Chapter 2: Microorganisms: Friend and Foe

2.1 Microorganisms

2.1.1 Introduction to Microorganisms

Microorganisms are living organisms around us that are so small in size that they cannot be seen with the unaided eye.
Visualizing Microbes requires a magnifying glass for larger structures like bread mould, or a microscope for tiny unicellular organisms.

2.1.2 Classification of Microbes

Major Groups of microorganisms are classified into four key categories: bacteria, fungi, protozoa, and some algae.
Common Examples include Chlamydomonas and Spirogyra (algae), Amoeba and Paramecium (protozoa), and Bread mould, Penicillium, and Aspergillus (fungi).

2.1.3 Viruses and Associated Diseases

Viruses are microscopic entities that reproduce only inside the host cells of bacteria, plants, or animals, remaining distinct from other microbes.
Viral Diseases include common ailments like cold, influenza (flu), and coughs, as well as serious conditions like polio and chicken pox.
Bacterial and Protozoan Illnesses range from dysentery and malaria (caused by protozoa) to typhoid and tuberculosis (caused by bacteria).

2.2 Where do Microorganisms Live?

2.2.1 Habitats and Cellular Structure

Cellular Forms of microorganisms can be unicellular (like bacteria, some algae, and protozoa) or multicellular (such as many algae and fungi).
Environmental Range of microbes spans across all extremes, from freezing ice-cold climates and hot springs to dry deserts and marshy lands.
Living Conditions include existing freely in the soil or water, growing on other organisms, and residing inside the bodies of animals and humans.

2.3 Microorganisms and Us

2.3.1 Friendly Microorganisms

Organic Waste Decomposition involves bacteria breaking down organic wastes like vegetable peels, animal remains, and faeces into harmless, usable substances.
Agricultural Application utilizes specific microbes in the soil to increase fertility by fixing atmospheric nitrogen.

2.3.2 Making of Curd and Bread

Lactobacillus is the specific bacterium that multiplies in milk to convert it into curd, promoting curd formation on a domestic scale.
Yeast Respiration produces carbon dioxide gas rapidly during respiration, which fills dough with bubbles and increases its volume.
Baking Industry utilizes the rapid multiplication and gas production of yeast to make breads, pastries, and cakes.

2.3.3 Commercial Use and Fermentation

Commercial Microbes are grown on natural sugars in grains like barley, wheat, rice, and fruit juices for the large-scale production of alcohol, wine, and acetic acid.
Fermentation is the chemical process of converting sugar into alcohol, discovered by Louis Pasteur in 1857.

2.3.4 Medicinal Use and Antibiotics

Antibiotics are medicines made from bacteria and fungi, such as streptomycin, tetracycline, and erythromycin, which kill or stop disease-causing microbes.
Penicillin was discovered in 1929 by Alexander Fleming after he observed green mould spores preventing bacterial growth in culture plates.
Medical Precautions require taking antibiotics only under qualified medical advice and finishing the full course to prevent drug resistance and protect helpful gut bacteria.

2.3.5 Vaccines and Immunity

Vaccination is the process of introducing dead or weakened microbes into a healthy body, prompting the immune system to produce antibodies to fight future infections.
Eradication Campaigns have successfully used vaccines to prevent diseases like cholera, tuberculosis, smallpox, and hepatitis, completely wiping out smallpox worldwide.
Smallpox Vaccine was discovered by Edward Jenner in 1798, paving the way for modern immunization.

2.3.6 Increasing Soil Fertility

Biological Nitrogen Fixers are specialized soil microbes, like cyanobacteria (blue-green algae), that capture and fix atmospheric nitrogen to enrich soil.

2.3.7 Cleaning the Environment

Decomposers are microorganisms that break down dead organic matter from plants and animals, converting them into simple nutrients recycled by other organisms.

2.4 Harmful Microorganisms

2.4.1 Pathogens and Communicable Diseases

Pathogens are disease-causing microorganisms that enter the body via air, water, food, or direct contact with an infected host.
Communicable Diseases are microbial infections that transmit from an infected person to a healthy one through environmental vectors, including common cold, cholera, and chicken pox.

2.4.2 Carriers of Disease (Insects and Animals)

Disease Carriers are vectors like the housefly, which collects pathogens from waste and transfers them to uncovered food, causing illness upon consumption.
Anopheles Mosquito acts as the carrier of the malaria parasite Plasmodium, while the female Aedes mosquito acts as the carrier of the dengue virus.
Breeding Control involves keeping surroundings dry and clean to prevent mosquitoes from breeding in stagnant water sources like coolers and flower pots.

2.4.3 Animal and Plant Diseases

Anthrax is a highly fatal human and cattle disease caused by the bacterium Bacillus anthracis, discovered by Robert Koch in 1876.
Plant Infections like Citrus Canker (bacterial), Rust of Wheat (fungal), and Yellow Vein Mosaic of Bhindi (viral) severely diminish crop yields.

2.4.4 Food Poisoning

Food Poisoning is a condition caused by consuming food containing toxic substances produced by the growth of spoilage microorganisms.

2.5 Food Preservation

2.5.1 Chemical Methods and Preservatives

Preservatives are chemicals like salts, edible oils, sodium benzoate, and sodium metabisulphite used to check microbial growth in food items like jams and squashes.

2.5.2 Preservation by Salt and Sugar

Salting dehydrates and preserves fish, meat, amla, raw mangoes, and tamarind by checking bacterial cell growth.
Sugar Preservation reduces the moisture content in sweet spreads like jams and jellies, inhibiting bacterial multiplication.

2.5.3 Preservation by Oil, Vinegar, and Temperature

Oil and Vinegar prevent microbial spoilage of pickles because food-spoiling bacteria cannot survive in such acidic environments.
Temperature Treatments utilize high heat (boiling) to destroy microbes, and low heat (refrigeration) to inhibit the growth of bacteria.

2.5.4 Pasteurisation and Storage

Pasteurisation is a process discovered by Louis Pasteur where milk is heated to 70^oC for 15 to 30 seconds and then suddenly chilled to prevent micro-organic growth.
Sealed Packaging protects dry fruits and vegetables from air moisture and direct exposure to airborne microbes.

2.6 Nitrogen Fixation

2.6.1 Rhizobium and Leguminous Plants

Rhizobium Bacteria establish a symbiotic relationship in the root nodules of leguminous plants, converting atmospheric nitrogen into soluble forms.

2.7 Nitrogen Cycle

2.7.1 Atmospheric Nitrogen and the Cyclic Process

Atmospheric Nitrogen comprises 78% of the atmosphere and is a structural component of proteins, chlorophyll, nucleic acids, and vitamins.
Nitrogen Cycling involves continuous biological conversions where soil bacteria fix atmospheric nitrogen, plants absorb it, animals consume plants, and decomposers return nitrogen back to the soil and atmosphere.