Class 8 NCERT Chapter 2 Biology 🎯 NEET Foundation

The Invisible Living World:
Beyond Our Naked Eye

Cells, microorganisms, and the hidden world that keeps our planet alive

🎯 NEET Foundation Content Included

πŸ”¬ Interactive Cell Comparator

Click each cell type to explore its structure. NEET aspirants β€” pay attention to differences between prokaryotic and eukaryotic cells!

πŸ“‹ Table of Contents

πŸ” Discovery of Microscope 🧬 What is a Cell? βš—οΈ Cell Organelles (NEET) πŸ“Š Levels of Organisation 🦠 Microorganisms 🌿 Microbes & Environment 🍞 Microbes & Food 🎯 Cell as Unit of Life (NEET) 🧠 MCQ Quiz (12 Qs) ✍️ Long Answer (5 Qs) ⚑ One Word Quiz (20 Qs)

🎬 Watch the Recorded Lesson

Watch the recorded lecture before starting the lesson.

πŸ”¬ Discovery of the Microscope

Section 1 Β· History of Science Β· NCERT Chapter 2

The human eye can only see objects above a certain size. Everything changed when people discovered that a curved piece of glass β€” shaped like a lentil seed, thick in the middle and thin at the edges β€” could magnify small objects. This curved glass was called a lens.

In 1665, Robert Hooke published Micrographia. Using his microscope (200–300Γ— magnification), he examined cork and saw tiny box-like compartments he named cells β€” the first use of this word in science. Antonie van Leeuwenhoek built far more powerful microscopes and was the first to see and describe bacteria and blood cells. He is called the "Father of Microbiology".

🌟 Key Timeline:
πŸ“– 1665 β€” Robert Hooke coins the word "cell" in Micrographia
πŸ”¬ 1670s β€” Leeuwenhoek sees bacteria and blood cells
πŸ† Leeuwenhoek = Father of Microbiology

πŸ§ͺ Activity 2.1 β€” Round-Bottom Flask Magnifier

  • Fill a round-bottom glass flask completely with water and seal with a cork.
  • Place it over an open book β€” the letters appear larger! The curved water-filled flask acts like a magnifying glass.
  • Now use a real magnifying glass to observe an ant β€” you can see body details much more clearly.

🎯 Types of Microscopes for NEET: The Light Microscope (LM) uses visible light β€” magnifies up to ~1,500Γ—. Shows cells and large organelles. The Electron Microscope (EM) uses electrons β€” magnifies up to 10,00,000Γ— (10 lakh times!). Reveals ribosomes, endoplasmic reticulum, membranes. Two types: TEM (internal structure) and SEM (surface structure). NEET frequently asks which organelle was discovered using which microscope!

History of microscope including Robert Hooke Micrographia and compound microscope

History of the Microscope: Robert Hooke’s Micrographia, cork cell drawing, labelled compound microscope, and magnification comparison from naked eye to electron microscope.

⚑ Quick Check β€” Section 1

1

Who coined the term "cell" and what did they use it to describe?

Robert Hooke (1665). He used it to describe tiny box-like compartments in cork β€” they reminded him of the small rooms (cells) in a monastery.
2

Why is Leeuwenhoek called the "Father of Microbiology"?

He built far more powerful microscopes than anyone before him and was the first to clearly see, describe, and study living microorganisms like bacteria and blood cells.
3

🎯 NEET: Which microscope magnifies up to 10 lakh times and is needed to see ribosomes?

NEETElectron Microscope (EM) β€” uses electrons instead of light, magnification up to 10,00,000Γ—. Needed to see tiny organelles like ribosomes (~20 nm) that cannot be resolved by light microscopes.

🧬 What Is a Cell? β€” Structure & Parts

Section 2 Β· Cell Biology Β· NCERT Chapter 2

All living beings are made of cells. The cell is the basic structural and functional unit of life. Every cell contains three fundamental parts: the cell membrane, the cytoplasm, and the nucleus. Plant cells have an additional outer layer β€” the cell wall.

In Activity 2.2 (onion peel), you see rectangular cells in a regular lattice β€” the rigid cell wall gives this shape. In Activity 2.3 (cheek cells), you see polygon-shaped flat cells β€” animal cells have no cell wall and are flexible.

