Microorganisms: Friend and Foe - Detailed Notes
Microorganisms: Friend and Foe
Introduction to Microorganisms
Microorganisms (or microbes) are living organisms around us that are normally invisible to the naked eye.
Example: Greyish-white patches on moist bread during the rainy season are due to microorganisms.
Observed through a magnifying glass, these patches reveal tiny, black rounded structures.
Activities to Observe Microorganisms
Activity 2.1: Collect moist soil, add water, let particles settle, and observe a drop of water under a microscope.
Activity 2.2: Take water from a pond, spread on a glass slide, and observe under a microscope.
These activities demonstrate that water and soil are full of tiny organisms.
These microorganisms can only be seen through a microscope or magnifying glass.
Classification of Microorganisms
Microorganisms are classified into four major groups:
Bacteria
Fungi
Protozoa
Algae
Viruses are also microscopic but differ from other microorganisms; they reproduce inside host cells (bacterium, plant, or animal).
Examples of Microorganisms
Bacteria: Shown in Fig. 2.1.
Algae: Examples include Chlamydomonas and Spirogyra (Fig. 2.2).
Protozoa: Examples include Amoeba and Paramecium (Fig. 2.3).
Fungi: Examples include Bread mould, Penicillium, and Aspergillus (Fig. 2.4).
Viruses: Shown in Fig. 2.5.
Common Ailments Caused by Microorganisms
Viruses: Common cold, influenza (flu), most coughs, polio, and chicken pox.
Protozoa: Dysentery and malaria.
Bacteria: Typhoid and tuberculosis (TB).
Where Microorganisms Live
Microorganisms can be single-celled (bacteria, some algae, and protozoa) or multicellular (many algae and fungi).
They thrive in diverse environments:
Ice cold climates to hot springs
Deserts to marshy lands
They are also found inside the bodies of animals, including humans.
Some grow on other organisms, while others exist freely.
Microorganisms and Their Role in Our Lives
Microorganisms play a significant role, being both beneficial and harmful.
They have been used in the production of alcohol for ages.
Friendly Microorganisms
Used in preparation of curd, bread, and cake.
Lactobacillus bacterium promotes curd formation by multiplying in milk and converting it into curd.
Involved in making cheese, pickles, and other food items.
Used in fermentation of rice idlis and dosa batter.
Clean up the environment by breaking down organic wastes into harmless substances.
Used in the preparation of medicines and to increase soil fertility by fixing nitrogen.
Making of Curd and Bread
Milk is turned into curd by bacteria.
Activity 2.3: Making dough with yeast powder demonstrates the rising effect due to carbon dioxide production.
Yeast reproduces rapidly and produces carbon dioxide during respiration.
Bubbles of the gas fill the dough and increase its volume (Fig. 2.6).
This is the basis of using yeast in the baking industry for making breads, pastries, and cakes.
Commercial Use of Microorganisms
Used for large-scale production of alcohol, wine, and acetic acid (vinegar).
Yeast is grown on natural sugars present in grains like barley, wheat, rice, and crushed fruit juices.
Activity 2.4: Demonstrates the production of alcohol by yeast from sugar solution.
The process of converting sugar into alcohol is known as fermentation, discovered by Louis Pasteur in 1857.
Medicinal Use of Microorganisms
Antibiotics are produced from microorganisms to kill or stop the growth of disease-causing microorganisms.
Examples: Streptomycin, tetracycline, and erythromycin are made from fungi and bacteria.
Antibiotics are manufactured by growing specific microorganisms and are used to cure a variety of diseases.
They are mixed with livestock and poultry feed to check microbial infection in animals and to control plant diseases.
Antibiotics should be taken only on the advice of a qualified doctor, and the prescribed course must be completed.
Overuse or wrong doses may make the drug less effective in the future and kill beneficial bacteria in the body.
Antibiotics are not effective against cold and flu, as these are caused by viruses.
Vaccine
When a disease-carrying microbe enters our body, the body produces antibodies to fight the invader.
If dead or weakened microbes are introduced, the body fights and kills them by producing suitable antibodies.
The antibodies remain in the body, providing protection from the disease-causing microbes forever.
Several diseases, including cholera, tuberculosis, smallpox, and hepatitis, can be prevented by vaccination.
Edward Jenner discovered the vaccine for smallpox in 1798.
Polio drops given to children are a vaccine as part of the Pulse Polio Programme.
Increasing Soil Fertility
Some bacteria (Fig. 2.7) fix nitrogen from the atmosphere to enrich the soil and increase its fertility.
These microbes are called biological nitrogen fixers.
Cleaning the Environment
Organic wastes are decomposed into harmless substances by microbes.
