Microbes in Human Welfare - Comprehensive NEET Biology Notes

1. Introduction to Microbes in Human Welfare

Microbes are microscopic organisms that play vital roles in maintaining ecological balance and contributing to human welfare. Though some microbes are pathogenic and cause diseases, many are beneficial and are used in various applications like food production, sewage treatment, industrial processes, and agriculture. This chapter focuses on the diverse ways in which microbes contribute to human welfare.

Did You Know?

Microbes can thrive in extreme environments like deep-sea vents, hot springs, and polar ice caps, where other life forms cannot survive.

2. Microbes in Household Products

2.1 Microbes in Fermentation

Microbes are commonly used in the production of household products such as curd, bread, and fermented foods like dosa and idli. Lactic acid bacteria (LAB), such as Lactobacillus, are responsible for curd formation by converting milk into curd. These bacteria improve the nutritional quality of curd by increasing vitamin B12 levels.

NEET Tip:

Focus on the role of Lactobacillus in curd production and the metabolic pathways involved in the fermentation process, as this is a frequently tested concept in NEET.

Visual Aid Suggestion:

A diagram showing the conversion of milk to curd by LAB can help in understanding the fermentation process.

2.2 Microbes in Bread and Alcohol Production

Baker’s yeast (Saccharomyces cerevisiae) is used in the preparation of bread. The yeast ferments the dough, producing carbon dioxide, which makes the bread rise. The same yeast is also used to ferment fruit juices and cereals to produce alcoholic beverages like wine and beer.

Quick Recap

  • Microbes like Lactobacillus are used in curd formation, while Saccharomyces cerevisiae is used in baking and alcoholic beverage production.
  • Fermentation plays a key role in enhancing the nutritional value of food and producing alcohol.

3. Microbes in Industrial Products

3.1 Fermented Beverages

Microbes have been used for the production of fermented beverages like wine, beer, whisky, and rum for centuries. Saccharomyces cerevisiae, commonly known as brewer's yeast, ferments malted cereals and fruit juices to produce ethanol. The type of beverage produced depends on whether the fermentation broth is distilled.

Real-life Application:

Fermented beverages like wine and beer are produced without distillation, while stronger drinks like whisky and rum are produced by distilling the fermented broth.

3.2 Antibiotics

Antibiotics are among the most significant contributions of microbes to human health. Penicillium notatum was the source of the first antibiotic, penicillin, discovered by Alexander Fleming. Antibiotics work by killing or inhibiting the growth of harmful microorganisms.

NEET Problem-Solving Strategy:

Focus on the discovery of penicillin and the role of antibiotics in treating bacterial infections, as these are commonly tested topics in NEET.

Visual Aid Suggestion:

A diagram illustrating the inhibition of bacterial growth around a colony of Penicillium can help visualize the action of antibiotics.

3.3 Chemicals, Enzymes, and Bioactive Molecules

Microbes are used industrially to produce organic acids, enzymes, and bioactive molecules. For example:

  • Citric acid is produced by Aspergillus niger.
  • Acetic acid is produced by Acetobacter aceti.
  • Ethanol is produced by Saccharomyces cerevisiae.

Enzymes like lipases are used in detergents, while streptokinase (produced by Streptococcus) is used to dissolve blood clots. Cyclosporin A, derived from Trichoderma polysporum, is an immunosuppressant used in organ transplants.

Quick Recap

  • Microbes are used in the production of fermented beverages, antibiotics, organic acids, and enzymes.
  • Antibiotics like penicillin revolutionized medicine by treating bacterial infections.
  • Microbes like Aspergillus and Saccharomyces are used in industrial production.

4. Microbes in Sewage Treatment

4.1 Primary and Secondary Sewage Treatment

Sewage treatment involves the use of heterotrophic microbes to degrade organic waste. The treatment process includes two main stages:

  • Primary Treatment: Involves the physical removal of large particles through filtration and sedimentation.
  • Secondary Treatment (Biological Treatment): Involves the use of aerobic microbes to decompose organic matter, significantly reducing the Biochemical Oxygen Demand (BOD) of the sewage.

NEET Tip:

Focus on the role of aerobic microbes in reducing BOD during secondary treatment, as this is an important concept for NEET.

4.2 Biogas Production from Sewage

Anaerobic bacteria, including methanogens like Methanobacterium, digest sludge in anaerobic sludge digesters during secondary treatment. These bacteria produce biogas (a mixture of methane, carbon dioxide, and hydrogen), which can be used as a renewable energy source.

