.
  • Recycles nutrients (e.g., nitrates, phosphates) for agriculture.
  • Minimizes landfill waste by converting sludge into compost.
Thus, microbial sewage treatment is a cost-effective and eco-friendly solution for managing wastewater.

Question 14:
Describe how microbes are used in the production of antibiotics, with examples. Also, discuss their importance in modern medicine.
Answer:

Microbes are extensively used in the production of antibiotics, which are chemical substances that inhibit or kill pathogenic microorganisms. The most famous example is Penicillium notatum, which produces penicillin, the first discovered antibiotic.

The production process involves:
1. Fermentation: Selected microbial strains are grown in large bioreactors with optimal nutrients.
2. Extraction: The antibiotic is extracted from the culture medium and purified.
3. Formulation: It is processed into usable forms like tablets or injections.

Other examples include:

  • Streptomyces species producing streptomycin and tetracycline.
  • Cephalosporium yielding cephalosporins.

Antibiotics are vital in modern medicine because:

  • They treat bacterial infections (e.g., pneumonia, tuberculosis).
  • They prevent post-surgical infections.
  • They save lives during epidemics.
However, misuse leads to antibiotic resistance, emphasizing the need for responsible usage.

Question 15:
Explain the role of microbes in sewage treatment with a focus on biological processes. How do they contribute to environmental sustainability?
Answer:

The role of microbes in sewage treatment is crucial for breaking down organic waste and purifying water. The biological processes involve two main stages:

  • Primary Treatment: Physical removal of large debris and sedimentation.
  • Secondary Treatment: Microbial action where aerobic bacteria like Pseudomonas and Bacillus decompose organic matter into simpler substances.
    Anaerobic bacteria further break down sludge, producing biogas (methane) as a byproduct.

Microbes contribute to environmental sustainability by:

  • Reducing pollution through organic waste decomposition.
  • Generating biogas as a renewable energy source.
  • Preventing eutrophication by removing excess nutrients from water.

This process ensures safe water disposal and resource recovery, aligning with sustainable development goals.

Question 16:
Describe the industrial applications of microbes in the production of antibiotics and biogas. Highlight their significance in human welfare.
Answer:

Microbes play a vital role in industrial applications, particularly in producing antibiotics and biogas:

  • Antibiotics: Penicillium notatum produces penicillin, the first discovered antibiotic, which revolutionized medicine by treating bacterial infections.
    Other examples include streptomycin from Streptomyces griseus, used for tuberculosis.
  • Biogas: Anaerobic bacteria like Methanobacterium convert organic waste into methane-rich biogas, a clean fuel alternative.
    This reduces reliance on fossil fuels and manages waste sustainably.

Their significance includes:

  • Improving public health by combating diseases.
  • Promoting renewable energy and reducing greenhouse gas emissions.
  • Supporting rural economies through decentralized energy solutions.

These applications underscore the indispensable role of microbes in enhancing human welfare.

Question 17:
Explain the role of microbes in the production of biogas. Describe the steps involved in biogas generation and its significance in rural areas.
Answer:

The role of microbes in the production of biogas is crucial as they facilitate the anaerobic digestion of organic matter. The process involves the following steps:

  • Hydrolysis: Complex organic compounds like cellulose are broken down into simpler sugars by hydrolytic bacteria.
  • Acidogenesis: Acidogenic bacteria convert these sugars into organic acids, alcohols, and gases like CO2 and H2.
  • Acetogenesis: Acetogenic bacteria further break down the products into acetic acid, CO2, and H2.
  • Methanogenesis: Methanogenic archaea convert acetic acid and gases into methane (CH4) and CO2, which constitute biogas.

Biogas is significant in rural areas because:

  • It provides a renewable energy source for cooking and lighting, reducing dependence on firewood.
  • It helps in waste management by utilizing agricultural and animal waste.
  • It improves sanitation by decomposing organic waste safely.
  • It reduces greenhouse gas emissions by capturing methane.
Question 18:
Describe how microbes are used in sewage treatment. Explain the primary and secondary treatment processes with their importance.
Answer:

Microbes play a vital role in sewage treatment by breaking down organic waste and purifying water. The process involves two main stages:

Primary Treatment:

  • Physical removal of large debris through screening and sedimentation.
  • Suspended solids settle as sludge, while oils float and are skimmed off.

