Microbes In Human Welfare
Microbes in Human Welfare - Complete NEET Guide with Diagrams & Practice Questions
Table of Contents
- Introduction
- Key Concepts
- Important Reactions & Associations
- Memory Techniques (Mnemonics)
- Previous Year Questions (NEET)
- Key Takeaways for Quick Revision
Introduction
While we often associate microbes with diseases, their beneficial roles are vast and indispensable to human life and the planet's ecosystems. The chapter "Microbes in Human Welfare" is a fascinating exploration of how these microscopic organisms are harnessed for our benefit, from making curd in our kitchens to producing life-saving antibiotics in large industries.
For the NEET exam, this chapter is considered high-yield and relatively easy to score. It is primarily a memory-based chapter, and you can expect 2-3 direct questions from it. A thorough understanding of the specific microbes and their corresponding products or functions is key to securing full marks. This guide will systematically break down each application, providing clear tables, diagrams, and memory aids to help you master the content.
Key Concepts
1. Microbes in Household Products
We use microbes or their products daily, often without realizing it.
- Curd: Produced from milk by Lactic Acid Bacteria (LAB), such as Lactobacillus. LAB produce acids that coagulate and partially digest milk proteins (casein). A small amount of curd acts as an inoculum or starter. Curd is also nutritionally superior to milk due to increased Vitamin B₁₂.
- Dough: The puffed-up appearance of dough used for making foods like dosa, idli, and bread is due to the production of CO₂ gas during fermentation.
- Bread: Fermented using Baker's Yeast (Saccharomyces cerevisiae).
- 'Toddy': A traditional drink from southern India, made by fermenting sap from palms.
- Cheese: One of the oldest food items involving microbes. The texture, flavor, and taste are determined by the specific microbe used.
- Swiss Cheese: Characterized by large holes due to the production of a large amount of CO₂ by the bacterium Propionibacterium sharmanii.
- Roquefort Cheese: Ripened by growing a specific fungus, Penicillium roqueforti, on it, which gives it a particular flavor.
Figure: Colonies of bacteria (a) and fungi (b) growing in a petri dish, which are cultured to study their properties and uses.
2. Microbes in Industrial Products
Microbes are grown in very large vessels called fermentors to produce beverages, antibiotics, and other chemicals on an industrial scale.
- Fermented Beverages:
- Yeast: Saccharomyces cerevisiae (Brewer's Yeast) is used for fermenting malted cereals and fruit juices to produce ethanol.
- Without Distillation: Wine and Beer are produced without distillation.
- With Distillation: Whisky, Brandy, and Rum are produced by distilling the fermented broth.
- Antibiotics:
- Definition: Chemical substances produced by some microbes that can kill or retard the growth of other (disease-causing) microbes.
- Penicillin: The first antibiotic to be discovered, it was a chance discovery by Alexander Fleming. He observed that the mould Penicillium notatum prevented the growth of Staphylococci bacteria. Its full potential was established by Ernest Chain and Howard Florey. The three shared the Nobel Prize in 1945.
- Chemicals, Enzymes, and other Bioactive Molecules: This is an extremely important section for NEET.
| Product | Microbe | Category | Function/Use |
|---|---|---|---|
| Citric Acid | Aspergillus niger | Fungus | Organic Acid |
| Acetic Acid | Acetobacter aceti | Bacterium | Organic Acid |
| Butyric Acid | Clostridium butylicum | Bacterium | Organic Acid |
| Lactic Acid | Lactobacillus | Bacterium | Organic Acid |
| Ethanol | Saccharomyces cerevisiae | Yeast (Fungus) | Alcohol |
| Lipases | (Various) | Enzyme | Used in detergent formulations to remove oily stains. |
| Pectinases & Proteases | (Various) | Enzymes | Used for clarifying bottled juices. |
| Streptokinase | Streptococcus | Enzyme | "Clot buster" for removing clots from blood vessels (myocardial infarction). |
| Cyclosporin A | Trichoderma polysporum | Fungus | Bioactive Molecule |
| Statins | Monascus purpureus | Yeast (Fungus) | Bioactive Molecule |
3. Microbes in Sewage Treatment
Sewage is municipal wastewater containing large amounts of organic matter and pathogenic microbes. It cannot be discharged into natural water bodies without treatment in Sewage Treatment Plants (STPs). The treatment is carried out in two stages:
-
Primary Treatment (Physical):
- Involves the physical removal of large and small particles through filtration and sedimentation.
