Microbes In Human Welfare Class 12 Biology Chapter 8 Notes

Microbes in Human Welfare Class 12 Biology Chapter 8 Notes

Microbes in Household Products

Everyday use of microbes and their products might surprise you.
An example: the transformation of milk into curd, involving microorganisms.
Commonly, Lactobacillus and other lactic acid bacteria (LAB) grow in milk to convert it into curd.
LAB produce acids during growth, coagulating and partially digesting milk proteins.
A small amount of curd added to fresh milk as a starter contains millions of LAB, converting milk into curd and improving its nutritional value by increasing vitamin B12.
LAB in our stomach play a beneficial role in preventing disease-causing microbes.

Fermentation of Dough:

Dough for foods like dosa and idli undergoes fermentation by bacteria.
The dough’s puffed-up appearance is due to the production of CO2 gas.
Discuss the metabolic pathway responsible for CO2 production.
Question where these bacteria for fermentation come from.
Similarly, bread dough is fermented using baker’s yeast (Saccharomyces cerevisiae).
Traditional drinks and foods are also made through microbial fermentation.
For instance, ‘toddy,’ a traditional drink in some parts of southern India, is made by fermenting palm sap.
Microbes are used to ferment fish, soybean, and bamboo shoots for food production.

Cheese and Microbes:

Cheese is one of the oldest food items in which microbes are employed.
Different cheese varieties are distinguished by their texture, flavor, and taste, all influenced by the microbes used.
Swiss cheese, known for its large holes, owes them to CO2 production by a bacterium named Propionibacterium sharmanii.
Roquefort cheese gets its unique flavor from specific fungi used in the ripening process.

Microbes in Industrial Products:

Microbes play a crucial role in the industrial production of various valuable products.
Large-scale production often requires the use of fermentors, which are vessels designed for microbial growth.

1. Fermented Beverages:

Microbes, particularly yeasts like Saccharomyces cerevisiae (brewer’s yeast), have been used for centuries to produce beverages such as wine, beer, whisky, brandy, and rum.
Brewer’s yeast ferments malted cereals and fruit juices to produce ethanol.
Discuss the metabolic reactions responsible for ethanol production by yeast.
Different types of alcoholic drinks are obtained based on the raw materials and processing methods. Wine and beer are produced without distillation, while whisky, brandy, and rum involve distillation.
Fermentation plant setups are used for large-scale production.

2. Antibiotics:

Antibiotics are chemical substances produced by microbes that can kill or inhibit the growth of disease-causing microbes.
The term “antibiotic” comes from the Greek words “anti” (against) and “bio” (life), signifying their action against disease-causing organisms.
Alexander Fleming’s chance discovery of Penicillin, produced by the mould Penicillium notatum, marked the beginning of antibiotic development.
Ernest Chain and Howard Florey later established Penicillin’s potential as an effective antibiotic.
Mention the significance of antibiotics in treating deadly diseases like plague, whooping cough, diphtheria, and leprosy.
Antibiotics have revolutionized medicine and are indispensable today.

3. Chemicals, Enzymes, and Bioactive Molecules:

Microbes are used for commercial and industrial production of various chemicals, enzymes, and bioactive molecules.
Examples include the production of organic acids (e.g., citric acid by Aspergillus niger, acetic acid by Acetobacter aceti), alcohols (e.g., ethanol by Saccharomyces cerevisiae), and enzymes.
Lipases, produced by microbes, are used in detergent formulations to remove oily stains.
Pectinases and proteases are used to clarify bottled fruit juices, making them clearer than homemade ones.
Streptokinase, produced by Streptococcus and modified through genetic engineering, is used as a clot-busting agent to remove blood clots in patients with myocardial infarction (heart attack).
Cyclosporin A, an immunosuppressive agent used in organ transplant patients, is produced by the fungus Trichoderma polysporum.
Statins, produced by Monascus purpureus yeast, are used as blood-cholesterol-lowering agents by inhibiting cholesterol synthesis.

Microbes in Sewage Treatment:

Large quantities of wastewater, including human excreta, are generated daily in cities and towns, forming what is commonly known as sewage.
Sewage contains organic matter and various microbes, including pathogens.
It cannot be directly discharged into natural water bodies like rivers and streams due to pollution concerns.
Sewage treatment plants (STPs) are essential to treat sewage and make it less polluting.
The treatment primarily relies on heterotrophic microbes naturally present in sewage.
Sewage treatment occurs in two stages: primary treatment and secondary treatment.

1. Primary Treatment:

Involves physical removal of particles (large and small) from sewage through filtration and sedimentation.
Sequential filtration initially removes floating debris, followed by sedimentation to remove grit (soil and small pebbles).
Solids settling form the primary sludge, while the supernatant becomes the effluent.
The effluent from the primary settling tank is sent for secondary treatment.

2. Secondary Treatment (Biological Treatment):

The primary effluent enters large aeration tanks where mechanical agitation and air pumping promote the growth of aerobic microbes into flocs.
These microbes, associated with fungal filaments, form mesh-like structures.
Aerobic microbes consume a significant portion of the organic matter in the effluent, reducing the Biochemical Oxygen Demand (BOD).
BOD measures the amount of oxygen consumed by microorganisms to oxidize the organic matter in one liter of water.
A lower BOD indicates reduced pollution potential.
After BOD reduction, the effluent is passed into a settling tank where bacterial flocs sediment, forming activated sludge.
A portion of activated sludge is recycled into the aeration tank as an inoculum.
The majority of the sludge is pumped into anaerobic sludge digesters where anaerobic bacteria digest the microbes and fungi in the sludge.
During digestion, bacteria produce gases like methane, hydrogen sulfide, and carbon dioxide, which form biogas and can be used as an energy source.
The treated effluent is typically released into natural water bodies like rivers and streams.

