World of Microbes Exercise Solutions | KalviGavani

Microorganisms (microbes) are living organisms that are too small to be seen with the naked eye. They are found everywhere — in soil, water, air, and inside other organisms.

The five major groups of microorganisms are: 1. Bacteria — unicellular, prokaryotic (e.g., Lactobacillus, Rhizobium, E. coli) 2. Viruses — acellular, replicate only inside a host (e.g., Influenza virus, HIV, Corona virus) 3. Fungi — eukaryotic, non-green, can be unicellular or multicellular (e.g., Yeast, Penicillium, Rhizopus) 4. Protozoa — unicellular, eukaryotic (e.g., Amoeba, Paramecium, Plasmodium) 5. Algae — eukaryotic, photosynthetic (e.g., Chlamydomonas, Spirogyra, Volvox)

Nitrogen fixation is the process of converting atmospheric nitrogen (N₂) gas into soluble nitrogen compounds (ammonia, nitrates) that plants can absorb and use for growth.

Role of microorganisms:

• Rhizobium: Symbiotic bacteria found in root nodules of leguminous plants (peas, beans, lentils). They fix atmospheric nitrogen into ammonia, which the plant uses. In return, the plant provides the bacteria with food and shelter.
• Azotobacter and Clostridium: Free-living bacteria in the soil that fix atmospheric nitrogen into usable forms.
• Blue-green algae (Cyanobacteria): e.g., Nostoc, Anabaena — fix nitrogen in aquatic and soil environments.

This natural process enriches the soil with nitrogen, reducing the need for chemical fertilisers.

Antibiotics are chemical substances produced by microorganisms (mainly fungi and bacteria) that kill or inhibit the growth of other microorganisms, especially pathogenic bacteria.

Examples: 1. Penicillin — obtained from the fungus Penicillium notatum. Discovered by Alexander Fleming (1928). Used to treat bacterial infections like pneumonia, syphilis, and wound infections. 2. Streptomycin — obtained from the bacterium Streptomyces griseus. Used to treat tuberculosis and other bacterial infections.

Other examples: Tetracycline, Erythromycin, Chloramphenicol, Amoxicillin.

Important note: Antibiotics are effective against bacterial infections, NOT viral infections (like common cold, flu, COVID-19).

Pathogenic microorganisms enter the body through contaminated food/water, air, insect bites, or direct contact. They multiply inside the body and produce toxins that damage cells and tissues, causing disease.

Bacterial diseases: 1. Tuberculosis (TB) — caused by Mycobacterium tuberculosis (affects lungs) 2. Cholera — caused by Vibrio cholerae (severe diarrhoea, dehydration)

Viral diseases: 1. Influenza (Flu) — caused by influenza virus (fever, cough, body aches) 2. Dengue — caused by dengue virus, transmitted by Aedes mosquito (high fever, joint pain, rash)

Decomposition is the process by which microorganisms (mainly bacteria and fungi) break down dead organic matter — dead plants, animals, and waste — into simpler substances.

Importance: 1. Nutrient cycling: Returns nutrients (carbon, nitrogen, phosphorus) back to the soil, making them available to plants again. 2. Cleaning the environment: Removes dead and waste material from the environment. 3. Soil fertility: Decomposed matter forms humus, which enriches the soil and improves its water-holding capacity. 4. Biogas production: Decomposition of organic waste by methanogens produces biogas (methane), a renewable fuel.

Without decomposers, dead matter would accumulate and nutrients would be locked up, disrupting the entire ecosystem.

Microorganisms are classified into five major groups:

• Unicellular, prokaryotic organisms (no well-defined nucleus or membrane-bound organelles).
• Found everywhere — soil, water, air, extreme environments (hot springs, deep-sea vents).
• Shapes: cocci (spherical), bacilli (rod-shaped), spirilla (spiral), vibrio (comma-shaped).
• Useful bacteria: Lactobacillus (curd), Rhizobium (nitrogen fixation), Acetobacter (vinegar), methanogens (biogas).
• Harmful bacteria: Salmonella (food poisoning), Mycobacterium tuberculosis (TB), Vibrio cholerae (cholera), Clostridium tetani (tetanus).

