REVISION NOTES
Chapter: Microorganisms – Friend and Foe
1. Microorganisms
Microorganisms are very tiny living organisms.
They cannot be seen with naked eye.
They can be seen using a microscope.
They are also called microbes.
Examples
Bacteria
Fungi
Protozoa
Algae
Viruses
2. Types of Microorganisms
1. Bacteria
Single celled organisms.
Found everywhere.
Some are useful, some cause diseases.
2. Fungi
Grow on dead and moist materials.
Example: Bread mould.
3. Protozoa
Single celled organisms.
Example: Amoeba, Paramecium.
4. Algae
Simple plant-like organisms.
Found in water.
5. Viruses
Smaller than bacteria.
Multiply only inside host cells.
3. Habitat of Microorganisms
Microorganisms live in different places:
Soil
Water
Air
Inside plants and animals
Ice cold regions
Hot springs
Deserts and marshy lands
They can survive in extreme environments.
4. Useful Microorganisms
1. Food Preparation
Microorganisms help in making:
Curd
Bread
Cheese
Pickles
Idli and dosa batter
Lactobacillus bacteria convert milk into curd.
2. Fermentation
Yeast converts sugar into alcohol.
This process is called Fermentation.
Uses:
Bread making
Wine production
Alcohol production
3. Production of Medicines
Microorganisms are used to make antibiotics.
Examples:
Penicillin
Streptomycin
Tetracycline
Antibiotics kill or stop growth of harmful microbes.
4. Vaccines
Vaccines protect the body from diseases.
Examples:
Polio
Cholera
Hepatitis
Tuberculosis
Vaccines contain weakened or dead microbes that help our body produce antibodies.
5. Increasing Soil Fertility
Some bacteria fix nitrogen from air.
Example:
Rhizobium
They increase soil fertility.
6. Cleaning the Environment
Microorganisms decompose dead plants and animals.
They convert waste into:
Simple substances
Manure
Thus they help clean the environment.
5. Harmful Microorganisms
Some microbes cause diseases in:
Humans
Animals
Plants
Such microbes are called pathogens.
Bacterial Diseases in Humans
Disease Mode of Transmission Pathogen Tuberculosis Contaminated air droplets Mycobacterium tuberculosis Typhoid Contaminated water or food Salmonella typhi Cholera Contaminated water or food Vibrio cholerae
| Disease | Mode of Transmission | Pathogen |
|---|---|---|
| Tuberculosis | Contaminated air droplets | Mycobacterium tuberculosis |
| Typhoid | Contaminated water or food | Salmonella typhi |
| Cholera | Contaminated water or food | Vibrio cholerae |
Viral Diseases in Humans
Disease Mode of Transmission Pathogen Hepatitis A Contaminated water or food Hepatitis A virus Chickenpox Contaminated air or direct contact Varicella-zoster virus Polio Contaminated air or water Poliovirus
| Disease | Mode of Transmission | Pathogen |
|---|---|---|
| Hepatitis A | Contaminated water or food | Hepatitis A virus |
| Chickenpox | Contaminated air or direct contact | Varicella-zoster virus |
| Polio | Contaminated air or water | Poliovirus |
Vector-Borne Diseases
Disease Carrier Pathogen Malaria Female Anopheles mosquito Plasmodium Dengue Female Aedes mosquito Dengue virus
| Disease | Carrier | Pathogen |
|---|---|---|
| Malaria | Female Anopheles mosquito | Plasmodium |
| Dengue | Female Aedes mosquito | Dengue virus |
Carriers of Diseases
Some organisms spread diseases.
Examples:
Housefly
Mosquito
Example:
Female Anopheles mosquito spreads malaria.
Diseases in Animals
Disease Transmission Pathogen Symptoms Foot and Mouth Disease Direct contact, contaminated air Aphthovirus Lesions, blisters, excessive salivation Anthrax Contaminated soil, food or water Bacillus anthracis Fever, breathing difficulty, convulsions
| Disease | Transmission | Pathogen | Symptoms |
|---|---|---|---|
| Foot and Mouth Disease | Direct contact, contaminated air | Aphthovirus | Lesions, blisters, excessive salivation |
| Anthrax | Contaminated soil, food or water | Bacillus anthracis | Fever, breathing difficulty, convulsions |
Diseases in Plants
| Plant Disease | Microorganism |
|---|---|
| Citrus canker | Bacteria |
| Rust of wheat | Fungi |
| Yellow vein mosaic of bhindi | Virus |
6. Food Poisoning
Food poisoning occurs when:
Microorganisms grow on food
They produce toxic substances
Symptoms:
Vomiting
Diarrhea
Stomach pain
Spoiled food:
Bad smell
Bad taste
Change in colour
7. Food Preservation
Food is preserved to prevent growth of microbes.
Methods of Preservation
Salt
Used in pickles, fish, meat.
Sugar
Used in jams and jellies.
Oil and Vinegar
Used in pickles.
Heat
Boiling kills microbes.
Refrigeration
Low temperature slows microbial growth.
Pasteurization
Milk heated to 70°C for 15–30 seconds and cooled quickly.
This process was discovered by Louis Pasteur.
8. Nitrogen Fixation
Nitrogen is essential for plants.
Plants cannot use atmospheric nitrogen directly.
Nitrogen Fixation
Conversion of nitrogen gas into usable compounds.
Performed by:
Rhizobium bacteria
Blue-green algae
9. Nitrogen Cycle
Steps:
Nitrogen in atmosphere.
Nitrogen fixation by bacteria.
Plants absorb nitrogen.
Animals eat plants.
Decomposers return nitrogen to soil.
Some bacteria release nitrogen back to atmosphere.
This cycle maintains constant nitrogen level in nature