Micro Organism

Micro-Organisms: Complete CBSE Class 8 Science Notes

Introduction to Micro-Organisms

Micro-organisms, also called microbes, are living creatures so tiny that they cannot be seen with the naked eye. These microscopic organisms are present everywhere around us - in the air we breathe, the water we drink, the soil beneath our feet, and even inside our bodies. The study of these fascinating organisms is called microbiology.

Discovery of Microbes

About 300 years ago, Anton van Leeuwenhoek, a Dutch storekeeper, first discovered the world of microbes using simple microscopes he built himself. This groundbreaking discovery opened a completely new field of biological science.

How to Observe Micro-Organisms

Microbes can only be seen through:

• Magnifying glass - for larger microbes like some fungi
• Light microscope - for bacteria, protozoa, and most microbes
• Electron microscope - for viruses and ultra-small structures

Classification and Types of Micro-Organisms

Micro-organisms are classified into five major groups based on their structure, characteristics, and cellular organization:

1. Bacteria

Bacteria are simple, single-celled organisms found everywhere in nature. They are prokaryotic, meaning they lack a defined nucleus.

Shapes of Bacteria:

• Bacilli - Rod-shaped bacteria
• Cocci - Spherical or round bacteria
• Spirilla - Spiral-shaped bacteria

Characteristics:

• Unicellular prokaryotes
• Reproduce rapidly through binary fission
• Form spores under unfavorable conditions
• Can be autotrophic or heterotrophic

2. Fungi

Fungi are plant-like organisms that lack chlorophyll (green pigment). They cannot make their own food and depend on other organisms.

Types:

• Unicellular fungi - Yeast
• Multicellular fungi - Bread mould (Rhizopus), Penicillium, Aspergillus, Mushrooms

Characteristics:

• Body made of thread-like structures called hyphae
• Prefer moist, warm environments
• Reproduce through spores
• Saprophytic (feed on dead organic matter)

3. Protozoa

Protozoa are unicellular, animal-like organisms that can move and capture food.

Examples:

• Amoeba - moves using pseudopodia (false feet)
• Paramecium - moves using cilia (hair-like structures)
• Euglena - moves using flagella

Characteristics:

• Eukaryotic cells with defined nucleus
• Mostly aquatic
• Can form cysts during unfavorable conditions
• Some are disease-causing (pathogenic)

4. Algae

Algae are plant-like organisms with cell walls and chlorophyll, capable of photosynthesis.

Types:

• Unicellular algae - Chlamydomonas
• Multicellular algae - Spirogyra, seaweeds

Characteristics:

• Mostly aquatic (live in water)
• Autotrophic (make their own food)
• Contain chlorophyll for photosynthesis
• Blue-green algae can fix atmospheric nitrogen

5. Viruses

Viruses are the smallest microbes, even smaller than bacteria. They show characteristics of both living and non-living things.

Characteristics:

• Lack cellular structure
• Cannot reproduce independently
• Need a host cell to multiply
• Consist of genetic material (DNA or RNA) surrounded by a protein coat
• Cause numerous diseases in plants, animals, and humans

Differences: Prokaryotes vs Eukaryotes

Feature	Prokaryotes	Eukaryotes
Nucleus	No defined nucleus	Well-defined nucleus with nuclear membrane
Chromosomes	Not present	Present inside nucleus
Genetic Material	Naked DNA in cytoplasm	DNA organized on chromosomes
Cell Structure	Simple, smaller cells	Complex, larger cells
Examples	Bacteria, Blue-green algae	Fungi, Protozoa, Algae, Plants, Animals
Cell Division	Binary fission	Mitosis and meiosis

Where Do Micro-Organisms Live?

Micro-organisms are omnipresent - found virtually everywhere:

• Extreme environments - From ice-cold Arctic regions to hot springs
• Deserts to marshy lands - Adapted to dry and wet conditions
• Deep ocean floors - Surviving under high pressure
• Inside living organisms - As parasites, symbionts, or commensals
• Soil and water - Decomposing organic matter
• Air - Floating as spores or attached to dust particles

Living Patterns:

• Solitary - Like Amoeba
• Colonies - Like bacteria and fungi growing together
• Parasitic - Inside or on other organisms (humans, animals, plants)
• Free-living - Independent existence