- Floating debris is removed by filtration.
- Grit (soil, pebbles) is removed by sedimentation.
- The settled solids form the primary sludge, and the supernatant forms the primary effluent.
-
Secondary Treatment (Biological):
- The primary effluent is passed into large aeration tanks.
- Air is pumped in, and it is mechanically agitated, leading to the vigorous growth of useful aerobic microbes into flocs (masses of bacteria associated with fungal filaments).
- These microbes consume the organic matter in the effluent, significantly reducing the BOD (Biochemical Oxygen Demand).
- BOD: A measure of the organic matter present in water. It is the amount of oxygen that would be consumed if all organic matter in one liter of water were oxidized by bacteria. Higher BOD indicates higher polluting potential.
- Once BOD is reduced, the effluent is passed into a settling tank where the flocs sediment. This sediment is called activated sludge.
- A small part of the activated sludge is pumped back into the aeration tank to serve as an inoculum.
- The remaining major part is pumped into large tanks called anaerobic sludge digesters. Here, anaerobic bacteria digest the organic matter and produce biogas.
The effluent from the secondary treatment plant is generally released into rivers and streams. The Ganga Action Plan and Yamuna Action Plan have been initiated by the Ministry of Environment and Forests to build more STPs.
Figure: An overview of a sewage treatment plant, showing the large primary and secondary treatment tanks.
4. Microbes in Production of Biogas
- Biogas: A mixture of gases (predominantly methane) produced by microbial activity, used as fuel.
- Methanogens: Bacteria that grow anaerobically on cellulosic material and produce a large amount of methane along with CO₂ and H₂. A common example is Methanobacterium.
- Location: Methanogens are found in:
- Anaerobic sludge during sewage treatment.
- The rumen (a part of the stomach) of cattle, where they help in cellulose digestion.
- Gobar Gas Plant: Cattle dung (gobar) is rich in methanogens and is used to produce biogas. The plant consists of a concrete tank where dung slurry is fed. A floating cover rises as gas is produced. The spent slurry is used as fertilizer.
5. Microbes as Biocontrol Agents
Biocontrol refers to the use of biological methods for controlling plant diseases and pests, reducing the dependence on chemical pesticides.
- Ladybird (beetle) and Dragonflies are used to get rid of aphids and mosquitoes, respectively.
- Bacillus thuringiensis (Bt): A bacterium used to control butterfly caterpillars. Available as dried spores, which are sprayed on plants. When ingested by the larvae, the toxin is released in their gut, killing them. This has been used to create genetically modified crops like Bt-cotton.
- Trichoderma: A free-living fungus, very common in root ecosystems. They are effective biocontrol agents of several plant pathogens.
- Baculoviruses: Pathogens that attack insects and other arthropods. The majority used are from the genus Nucleopolyhedrovirus. They are excellent candidates for species-specific, narrow-spectrum insecticidal applications, meaning they do not harm non-target insects, plants, birds, or mammals.
6. Microbes as Biofertilisers
Biofertilisers are organisms that enrich the nutrient quality of the soil.
- Bacteria:
- Rhizobium: Forms a symbiotic association with the roots of leguminous plants (root nodules) to fix atmospheric nitrogen.
- Azospirillum and Azotobacter: Free-living bacteria in the soil that can fix atmospheric nitrogen.
- Fungi:
- Mycorrhiza: A symbiotic association between fungi and the roots of higher plants. The fungus, often from the genus Glomus, absorbs phosphorus from the soil and passes it to the plant. The plant, in turn, provides benefits like resistance to root-borne pathogens and tolerance to salinity and drought.
- Cyanobacteria (Blue-Green Algae):
- Autotrophic microbes like Anabaena, Nostoc, and Oscillatoria can fix atmospheric nitrogen. They are important biofertilisers, especially in paddy fields.
