Microorganisms: Friend and Foe - Comprehensive Notes

Microorganisms: Friend and Foe

Introduction

• 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 such as mold, which thrive in humid climate conditions, highlighting both their role in decomposition and their potential to spoil food.

  • These organisms can be beneficial, aiding in processes like fermentation and nutrient cycling, as well as harmful, causing diseases and foodborne illnesses.

Classification of Microorganisms

• Microorganisms are classified into four major groups:

  • Bacteria- e. coli

  • Fungi- mushrooms

  • Protozoa- ameoba

  • Algae- spirogyra

• Viruses are also microscopic but different; they reproduce inside a host cell (bacterium, plant, or animal).

• Common ailments c-aused by viruses: cold, influenza (flu), coughs, polio, chickenpox.

• Diseases caused by protozoa: dysentery and malaria.

• Bacterial diseases: typhoid and tuberculosis (TB).

2.2 Where do Microorganisms Live?

• Microorganisms can be:

  • Single-celled (bacteria, some algae, protozoa)

  • Multicellular (many algae and fungi)

• They inhabit diverse environments:

  • Ice-cold climates to hot springs

  • Deserts to marshy lands

• They can be found inside the bodies of animals, including humans.

• Some grow on other organisms, while others exist freely.

2.3 Microorganisms and Us

• Microorganisms play an important role in our lives; some are beneficial, others are harmful.

Friendly Microorganisms

• Used in the production of alcohol, curd, bread, and cake.

• Lactobacillus promotes curd formation by multiplying in milk and converting it into curd.

• Used in making cheese, pickles, and other food items.

• Important in fermentation of rice idlis and dosa batter.

• Helpful in cleaning the environment by breaking down organic wastes into harmless substances.

• Used in the preparation of medicines and in agriculture to increase soil fertility by fixing nitrogen.

Making of Curd and Bread

• Milk is turned into curd by bacteria.

• Yeast reproduces rapidly and produces carbon dioxide during respiration.

• Bubbles of the gas fill the dough and increase its volume.

• Basis of using yeast in the baking industry for making bread, 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 in grains like barley, wheat, rice, and crushed fruit juices.

• Fermentation: The process of conversion of sugar into alcohol.

  • Discovered by Louis Pasteur in 1857.

Medicinal Use of Microorganisms

• Source of antibiotics like penicillin.

  • Alexander Fleming discovered penicillin in 1929 while working on bacteria.

• Antibiotics kill or stop the growth of disease-causing microorganisms; produced from bacteria and fungi.

• Examples: streptomycin, tetracycline, and erythromycin.

• Used to cure a variety of diseases in humans and animals and to control plant diseases.

• Important to take antibiotics only on the advice of a qualified doctor and to complete the prescribed course.

• Overuse or misuse may lead to drug resistance and killing of beneficial bacteria.

• Antibiotics are not effective against cold and flu (viral infections).

Vaccine

• When disease-carrying microbes enter the body, the body produces antibodies to fight the invader.

• The body remembers how to fight if the microbe enters again.

• Vaccines contain dead or weakened microbes, which stimulate the body to produce antibodies for future protection.

• Several diseases like cholera, tuberculosis, smallpox, and hepatitis can be prevented by vaccination.

• Edward Jenner discovered the vaccine for smallpox in 1798.

• Polio drops are a vaccine (Pulse Polio Programme).

Increasing Soil Fertility

• Some bacteria can fix nitrogen from the atmosphere to enrich the soil.

• These microbes are called biological nitrogen fixers.

Cleaning the Environment

• Microorganisms decompose dead organic waste of plants and animals into simple substances.

• These substances are used by other plants and animals.

• Microorganisms degrade harmful and smelly substances, cleaning up the environment.

2.4 Harmful Microorganisms

• Some microorganisms cause diseases in humans, plants, and animals; these are called pathogens.

• Some spoil food, clothing, and leather.

Disease-Causing Microorganisms in Humans

• Pathogens enter the body through air, water, food, or direct contact.