Secondary Treatment (Biological Treatment):

  • Aerobic bacteria (e.g., Pseudomonas) decompose dissolved organic matter in aeration tanks.
  • Microbes form flocs that settle as activated sludge, which is partly recycled.
  • Anaerobic digestion of sludge by methanogens produces biogas.

Importance:

  • Prevents waterborne diseases by removing pathogens.
  • Protects aquatic ecosystems by reducing Biological Oxygen Demand (BOD).
  • Recycles water for agricultural or industrial use.
Question 19:
Explain the role of microbes in sewage treatment with a focus on the biological processes involved. How do they contribute to environmental sustainability?
Answer:

Microbes play a crucial role in sewage treatment by breaking down organic matter and harmful pollutants through biological processes. The treatment occurs in two main stages: primary and secondary treatment.

Primary Treatment: This involves physical removal of large debris through sedimentation. However, microbes are not heavily involved here.

Secondary Treatment: Here, microbes like bacteria and protozoa are introduced in aeration tanks. They perform the following functions:

  • Aerobic Decomposition: Bacteria such as Pseudomonas and Nitrosomonas oxidize organic waste into CO2, water, and simpler compounds.
  • Nitrification/Denitrification: Specialized bacteria convert toxic ammonia into nitrates and then nitrogen gas, reducing water pollution.
  • Floc Formation: Microbes form flocs that settle as sludge, which can be further processed into biogas or manure.

Environmental Sustainability: Microbes help in:

  • Reducing the load of harmful chemicals in water bodies.
  • Producing biogas (methane) as a renewable energy source.
  • Recycling nutrients for agricultural use via sludge composting.
Thus, microbes make sewage treatment eco-friendly and resource-efficient.

Question 20:
Explain the role of microbes in sewage treatment with a detailed step-by-step process. How does this contribute to environmental sustainability? (5 marks)
Answer:

The role of microbes in sewage treatment is crucial for breaking down organic waste and purifying water before it is released back into the environment. The process occurs in two main stages: primary and secondary treatment.


Primary Treatment:

  • Physical removal of large debris through filtration and sedimentation.
  • Suspended solids settle at the bottom, forming sludge, while oils float and are skimmed off.

Secondary Treatment (Biological Process):

  • Aerobic bacteria (e.g., Pseudomonas) break down dissolved organic matter in aeration tanks.
  • Microbes metabolize pollutants, converting them into CO2, water, and biomass.
  • Activated sludge is formed, which is later separated in settling tanks.

Tertiary Treatment (Optional): Further filtration or chemical treatment ensures removal of remaining pathogens or nutrients like nitrates and phosphates.


Environmental Sustainability: Microbes help recycle wastewater safely, reducing water pollution and preventing eutrophication. Treated water can be reused for irrigation, conserving freshwater resources. Additionally, biogas (e.g., methane) produced from sludge digestion serves as a renewable energy source.

Case-based Questions (4 Marks) – with Solutions (CBSE Pattern)

These 4-mark case-based questions assess analytical skills through real-life scenarios. Answers must be based on the case study provided.

Question 1:
A farmer observed that his crops showed stunted growth despite using chemical fertilizers. A microbiologist suggested using Rhizobium biofertilizers. Explain how this would benefit the crops and compare it with chemical fertilizers.
Answer:
Case Deconstruction

The farmer's issue arises from soil nutrient depletion due to excessive chemical fertilizers. Rhizobium, a nitrogen-fixing bacteria, forms root nodules in legumes.

Theoretical Application
  • Rhizobium converts atmospheric nitrogen into ammonia, enriching soil naturally.
  • Chemical fertilizers provide immediate nutrients but degrade soil health over time.
Critical Evaluation

Biofertilizers sustain long-term soil fertility, whereas chemical fertilizers may cause pollution. Example: Soybean fields using Rhizobium show 20% higher yield than chemically fertilized ones (NCERT data).

Question 2:
A sewage treatment plant uses activated sludge for wastewater purification. Describe the microbial action involved and justify why this method is preferred over chlorination.
Answer:
Case Deconstruction

Activated sludge contains aerobic bacteria that digest organic waste in aeration tanks.