Important Reactions & Associations
| Microbe | Substrate / Location | Product / Function |
|---|---|---|
| Lactobacillus | Milk | Curd |
| Saccharomyces cerevisiae | Dough / Malted cereals | Bread / Ethanol |
| Propionibacterium sharmanii | Cheese | Swiss Cheese (CO₂ holes) |
| Aspergillus niger | - | Citric Acid |
| Streptococcus | - | Streptokinase (clot buster) |
| Trichoderma polysporum | - | Cyclosporin A (immunosuppressant) |
| Monascus purpureus | - | Statins (cholesterol lowering) |
| Methanobacterium | Rumen of cattle / Sludge | Methane (Biogas) |
| Bacillus thuringiensis | - | Bt toxin (biocontrol) |
| Glomus (Mycorrhiza) | Roots of higher plants | Phosphorus absorption |
Memory Techniques (Mnemonics)
- Industrial Chemicals:
- Asparagus has a Citrus taste -> Aspergillus niger -> Citric Acid.
- Stats Matter -> Statins from Monascus purpureus.
- Cycling on a Trike -> Cyclosporin A from Trichoderma.
- A Big Claw for Butter -> Clostridium butylicum -> Butyric Acid.
- Cheese:
- The Swiss army uses Props -> Swiss Cheese -> Propionibacterium.
- Rocky Fort has a Pen -> Roquefort Cheese -> Penicillium.
- Biofertilisers vs. Biocontrol:
- Fertilisers enrich the soil (Rhizobium, Glomus, Nostoc).
- Control agents kill pests (Trichoderma, Bt, Baculovirus).
Previous Year Questions (NEET)
Q1. Statins, used for lowering blood-cholesterol level, are extracted from: (NEET 2022) a) Algae b) Bacteria c) Yeast d) Fungi
Explanation: Statins are produced by the yeast Monascus purpureus. Yeast is a type of fungus. Answer: (c) Yeast (or (d) Fungi, as yeast is a fungus. NEET often uses yeast as a distinct option. The most precise answer from the textbook source is Yeast).
Q2. Which of the following is a commercial blood cholesterol-lowering agent? (NEET 2019) a) Statin b) Streptokinase c) Cyclosporin A d) Lipase
Explanation: Statins, produced by the yeast Monascus purpureus, are used as blood-cholesterol lowering agents. Streptokinase is a clot buster, and Cyclosporin A is an immunosuppressant. Answer: (a) Statin
Q3. Which of the following is put into an anaerobic sludge digester for further sewage treatment? (NEET 2018) a) Primary sludge b) Floating debris c) Effluents of primary treatment d) Activated sludge
Explanation: After the aeration tank in secondary treatment, the bacterial flocs sediment to form activated sludge. A major part of this activated sludge is pumped into anaerobic sludge digesters. Answer: (d) Activated sludge
Q4. Trichoderma harzianum has proved a useful microorganism for: (NEET 2008) a) Bioremediation of contaminated soils b) Reclamation of wastelands c) Gene transfer in higher plants d) Biological control of soil-borne plant pathogens
Explanation: Trichoderma species are free-living fungi that are very effective as biocontrol agents, particularly against several soil-borne plant pathogens. Answer: (d) Biological control of soil-borne plant pathogens
Key Takeaways for Quick Revision
- Lactic Acid Bacteria (LAB) convert milk to curd, increasing Vitamin B₁₂.
- Saccharomyces cerevisiae is used for making bread (Baker's yeast) and for fermenting beverages (Brewer's yeast).
- Remember the table of industrial products, especially Statins, Cyclosporin A, and Streptokinase along with their microbial sources and functions.
- Sewage treatment reduces BOD. Primary treatment is physical, while secondary treatment is biological (using flocs). The final sludge is digested anaerobically to produce biogas.
- Biocontrol agents provide a specific, non-polluting alternative to chemical pesticides. Key examples are Bt, Trichoderma, and Baculoviruses.
- Biofertilisers enrich soil nutrients. Rhizobium (symbiotic), Azotobacter (free-living), and Mycorrhiza (phosphorus uptake) are key examples.