Useful Micro-Organisms: Friends of Humans

1. Preparation of Food Items

A. Curd Formation

• Bacterium involved:Lactobacillus
• Process: When curd (starter) containing Lactobacillus is added to warm milk, bacteria multiply rapidly and convert lactose (milk sugar) into lactic acid
• Result: Milk coagulates to form curd
• Benefits: Aids digestion, provides probiotics, inhibits harmful bacteria

B. Bread and Bakery Products

• Microbe involved: Yeast (Saccharomyces cerevisiae)
• Process - Fermentation:
  • Yeast is mixed with flour, sugar, and warm water
  • Yeast respires anaerobically, producing carbon dioxide (CO₂)
  • CO₂ bubbles get trapped in the dough, making it rise
  • During baking, yeast dies but dough remains soft and spongy
• Products: Bread, cakes, pastries, pizza base

C. Other Food Items

• Cheese: Produced by bacteria acting on milk proteins (casein)
• Idli and Dosa: Natural fermentation of rice and dal paste by bacteria
• Vinegar: Produced from alcohol by Acetobacter aceti bacteria

2. Industrial Applications

A. Alcohol and Wine Production

• Process: Yeast ferments natural sugars in grains (barley, wheat, rice) or fruits
• Chemical reaction: C₆H₁₂O₆ (glucose) → 2C₂H₅OH (ethanol) + 2CO₂ (carbon dioxide)
• Products: Beer, wine, whiskey, rum, ethanol

B. Acetic Acid (Vinegar)

• Produced when Acetobacter bacteria oxidize alcohol
• Used as preservative and condiment

3. Medicinal Uses

A. Antibiotics

Antibiotics are medicines that kill or stop the growth of disease-causing microorganisms (pathogens).

Antibiotic	Source	Discovered By	Uses
Penicillin	Penicillium notatum (fungus)	Sir Alexander Fleming (1929)	Bacterial infections
Streptomycin	Streptomyces bacteria	Selman Waksman	Tuberculosis
Tetracycline	Streptomyces bacteria	Benjamin Duggar	Broad-spectrum antibiotic
Erythromycin	Streptomyces bacteria	J.M. McGuire	Respiratory infections

Important Precautions:

• Take antibiotics only on doctor's prescription
• Complete the full course even if feeling better
• Never use antibiotics for viral infections (cold, flu)
• Unnecessary use creates antibiotic-resistant bacteria

B. Vaccines

Vaccines contain killed or weakened disease-causing microbes that stimulate the body to produce antibodies without causing illness.

How Vaccines Work:

1. Weakened/killed pathogen is introduced to the body
2. Body's immune system recognizes it as foreign
3. Body produces antibodies to fight the pathogen
4. Antibodies remain in the body as "memory"
5. If actual disease-causing microbe enters later, antibodies quickly destroy it

Common Vaccines:

• DPT - Diphtheria, Pertussis (whooping cough), Tetanus
• BCG - Tuberculosis
• OPV - Oral Polio Vaccine
• MMR - Measles, Mumps, Rubella
• Hepatitis B vaccine

Success Story: Smallpox has been completely eradicated worldwide through vaccination campaigns.

4. Agriculture - Increasing Soil Fertility

Nitrogen Fixation

Atmospheric nitrogen (N₂) makes up 78% of air but cannot be directly used by plants. Certain microbes convert it into usable forms.

Nitrogen-fixing Microorganisms:

Microbe	Type	Location	Process
Rhizobium	Bacteria	Root nodules of legumes (beans, peas, pulses)	Symbiotic nitrogen fixation
Blue-green algae (Cyanobacteria)	Algae	Soil and water	Free-living nitrogen fixation
Azotobacter	Bacteria	Soil	Free-living nitrogen fixation

Benefits:

• Enriches soil with nitrogen compounds (nitrates, nitrites)
• Increases soil fertility naturally
• Reduces need for chemical fertilizers
• Sustainable farming practice

5. Cleaning the Environment

Decomposition is the breakdown of dead organic matter into simpler substances by microbes.

Role of Microbes:

• Bacteria and fungi act as decomposers
• Break down dead plants, animals, and waste materials
• Convert complex organic matter into simple substances
• Return nutrients to soil, water, and air
• Prevent accumulation of waste and foul smell

Environmental Applications:

• Sewage treatment - Bacteria break down organic waste in water
• Composting - Microbes convert kitchen and garden waste into manure
• Bioremediation - Cleaning oil spills and pollution using microbes

Important Note: Microbes cannot decompose non-biodegradable materials like plastics, glass, and metals.