Real-life Application:

Biogas plants utilize cattle dung to produce biogas (gobar gas), which is used in rural areas for cooking and lighting.

Quick Recap

  • Sewage treatment involves primary and secondary treatments to reduce organic pollution.
  • Methanogens in anaerobic digesters produce biogas, a sustainable source of energy.

5. Microbes as Biocontrol Agents

5.1 Biological Control of Pests

Biocontrol involves the use of biological methods, such as natural predators and pathogens, to control pests. This approach is environmentally friendly and reduces the use of chemical pesticides. For example:

  • Bacillus thuringiensis (Bt): A bacterium that produces toxins lethal to insect larvae. Bt-toxins are now genetically engineered into crops like Bt cotton to protect against pests.
  • Ladybird beetles and dragonflies are natural predators used to control aphids and mosquitoes, respectively.

Real-life Application:

Bt cotton is widely grown in India, providing resistance to insect pests and reducing pesticide use.

Visual Aid Suggestion:

A diagram showing the action of Bt toxin on insect larvae can help students understand how biocontrol agents work.

Quick Recap

  • Biocontrol involves using natural predators and microbial agents like Bt to manage pests.
  • This method is environmentally sustainable and reduces the need for chemical pesticides.

6. Microbes as Biofertilisers

6.1 Bacterial Biofertilisers

Biofertilisers are living organisms that enrich the nutrient quality of the soil. Bacterial biofertilisers include:

  • Rhizobium: Symbiotic bacteria that fix atmospheric nitrogen in the root nodules of leguminous plants.
  • Azospirillum and Azotobacter: Free-living bacteria that also fix nitrogen, enriching the soil.

6.2 Fungal Biofertilisers

Mycorrhizae are symbiotic associations between fungi (such as Glomus) and plant roots. The fungal symbiont helps plants absorb phosphorus from the soil and provides additional benefits like resistance to root pathogens and drought tolerance.

NEET Problem-Solving Strategy:

Focus on the roles of Rhizobium and mycorrhizae in nitrogen fixation and nutrient absorption, as these are key topics in NEET.

Visual Aid Suggestion:

A diagram showing the root nodules of legumes with Rhizobium can help students visualize nitrogen fixation.

Quick Recap

  • Biofertilisers like Rhizobium and mycorrhizae help improve soil fertility by fixing nitrogen and increasing nutrient absorption.
  • Biofertilisers reduce the need for chemical fertilizers, promoting sustainable agriculture.

NEET Exam Strategy

  • Focus on the roles of microbes in household products, industrial processes, sewage treatment, and agriculture.
  • Practice diagram-based questions, particularly those involving biogas production, biofertilisers, and biocontrol agents.
  • Understand the key microbial processes involved in sewage treatment and the production of antibiotics, biofertilisers, and biocontrol agents.

Practice Questions

  1. Which microbe is used in the production of curd?
    Solution: b) Lactobacillus
    • a) Saccharomyces cerevisiae
    • b) Lactobacillus
    • c) Rhizobium
    • d) Acetobacter aceti
  3. Which of the following is used as a biocontrol agent for insect larvae?
    Solution: b) Bacillus thuringiensis
    • a) Trichoderma
    • b) Bacillus thuringiensis
    • c) Azospirillum
    • d) Penicillium
  5. What is the role of methanogens in sewage treatment?
    Solution: c) They produce biogas in anaerobic sludge digesters.
    • a) They degrade organic waste aerobically.
    • b) They produce ethanol.
    • c) They produce biogas in anaerobic sludge digesters.
    • d) They increase the BOD of sewage.
  7. Which of the following is an example of a biofertiliser?
    Solution: a) Azotobacter
    • a) Azotobacter
    • b) Aspergillus niger
    • c) Penicillium notatum
    • d) Streptococcus
  9. Which of the following produces the antibiotic penicillin?
    Solution: b) Penicillium notatum
    • a) Bacillus
    • b) Penicillium notatum
    • c) Saccharomyces cerevisiae
    • d) Lactobacillus

Glossary

  • Fermentation: A metabolic process where microbes convert carbohydrates into alcohol or acids under anaerobic conditions.
  • Antibiotic: A chemical substance produced by microbes that inhibits the growth of other harmful microbes.
  • Biocontrol: The use of natural predators and microbial agents to control pests and plant diseases.
  • Biofertiliser: A substance containing living microbes that enriches the nutrient content of the soil.