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CBSE · Class 8 · 🔬 Science · Chapter 2

The Invisible Living World: Beyond Our Naked Eye

CellsMicroorganismsUnicellular organismsMulticellular organismsLevels of organizationMicroalgae

Chapter 2, 'The Invisible Living World: Beyond Our Naked Eye', introduces students to the microscopic world that exists all around us. It delves into the basic unit of life, the cell, and its variations in shape and structure. Students learn about the levels of organization from cells to organisms, and distinguish between unicellular and multicellular life forms. The chapter also explores the diversity and importance of microorganisms, including their presence in various environments and their roles in nature and daily life, such as decomposition and oxygen production by microalgae.

Microorganisms: Friends and Foe

Microorganisms ya microbes bahut chhote living organisms hote hain, jinhe hum apni naked eye se nahi dekh sakte. Inhe dekhne ke liye microscope ki zaroorat padti hai.

  • Diversity of Microorganisms:
  • Ye unicellular (single-celled) bhi ho sakte hain, jaise bacteria, kuch algae aur protozoa.
  • Aur multicellular (many-celled) bhi ho sakte hain, jaise fungi aur kuch algae.
  • Habitat: Ye har tarah ke environment mein milte hain – ice cold climate se lekar hot springs tak, deserts se lekar marshy lands tak. Ye animals aur humans ki body ke andar bhi paaye jaate hain.
  • Major Groups: Microorganisms ko four major groups mein classify kiya jaata hai:
  • Bacteria
  • Fungi
  • Protozoa
  • Algae
  • Viruses: Ye bhi microscopic hote hain, but other microorganisms se different hain. Viruses sirf host organism ke andar hi reproduce karte hain (jaise bacteria, plant ya animal cell). Common ailments jaise cold, flu, aur cough viruses se hote hain. Serious diseases jaise polio aur chickenpox bhi viruses se hoti hain.

Types of Microorganisms

1. Bacteria

  • Structure: Single-celled organisms. Different shapes ke hote hain – rod-shaped (Bacilli), spherical (Cocci), spiral (Spirilla), comma-shaped (Vibrio).
  • Reproduction: Rapidly multiply karte hain.
  • Examples: Lactobacillus (curd formation), Rhizobium (nitrogen fixation), E. coli (intestine mein).

2. Fungi

  • Structure: Mostly multicellular, but yeast unicellular hota hai. Non-photosynthetic organisms.
  • Nutrition: Saprophytic (dead aur decaying matter se nutrition lete hain) ya parasitic (living organisms se nutrition lete hain).
  • Examples: Yeast (bread making), Penicillium (antibiotic), Mushroom (edible fungi), Bread mould (spoilage).

3. Protozoa

  • Structure: Mostly unicellular. Animal-like characteristics hote hain.
  • Movement: Kuchh amoeba ki tarah pseudopodia se move karte hain, kuchh flagella ya cilia se.
  • Habitat: Water, soil, aur dusre organisms mein paaye jaate hain.
  • Examples: Amoeba, Paramecium (free-living), Plasmodium (malaria causing), Entamoeba (dysentery causing).

4. Algae

  • Structure: Plant-like organisms. Unicellular ya multicellular ho sakte hain. Chlorophyll hota hai, isliye autotrophic hote hain (apna food khud banate hain).
  • Habitat: Mostly aquatic (water mein).
  • Examples: Chlamydomonas, Spirogyra, Volvox, Diatoms.

5. Viruses

  • Structure: Non-cellular entities. Living aur non-living ke beech ki link maane jaate hain.
  • Reproduction: Sirf host cell ke andar hi reproduce karte hain.
  • Diseases: Cold, influenza, measles, polio, AIDS, chickenpox.
❗Important

Robert Hooke ne 1665 mein cork cells ko observe kiya tha aur 'cell' term coin kiya tha. Ye pehla observation tha microscopic world ka.

⭐Remember

Viruses ko connecting link between living and non-living mana jaata hai kyunki host ke bahar ye non-living ki tarah behave karte hain aur host ke andar living ki tarah reproduce karte hain.

Where do Microorganisms Live?

Microorganisms har jagah paaye jaate hain, inki ubiquitous presence hoti hai. Ye extreme conditions mein bhi survive kar sakte hain.