Activity 2.5: Shows plant waste decomposing into manure due to microbes, while non-degradable items do not change.
Microorganisms decompose dead organic waste of plants and animals, converting them into simple substances.
Microorganisms can degrade harmful and smelly substances, cleaning up the environment.
Harmful Microorganisms
Microorganisms can cause diseases in humans, plants, and animals.
Disease-causing microorganisms are called pathogens.
Some microorganisms spoil food, clothing, and leather.
Disease-Causing Microorganisms in Humans
Pathogens enter the body through air, water, or food.
They can be transmitted by direct contact with an infected person or carried by an animal.
Microbial diseases that spread from an infected person to a healthy person are called communicable diseases (e.g., cholera, common cold, chicken pox, tuberculosis).
Sneezing spreads viruses in the air.
Insects and animals can act as carriers of disease-causing microbes.
Houseflies carry pathogens from garbage and animal excreta to uncovered food.
Female Anopheles mosquito carries the parasite of malaria (Plasmodium).
Female Aedes mosquito carries the dengue virus.
Preventive measures include keeping food covered, maintaining hygiene, and controlling mosquito breeding by not allowing water to collect in the surroundings.
Disease-Causing Microorganisms in Animals
Several microorganisms cause diseases in animals.
Example: Anthrax is a dangerous human and cattle disease caused by a bacterium.
Foot and mouth disease of cattle is caused by a virus.
Disease-Causing Microorganisms in Plants
Microorganisms cause diseases in plants like wheat, rice, potato, sugarcane, orange, and apple.
These diseases reduce crop yield.
They can be controlled by chemicals that kill the microbes.
Food Poisoning
Food poisoning can occur due to the consumption of food spoiled by microorganisms, which produce toxic substances.
Spoiled food emits a bad smell, has a bad taste, and changed color.
It is important to preserve food to prevent spoilage.
Food Preservation
Preserve food to prevent it from being attacked by microorganisms.
Chemical Method
Salts and edible oils are commonly used to check the growth of microorganisms and are called preservatives.
Sodium benzoate and sodium metabisulphite are common preservatives used in jams and squashes.
Preservation by Common Salt
Common salt is used to preserve meat and fish by covering them with dry salt to check bacterial growth.
Salting is also used to preserve amla, raw mangoes, and tamarind.
Preservation by Sugar
Sugar is used to preserve jams, jellies, and squashes.
Sugar reduces moisture content, inhibiting bacterial growth.
Preservation by Oil and Vinegar
Oil and vinegar prevent spoilage of pickles because bacteria cannot live in such an environment.
Vegetables, fruits, fish, and meat are often preserved by this method.
Heat and Cold Treatments
Boiling milk kills many microorganisms.
Refrigeration inhibits the growth of microbes.
Pasteurisation
Pasteurised milk can be consumed without boiling as it is free from harmful microbes.
The milk is heated to about 70^{\circ}C for 15 to 30 seconds and then suddenly chilled and stored.
This process, discovered by Louis Pasteur, prevents the growth of microbes.
Storage and Packing
Dry fruits and vegetables are sold in sealed airtight packets to prevent microbial attack.
Nitrogen Fixation
Rhizobium bacterium fixes nitrogen in leguminous plants (pulses).
Rhizobium lives in the root nodules of leguminous plants (Fig. 2.9), such as beans and peas, in a symbiotic relationship.
Nitrogen can also be fixed through lightning.
Nitrogen Cycle
The atmosphere contains 78% nitrogen gas, which is essential for living organisms as part of proteins, chlorophyll, nucleic acids, and vitamins.
Atmospheric nitrogen cannot be directly taken by plants and animals.
Certain bacteria and blue-green algae in the soil fix nitrogen from the atmosphere and convert it into compounds of nitrogen.
These compounds are utilized by plants through their root system.
Nitrogen is used for the synthesis of plant proteins and other compounds.
Animals feeding on plants obtain these proteins and nitrogen compounds (Fig. 2.10).
When plants and animals die, bacteria and fungi convert the nitrogenous wastes into nitrogenous compounds, which are used by plants again.
Some bacteria convert part of these compounds into nitrogen gas, which returns to the atmosphere.
This cycle maintains a more or less constant percentage of nitrogen in the atmosphere.
Keywords
Algae
Antibiotics
Antibodies
Bacteria
Carrier
Communicable Diseases
Fermentation
Fungi
Lactobacillus
Microorganism
Nitrogen Cycle
Nitrogen Fixation
Pasteurisation
Pathogen
Preservation
Protozoa
Rhizobium
Vaccine
Virus
Yeast