6. Microbes as Food

• Mushrooms - Edible fungi rich in protein
• Seaweeds - Used as food in China and Japan
• Algal extracts - Used to thicken ice creams and jellies
• Spirulina - Protein-rich blue-green algae used as supplement

Harmful Micro-Organisms: Enemies of Health

1. Disease-Causing Microorganisms (Pathogens)

Pathogens are microbes that cause diseases in humans, animals, and plants.

A. Diseases in Humans

Communicable Diseases can spread from infected person to healthy person through:

• Air - Coughing, sneezing (tuberculosis, common cold, measles)
• Water - Contaminated drinking water (cholera, typhoid, hepatitis)
• Food - Contaminated food (food poisoning, cholera)
• Physical contact - Direct touch (ringworm, chickenpox)
• Carriers - Insects and animals (malaria through mosquitoes)

Disease	Causative Microbe	Mode of Transmission	Prevention
Tuberculosis (TB)	Bacteria	Air	Vaccination (BCG), isolation
Cholera	Bacteria	Water/Food	Boiled water, hygiene, vaccination
Typhoid	Bacteria	Water	Clean water, vaccination
Malaria	Protozoa (Plasmodium)	Mosquito bite (Anopheles)	Mosquito nets, repellents, eliminate breeding sites
Common Cold	Virus	Air droplets	Hygiene, avoid contact
Measles	Virus	Air	Vaccination (MMR)
Chickenpox	Virus	Air/Contact	Vaccination, isolation
Polio	Virus	Air/Water	Vaccination (OPV)
Hepatitis B	Virus	Water/Blood	Vaccination, safe practices
Ringworm	Fungus	Contact	Hygiene, antifungal treatment

Malaria Prevention:

• Use mosquito nets while sleeping
• Apply mosquito repellents
• Spray insecticides in homes
• Eliminate stagnant water (breeding ground)
• Spray kerosene on water surfaces to kill larvae

B. Diseases in Animals

Microbe	Disease	Affected Animals
Virus	Foot and mouth disease	Cattle
Bacteria	Anthrax	Cattle, humans
Protozoa	Sleeping sickness	Cattle, pigs, horses

C. Diseases in Plants

Plant Disease	Microorganism	Mode of Transmission
Citrus canker	Bacteria	Air
Rust of wheat	Fungi	Air, seeds
Yellow vein mosaic (Okra)	Virus	Insect vectors
Tobacco mosaic	Virus	Direct sap contact

Control Measures:

• Use disease-resistant plant varieties
• Treat seeds with fungicides
• Spray appropriate pesticides and insecticides
• Maintain field hygiene
• Crop rotation

2. Food Spoilage

Food Poisoning occurs when harmful microbes grow on food and produce toxic substances.

Signs of Food Spoilage:

• Bad or foul smell
• Change in taste
• Change in color and texture
• Loss of nutritive value
• Visible mold growth

Causes:

• Bacteria multiply on food and release toxins
• Fungi grow and produce poisonous metabolites
• Enzyme action breaks down food molecules

Food Preservation Methods

Food preservation prevents microbial growth and spoilage, extending shelf life.

1. Sun Drying (Dehydration)

• Process: Expose food to sunlight
• Principle: Removes moisture; microbes cannot grow without water
• Examples: Dried vegetables (spinach, methi), dried fruits, fish, meat

2. Smoking

• Process: Food is dried using heat and smoke
• Examples: Smoked fish, smoked meat
• Principle: Dehydration and antimicrobial compounds in smoke

3. Preservation by Common Salt

• Process: Food is covered with dry salt or kept in concentrated salt solution
• Principle: Salt draws out moisture and creates high osmotic pressure, preventing bacterial growth
• Examples: Salted fish, salted meat, pickles, amla, raw mangoes

4. Preservation by Sugar

• Process: Food is cooked with high concentration of sugar
• Principle: Sugar reduces moisture and creates unfavorable environment for microbes
• Examples: Jams, jellies, squashes, marmalades

5. Preservation by Oil and Vinegar

• Process: Food is immersed in oil or vinegar
• Principle: Prevents oxygen contact and creates acidic/oxygen-free environment
• Examples: Pickles (vegetables, fruits, fish, meat)