  • Soil: Soil mein bahut saare bacteria aur fungi hote hain jo decomposition mein help karte hain aur soil fertility badhate hain.
  • Water: Lakes, rivers, ponds, oceans, aur even tap water mein bhi microorganisms hote hain. Kuchh harmful hote hain (pathogens) aur kuchh beneficial (jaise microalgae).
  • Air: Air mein dust particles ke saath spores of fungi aur bacteria present hote hain. Ye airborne diseases spread kar sakte hain.
  • Inside Living Organisms: Human aur animal bodies mein bhi microorganisms hote hain. Kuchh beneficial hote hain (jaise gut bacteria jo digestion mein help karte hain), aur kuchh harmful (disease-causing).
  • Extreme Environments:
  • Hot springs (thermophilic bacteria).
  • Polar regions (psychrophilic bacteria).
  • Deserts (xerophilic bacteria).
  • Deep sea vents (chemoautotrophic bacteria).

Ye adaptability hi inki success ka reason hai.

❗Important

Microalgae Earth ki oxygen supply ka aadhe se zyada hissa produce karte hain aur aquatic food chain ka base hain. Ye biofuel aur health supplements mein bhi use hote hain.

Microorganisms and Us (Beneficial Microorganisms)

Microorganisms sirf diseases hi nahi failate, balki hamare liye bahut beneficial bhi hote hain. Inke roles ko samajhna zaroori hai.

1. Curd and Bread Making

  • Curd: Lactobacillus bacteria milk ko curd mein convert karta hai. Ye bacteria milk mein multiply karte hain aur usko curd mein ferment kar dete hain.
  • Bread/Cake/Pastry: Yeast ka use baking industry mein hota hai. Yeast rapid reproduction karta hai aur respiration ke dauran carbon dioxide gas produce karta hai. Ye gas dough mein bubbles banati hai aur usko rise kar deti hai, jisse bread aur cakes soft aur fluffy bante hain.

2. Commercial Use

  • Alcohol, Wine, Acetic Acid (Vinegar): Yeast ka use fermentation process mein large scale par alcohol, wine aur acetic acid banane ke liye hota hai. Sugar ko alcohol mein convert karne ka process fermentation kehlata hai, jise Louis Pasteur ne 1857 mein discover kiya tha.
  • Antibiotics: Ye medicines hoti hain jo disease-causing microorganisms ki growth ko stop karti hain ya unhe kill karti hain. Penicillin pehla antibiotic tha, jo Alexander Fleming ne 1929 mein discover kiya tha. Common antibiotics Streptomycin, Tetracycline, Erythromycin hain, jo fungi aur bacteria se banaye jaate hain.
  • Vaccines: Vaccine mein dead ya weakened microorganisms hote hain. Jab ye healthy body mein inject kiye jaate hain, toh body antibodies produce karti hai to fight the invaders. Ye antibodies future mein real disease-causing microbes se protect karte hain. Edward Jenner ne 1798 mein smallpox vaccine discover kiya tha.

3. Environmental Cleaning

  • Decomposition: Microorganisms (bacteria aur fungi) organic waste (dead plants, animals, animal excreta) ko decompose karke simple substances mein convert karte hain. Ye substances soil mein mix ho jaate hain aur plants dwara use kiye jaate hain. Is process se environment clean rehta hai aur nutrients recycle hote hain.

4. Increasing Soil Fertility

  • Nitrogen Fixation: Kuchh bacteria (jaise Rhizobium leguminous plants ki root nodules mein) aur blue-green algae (Cyanobacteria) atmospheric nitrogen ko fix karke soil mein nitrogen compounds mein convert karte hain. Ye nitrogen compounds soil ki fertility badhate hain aur plants ke liye available hote hain.

5. Medicinal Use

  • Antibiotics aur vaccines ke alawa, microorganisms se kai aur medicines bhi banti hain.
📖Definition

Fermentation: The process of conversion of sugar into alcohol by yeast is known as fermentation.

❗Important

Louis Pasteur ne fermentation discover kiya tha (1857) aur Alexander Fleming ne Penicillin (1929). Edward Jenner ne smallpox vaccine (1798).

Harmful Microorganisms

Beneficial hone ke saath-saath, microorganisms hamare liye harmful bhi ho sakte hain. Ye diseases cause karte hain, food spoil karte hain, aur materials ko damage karte hain.