• Communicable diseases spread from an infected person to a healthy person (e.g., cholera, common cold, chicken pox, tuberculosis).

• Sneezing spreads viruses in the air.

• Insects and animals act as carriers (e.g., housefly, female Anopheles mosquito, female Aedes mosquito).

• Female Anopheles mosquito carries the parasite of malaria (Plasmodium).

• Female Aedes mosquito acts as a carrier of dengue virus.

• Control measures include keeping surroundings clean and dry to prevent mosquitoes from breeding.

Disease-Causing Microorganisms in Animals

• Microorganisms cause diseases in animals (e.g., anthrax, foot and mouth disease).

• 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

• Cause diseases in plants like wheat, rice, potato, sugarcane, orange, apple, etc., reducing crop yield.

• Can be controlled by certain chemicals which kill the microbes.

Food Poisoning

• Caused by consuming food spoilt by microorganisms.

• Microorganisms produce toxic substances that make food poisonous.

2.5 Food Preservation

• Preservation prevents food from being spoilt.

• Spoiled food emits a bad smell and has a bad taste and changed color.

Chemical Method

• Salts and edible oils are common preservatives used to check the growth of microorganisms.

• Salt or acid preservatives are added to pickles.

• Sodium benzoate and sodium metabisulphite are common preservatives in jams and squashes.

Preservation by Common Salt

• Used to preserve meat and fish for ages.

• Salting is also used to preserve amla, raw mangoes, tamarind, etc.

Preservation by Sugar

• Used to preserve jams, jellies, and squashes.

• Sugar reduces moisture content, inhibiting bacterial growth.

Preservation by Oil and Vinegar

• Prevents spoilage of pickles; bacteria cannot live in such an environment.

• Used to preserve vegetables, fruits, fish, and meat.

Heat and Cold Treatments

• Boiling kills many microorganisms.

• Refrigeration inhibits microbial growth.

• Pasteurization: Milk is heated to about 70^\circ C for 15 to 30 seconds and then suddenly chilled and stored to prevent microbial growth.

  • Discovered by Louis Pasteur.

Storage and Packing

• Dry fruits and vegetables are sold in sealed airtight packets to prevent microbial attack.

2.6 Nitrogen Fixation

• Rhizobium: Bacterium involved in nitrogen fixation in leguminous plants (pulses).

• Rhizobium lives in the root nodules of leguminous plants (beans and peas) in a symbiotic relationship.

• Nitrogen can also be fixed through the action of lightning.

2.7 Nitrogen Cycle

• Atmosphere contains 78% nitrogen gas.

• Nitrogen is an essential constituent of all living organisms (proteins, chlorophyll, nucleic acids, and vitamins).

• Atmospheric nitrogen cannot be directly taken by plants and animals.

• Certain bacteria and blue-green algae fix nitrogen from the atmosphere and convert it into nitrogen compounds.

• Plants utilize these compounds from the soil through their root system.

• Nitrogen is used for the synthesis of plant proteins and other compounds.

• Animals obtain these proteins and nitrogen compounds by feeding on plants.

• When plants and animals die, bacteria and fungi convert nitrogenous wastes into nitrogenous compounds.

• Other bacteria convert some of these compounds into nitrogen gas, which goes back into the atmosphere.

• The percentage of nitrogen in the atmosphere remains more or less constant.

Did You Know?

• Bacteria can survive under extreme conditions such as boiling mudpots, extremely cold icy waters, lakes of caustic soda, and pools of concentrated sulphuric acid.

• They can survive at depths of several kilometers and possibly in space.

Microorganisms have both beneficial and harmful effects. Some beneficial roles include aiding in the production of foods like curd, bread, and alcohol, cleaning the environment by decomposing organic waste, increasing soil fertility through nitrogen fixation, and producing antibiotics and vaccines. On the other hand, harmful effects include causing diseases in humans, animals, and plants (acting as pathogens), spoiling food, and leading to food poisoning.