CBSE Class 12 Biology: Microbes In Human Welfare Notes

Glossary of Exam-Essential Terms

BOD (Biochemical Oxygen Demand)

The amount of oxygen consumed if all the organic matter in one liter of water were oxidized by bacteria.

Lactobacillus (LAB)

Lactic Acid Bacteria that convert milk into curd and improve nutritional value by increasing Vitamin B12.

Activated Sludge

The sedimented mass of bacterial and fungal flocs settled during the secondary treatment of sewage.

Flocs

Masses of bacterial cells associated with fungal filaments to form mesh-like structures.

Mycorrhiza

A symbiotic association between fungi (primarily genus Glomus) and the roots of higher plants to aid phosphorus absorption.

Biofertilizers

Organisms (bacteria, fungi, cyanobacteria) that enrich the nutrient quality of soil.

Microbial Role in Domestic and Industrial Environments

Microbes play an indispensable role in household and industrial production. In domestic settings, Lactic Acid Bacteria (LAB) convert lactose milk sugars into lactic acid, which coagulates milk proteins to form curd. LAB also enhances the nutritional value of curd by increasing Vitamin B12. In baking and brewing, the yeast Saccharomyces cerevisiae (commonly known as Brewer's or Baker's Yeast) carries out anaerobic fermentation, releasing carbon dioxide ($CO_2$) which gives bread its characteristic puffed-up appearance. On an industrial scale, large vessels called fermenters are utilized to scale up production. Microbes synthesize crucial bioactive molecules, including cyclosporin A (an immunosuppressive agent obtained from the fungus Trichoderma polysporum) and statins (produced by Monascus purpureus to competitively inhibit cholesterol synthesis enzymes). Additionally, enzymes like streptokinase (produced by Streptococcus) act as clot-busters to remove blood clots from the blood vessels of patients suffering from myocardial infarction.

The Step-by-Step Sewage Treatment Process

1. Primary Physical Treatment — Removal of floating debris via sequential filtration followed by grit removal through sedimentation. The settled solids form primary sludge, and supernatant forms the effluent.
2. Biological Aeration Tank Treatment — Primary effluent is passed into large aeration tanks and constantly agitated. Aerobic bacteria grow into flocs and consume organic matter, lowering the Biochemical Oxygen Demand (BOD).
3. Secondary Sedimentation — Once BOD is reduced, the effluent is transferred to settling tanks where bacterial flocs settle down as activated sludge.
4. Anaerobic Digestion — A small fraction of activated sludge is recycled as inoculum. The bulk is pumped into anaerobic sludge digesters where anaerobic bacteria digest microbes to produce biogas (methane, CO2, H2S).

Must-Remember Key Facts

• Swiss Cheese: Large holes are formed due to Propionibacterium sharmanii releasing huge amounts of CO2.
• Roquefort Cheese: Ripened with Penicillium roqueforti to give it a specific flavor.
• Antibiotics: Alexander Fleming discovered Penicillin from Penicillium notatum, while its full commercial potential was established by Chain and Florey.
• Fruit Juice Clarification: Bottled juices are cleared using pectinases and proteases.
• Biocontrol (Bt): Bacillus thuringiensis produces toxic cry proteins that specifically kill insect larvae/caterpillars.
• Baculoviruses: Genus Nucleopolyhedrovirus acts as narrow-spectrum, species-specific biocontrol agents targeting pests without harming other animals.

Real-World Diagnostic and Agricultural Scenarios

• {"scenario":"Myocardial Infarction","description":"A patient with a blood clot in the coronary artery is administered Streptokinase (derived from Streptococcus) to act as a clot-buster and restore circulation."}
• {"scenario":"Organ Transplantation","description":"To prevent organ rejection post-surgery, patients are prescribed Cyclosporin A, a bioactive molecule extracted from the fungus Trichoderma polysporum."}
• {"scenario":"Organic Farming & N-Fixation","description":"In paddy fields, cyanobacteria such as Anabaena and Nostoc are introduced as biofertilizers to fix atmospheric nitrogen organically."}

Pro-Tips for Boards & Direct Scoring Questions

1. Watch out for Microbe-Product Matches: Direct match-the-following questions are extremely common. Memorize scientific names along with their exact bioactive product (e.g., Monascus purpureus -> Statins, Trichoderma polysporum -> Cyclosporin A).

2. BOD Relationship: Remember, high BOD = high organic pollution = high microbial activity. BOD decreases as the treatment process cleans the water.

3. Baculoviruses: When writing about Integrated Pest Management (IPM), specifically mention the genus Nucleopolyhedrovirus and the phrase 'no negative impacts on non-target pathogens'.

Quick Revision Self-Check

• Why is BOD used as an index for measuring water pollution? BOD measures the rate of oxygen uptake by bacteria. High BOD indicates high organic content, which signifies high water pollution.
• Name the microbe used for statin production and explain its mechanism of action. Statins are produced by the yeast Monascus purpureus. They act as competitive inhibitors of the enzyme responsible for synthesizing cholesterol.
• How do Glomus species act as biofertilizers? Fungi of the genus Glomus form symbiotic mycorrhizal associations with plant roots, absorbing phosphorus from the soil and transferring it to the plant.
• What are 'flocs' in sewage treatment and what is their role? Flocs are mesh-like masses of bacteria and fungal filaments. They rapidly consume organic matter in effluent, drastically reducing BOD.

Frequently Asked Questions