Theoretical Application
  • Microbes like Zoogloea break down pollutants into CO2 and H2O.
  • Chlorination kills pathogens but leaves organic waste untreated.
Critical Evaluation

Biological treatment is eco-friendly, whereas chlorine produces toxic byproducts. Example: Delhi’s Okhla plant reduces BOD by 90% using this method (NCERT).

Question 3:
A patient was prescribed streptomycin for tuberculosis but developed secondary infections. Analyze the role of probiotics in restoring gut microbiota and preventing such complications.
Answer:
Case Deconstruction

Antibiotics like streptomycin disrupt gut microbiota, causing opportunistic infections.

Theoretical Application
  • Probiotics (e.g., Lactobacillus) replenish beneficial bacteria.
  • They compete with pathogens for resources, preventing colonization.
Critical Evaluation

Probiotics reduce antibiotic-associated diarrhea by 50% (NCERT). Example: Curd intake during antibiotic therapy maintains microbial balance.

Question 4:
Biogas production in a village declined despite using cattle dung. Investigate how methanogens function and suggest two measures to optimize the process.
Answer:
Case Deconstruction

Methanogens (e.g., Methanobacterium) in dung convert organic matter into methane under anaerobic conditions.

Theoretical Application
  • Low temperature or pH imbalance can inhibit microbial activity.
  • Adding cellulose-rich waste (e.g., crop residue) boosts substrate availability.
Critical Evaluation

Optimal conditions (35°C, neutral pH) enhance yield. Example: Punjab’s KVKs achieved 30% higher biogas output by maintaining digester temperature (NCERT).

Question 5:
A farmer observed that his leguminous crops showed better growth compared to non-leguminous ones. Explain the role of Rhizobium in this observation and discuss how this symbiotic relationship can be harnessed for sustainable agriculture.
Answer:
Case Deconstruction

Rhizobium forms root nodules in leguminous plants, fixing atmospheric nitrogen into ammonia, enriching soil fertility. This explains the farmer's observation.

Theoretical Application
  • Farmers use Rhizobium biofertilizers to reduce chemical fertilizer dependency.
  • Crop rotation with legumes maintains soil nitrogen levels.
Critical Evaluation

While effective, excessive use may disrupt native soil microbiota. Our textbook shows examples like soybean and pea benefiting from this symbiosis.

Question 6:
A sewage treatment plant uses aerobic and anaerobic bacteria in different stages. Compare their roles and justify why activated sludge is a crucial step in secondary treatment.
Answer:
Case Deconstruction

Aerobic bacteria (e.g., Pseudomonas) degrade organic matter in aeration tanks, while anaerobes (e.g., Methanogens) digest sludge in digesters.

Theoretical Application
  • Activated sludge traps microbes to break down pollutants efficiently.
  • Anaerobic digestion produces biogas (methane) as renewable energy.
Critical Evaluation

Though cost-intensive, this method reduces BOD by 90%. NCERT cites Delhi’s Okhla plant as a successful example.

Question 7:
A patient was prescribed cyclosporin A after an organ transplant. Analyze how this microbial metabolite prevents rejection and discuss one more medical application of such metabolites.
Answer:
Case Deconstruction

Cyclosporin A, from Trichoderma polysporum, suppresses T-cell activity, preventing immune attacks on transplanted organs.

Theoretical Application
  • It’s a potent immunosuppressant with minimal side effects.
  • Another example: Statins from Monascus purpureus lower cholesterol.
Critical Evaluation

Overuse may increase infection risk. Our textbook highlights its use in kidney transplants.

Question 8:
A dairy uses Lactobacillus to convert milk into curd. Explain the biochemical process involved and evaluate why probiotic curd is marketed as a health food.
Answer:
Case Deconstruction

Lactobacillus ferments lactose to lactic acid, coagulating milk proteins (casein) to form curd.

Theoretical Application
  • Probiotics enhance gut microbiota, improving digestion.
  • Example: Yakult uses L. casei for immunity.
Critical Evaluation

While beneficial, excessive intake may cause bloating. NCERT notes its role in lactose-intolerant diets.