Microbes in the Production of Biogas:

Biogas is a gas mixture primarily composed of methane (CH4) produced through microbial activity. It can be used as a fuel source.
Different types of gases are produced during microbial growth and metabolism, depending on the microbes and organic substrates involved.
Methane-producing bacteria, collectively known as methanogens, produce significant amounts of methane along with carbon dioxide (CO2) and hydrogen (H2).
Methanogens, such as Methanobacterium, are commonly found in anaerobic environments like sewage sludge and the rumen of cattle.

Biogas Production from Cattle Dung (Gobar):

In the rumen of cattle, methanogens play a crucial role in breaking down cellulose, aiding in the digestion of cellulose-rich food.
Human beings are unable to digest cellulose present in their food.
Cattle dung, rich in methanogens, can be used for biogas generation, commonly known as gobar gas.
A biogas plant typically consists of a concrete tank (10-15 feet deep) where bio-wastes and a dung slurry are collected.
A floating cover is placed over the slurry, which rises as gas is produced due to microbial activity.
The biogas plant has an outlet connected to a pipe for supplying biogas to nearby houses.
The spent slurry, a byproduct of the process, can be used as fertilizer.
Biogas plants are more commonly found in rural areas where cattle dung is readily available in large quantities.
The biogas produced is utilized for cooking and lighting.

Development and Implementation:

The technology of biogas production was developed in India, mainly due to the efforts of institutions like the Indian Agricultural Research Institute (IARI) and the Khadi and Village Industries Commission (KVIC).
The widespread use of biogas in rural areas has made it a sustainable and eco-friendly energy source.
Schools located in or near villages can explore nearby biogas plants, visiting them and learning from those who manage them.

Microbes as Biocontrol Agents

Biocontrol involves the use of biological methods to control plant diseases and pests, as an alternative to chemical pesticides and insecticides.
Chemical methods have adverse effects on human health, animals, and the environment, leading to pollution of soil and groundwater.
Biological control focuses on natural predation within ecosystems to manage pests and diseases.

Biological Control in Agriculture:

Organic farming practices emphasize biodiversity and a holistic approach to pest control.
Instead of eradicating pests, organic farmers aim to maintain manageable pest levels within a complex ecosystem.
Biodiversity is seen as essential for sustainability.
The organic farmer relies on checks and balances among organisms in the ecosystem, allowing beneficial predatory and parasitic insects to thrive.
This approach reduces dependence on toxic chemicals and pesticides.

Understanding Ecosystems for Biocontrol:

Organic farmers study field fauna and flora, including predators and pests, their life cycles, feeding patterns, and habitats.
This understanding helps develop appropriate biocontrol methods.

Examples of Biocontrol Agents:

Ladybirds (Ladybugs) and dragonflies are useful for controlling aphids and mosquitoes, respectively.
Bacillus thuringiensis (Bt) bacteria are microbial biocontrol agents that can be introduced to control butterfly caterpillars. Bt is available as dried spores mixed with water and sprayed onto vulnerable plants. The toxin is released in the larval gut, killing the caterpillars without harming other insects.
Genetic engineering has allowed the insertion of B. thuringiensis toxin genes into plants, making them resistant to insect pests (e.g., Bt-cotton).

Biocontrol for Plant Diseases:

Trichoderma fungi are being developed as biological control agents for plant diseases. These fungi are common in root ecosystems and effectively control several plant pathogens.

Baculoviruses as Biocontrol Agents:

Baculoviruses are pathogens that attack insects and arthropods.
Nucleopolyhedrovirus genus baculoviruses are used as biological control agents, often with a narrow spectrum, species-specific insecticidal application.
They have no negative impacts on plants, mammals, birds, fish, or non-target insects, making them suitable for integrated pest management (IPM) programs and ecologically sensitive areas.

Microbes as Biofertilisers

The excessive use of chemical fertilisers has raised concerns about environmental pollution.
Organic farming, which incorporates biofertilisers, is gaining popularity as an eco-friendly alternative.
Biofertilisers consist of organisms that enhance soil nutrient quality and reduce the need for chemical fertilisers.
Bacteria, fungi, and cyanobacteria are the primary sources of biofertilisers.

Bacterial Biofertilisers:

Rhizobium bacteria establish symbiotic associations with leguminous plants, forming nodules on their roots.
These bacteria convert atmospheric nitrogen into organic forms that the plant can utilize as a nutrient.
Other bacteria like Azospirillum and Azotobacter can independently fix atmospheric nitrogen in the soil, enriching its nitrogen content.

Fungal Biofertilisers (Mycorrhiza):

Fungi, particularly those from the genus Glomus, create mycorrhizal associations with plants.
Mycorrhizal fungi aid plants in absorbing phosphorus from the soil and transferring it to the plant.
Plants in mycorrhizal associations enjoy several benefits, including resistance to root-borne pathogens, tolerance to salinity and drought, and overall improved growth and development.
In return, the fungus receives carbohydrates from the host plant.

Cyanobacteria as Biofertilisers:

Cyanobacteria, autotrophic microbes found in various environments, possess the ability to fix atmospheric nitrogen.
Cyanobacteria like Anabaena, Nostoc, and Oscillatoria serve as biofertilisers, particularly in paddy fields.
They enhance soil fertility and contribute organic matter to the soil.
Blue-green algae, a type of cyanobacteria, also benefit soil fertility.

Commercial Use of Biofertilisers:

Biofertilisers are commercially available in India and other countries.
Farmers utilize these biofertilisers to replenish soil nutrients while reducing their reliance on chemical fertilisers.
Biofertilisers play a pivotal role in promoting sustainable and eco-friendly agricultural practices.