Chapter 8: Useful and Harmful Microbes
Comprehensive chapter summary with detailed explanations and examples.
Grade 9 Learning: Chapter 8: Useful and Harmful Microbes
Introduction
Microorganisms, though invisible to the naked eye, are omnipresent and profoundly impact our lives. While some are notorious for causing diseases, a vast majority of them are incredibly beneficial and essential for various processes, from food production to maintaining environmental balance. This chapter explores the dual nature of microbes, highlighting their useful applications and the ways in which harmful microbes affect living organisms.
Useful Microbes
Many microorganisms are vital for human welfare and ecological processes. Their applications span across various fields:
1. Food Production
- Dairy Products:
- Yogurt/Curd: Bacteria like Lactobacillus convert lactose in milk to lactic acid, causing milk to coagulate.
- Cheese: Specific bacteria and fungi are used for fermentation and ripening, contributing to distinct flavors and textures.
- Bread: Yeast (Saccharomyces cerevisiae) ferments sugars in dough, producing carbon dioxide gas which makes the bread rise and become soft.
- Fermented Foods: Microbes are essential for idli, dosa, dhokla, pickles, and traditional beverages.
- Vinegar: Acetic acid bacteria convert ethanol into acetic acid.
- Probiotics: Live beneficial bacteria (e.g., Lactobacillus acidophilus, Bifidobacterium) found in fermented foods like yogurt and supplements, which improve gut health.
Example: Making Yogurt
When a small amount of old curd (which contains Lactobacillus bacteria) is added to warm milk, these bacteria multiply rapidly, converting the milk into new curd within a few hours.
2. Medicine and Healthcare
- Antibiotics: Revolutionized medicine. These are chemical substances produced by certain microorganisms (e.g., Penicillium mold produces Penicillin; Streptomyces bacteria produce Streptomycin) that can inhibit the growth or kill other harmful microbes.
- Vaccines: Prepared using weakened, killed, or parts of microbes. They stimulate the body's immune system to produce antibodies, providing immunity against specific diseases.
- Enzymes and Vitamins: Microbes are used in industrial production of various enzymes (e.g., amylase, protease) and vitamins (e.g., Vitamin B complex, Vitamin K).
- Insulin Production: Genetically engineered bacteria are used to produce human insulin for diabetics.
Discovery of Penicillin
Alexander Fleming discovered Penicillin in 1928 when he noticed that a mold (Penicillium notatum) inhibited the growth of bacteria (Staphylococcus) on a culture plate. This accidental discovery led to the first widely used antibiotic.
3. Agriculture and Environment
- Nitrogen Fixation: Bacteria (e.g., Rhizobium in legume root nodules, free-living Azotobacter) convert atmospheric nitrogen into usable forms (ammonia, nitrates) for plants, enhancing soil fertility.
- Decomposition: Saprophytic bacteria and fungi break down dead organic matter (plants, animals, waste) into simpler inorganic substances. This process recycles nutrients back into the soil, crucial for nutrient cycling.
- Bioremediation: Microbes are used to clean up environmental pollution. For example, specific bacteria can degrade oil spills, pesticides, and other toxic chemicals.
- Sewage Treatment: Microorganisms play a vital role in breaking down organic waste in wastewater treatment plants, purifying water before discharge.
- Biogas Production: Anaerobic bacteria break down organic waste (like animal dung) to produce biogas (methane), a renewable energy source.
Harmful Microbes (Pathogens)
While many microbes are beneficial, a significant number are pathogenic, meaning they cause diseases in humans, animals, and plants. These disease-causing microbes are known as pathogens.
1. Diseases in Humans
Pathogens can cause a wide range of infectious diseases:
- Bacterial Diseases: Tuberculosis (Mycobacterium tuberculosis), Cholera (Vibrio cholerae), Typhoid (Salmonella typhi), Pneumonia, Tetanus, Diphtheria.
- Viral Diseases: Common Cold, Influenza (Flu), Measles, Mumps, Polio, AIDS (HIV), COVID-19, Dengue, Chickenpox.
- Fungal Diseases: Ringworm, Athlete's foot, Candidiasis (Thrush).
- Protozoan Diseases: Malaria (Plasmodium), Amoebic Dysentery (Entamoeba histolytica), Sleeping Sickness.
Transmission of Diseases
Diseases can spread through various routes:
- Air: Coughing, sneezing (e.g., cold, flu, TB).
- Water/Food: Contaminated sources (e.g., cholera, typhoid, food poisoning).
- Direct Contact: Physical contact (e.g., skin infections, STIs).
- Vectors: Insects or animals (e.g., mosquitoes for malaria, flies for typhoid).
2. Food Spoilage
Microbes are a primary cause of food spoilage, leading to changes in taste, smell, texture, and appearance of food, making it unfit for consumption.
- Bacteria and fungi grow on food, producing toxins or breaking down food components.
- Examples: Mold on bread, souring of milk, rotting of fruits and vegetables, putrefaction of meat.
Food Preservation Methods
To prevent microbial spoilage, various methods are used:
- Refrigeration/Freezing: Slows down microbial growth.
- Heating (Pasteurization, Boiling): Kills microbes.
- Salting/Sugaring: Removes water, inhibiting growth.
- Drying: Removes moisture.
- Chemical Preservatives: Inhibit microbial growth.
3. Diseases in Animals and Plants
- Animal Diseases: Many microbes cause diseases in livestock and pets, leading to economic losses (e.g., Anthrax in cattle, Foot-and-mouth disease, Bird flu).
- Plant Diseases: Microbes cause significant damage to crops, leading to reduced yields and economic losses (e.g., Citrus canker (bacterial), Rust of wheat (fungal), Tobacco mosaic disease (viral), Potato blight (fungal)).
Conclusion
Microorganisms are a double-edged sword. Their beneficial activities are indispensable for various industrial processes, environmental sustainability, and human health. Simultaneously, harmful microbes pose significant threats as pathogens, causing diseases and leading to food spoilage. Understanding this balance is crucial for harnessing the power of useful microbes and combating the challenges posed by harmful ones.
References
- Maharashtra State Board Science and Technology Standard Nine Textbook (Latest Edition) - Chapter 8: Useful and Harmful Microbes.
- Maharashtra State Board 9th Standard Science Syllabus.
- Balbharati Science and Technology Textbook Part 1.