Microorganisms: Friend and Foe - Science Insights

Microorganisms: Friend and Foe

Exploring the Tiny World of Microbes - Class VIII Science Notes

By Abhinav Sir

Introduction to Microorganisms

Microorganisms, or microbes, are tiny organisms invisible to the naked eye, often single-celled. These fascinating life forms are classified into four major groups: bacteria, fungi, protozoa, and some algae (including red, brown, and green algae). Additionally, viruses, though microscopic, are unique as they reproduce only inside the cells of a host organism, such as bacteria, plants, or animals.

Microorganisms viewed under a microscope

Where Do Microorganisms Live?

Microorganisms are incredibly adaptable, thriving in diverse environments:

They survive in extreme conditions, from ice-cold climates to hot springs, deserts, and marshy lands.
They inhabit the bodies of other organisms, including humans.
Some depend on other organisms for growth, while others live freely.
Microbes like amoebas live alone, while fungi and bacteria often form colonies.

"From icy glaciers to scorching deserts, microorganisms are everywhere, shaping our world in ways we can barely imagine!"

Microorganisms and Us: Friends or Foes?

Microorganisms play a dual role in our lives. Some are beneficial, aiding in food production, environmental cleanup, and agriculture, while others are harmful, causing diseases in humans, animals, and plants.

Friendly Microorganisms

Microbes are indispensable in various processes:

Food Production: Microorganisms are used to make curd, bread, and cake. Yeast ferments sugars to produce alcohol, a practice used for centuries.
Environmental Cleanup: Bacteria decompose organic waste (e.g., vegetable peels, animal remains, feces) into harmless, usable substances, acting as nature’s recyclers.
Agriculture: Microbes like bacteria and blue-green algae fix atmospheric nitrogen, enriching soil fertility for better crop growth.
Commercial Uses: Yeast is grown on natural sugars in grains (barley, wheat, rice) or fruit juices to produce alcohol, wine, and acetic acid (vinegar).
Medicinal Uses: Antibiotics like penicillin, derived from bacteria and fungi, kill or inhibit disease-causing microbes. They’re also used in livestock feed and to control plant diseases.
Vaccines: Vaccines introduce weakened or dead microbes to stimulate antibody production, protecting against diseases like cholera, tuberculosis, smallpox, and hepatitis.

Antibiotics derived from microorganisms

Harmful Microorganisms: The Pathogens

Some microorganisms, known as pathogens, cause diseases in humans, animals, and plants, and spoil food, clothing, and leather.

Diseases in Humans

Pathogens enter the body through air, water, food, or physical contact. Communicable diseases like cholera, the common cold, chickenpox, and tuberculosis spread from infected to healthy individuals. Vectors like:

Houseflies: Transfer pathogens from garbage or excreta to food, causing food poisoning.
Mosquitoes: Female Anopheles mosquitoes carry malaria parasites, while Aedes mosquitoes transmit the dengue virus.

Preventive Measures: Avoid water stagnation (e.g., in coolers, tires, flowerpots) to prevent mosquito breeding, maintain hygiene, and use vaccinations.

Mosquitoes as carriers of disease-causing microbes

Common Human Diseases

Human Disease	Causative Microorganism	Mode of Transmission	Preventive Measures
Tuberculosis	Bacteria	Air	Patient isolation, vaccination
Chicken Pox	Virus	Air/Contact	Vaccination
Polio	Virus	Air/Water	Vaccination
Cholera	Bacteria	Water/Food	Hygiene, boiled water, vaccination
Typhoid	Bacteria	Water	Boiled water, vaccination
Hepatitis B	Virus	Water	Vaccination
Malaria	Protozoa	Mosquito	Mosquito nets, repellents, control breeding

Diseases in Animals

Microbes also affect animals, causing diseases like:

Anthrax: A bacterial disease affecting humans and cattle.
Foot-and-mouth disease: A viral disease in cattle.

Diseases in Plants

Microorganisms reduce crop yields by causing diseases in plants like wheat, rice, potatoes, sugarcane, oranges, and apples. These can be controlled with pesticides.

Plant Disease	Microorganism	Mode of Transmission
Citrus Canker	Bacteria	Air
Rust of Wheat	Fungi	Air, Seeds
Yellow Vein Mosaic of Bhindi (Okra)	Virus	Insect

Food Poisoning and Preservation

Microorganisms can spoil food, producing toxins that cause food poisoning. Spoiled food smells bad, tastes unpleasant, and changes color. To prevent spoilage, various preservation methods are used:

Chemical Method: Preservatives like salt, edible oils, sodium benzoate, and sodium metabisulfite inhibit microbial growth in pickles, jams, and squashes.
Common Salt: Used to preserve meat, fish, amla, raw mangoes, and tamarind by dehydrating bacteria.
Sugar: Reduces moisture in jams, jellies, and squashes, preventing bacterial growth.
Oil and Vinegar: Create an inhospitable environment for bacteria, preserving vegetables, fruits, fish, and meat.
Heat and Cold Treatments:
- Boiling milk kills microbes.
- Refrigeration slows microbial growth.
- Pasteurization (heating milk to 70°C for 15–30 seconds, then chilling) eliminates harmful microbes, discovered by Louis Pasteur.
Storage and Packing: Dry fruits and vegetables are sealed in airtight packets to prevent microbial contamination.

Preserving food to prevent microbial spoilage

The Nitrogen Cycle and Environmental Cleanup

Microorganisms are vital for ecological balance:

Nitrogen Fixation: Bacteria like Rhizobium (in leguminous plants) and blue-green algae fix atmospheric nitrogen into compounds plants can use. Lightning also contributes, but microbes are the primary drivers.
Nitrogen Cycle: Nitrogen, comprising 78% of the atmosphere, is essential for proteins, chlorophyll, nucleic acids, and vitamins. Soil bacteria and fungi convert nitrogenous wastes into compounds for plants. Some bacteria release nitrogen gas back into the atmosphere, maintaining its constant level.
Environmental Cleanup: Microbes decompose organic waste (e.g., plant, vegetable, and fruit scraps) in pits, turning it into manure, thus cleaning the environment.

The nitrogen cycle driven by microorganisms

Conclusion

Microorganisms are a double-edged sword—essential for life yet capable of causing harm. From producing food, medicines, and manure to causing diseases and spoilage, their impact is profound. By understanding their roles and implementing preventive measures like vaccination, hygiene, and food preservation, we can harness their benefits while minimizing risks. Let’s continue exploring the wonders of science!

"Microorganisms: tiny in size, but mighty in impact!"