6. Heat Treatment

Boiling

• Kills many microorganisms
• Example: Boiling milk before storage

Pasteurization

• Discovered by: Louis Pasteur
• Process: Milk is heated to 70°C for 15-30 seconds, then suddenly cooled
• Result: Kills harmful microbes without destroying nutrients
• Product: Pasteurized milk (safe to consume without boiling)

7. Cold Treatment (Refrigeration)

• Process: Store food at low temperatures (below 5°C)
• Principle: Low temperature inhibits microbial growth (doesn't kill, just slows down)
• Storage: Refrigerators, freezers

8. Chemical Preservatives

• Common preservatives:
  • Sodium benzoate
  • Sodium metabisulphite
  • Citric acid
  • Acetic acid (vinegar)
• Used in: Jams, squashes, juices, sauces, pickles

9. Storage and Packing

• Process: Food sealed in airtight packets
• Principle: Prevents microbial contamination and oxygen exposure
• Examples: Packaged dry fruits, chips, biscuits, instant noodles

The Nitrogen Cycle

The nitrogen cycle is the continuous circulation of nitrogen between the atmosphere, soil, and living organisms.

Importance of Nitrogen

• Essential component of proteins, DNA, RNA, chlorophyll, and vitamins
• Plants cannot use atmospheric nitrogen (N₂) directly
• Must be converted to nitrates or ammonia first

Steps in the Nitrogen Cycle

1. Nitrogen Fixation

Conversion of atmospheric nitrogen (N₂) to nitrogen compounds

Methods:

• Biological fixation:
  • Rhizobium bacteria in root nodules of legumes
  • Blue-green algae (cyanobacteria) in soil and water
  • Free-living bacteria like Azotobacter
• Lightning fixation: High temperature during lightning converts N₂ to nitrogen oxides
• Industrial fixation: Haber process for fertilizer production

2. Nitrification

Conversion of ammonia to nitrites and then nitrates

• Nitrosomonas bacteria: Ammonia → Nitrites (NO₂⁻)
• Nitrobacter bacteria: Nitrites → Nitrates (NO₃⁻)
• Plants absorb nitrates through roots

3. Assimilation

• Plants use nitrates to synthesize proteins and other nitrogen-containing compounds
• Animals obtain nitrogen by eating plants

4. Ammonification

• When plants and animals die, decomposers (bacteria and fungi) break down proteins
• Release ammonia back into soil

5. Denitrification

• Denitrifying bacteria (Pseudomonas, Thiobacillus) convert nitrates back to N₂ gas
• Nitrogen returns to atmosphere
• Maintains atmospheric nitrogen at ~78%

Microbial Growth Factors

For microorganisms to grow and multiply, they need:

1. Nutrients

• Carbon source (sugars, organic acids)
• Nitrogen (proteins, amino acids)
• Minerals (phosphorus, sulfur, potassium)
• Vitamins and growth factors

2. Temperature

• Psychrophiles: 0-20°C (cold-loving)
• Mesophiles: 20-45°C (moderate temperature) - most human pathogens
• Thermophiles: 45-80°C (heat-loving)

3. Moisture

• Water is essential for metabolic activities
• High moisture promotes microbial growth
• Drying prevents growth

4. pH (Acidity/Alkalinity)

• Most bacteria prefer neutral pH (6.5-7.5)
• Some fungi prefer acidic conditions
• Yeasts tolerate acidic pH

5. Oxygen Requirements

• Aerobes: Need oxygen (most fungi)
• Anaerobes: Grow without oxygen (fermentation bacteria)
• Facultative anaerobes: Can grow with or without oxygen

6. Time

• Bacteria can double every 20-30 minutes under favorable conditions
• Exponential growth leads to millions in hours

Sterilization and Disinfection

Sterilization

Complete elimination of all microorganisms including spores

Methods:

1. Heat sterilization:
   • Autoclaving (121°C, 15 psi pressure, 15-20 minutes)
   • Dry heat (160°C for 2 hours)
2. Chemical sterilization:
   • Ethylene oxide gas
   • Formaldehyde
3. Radiation:
   • UV light
   • Gamma radiation
4. Filtration:
   • HEPA filters
   • Membrane filters (0.22 μm)