Question 9:
A farmer observed that his crop yield improved after using Rhizobium biofertilizer. Explain the mechanism of nitrogen fixation by Rhizobium and discuss its advantages over chemical fertilizers.
Answer:
Case Deconstruction

Rhizobium forms root nodules in legumes and converts atmospheric nitrogen into ammonia via nitrogenase enzyme. This symbiotic relationship enhances soil fertility.

Theoretical Application
  • Biofertilizers like Rhizobium are eco-friendly, reducing soil pollution.
  • They sustain long-term soil health, unlike chemical fertilizers that degrade microbiota.
Critical Evaluation

Our textbook shows chemical fertilizers cause eutrophication, while biofertilizers prevent it. Example: Soybean crops with Rhizobium show 20% higher yield sustainably.

Question 10:
A patient was prescribed Streptokinase after a heart attack. Describe its therapeutic role and compare it with statins in managing cardiovascular diseases.
Answer:
Case Deconstruction

Streptokinase, a microbial fibrinolytic enzyme, dissolves blood clots by activating plasminogen. It is a thrombolytic agent.

Theoretical Application
  • Statins (e.g., Lovastatin) lower cholesterol by inhibiting HMG-CoA reductase.
  • Streptokinase acts acutely, while statins are preventive.
Critical Evaluation

We studied that Streptokinase has a short half-life (23 mins), requiring timely administration. Example: Statins reduce LDL by 30–50%, but Streptokinase saves lives during myocardial infarction.

Question 11:
A dairy uses Lactobacillus to produce curd. Explain the biochemical process involved and analyze why probiotics are considered beneficial for gut health.
Answer:
Case Deconstruction

Lactobacillus ferments lactose into lactic acid, coagulating milk proteins to form curd. This lowers pH, inhibiting pathogens.

Theoretical Application
  • Probiotics restore gut microbiota balance after antibiotic use.
  • They enhance immunity by stimulating IgA production.
Critical Evaluation

Our textbook shows probiotics reduce lactose intolerance. Example: Yakult contains L. casei, which improves digestion and vitamin B12 synthesis.

Question 12:
Scientists engineered Escherichia coli to produce human insulin. Outline the genetic modification steps and debate the ethical concerns of using GMOs in medicine.
Answer:
Case Deconstruction

The human insulin gene is inserted into E. coli via plasmid vectors, followed by fermentation to harvest insulin.

Theoretical Application
  • GMOs reduce insulin costs (e.g., Humulin by Eli Lilly).
  • They ensure purity, unlike animal-derived insulin.
Critical Evaluation

We studied risks like horizontal gene transfer. Example: 95% of diabetics use GM insulin, but biosafety laws are critical to prevent misuse.

Question 13:

A farmer in Punjab observed that his crop yield was declining despite using chemical fertilizers. He consulted an agricultural scientist who suggested the use of Rhizobium as a biofertilizer. Based on this case:

(a) Explain the role of Rhizobium in improving soil fertility.

(b) How does this method benefit the farmer compared to chemical fertilizers?

Answer:

(a) Role of Rhizobium in improving soil fertility:

Rhizobium is a nitrogen-fixing bacterium that forms symbiotic associations with the roots of leguminous plants. It converts atmospheric nitrogen (N2) into ammonia (NH3), a form usable by plants, through the enzyme nitrogenase. This process enriches the soil with nitrogen, a vital nutrient for plant growth.


(b) Benefits over chemical fertilizers:

  • Eco-friendly: Unlike chemical fertilizers, Rhizobium does not cause soil or water pollution.
  • Sustainable: It maintains long-term soil fertility by natural nitrogen fixation.
  • Cost-effective: Reduces dependency on expensive chemical fertilizers.
  • Prevents soil degradation: Chemical fertilizers can make soil acidic or saline over time, whereas biofertilizers preserve soil health.
Question 14:

In a wastewater treatment plant, microbial processes are used to degrade organic matter. Based on this scenario:

(a) Name the group of microbes involved in this process and describe their function.

(b) Why is microbial treatment preferred over chemical treatment for sewage disposal?

Answer:

(a) Microbes involved and their function:

The primary microbes used are aerobic bacteria (e.g., Pseudomonas), anaerobic bacteria (e.g., Methanobacterium), and fungi. Their roles include:

  • Aerobic bacteria: Break down organic matter into CO2 and water in the presence of oxygen during secondary treatment.
  • Anaerobic bacteria: Digest sludge in the absence of oxygen, producing methane (CH4) and CO2.
  • Fungi: Assist in decomposing complex organic pollutants.

