Learning Objectives
- Classify the major groups of microorganisms
- Understand useful and harmful roles of microorganisms
- Learn about diseases caused by microorganisms
- Understand methods of food preservation
Key Concepts
Types of Microorganisms
Microorganisms are living organisms too small to be seen with the naked eye. They are classified into four major groups:
- Bacteria: Single-celled, prokaryotic. Examples: Lactobacillus (curd), Rhizobium (nitrogen fixation).
- Fungi: May be unicellular or multicellular. Examples: yeast (fermentation), Penicillium (antibiotic), mushroom.
- Protozoa: Unicellular, eukaryotic. Examples: Amoeba, Plasmodium (malaria), Paramecium.
- Algae: Plant-like, photosynthetic. Examples: Chlamydomonas, Spirogyra. Found in water bodies.
Viruses: Not truly living; they reproduce only inside a host cell. Examples: influenza virus, HIV, bacteriophage. Cause diseases like common cold, flu, polio.
Friendly Microorganisms
In food: Lactobacillus converts milk to curd. Yeast is used in making bread, cake, and alcohol (fermentation). Bacteria help in making cheese, pickles, and idli/dosa batter.
In medicine: Antibiotics like penicillin are made from fungi. Vaccines are made from weakened or dead microbes to prevent diseases.
In agriculture: Rhizobium bacteria fix atmospheric nitrogen in legume root nodules. Blue-green algae (cyanobacteria) also fix nitrogen and enrich soil.
In cleaning: Microorganisms decompose organic waste and help in sewage treatment.
Harmful Microorganisms
Some microorganisms cause diseases in humans, animals, and plants. These are called pathogens.
- Human diseases: Tuberculosis (bacteria), malaria (protozoa), common cold (virus), ringworm (fungi).
- Animal diseases: Anthrax (bacteria), foot-and-mouth disease (virus).
- Plant diseases: Citrus canker (bacteria), rust of wheat (fungi), yellow vein mosaic of okra (virus).
Food Preservation
Methods to prevent microbial spoilage of food:
- Chemical preservation: Salt, sugar, oil, vinegar (e.g., pickles, jams)
- Heat treatment: Pasteurisation (heating to 70°C then rapid cooling)
- Cold storage: Refrigeration slows microbial growth
- Drying: Removing moisture (sun-drying of fish, vegetables)
Nitrogen Fixation
Atmospheric nitrogen is converted to usable forms by lightning and by nitrogen-fixing bacteria like Rhizobium. This process is essential for the nitrogen cycle.
Summary
Microorganisms include bacteria, fungi, protozoa, and algae. They can be beneficial (food production, medicine, agriculture, decomposition) or harmful (causing diseases, food spoilage). Viruses reproduce only inside host cells. Food preservation methods prevent microbial growth and spoilage.
Important Terms
- Microorganism: An organism too small to be seen without a microscope
- Pathogen: A microorganism that causes disease
- Antibiotic: A medicine that kills or stops the growth of bacteria
- Vaccine: A preparation of weakened/dead microbes that provides immunity
- Fermentation: Conversion of sugar to alcohol/acid by yeast or bacteria
- Pasteurisation: Heating milk to 70°C and then rapidly cooling it
- Nitrogen Fixation: Conversion of atmospheric nitrogen to usable compounds
Quick Revision
- Four groups: bacteria, fungi, protozoa, algae (+ viruses)
- Lactobacillus → curd; Yeast → bread/alcohol; Rhizobium → nitrogen fixation
- Antibiotics kill bacteria (e.g., penicillin from Penicillium fungus)
- Pathogens cause diseases; vaccines prevent them
- Preservation: salt, sugar, oil, vinegar, pasteurisation, refrigeration, drying
- Viruses are not truly living; reproduce only inside host cells