Class 12 Biology · Chapter 8 NotesMicrobes in Human Welfare
Explore the beneficial roles of microbes in agriculture, industry, medicine, and environmental sustainability with these comprehensive Class 12 Biology notes.
This chapter explores the diverse and beneficial roles of microbes in human life. While microbes are often associated with diseases, they also contribute significantly to agriculture, industry, medicine, and environmental sustainability. Students will learn about the various applications of microbes in producing food, industrial products, medicines, and treating waste. The chapter also covers the use of microbes as biofertilizers and biocontrol agents, highlighting their importance in sustainable agriculture and environmental protection.
What you'll learn
1Understand the role of microbes in agriculture and soil health
2Explain the industrial applications of microbes in production processes
3Describe the use of microbes in medicine and disease treatment
4Analyze the role of microbes in sewage treatment and biofuel production
5Identify microbes as biocontrol agents and biofertilizers
Chapter at a glance
01Microbes in Agriculture and Soil
02Microbes in Industry and Production
03Microbes in Medicine and Disease Treatment
04Microbes in Sewage Treatment and Biofuels
05Microbes as Biocontrol Agents and Biofertilizers
Detailed chapter notes
01
Microbes in Agriculture and Soil
Microbes play a crucial role in agriculture by enhancing soil fertility and promoting plant growth. Rhizobium bacteria form symbiotic relationships with leguminous plants, fixing atmospheric nitrogen into a form that plants can use. This process enriches the soil with nitrogen, reducing the need for chemical fertilizers. Other bacteria, such as Azospirillum and Azotobacter, also fix nitrogen while free-living in the soil. Fungi form mycorrhizal associations with plant roots, helping to absorb phosphorus and other nutrients. Cyanobacteria, like Anabaena and Nostoc, fix nitrogen and add organic matter to the soil, making them valuable biofertilizers in paddy fields.
Rhizobium fixes nitrogen in leguminous plants
Azospirillum and Azotobacter fix nitrogen in soil
Mycorrhizal fungi help absorb phosphorus
Cyanobacteria add organic matter to soil
02
Microbes in Industry and Production
Microbes are extensively used in various industrial processes. Lactic acid bacteria (LAB) convert milk into curd, improving its nutritional quality. Yeasts like Saccharomyces cerevisiae are used in baking and brewing to produce carbon dioxide, which helps dough rise and ferment sugars into alcohol. Microbes also produce organic acids, enzymes, and other bioactive molecules. For example, Aspergillus niger produces citric acid, and Streptococcus produces streptokinase, a clot-busting enzyme. These microbial products are used in food, pharmaceuticals, and other industries.
LAB converts milk into curd
Yeast ferments dough and produces alcohol
Microbes produce organic acids and enzymes
Streptokinase is used as a clot buster
03
Microbes in Medicine and Disease Treatment
Microbes have been instrumental in the production of antibiotics, which have revolutionized the treatment of infectious diseases. Penicillin, the first antibiotic discovered, is produced by the mould Penicillium notatum. Other antibiotics like streptomycin and tetracycline are derived from microbes. Antibiotics have significantly reduced the mortality rates from diseases like plague, diphtheria, and leprosy. Additionally, microbes are used to produce vaccines and other medicinal compounds, contributing to human health and welfare.
Penicillin is the first discovered antibiotic
Antibiotics treat infectious diseases
Microbes produce vaccines and medicinal compounds
Reduced mortality from diseases like plague and leprosy
04
Microbes in Sewage Treatment and Biofuels
Microbes play a vital role in sewage treatment by breaking down organic matter and reducing the biochemical oxygen demand (BOD) of waste water. In primary treatment, physical methods remove large particles and grit. Secondary treatment involves aerobic microbes that form flocs, consuming organic matter and reducing BOD. The resulting activated sludge can be further digested by anaerobic microbes to produce biogas, a mixture of methane, hydrogen sulphide, and carbon dioxide. Biogas is used as a source of energy in rural areas, highlighting the dual role of microbes in waste management and energy production.
Primary treatment removes large particles
Secondary treatment reduces BOD using aerobic microbes
Activated sludge produces biogas
Biogas is used as a source of energy
05
Microbes as Biocontrol Agents and Biofertilizers
Microbes are used as biocontrol agents to manage pests and diseases in agriculture. Bacillus thuringiensis (Bt) produces toxins that kill insect larvae, making it an effective biocontrol agent. Trichoderma species are fungi that control plant pathogens. Baculoviruses are used to target specific insect pests without harming non-target species. Biofertilizers, derived from microbes like Rhizobium, Azospirillum, and cyanobacteria, enrich soil fertility by fixing nitrogen and adding organic matter. These biological methods reduce the reliance on chemical pesticides and fertilizers, promoting sustainable agriculture.
Bt produces toxins to kill insect larvae
Trichoderma controls plant pathogens
Baculoviruses target specific insect pests
Biofertilizers enrich soil fertility
Want the complete chapter resources?Topic notes, quizzes and flashcards for Microbes in Human Welfare.
Which of the following is a nitrogen-fixing bacterium commonly used in agriculture?
ARhizobium
BBacillus cereus
CStaphylococcus aureus
DVibrio cholerae
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Answer: (A) Rhizobium
Rhizobium is a symbiotic nitrogen-fixing bacterium that forms root nodules in leguminous plants and converts atmospheric nitrogen into usable forms. Other options are pathogenic or non-beneficial bacteria.