Disinfection

Reduction of pathogenic microorganisms to safe levels

Common Disinfectants:

• Bleach (sodium hypochlorite)
• Alcohol (70% ethanol or isopropanol)
• Hydrogen peroxide
• Phenolic compounds
• Quaternary ammonium compounds

Immunity and Microbes

The Immune System

The body's defense mechanism against pathogens

Components:

1. Physical barriers:
   • Skin
   • Mucous membranes
   • Stomach acid
2. Innate immunity:
   • White blood cells (phagocytes)
   • Inflammation response
   • Fever
3. Adaptive immunity:
   • Antibodies: Proteins produced by B-cells that recognize and neutralize specific pathogens
   • Memory cells: Remember pathogens for faster future response
   • T-cells: Kill infected cells

How Vaccines Create Immunity

1. Vaccine introduces weakened/killed pathogen
2. Body recognizes as foreign invader
3. Produces specific antibodies
4. Memory cells store information
5. Upon actual infection, rapid antibody production
6. Disease prevented or severity reduced

The Human Microbiome

What is the Microbiome?

The collection of all microorganisms living in and on the human body

Locations:

• Gut: Largest population (~100 trillion bacteria)
• Skin: Protection against pathogens
• Mouth: Hundreds of bacterial species
• Respiratory tract
• Reproductive system

Benefits of Microbiome:

1. Digestion: Break down complex carbohydrates and fibers
2. Vitamin production: Synthesize vitamin K and B vitamins
3. Immune system development: Train immune responses
4. Protection: Compete with harmful bacteria
5. Mental health: Gut-brain axis influences mood

Maintaining Healthy Microbiome:

• Eat fiber-rich foods
• Include probiotics (curd, yogurt)
• Avoid unnecessary antibiotics
• Reduce stress
• Stay hydrated

Laboratory Methods to Study Microorganisms

1. Microscopy

• Light microscope: Bacteria, fungi, protozoa (up to 1000x magnification)
• Electron microscope: Viruses, internal structures (up to 1,000,000x)

2. Culturing Microbes

Process:

1. Prepare sterile nutrient medium (agar plates)
2. Inoculate sample using sterile loop
3. Incubate at appropriate temperature (usually 37°C)
4. Observe colony formation (24-48 hours)
5. Identify based on colony characteristics

3. Staining Techniques

• Gram staining: Differentiates bacteria into Gram-positive (purple) and Gram-negative (pink)
• Acid-fast staining: Identifies TB bacteria
• Spore staining: Detects bacterial spores

4. Biochemical Tests

• Sugar fermentation tests
• Enzyme tests (catalase, oxidase)
• Motility tests
• Nitrate reduction

5. Molecular Methods

• PCR (Polymerase Chain Reaction): Amplifies DNA for identification
• DNA sequencing: Precise identification
• ELISA: Detects antibodies or antigens

Practical Experiments with Microorganisms

Experiment 1: Growing Microorganisms

Materials: Moist soil, beaker, water, microscope, glass slide

Procedure:

1. Add moist soil to beaker with water
2. Let it settle for few hours
3. Place a drop of water from top on glass slide
4. Observe under microscope
5. Identify different microorganisms

Experiment 2: Observing Bread Mould

Materials: Bread slice, water, plastic bag

Procedure:

1. Moisten bread slice slightly
2. Keep in warm, dark place inside plastic bag
3. Observe after 3-4 days
4. Grayish-white patches appear (fungus)
5. Observe under magnifying glass

Experiment 3: Making Alcohol

Materials: 500 mL beaker, water, sugar, yeast

Procedure:

1. Fill beaker ¾ with water
2. Dissolve 2-3 teaspoons sugar
3. Add half teaspoon yeast powder
4. Cover and keep in warm place 4-5 hours
5. Smell the solution - alcohol odor indicates fermentation

Experiment 4: Decomposition Test

Materials: Two pots with soil, plant waste, plastic items

Procedure:

1. Put plant waste in pot A
2. Put plastics, glass in pot B
3. Observe after 3-4 weeks
4. Pot A: Plant waste decomposed
5. Pot B: No decomposition