1. Disease-Causing Microorganisms (Pathogens)

  • Pathogens: Wo microorganisms jo disease cause karte hain, unhe pathogens kehte hain.
  • Communicable Diseases: Ye diseases jo infected person se healthy person tak air, water, food ya physical contact se spread hoti hain, unhe communicable diseases kehte hain. Examples: Cholera, common cold, chickenpox, tuberculosis.
  • Transmission:
  • Air: Sneezing/coughing se droplets air mein release hote hain (e.g., common cold, TB).
  • Water: Contaminated water se (e.g., Cholera, Typhoid).
  • Food: Contaminated food se (e.g., Food poisoning).
  • Direct Contact: Physical contact se (e.g., Chickenpox, ringworm).
  • Insects/Animals (Carriers): Kuchh insects aur animals disease-causing microbes ko carry karte hain. Jaise:
  • Female Anopheles mosquito: Malaria parasite (Plasmodium) ka carrier.
  • Female Aedes mosquito: Dengue virus ka carrier.
  • Housefly: Food par baithkar pathogens transfer karti hai, jisse cholera, typhoid jaise diseases hoti hain.

2. Diseases in Humans

  • Bacterial Diseases: Tuberculosis (TB), Cholera, Typhoid, Anthrax.
  • Viral Diseases: Measles, Chickenpox, Polio, Hepatitis B, Dengue, AIDS.
  • Protozoan Diseases: Malaria, Dysentery.
  • Fungal Diseases: Ringworm, Athlete's foot.

3. Diseases in Animals

  • Anthrax: Humans aur cattle mein hone wali dangerous bacterial disease, jo Bacillus anthracis se hoti hai. Robert Koch ne 1876 mein is bacteria ko discover kiya tha.
  • Foot and Mouth Disease: Cattle mein virus se hoti hai.

4. Diseases in Plants

  • Microorganisms plants mein bhi diseases cause karte hain, jisse crop yield kam ho jaati hai.
  • Examples:
  • Citrus Canker (Bacteria): Air se spread hota hai.
  • Rust of Wheat (Fungi): Air aur seeds se spread hota hai.
  • Yellow Vein Mosaic of Okra (Bhindi) (Virus): Insect se spread hota hai.

5. Food Poisoning

  • Food poisoning microorganisms dwara produce kiye gaye toxic substances se hoti hai. Ye microorganisms food mein grow karte hain aur toxins release karte hain. Symptoms mein vomiting, diarrhoea, abdominal pain, fever, aur severe cases mein death bhi ho sakti hai.
  • Food ko cover karke rakhna aur proper cooking/storage food poisoning se bachne ke important steps hain.
🚧Misconception

Students often confuse vector (carrier) with pathogen (disease-causing microbe). Yaad rakho, mosquito vector hai, Plasmodium pathogen hai.

❗Important

Robert Koch ne Anthrax bacteria (Bacillus anthracis) ko discover kiya tha. Ye Koch's Postulates ke liye bhi jaane jaate hain, jo disease-causing microbes ko identify karne ke principles hain.

Food Preservation

Food spoilage se bachne ke liye aur uski shelf life badhane ke liye food preservation methods use kiye jaate hain. Microorganisms food ko spoil karte hain, isliye unki growth ko rokna zaroori hai.

1. Chemical Methods

  • Salt aur Edible Oils: Ye common chemical preservatives hain. Salt ka use meat, fish, amla, raw mangoes ko preserve karne mein hota hai. Oil ka use pickles mein hota hai. Ye microorganisms ki growth ko inhibit karte hain.
  • Sodium Benzoate aur Sodium Metabisulphite: Ye common preservatives hain jo jams, jellies, aur squashes mein use hote hain. Ye spoilage ko prevent karte hain.

2. Preservation by Sugar

  • Sugar ka use jams, jellies, aur squashes ko preserve karne mein hota hai. Sugar moisture content ko reduce karta hai, jisse bacteria ki growth inhibit hoti hai.

3. Preservation by Oil and Vinegar

  • Oil aur vinegar ka use pickles, vegetables, fruits, fish, aur meat ko preserve karne mein hota hai. Bacteria aise environment mein live nahi kar sakte.

4. Heat and Cold Treatments

  • Heating: Food ko heat karne se usme present microorganisms kill ho jaate hain. Jaise milk ko boil karna.
  • Cooling/Refrigeration: Low temperature microorganisms ki growth ko inhibit karta hai. Isliye food ko refrigerator mein rakhte hain.
  • Pasteurisation: Ye method Louis Pasteur ne discover kiya tha. Milk ko 70°C par 15 se 30 seconds ke liye heat karte hain aur phir rapidly cool karke store karte hain. Isse milk mein present harmful microbes kill ho jaate hain aur milk spoil nahi hota. Ye milk bina boil kiye bhi use kiya ja sakta hai.