Question 02
Which microorganism is primarily used in the large-scale production of antibiotics like penicillin?
APenicillium notatum
BSaccharomyces cerevisiae
CLactobacillus bulgaricus
DAspergillus niger
Show answer
Answer: (A) Penicillium notatum
Penicillium notatum is a fungus that produces penicillin, one of the most important antibiotics. It was discovered by Alexander Fleming and is used extensively in industrial antibiotic production.
Question 03
Which of the following antibiotics is produced by the fungus Penicillium notatum?
APenicillin
BStreptomycin
CTetracycline
DChloramphenicol
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Answer: (A) Penicillin
Penicillin is the first antibiotic discovered by Alexander Fleming from the fungus Penicillium notatum in 1928. It revolutionized medicine by effectively treating bacterial infections.
Question 04
Which microorganism is primarily responsible for the decomposition of organic matter in the primary treatment stage of sewage?
ABacteria
BViruses
CFungi
DProtozoa
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Answer: (A) Bacteria
Bacteria are the main decomposers in sewage treatment plants, breaking down complex organic compounds into simpler forms. They play a crucial role in both aerobic and anaerobic treatment processes.
Question 05
Which of the following microorganisms is commonly used as a biocontrol agent against crop pests?
ABacillus thuringiensis (Bt)
BEscherichia coli
CVibrio cholerae
DClostridium botulinum
Show answer
Answer: (A) Bacillus thuringiensis (Bt)
Bacillus thuringiensis produces Cry proteins that are toxic to insect larvae, making it an effective biocontrol agent used in organic farming. Other options are pathogens or non-beneficial bacteria.
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Q1. What is the role of nitrogen-fixing bacteria in soil? Name one example of such bacteria and explain how it benefits agriculture.
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Model answer
Nitrogen-fixing bacteria convert atmospheric nitrogen (N₂) into ammonia (NH₃) or nitrates, making nitrogen available to plants in a usable form. An example is Rhizobium, which forms symbiotic associations with leguminous plants like peas, beans, and clover. These bacteria live in root nodules and fix atmospheric nitrogen, enriching the soil and reducing the need for artificial nitrogen fertilizers, thereby improving soil fertility and crop yield.
Sample question3 marks
Q2. Name two microorganisms commonly used in the production of antibiotics and briefly explain why they are preferred for industrial use.
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Model answer
Penicillium notatum and Streptomyces are the two main microorganisms used in antibiotic production. Penicillium notatum produces penicillin, while Streptomyces produces streptomycin and other antibiotics. They are preferred because they naturally produce these compounds in high yields, grow well in industrial fermentation tanks, and are relatively safe and non-pathogenic to humans. Their metabolic processes can be easily controlled and optimized for large-scale production.
Sample question3 marks
Q3. What are antibiotics? Name any two antibiotics and explain how they help in treating bacterial infections in humans.
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Model answer
Antibiotics are chemical substances produced by microorganisms that kill or inhibit the growth of pathogenic bacteria. Examples include penicillin (produced by Penicillium fungus) and streptomycin (produced by Streptomyces bacterium). Penicillin works by disrupting bacterial cell wall synthesis, causing bacterial cells to lyse and die. Streptomycin inhibits bacterial protein synthesis, preventing the bacteria from reproducing. These antibiotics selectively target bacterial cells without harming human cells, making them effective in treating infections like pneumonia, urinary tract infections, and wound infections.
Sample question3 marks
Q4. Explain the role of microorganisms in the primary and secondary stages of sewage treatment. Why is aeration important during these stages?
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Model answer
In the primary stage, physical processes like settling remove larger particles and sludge. In the secondary stage, aerobic bacteria decompose dissolved organic matter and nutrients, converting them into simpler compounds and biomass. Aeration is crucial because it provides oxygen required by aerobic bacteria to respire and efficiently break down organic pollutants, preventing anaerobic decomposition which produces foul-smelling gases.
Sample question3 marks
Q5. What are biocontrol agents? Name any two microorganisms used as biocontrol agents and explain how they control pests.
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Model answer
Biocontrol agents are living organisms, particularly microorganisms, used to control harmful pests and pathogens in crops naturally. Bacillus thuringiensis (Bt) is a bacterium that produces crystalline proteins toxic to insect larvae, killing them when ingested. Trichoderma is a fungus that parasitizes harmful fungal pathogens in soil, preventing plant diseases. These agents reduce the need for chemical pesticides and are environmentally friendly.
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What are the benefits of using microbes in agriculture?
Microbes enhance soil fertility through nitrogen fixation and mycorrhizal associations, reducing the need for chemical fertilizers and promoting sustainable agriculture.
How do microbes contribute to industrial production?
Microbes are used to produce organic acids, enzymes, and other bioactive molecules, which are essential in food, pharmaceuticals, and other industries.
What role do microbes play in sewage treatment?
Microbes break down organic matter and reduce the biochemical oxygen demand (BOD) of waste water, producing biogas as a source of energy.
How are microbes used as biocontrol agents?
Microbes like Bacillus thuringiensis produce toxins that kill insect larvae, while Trichoderma species control plant pathogens, reducing the reliance on chemical pesticides.
What are biofertilizers and how do they work?
Biofertilizers are derived from microbes like Rhizobium and cyanobacteria, which fix nitrogen and add organic matter to the soil, enriching its fertility.