Microorganisms: Friend and Foe - Chapter Notes

What are Microorganisms?

Microorganisms, or microbes, are living organisms that are too small to be seen with the naked eye. They can only be observed through a microscope. They are found everywhere – in air, water, soil, and even inside the bodies of other living organisms. Microbes are classified into five major groups: Bacteria, Fungi, Protozoa, Algae, and Viruses.

• Bacteria: These are single-celled organisms with a rigid cell wall. They come in various shapes like rod-shaped (bacilli), spherical (cocci), and spiral (spirilla). Examples include Lactobacillus (used in curd) and E. coli.
• Fungi: These are non-green, plant-like organisms. They can be unicellular (like yeast) or multicellular (like bread mould, mushrooms). They obtain nutrition from decaying organic matter.
• Protozoa: These are unicellular animals. Most are heterotrophic. Examples include Amoeba and Plasmodium (causes malaria).
• Algae: These are simple, plant-like organisms that can perform photosynthesis. They can be unicellular (like Chlamydomonas) or multicellular (like Spirogyra).
• Viruses: Viruses are unique because they are on the border of living and non-living. They can only reproduce inside the cells of a host organism (a plant, animal, or bacterium). Outside a host, they are inactive. Examples include the Influenza virus and HIV.

Key Terms to Remember

Microorganisms

Living organisms that are microscopic, meaning they are too small to be seen with the naked eye.

Pathogens

Disease-causing microorganisms.

Fermentation

The process of conversion of sugar into alcohol by yeast. This process is used in making wine, beer, and bread.

Antibiotics

Medicines that kill or stop the growth of disease-causing microorganisms, particularly bacteria.

Vaccine

A substance containing dead or weakened microbes that is introduced into the body to stimulate the production of antibodies and provide immunity against a specific disease.

Pasteurization

The process of heating a liquid (like milk) to a high temperature (about 70°C) for 15-30 seconds and then suddenly chilling it to kill harmful microbes.

Nitrogen Fixation

The process by which atmospheric nitrogen is converted into nitrogen compounds (like nitrates) that can be used by plants. This is done by bacteria like Rhizobium.

Communicable Diseases

Microbial diseases that can spread from an infected person to a healthy person through air, water, food, or physical contact.

Carriers

Insects or animals that carry disease-causing microbes and transfer them from an infected person to a healthy one. Example: Housefly, female Anopheles mosquito.

Friendly vs. Harmful Microbes

Must Remember Facts

• {"point":"Viruses are a special case; they reproduce only inside a host organism's cells."}
• {"point":"Louis Pasteur discovered fermentation in 1857 and developed the process of pasteurization."}
• {"point":"Alexander Fleming discovered the first antibiotic, Penicillin, in 1928 from the fungus Penicillium notatum."}
• {"point":"Edward Jenner discovered the vaccine for smallpox in 1798."}
• {"point":"Rhizobium bacteria, found in the root nodules of leguminous plants, help in nitrogen fixation."}
• {"point":"Female Anopheles mosquito is a carrier for the malaria parasite (Plasmodium), and female Aedes mosquito is a carrier for the dengue virus."}
• {"point":"Common food preservation methods include: Chemical (salts, oil, vinegar), Pasteurization, Freezing, and Dehydration (drying)."}
• {"point":"Communicable diseases like cholera, common cold, and chickenpox spread through air, water, or contact."}
• {"point":"Antibiotics are effective against bacteria but not against viruses like those causing the common cold or flu."}

The Nitrogen Cycle Explained

1. —
2. —
3. —
4. —
5. —

Common Human Diseases Caused by Microorganisms

• Bacterial Diseases Tuberculosis: Caused by Mycobacterium tuberculosis, spreads through air. Cholera: Caused by Vibrio cholerae, spreads through contaminated water/food. Typhoid: Caused by Salmonella typhi, spreads through contaminated water.
• Viral Diseases Common Cold: Caused by Rhinovirus, spreads through air. Polio: Caused by Poliovirus, spreads through air/water. Measles: Caused by Morbillivirus, spreads through air.
• Protozoan Diseases Malaria: Caused by Plasmodium, spread by the female Anopheles mosquito. Amoebic Dysentery: Caused by Entamoeba histolytica, spreads through contaminated water.

Exam Revision Tips

For this chapter, focus on tables and diagrams. Create a table listing diseases, their causative microbes, mode of transmission, and preventive measures. Practice drawing the Nitrogen Cycle with all labels. Questions often ask about the specific roles of microorganisms, so remember names like Lactobacillus, Yeast, and Rhizobium. Understand the principles behind food preservation techniques (e.g., salt removes water via osmosis, preventing microbial growth). Don't confuse antibiotics and vaccines – antibiotics treat bacterial infections, while vaccines prevent diseases.

Quick Revision Check

• Why are antibiotics not effective against the common cold? The common cold is caused by a virus. Antibiotics are designed to kill bacteria and are ineffective against viruses.
• Name the microorganism that helps in the production of bread and the process involved. Yeast is the microorganism. The process is fermentation, where yeast produces carbon dioxide, making the dough rise.
• What is the role of Rhizobium bacteria in the soil? Rhizobium bacteria live in the root nodules of leguminous plants and perform nitrogen fixation, converting atmospheric nitrogen into a form that plants can use.
• How does a vaccine work to provide immunity? A vaccine introduces weakened or dead microbes into the body. This prompts the immune system to produce antibodies. These antibodies remain in the body and fight off future infections by the same microbe.

Frequently Asked Questions

Frequently Asked Questions