• Acellular (not cells) — consist of genetic material (DNA or RNA) enclosed in a protein coat called capsid.
• Obligate intracellular parasites — can reproduce ONLY inside a living host cell.
• Show living characteristics inside host (reproduce, mutate) but non-living outside (no metabolism, can be crystallised).
• Considered borderline between living and non-living.
• Examples: Influenza virus (flu), HIV (AIDS), Corona virus (COVID-19), Dengue virus, Polio virus, Rabies virus.

• Eukaryotic, non-green organisms (lack chlorophyll — cannot photosynthesise).
• Can be unicellular (yeast) or multicellular (moulds, mushrooms).
• Cell walls made of chitin.
• Reproduce by spores.
• Saprophytic nutrition — feed on dead and decaying organic matter.
• Useful fungi: Yeast (bread, alcohol), Penicillium (antibiotic), Agaricus (edible mushroom).
• Harmful fungi: Rhizopus (bread mould), Aspergillus (causes respiratory infections), dermatophytes (ringworm, athlete's foot).

• Unicellular, eukaryotic organisms.
• Found in water, moist soil, or as parasites inside other organisms.
• Move using pseudopodia (Amoeba), cilia (Paramecium), or flagella (Euglena).
• Useful protozoa: Amoeba, Paramecium (feed on bacteria, help maintain aquatic ecosystems).
• Harmful protozoa: Plasmodium (malaria), Entamoeba histolytica (amoebic dysentery), Trypanosoma (sleeping sickness).

• Eukaryotic, photosynthetic organisms (contain chlorophyll).
• Can be unicellular (Chlamydomonas, diatoms) or multicellular (Spirogyra, seaweed).
• Found in water (freshwater and marine), moist soil, and tree bark.
• Produce oxygen through photosynthesis — major oxygen producers on Earth.
• Useful algae: Spirulina (protein-rich food), seaweed (food, iodine source), diatoms (diatomaceous earth used in filters).
• Harmful algae: Blue-green algae (cyanobacteria) blooms can produce toxins harmful to aquatic life.

Microorganisms play many beneficial roles in nature, industry, and medicine:

• Rhizobium bacteria in root nodules of leguminous plants convert atmospheric nitrogen (N₂) into ammonia and nitrates.
• Free-living bacteria like Azotobacter and Clostridium also fix nitrogen in soil.
• This enriches soil fertility naturally and reduces dependence on chemical fertilisers.

• Saprophytic bacteria and fungi break down dead plants, animals, and organic waste.
• They release simple inorganic nutrients (carbon, nitrogen, phosphorus) back into the soil.
• This process is essential for maintaining soil fertility and the carbon and nitrogen cycles.

• Antibiotics: Penicillin (from Penicillium), Streptomycin (from Streptomyces), Tetracycline, Erythromycin — kill or inhibit pathogenic bacteria.
• Vaccines: Weakened or killed microorganisms (or their parts) are used to stimulate immunity against diseases — e.g., polio vaccine, COVID-19 vaccine, BCG vaccine for TB.
• Insulin: Genetically modified bacteria (E. coli) produce human insulin for diabetes treatment.
• Vitamin B₁₂: Produced by bacteria (Pseudomonas, Streptomyces).

• Alcohol production: Yeast ferments sugar molasses to produce ethanol (industrial alcohol).
• Enzyme production: Bacteria and fungi produce enzymes like amylase, protease, and lipase used in detergents and food processing.
• Acetic acid, citric acid, lactic acid: Produced by microbial fermentation for industrial use.

• Methanogenic bacteria (methanogens) decompose organic waste (cow dung, agricultural waste) in biogas plants to produce biogas (mainly methane, CH₄).
• Biogas is used as a renewable fuel for cooking and electricity generation.
• The leftover slurry is used as organic manure.