🌟 Three Basic Parts of ALL Cells:
πŸ”΅ Cell membrane β€” outer boundary; porous; controls what enters/exits
🟑 Cytoplasm β€” jelly-like fluid; site of most life processes; contains carbohydrates, proteins, fats, mineral salts
πŸ”΄ Nucleus β€” "control centre"; contains DNA; regulates all cell activities and growth
🌿 Extra Parts in Plant Cells Only:
🟩 Cell wall β€” rigid outer layer (cellulose); provides shape and strength
🌱 Chloroplasts β€” contain chlorophyll; site of photosynthesis; give green colour
πŸ’§ Large central vacuole β€” stores water, nutrients, waste; maintains cell shape (turgor pressure)

πŸ§ͺ Activity 2.2 β€” Onion Peel Practical

  • Peel thin inner layer from onion using forceps β†’ stain with safranin (30 sec) β†’ rinse in water.
  • Mount on glass slide with glycerin drop β†’ add coverslip at 45Β° β†’ observe under microscope.
  • You see rectangular cells with cell wall, nucleus, and cytoplasm clearly. Glycerin prevents drying; safranin stains cells pink for visibility.
FeaturePlant CellAnimal Cell
Cell wallβœ… Present (cellulose)❌ Absent
Cell membraneβœ… Presentβœ… Present
Nucleusβœ… Presentβœ… Present
Chloroplastsβœ… In green parts❌ Absent
Vacuoleβœ… Large central vacuole❌ Usually absent/very small
ShapeRegular, rectangular (rigid)Irregular, variable (flexible)

🎯 Cell Shape Relates to Function (NEET Core Concept):
β€’ Spindle-shaped muscle cells β†’ contract and shorten to create movement
β€’ Neurons β†’ long axon + many dendrites β†’ receive from many cells, transmit signals over long distances
β€’ Flat cheek cells (epithelial) β†’ form smooth protective lining
β€’ Biconcave RBCs β†’ max surface area for Oβ‚‚ transport; no nucleus in humans = more space for haemoglobin
This principle β€” structure is related to function β€” is a core NEET concept tested every year!

Plant cell and animal cell labelled diagram

Plant Cell vs Animal Cell: Labelled diagrams showing cell wall, cell membrane, nucleus, cytoplasm, chloroplasts, vacuole, and mitochondria.

⚑ Quick Check β€” Section 2

1

Name the three basic parts found in ALL cells.

Cell membrane, Cytoplasm, and Nucleus. Every living cell must have all three.
2

Give three differences between plant and animal cells.

(1) Cell wall present in plant cells (cellulose) β€” absent in animal cells. (2) Chloroplasts present in plant cells β€” absent in animal cells. (3) Large central vacuole in plant cells β€” usually absent or tiny in animal cells.
3

🎯 NEET: Why is the neuron so long with many branches?

NEETThe long axon allows electrical signals to travel quickly over long distances. The branches (dendrites) allow the neuron to receive signals from many different cells simultaneously. This is structure adapted for function.

βš—οΈ Cell Organelles β€” NEET Foundation

Section 3 Β· Beyond Class 8 Β· Explained Simply for NEET

Your NCERT introduces basic cell parts. NEET biology goes deeper β€” you need to know the organelles inside cytoplasm, what they do, and why. Think of organelles as "tiny organs" inside a cell β€” just like your body organs have specific jobs, organelles have specific jobs.

🎯 Key Organelles β€” Simplified for NEET:
OrganelleNicknameFunction (simple)Where found?
MitochondriaPowerhouseMakes energy (ATP) from food β€” like a power plantAll eukaryotic cells
ChloroplastKitchen of plantPhotosynthesis β€” makes glucose using sunlightGreen plant cells only
RibosomeProtein factoryMakes proteins β€” like a manufacturing unitAll cells (even bacteria)
VacuoleStorage tankStores water, sap, waste; maintains cell shapeLarge in plants; tiny/absent in animals
Endoplasmic ReticulumTransport highwayTransports materials; makes lipids (smooth ER) or proteins (rough ER)Eukaryotic cells
Golgi ApparatusPost officeSorts, packages, and sends out proteins made by EREukaryotic cells
LysosomeSuicidal bag / DustbinBreaks down old/damaged cell parts and foreign particlesAnimal cells mainly
NucleusControl centreContains DNA; controls all cell activities and divisionAll eukaryotic cells

🎯 MOST IMPORTANT NEET CONCEPT β€” Prokaryote vs Eukaryote:

Eukaryotic cells (eu = true, karyon = nucleus): have a TRUE nucleus enclosed in a nuclear membrane. Have all membrane-bound organelles. Examples: plant cells, animal cells, fungi, protozoa, algae.

Prokaryotic cells (pro = before, karyon = nucleus): NO true nucleus β€” DNA floats in a region called the nucleoid with NO nuclear membrane. NO membrane-bound organelles. Have ribosomes but smaller: 70S type (not 80S). Example: Bacteria only.

