Microorganisms: Friend and Foe Class 8 Science
Microorganisms are classified based on their size, structure, and habitat. They play a crucial dual role in our ecosystem and daily life.
Major Types of Microorganisms
Microbes are mainly categorized into five groups:
- Bacteria: Single-celled, prokaryotic organisms. Some are useful (e.g., Lactobacillus in curd) while others cause diseases like typhoid.
- Fungi: Multicellular (like mushrooms) or unicellular (like yeast). Used in baking and antibiotic production.
- Protozoa: Single-celled eukaryotes, mostly found in water. Some, like Amoeba, are harmless, while others cause malaria.
- Algae: Aquatic, photosynthetic organisms. They produce oxygen and are used in food items like ice-creams.
- Viruses: Considered on the border of living and non-living. They cause diseases like common cold, flu, and COVID-19.
Friendly Microorganisms (Useful Microbes)
Microbes are indispensable in many fields:
1. In Food Production
- Fermentation: Yeast is used to make bread, cakes, and idli dough rise.
- Dairy: Bacteria (Lactobacillus) convert milk into curd, cheese, and yogurt.
- Beverages: Yeast ferments sugar to produce alcohol in wines and beers.
2. In Medicine
- Antibiotics: Penicillin, derived from the fungus Penicillium, kills or inhibits bacteria.
- Vaccines: Weakened or killed microbes are used to develop immunity against diseases like polio and tuberculosis.
3. In Environment
- Nitrogen Fixation: Rhizobium bacteria in legume roots convert atmospheric nitrogen into usable forms for plants.
- Decomposition: Microbes break down dead organic matter, recycling nutrients in the soil.
- Sewage Treatment: Bacteria help decompose organic waste in water treatment plants.
Harmful Microorganisms (Disease-Causing Microbes)
Microbes that cause diseases are called pathogens. They can spread through air, water, food, or physical contact.
Common Microbial Diseases in Humans
- Bacterial Diseases: Cholera, Typhoid, Tuberculosis (TB)
- Viral Diseases: Common Cold, Influenza, Dengue, AIDS
- Protozoan Diseases: Malaria (caused by Plasmodium), Amoebic dysentery
- Fungal Diseases: Skin infections like ringworm and athlete's foot.
Diseases in Plants and Animals
Microbes affect crops and livestock, impacting agriculture. Examples include Citrus canker in plants (bacterial) and Anthrax in cattle (bacterial).
Food Preservation: Preventing Microbial Spoilage
Microbes spoil food by growing on it. Preservation methods stop their growth:
- Chemical Method: Using salt, sugar, oil, or vinegar (e.g., pickles, jams).
- Preservation by Common Salts: Used for meat and fish.
- Preservation by Sugar: Reduces moisture, used in jams and jellies.
- Preservation by Oil and Vinegar: Creates an unsuitable environment for microbes.
- Heat and Cold Treatments: Pasteurization (heating milk) and refrigeration.
- Storage and Packing: Airtight packets, nitrogen flushing to prevent oxidation.
Key Takeaways for Class 8
Microorganisms are a vital part of life on Earth. While they are essential for processes like decomposition, food production, and nitrogen cycle, they can also be harmful as pathogens. Understanding their role helps us harness their benefits and protect ourselves from diseases through hygiene, vaccination, and proper food preservation techniques.