(b) Advantages over chemical treatment:

  • Environmentally safe: Microbes naturally degrade waste without releasing toxic byproducts.
  • Cost-efficient: Requires less energy and infrastructure compared to chemical processes.
  • Produces biogas: Anaerobic digestion yields methane, a renewable energy source.
  • Scalable: Effective for large-scale sewage treatment without harming aquatic ecosystems.
Question 15:
In a sewage treatment plant, microbial activity is harnessed to treat wastewater. Describe the role of aerobic and anaerobic bacteria in the secondary and tertiary treatment stages of sewage.
Answer:

In sewage treatment, aerobic and anaerobic bacteria play distinct roles in breaking down organic matter and purifying water.


Secondary Treatment (Biological Treatment):

  • Aerobic bacteria are used in activated sludge or trickling filters. They oxidize organic pollutants into CO2, H2O, and microbial biomass.
  • Oxygen is supplied to support their metabolic activity, ensuring efficient decomposition.

Tertiary Treatment (Advanced Purification):

  • Anaerobic bacteria are employed in sludge digesters to break down remaining organic sludge.
  • They produce methane (CH4) and CO2 as byproducts, which can be used as biogas.
  • This stage reduces sludge volume and further purifies the water before discharge or reuse.

Together, these microbial processes ensure effective wastewater treatment, minimizing environmental pollution and promoting resource recovery.

Question 16:
A farmer observed that his crops were not growing well due to soil depletion. He consulted an agricultural expert who suggested the use of Rhizobium as a biofertilizer. Explain how Rhizobium benefits the crops and describe the process of nitrogen fixation.
Answer:

Rhizobium is a symbiotic bacterium that forms nodules on the roots of leguminous plants. It plays a crucial role in nitrogen fixation, converting atmospheric nitrogen (N2) into ammonia (NH3), which plants can absorb and utilize for growth.


The process involves the following steps:

  • Rhizobium infects the root hairs of the host plant and forms nodules.
  • Inside the nodules, the bacterium produces the enzyme nitrogenase, which converts N2 into NH3.
  • The plant provides carbohydrates to the bacterium as an energy source for this process.
  • The fixed nitrogen is then assimilated into amino acids and other nitrogenous compounds essential for plant growth.

This symbiotic relationship enriches the soil with nitrogen, reducing the need for chemical fertilizers and promoting sustainable agriculture.

Question 17:
A farmer observed that his crop yield improved significantly after using a certain biofertilizer. Upon analysis, it was found that the biofertilizer contained Rhizobium bacteria. Explain the role of Rhizobium in enhancing crop yield and describe how it benefits both the plant and the environment.
Answer:

Rhizobium is a nitrogen-fixing bacterium that forms a symbiotic relationship with the roots of leguminous plants. Here’s how it enhances crop yield and benefits the ecosystem:

  • Nitrogen Fixation: Rhizobium converts atmospheric nitrogen (N2) into ammonia (NH3), a form usable by plants, through the enzyme nitrogenase.
  • Plant Growth: The fixed nitrogen is absorbed by the plant, promoting healthy growth and higher yield without chemical fertilizers.
  • Soil Fertility: It enriches the soil with organic nitrogen, reducing dependency on synthetic fertilizers.
  • Eco-friendly: Minimizes water pollution caused by fertilizer runoff and maintains soil health sustainably.

This mutualistic relationship ensures long-term agricultural productivity while conserving the environment.

Question 18:
In a sewage treatment plant, microbial activity plays a crucial role in breaking down organic waste. Identify the microbes involved in this process and explain their functions in the secondary treatment stage. Also, mention the significance of this stage in wastewater management.
Answer:

In the secondary treatment of sewage, aerobic bacteria and fungi are the primary microbes involved. Here’s their role and the stage’s importance:

  • Microbial Action: Aerobic bacteria like Pseudomonas and Bacillus metabolize organic matter, converting it into CO2, water, and microbial biomass.
  • Floc Formation: Fungi and bacteria form flocs (clumps) that settle as sludge, which can later be used as manure.
  • Pollution Reduction: This stage significantly reduces BOD (Biochemical Oxygen Demand), making water safer for discharge.