5. Storage and Packing

  • Dry fruits aur vegetables ko airtight sealed packets mein store karte hain, jisse unhe microbial attack se bachaya ja sake. Air aur moisture ki absence microorganisms ki growth ko rokti hai.
💡Tip

Food preservation methods aur unke examples yaad rakho. Especially Pasteurisation process aur uske inventor ka naam.

Nitrogen Fixation

Atmosphere mein 78% nitrogen gas hoti hai. Plants aur animals is atmospheric nitrogen ko directly use nahi kar sakte. Unhe nitrogen ke fixed forms (compounds) chahiye hote hain. Nitrogen fixation wo process hai jisme atmospheric nitrogen ko usable nitrogenous compounds mein convert kiya jaata hai.

  • Biological Nitrogen Fixation:
  • Kuchh bacteria aur blue-green algae (cyanobacteria) atmospheric nitrogen ko fix kar sakte hain.
  • Rhizobium bacteria leguminous plants (jaise peas, beans, lentils) ki root nodules mein symbiotic association mein rehta hai. Ye bacteria atmospheric nitrogen ko fix karke plants ko provide karta hai, aur badle mein plant se shelter aur food leta hai.
  • Blue-green algae (e.g., Nostoc, Anabaena) bhi soil mein free-living hokar nitrogen fix karti hain.
  • Atmospheric Nitrogen Fixation:
  • Lightning (bijli chamakna) ke dauran, high temperature aur pressure par atmospheric nitrogen oxygen se react karke nitrogen ke oxides banati hai.
  • Ye oxides rain ke saath dissolve hokar soil mein aate hain aur plants dwara use kiye jaate hain.
❗Important

Rhizobium bacteria ka role nitrogen fixation mein bahut important hai, especially leguminous crops ke liye. Isliye farmers ko nitrogen fertilizers kam use karne padte hain agar wo leguminous crops grow karte hain.

Nitrogen Cycle

Nitrogen cycle wo process hai jisme nitrogen atmosphere, soil, aur living organisms ke beech circulate karti hai. Ye ek continuous process hai.

Steps of Nitrogen Cycle:

  1. Nitrogen Fixation:
  • Atmospheric nitrogen (N₂) ko nitrogen-fixing bacteria (e.g., Rhizobium, Azotobacter) aur blue-green algae dwara ammonia (NH₃) mein convert kiya jaata hai.
  • Lightning bhi nitrogen ko fix karti hai.
  1. Nitrification:
  • Ammonia ko nitrifying bacteria (e.g., Nitrosomonas) dwara nitrites (NO₂⁻) mein oxidize kiya jaata hai.
  • Nitrites ko phir nitrates (NO₃⁻) mein oxidize kiya jaata hai by other nitrifying bacteria (e.g., Nitrobacter).
  • Plants nitrates ko soil se absorb karte hain.
  1. Assimilation:
  • Plants absorbed nitrates ko proteins aur other organic compounds banane mein use karte hain.
  • Animals plants ko kha kar nitrogen compounds ko apni body mein assimilate karte hain.
  1. Ammonification:
  • Jab plants aur animals mar jaate hain, ya unka waste product (excreta) release hota hai, toh decomposers (bacteria aur fungi) unke complex organic nitrogen compounds ko ammonia mein convert karte hain.
  1. Denitrification:
  • Kuchh bacteria (e.g., Pseudomonas) soil mein present nitrates ko wapas atmospheric nitrogen gas (N₂) mein convert kar dete hain.
  • Ye N₂ gas atmosphere mein wapas chali jaati hai, jisse nitrogen cycle complete hota hai.

Importance of Nitrogen Cycle:

  • Nitrogen living organisms ke liye essential hai kyunki ye proteins, nucleic acids (DNA, RNA), chlorophyll, aur vitamins ka component hai.
  • Ye cycle atmospheric nitrogen ke balance ko maintain karta hai.
⭐Remember

Nitrogen cycle ke sabhi steps aur unme involved microorganisms ko yaad rakhna bahut important hai. Ye ecosystem ke balance ke liye critical hai.

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