Chapter 2: Microorganisms: Friend and Foe
What are Microorganisms?
Microorganisms, or microbes, are living organisms that are so small they can only be seen with a microscope. They are found everywhere—in air, water, soil, and even inside the bodies of other living beings.
Major Groups of Microorganisms
Microorganisms are classified into four major groups:
- Bacteria: Single-celled organisms. Examples include Lactobacillus (used in curd) and E. coli.
- Fungi: Can be single-celled (like yeast) or multi-cellular (like bread mould). They are not plants as they lack chlorophyll.
- Protozoa: Single-celled organisms, often found in aquatic environments. Examples include Amoeba and Paramecium.
- Algae: Simple, plant-like organisms that contain chlorophyll. Examples include Chlamydomonas and Spirogyra.
A Note on Viruses: Viruses are also microscopic but are different from other microorganisms. They are on the borderline of living and non-living, as they can only reproduce inside the cells of a host organism (like a bacterium, plant, or animal).
Friendly Microorganisms: Our Allies
Many microorganisms are beneficial to us and the environment.
Commercial and Medicinal Uses
- Making Curd and Bread: The bacterium Lactobacillus promotes the formation of curd from milk. Yeast is used in the baking industry for making bread, pastries, and cakes due to the process of fermentation, which produces carbon dioxide.
- Alcohol Production: Yeast is used for the large-scale production of alcohol, wine, and acetic acid (vinegar) through fermentation.
- Antibiotics: Certain bacteria and fungi produce medicines called antibiotics that kill or stop the growth of pathogens. In 1928, Alexander Fleming discovered Penicillin from a mould.
- Vaccines: Weakened or dead microbes are introduced into the body to stimulate the production of antibodies, providing immunity. Edward Jenner discovered the vaccine for smallpox in 1798, pioneering this critical medical advancement.
Environmental Uses
- Increasing Soil Fertility: Some bacteria (like Rhizobium) and blue-green algae can fix atmospheric nitrogen into usable compounds in the soil, enhancing its fertility. These are known as biological nitrogen fixers.
- Cleaning the Environment: Decomposers (certain bacteria and fungi) break down dead organic waste from plants and animals, converting them into simpler substances and cleaning up the environment.
Harmful Microorganisms: Pathogens
Disease-causing microorganisms are called pathogens. They can enter our bodies through the air we breathe, the water we drink, or the food we eat. Diseases that can spread from an infected person to a healthy person are called communicable diseases.
Historical Context: In 1876, Robert Koch discovered the bacterium Bacillus anthracis, which causes anthrax disease, establishing a direct link between a specific microbe and a disease.
Common Human Diseases
| Human Disease | Causative Microorganism | Mode of Transmission |
|---|---|---|
| Tuberculosis | Bacteria | Air |
| Cholera | Bacteria | Water/Food |
| Common Cold | Virus | Air |
| Malaria | Protozoa | Mosquito (Anopheles) |
| Dengue | Virus | Mosquito (Aedes) |
Food Preservation
Food preservation involves treating and handling food to stop or slow down spoilage caused by microorganisms. This prevents food poisoning and extends the shelf life of food products.
Common Methods
- Chemical Method: Using preservatives like salt, sugar, and edible oils. Chemicals like sodium benzoate are used in jams and squashes.
- Heat and Cold Treatments: Boiling kills many microorganisms. Refrigeration inhibits their growth. Pasteurization, discovered by Louis Pasteur, involves heating milk to about 70°C for 15-30 seconds and then suddenly chilling it. This process kills harmful microbes without spoiling the milk.
- Storage and Packing: Sealing food in air-tight packets (like chips and nuts) prevents contact with air and moisture, inhibiting microbial growth.
The Nitrogen Cycle
The nitrogen cycle is the process by which nitrogen is converted between its various chemical forms, circulating between the atmosphere, terrestrial, and marine ecosystems. The amount of nitrogen in the atmosphere remains constant through this cycle.
Key Steps:
- Nitrogen Fixation: Atmospheric nitrogen is converted into nitrogenous compounds by lightning or by biological nitrogen fixers like Rhizobium bacteria and blue-green algae.
- Nitrogen Assimilation: Plants absorb these compounds from the soil through their roots and use them to synthesize proteins. Animals get nitrogen by eating plants.
- Ammonification & Nitrification: When plants and animals die, bacteria and fungi in the soil convert the nitrogenous wastes back into compounds that can be used by plants again.
- Denitrification: Certain bacteria (e.g., Pseudomonas) convert some of the nitrogen compounds back into nitrogen gas, which is released into the atmosphere.
Frequently Asked Questions (FAQ)
Who discovered the first vaccine?
Edward Jenner discovered the first vaccine for smallpox in 1798. His work laid the foundation for immunology.
Who discovered pasteurization?
The process of pasteurization was discovered by the renowned French scientist Louis Pasteur.
Who discovered penicillin?
Alexander Fleming discovered penicillin in 1928, which became the world's first mass-produced antibiotic.
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