Significance: Secondary treatment ensures the removal of dissolved organic pollutants, preventing eutrophication in water bodies and promoting sustainable water reuse. It’s a cost-effective and eco-friendly solution for wastewater management.

Question 19:
A farmer observed that his crops were not growing well due to poor soil fertility. He consulted an agricultural expert who suggested the use of Rhizobium as a biofertilizer. Explain how Rhizobium improves soil fertility and benefits the crops. Also, mention one advantage of using biofertilizers over chemical fertilizers.
Answer:

Rhizobium is a nitrogen-fixing bacterium that forms a symbiotic relationship with the roots of leguminous plants. It converts atmospheric nitrogen (N2) into ammonia (NH3), which is then utilized by the plant for growth. This process is called biological nitrogen fixation.


The benefits of Rhizobium include:

  • Enriches soil with nitrogen, reducing the need for chemical fertilizers.
  • Improves plant growth and yield sustainably.


One advantage of biofertilizers over chemical fertilizers is that they are eco-friendly and do not cause soil degradation or water pollution, unlike chemical fertilizers which can lead to eutrophication and soil acidification.

Question 20:
In a sewage treatment plant, microbial activity plays a crucial role in the secondary treatment of wastewater. Describe the process of secondary treatment and explain how microbes help in reducing the organic load of the wastewater. Also, name the gases produced during this process.
Answer:

The secondary treatment of wastewater involves the biological degradation of organic matter by microbes. It occurs in two stages:

  • Aeration tank: Aerobic microbes like Bacillus and Pseudomonas break down organic waste into simpler substances.
  • Sludge digestion: Anaerobic bacteria further decompose the sludge, reducing its volume.


Microbes reduce the organic load by:

  • Oxidizing organic matter into CO2 and water in the presence of oxygen.
  • Converting harmful substances into less toxic forms.


The gases produced during this process are methane (CH4), carbon dioxide (CO2), and hydrogen sulfide (H2S). Methane can even be used as a biogas fuel.

Question 21:
A farmer observed that his crops were not yielding well due to soil depletion. He consulted an agricultural expert who suggested the use of Rhizobium as a biofertilizer. Explain how Rhizobium benefits the crops and describe the process of nitrogen fixation it carries out.
Answer:

Rhizobium is a symbiotic bacterium that forms nodules on the roots of leguminous plants. It plays a crucial role in nitrogen fixation, converting atmospheric nitrogen (N2) into ammonia (NH3), which plants can absorb and utilize for growth.


The process involves the following steps:

  • Rhizobium infects the root hairs of the host plant and forms nodules.
  • Inside the nodules, the bacterium synthesizes the enzyme nitrogenase, which converts N2 into NH3.
  • The plant provides carbohydrates to the bacterium as an energy source for this process.
  • The fixed nitrogen is then assimilated into amino acids and other nitrogenous compounds essential for plant growth.

This symbiotic relationship enhances soil fertility naturally, reducing the need for chemical fertilizers and promoting sustainable agriculture.

Question 22:
In a sewage treatment plant, microbial activity is crucial for breaking down organic waste. Describe the role of aerobic and anaerobic bacteria in the secondary and tertiary treatment stages of sewage. Also, mention how this process helps in environmental conservation.
Answer:

In sewage treatment, aerobic and anaerobic bacteria play distinct roles in purifying wastewater:


Secondary Treatment (Biological Treatment):

  • Aerobic bacteria (e.g., Pseudomonas) break down organic matter in the presence of oxygen, converting it into carbon dioxide, water, and microbial biomass.
  • This occurs in aeration tanks, where air is pumped to support bacterial activity.

Tertiary Treatment (Advanced Purification):

  • Anaerobic bacteria (e.g., Methanogens) act in the absence of oxygen, decomposing sludge and producing methane and carbon dioxide as byproducts.
  • This stage further reduces pollutants and pathogens, making the water safe for discharge or reuse.

Environmental Benefits:

  • Reduces water pollution by removing harmful organic waste.
  • Produces biogas (methane) as a renewable energy source.
  • Prevents eutrophication by minimizing nutrient release into water bodies.
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