• Bacteria decompose organic matter in sewage water, cleaning it before it is released into water bodies.

Harmful microorganisms (Pathogens): Pathogens are disease-causing microorganisms that enter the body through contaminated food/water, air, insect bites, or direct contact, multiply inside the body, and produce toxins that damage tissues.

A. Bacterial Diseases:

B. Viral Diseases:

C. Fungal Diseases:

• Ringworm — caused by dermatophyte fungi; itchy, ring-shaped red patches on skin.
• Athlete's foot — fungal infection between toes; itching, cracking, scaling.
• Aspergillosis — lung infection by Aspergillus; breathing difficulty.

D. Protozoan Diseases:

• Malaria — caused by Plasmodium; transmitted by female Anopheles mosquito; symptoms: high fever with chills, headache, sweating.
• Amoebic dysentery — caused by Entamoeba histolytica; contaminated food/water; symptoms: diarrhoea with blood and mucus, abdominal pain.
• Sleeping sickness — caused by Trypanosoma; transmitted by tsetse fly; symptoms: fever, headache, drowsiness.

Other Harmful Effects:

• Food spoilage: Bacteria and fungi grow on food, making it unfit for consumption (bread mould, fruit rot, milk souring).
• Plant diseases: Rust (wheat), blight (potato), wilt (banana) — caused by fungi and bacteria, destroying crops.
• Material damage: Fungi damage leather, cloth, wood, and paper (mould growth).

Food preservation is the process of treating and handling food to prevent spoilage by microorganisms (bacteria, fungi), enzymes, and environmental factors (moisture, oxygen), thereby extending its shelf life.

Principle: Create conditions that are unfavourable for the growth and survival of microorganisms — remove moisture, change temperature, change pH, or add chemicals.

Methods of Food Preservation:

• Removing water from food to prevent microbial growth (microorganisms need moisture).
• Examples: Dried fruits (raisins, figs, dates), dried fish, dried vegetables, milk powder.
• Method: Sun drying, mechanical drying, freeze drying.

• Adding salt draws out water from food through osmosis, making it inhospitable for microbes.
• Examples: Pickles (mango, lemon, fish), cured meat, salted fish.
• Salt creates a hypertonic environment that dehydrates and kills microorganisms.

• Adding high concentrations of sugar binds water, preventing microbial growth.
• Examples: Jams, jellies, marmalades, squashes, candied fruits.
• Used for preserving fruits and fruit products.

• Combining salt, oil, and vinegar (acetic acid) preserves food by creating an acidic environment and removing moisture.
• Examples: Mango pickle, lemon pickle, mixed vegetable pickle, fish pickle.
• Common in Indian households.

• Heating food to a specific temperature (about 72°C for 15 seconds for milk) and then rapidly cooling it.
• Kills harmful bacteria without destroying nutrients or significantly altering taste.
• Named after Louis Pasteur.
• Examples: Milk, fruit juices, canned beer.

• Low temperatures slow down or stop microbial growth and enzyme activity.
• Refrigeration (0–5°C): Short-term storage of milk, vegetables, fruits, cooked food.
• Freezing (below −18°C): Long-term storage of meat, fish, frozen vegetables, ice cream.

• Food is sealed in airtight containers (cans or bottles) after sterilisation by heating.
• The sealed container prevents re-contamination by microorganisms.
• Examples: Canned fruits, canned beans, bottled jams, canned fish.

• Adding safe food-grade chemicals that inhibit microbial growth.
• Examples: Sodium benzoate (sauces, squashes), sulphur dioxide (dried fruits, wine), citric acid (jams, beverages), vinegar/acetic acid (pickles, sauces).
• Must use only approved preservatives within safe limits.

• Exposing food to ionising radiation (gamma rays, X-rays) to kill microorganisms and insects.
• Extends shelf life without significantly affecting nutritional quality.
• Examples: Spices, potatoes, onions, meat products.