Key Formulas and Processes

Process	Formula/Representation	Explanation
Fermentation (Alcohol)	C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂ + Energy	Glucose converted to ethanol and carbon dioxide by yeast
Fermentation (Lactic Acid)	C₆H₁₂O₆ → 2C₃H₆O₃ + Energy	Glucose converted to lactic acid by Lactobacillus
Nitrogen Fixation	N₂ + 3H₂ → 2NH₃	Atmospheric nitrogen converted to ammonia
Nitrification (Step 1)	2NH₃ + 3O₂ → 2NO₂⁻ + 2H⁺ + 2H₂O	Ammonia oxidized to nitrite
Nitrification (Step 2)	2NO₂⁻ + O₂ → 2NO₃⁻	Nitrite oxidized to nitrate
Denitrification	2NO₃⁻ → N₂ + 3O₂	Nitrates converted back to atmospheric nitrogen
Pasteurization Temperature	70°C for 15-30 seconds	Heat treatment to kill pathogens in milk
Bacterial Growth (Exponential)	N = N₀ × 2ⁿ	N=final number, N₀=initial number, n=generations

Important Definitions

Term	Definition
Micro-organisms/Microbes	Living organisms too small to be seen with naked eye
Microbiology	The scientific study of microorganisms
Pathogens	Disease-causing microorganisms
Antibiotics	Medicines that kill or inhibit bacterial growth
Antibodies	Proteins produced by immune system to fight pathogens
Vaccines	Preparations of killed/weakened microbes to create immunity
Communicable diseases	Diseases that spread from infected to healthy individuals
Carriers	Organisms that transmit disease without being affected
Fermentation	Anaerobic breakdown of glucose by microorganisms
Pasteurization	Heat treatment process to kill pathogens without destroying nutrients
Nitrogen fixation	Conversion of atmospheric nitrogen to usable compounds
Decomposers	Organisms that break down dead organic matter
Host	Organism in which a parasite or virus lives and reproduces
Spores	Dormant, resistant structures formed by bacteria and fungi
Cysts	Protective covering formed by protozoa in unfavorable conditions
Pseudopodia	False feet - temporary projections in Amoeba for movement and feeding
Hyphae	Thread-like filamentous structures in fungi
Symbiosis	Mutually beneficial relationship between two organisms

Chapter Summary

Micro-organisms are microscopic living creatures invisible to the naked eye, discovered by Anton van Leeuwenhoek about 300 years ago. They are classified into five groups: bacteria (rod, spherical, spiral shapes), fungi (unicellular yeast, multicellular moulds), protozoa (animal-like unicellular organisms), algae (plant-like with chlorophyll), and viruses (smallest, non-cellular).

Useful microbes help in food preparation (curd, bread, cheese), industrial production (alcohol, wine, vinegar), medicine (antibiotics, vaccines), agriculture (nitrogen fixation by Rhizobium and blue-green algae), and environmental cleaning (decomposition). Harmful microbes cause diseases in humans (tuberculosis, cholera, malaria, typhoid), animals (anthrax, foot-and-mouth disease), and plants (citrus canker, rust of wheat), and spoil food.

Food preservation methods prevent microbial growth: sun drying, salting, sugaring, oil/vinegar preservation, pasteurization, refrigeration, and chemical preservatives. The nitrogen cycle involves nitrogen fixation (converting N₂ to nitrates), plant assimilation, animal consumption, decomposition, and denitrification, maintaining atmospheric nitrogen at 78%.

Prevention of diseases involves vaccination, personal hygiene, consuming clean water and food, and controlling disease carriers. Understanding microorganisms helps us use beneficial ones while protecting ourselves from harmful pathogens.

Conclusion

The microscopic world of microorganisms is vast, diverse, and critically important to life on Earth. While some microbes cause diseases and problems, the majority are either harmless or incredibly beneficial. They are essential for nutrient cycling, food production, medicine, agriculture, and maintaining ecological balance.

Understanding micro-organisms helps us:

• Use beneficial microbes for food, medicine, and agriculture
• Prevent and control infectious diseases
• Preserve food and prevent spoilage
• Maintain environmental health
• Develop new biotechnological applications

As Class 8 students, mastering this chapter provides foundation for higher studies in biology, microbiology, medicine, and biotechnology. The principles learned here apply to real-life situations - from understanding why we fall sick to how our food is prepared and preserved.

Other Helpful Realted Resources

Class 8 Science Chapter 2 Microorganisms: Friend and Foe

NCERT Exemplar Solutions for Class 8 Science Microorganisms

Class 8 Science NCERT Book