Viruses = neither (acellular β€” not cells at all!). This difference comes up in NEET almost every year.

⚠️ NEET Trap β€” Ribosomes in Bacteria: Bacteria DO have ribosomes (70S), but they lack membrane-bound organelles. Eukaryotes have 80S ribosomes in cytoplasm (but 70S in mitochondria/chloroplasts!). Antibiotics like streptomycin target 70S bacterial ribosomes without harming our 80S ribosomes β€” this is why antibiotics kill bacteria but not us!
Comparison of prokaryotic and eukaryotic cells

Prokaryotic vs Eukaryotic Cells: Comparison showing nucleus, organelles, ribosomes, nucleoid region, cell wall, and flagellum.

⚑ Quick Check β€” Section 3

1

🎯 Why is mitochondria called the "powerhouse of the cell"?

NEETMitochondria produce ATP (adenosine triphosphate) β€” the energy currency of the cell β€” through cellular respiration. All cell activities need ATP, so mitochondria supply the "power" for everything the cell does.
2

🎯 What is the key difference between prokaryotic and eukaryotic cells?

NEETProkaryotes have NO true nucleus β€” DNA is in a nucleoid region with no nuclear membrane. They also lack membrane-bound organelles. Eukaryotes have a TRUE nucleus with a nuclear membrane and all membrane-bound organelles (mitochondria, Golgi, ER, etc.).
3

🎯 Why is the Golgi apparatus called the "post office" of the cell?

NEETLike a post office, the Golgi apparatus receives, sorts, labels (tags), packages, and dispatches proteins made by the rough ER to the correct destinations β€” either within the cell or to be secreted outside.

πŸ—οΈ Levels of Organisation in Living Organisms

Section 4 Β· Organisation Β· NCERT Chapter 2

The body of a complex organism is organised hierarchically β€” from the smallest unit (cell) to the whole organism. Think of it like building a skyscraper: individual bricks β†’ walls β†’ rooms β†’ floors β†’ the complete building.

🦠
CELL
Basic unit
β†’
🧱
TISSUE
Similar cells
β†’
πŸ«€
ORGAN
Different tissues
β†’
βš™οΈ
ORGAN SYSTEM
Several organs
β†’
🧍
ORGANISM
Complete being
πŸ’‘ Examples at each level (Digestive System):
🦠 Cell β†’ Single muscle cell or secretory cell
🧱 Tissue β†’ Muscle tissue (many muscle cells together)
πŸ«€ Organ β†’ Stomach (muscle + secretory + other tissues)
βš™οΈ Organ System β†’ Digestive system (mouth, oesophagus, stomach, intestines)
🧍 Organism β†’ Complete human being

All complex organisms begin life as a single cell β€” the egg, which divides repeatedly to form millions of cells. Organisms made of many cells = multicellular (plants, animals). Fun fact from NCERT: the ostrich egg yolk is the largest single cell in the world β€” 130–170 mm diameter!

🎯 Four Types of Animal Tissue (NEET Class 9 preview):
(1) Epithelial tissue β€” covers surfaces and organs (cheek cells, skin)
(2) Connective tissue β€” connects and supports (blood, bone, cartilage, fat)
(3) Muscle tissue β€” movement (striated/skeletal, smooth, cardiac)
(4) Nervous tissue β€” transmits signals (neurons + glial cells)
In plants: Meristematic tissue (dividing cells at tips) and Permanent tissue (xylem for water, phloem for food, epidermis for protection).

⚑ Quick Check β€” Section 4

1

Write the correct order of levels of organisation from smallest to largest.

Cell β†’ Tissue β†’ Organ β†’ Organ System β†’ Organism
2

What is the difference between unicellular and multicellular organisms? Give one example of each.

Unicellular: one cell performs all life functions. Example: Amoeba, bacteria, yeast.
Multicellular: many specialised cells cooperate. Example: humans, plants, mushrooms (multicellular fungi).
3

🎯 NEET: Name the four types of animal tissue with one example each.

NEET(1) Epithelial β€” cheek/skin lining; (2) Connective β€” blood, bone; (3) Muscle β€” heart wall (cardiac), arm muscles (striated); (4) Nervous β€” brain neurons.

🦠 Microorganisms β€” The Invisible World

Section 5 Β· Microbiology Β· NCERT Chapter 2

Microorganisms (microbes) are organisms too small to be seen with the naked eye. They are found everywhere β€” water, soil, air, food, inside our bodies, even in hot springs and frozen ice. A microscope (100–400Γ— magnification) is needed to see them.

🦠

Bacteria

Prokaryotic. Shapes: spherical (cocci), rod (bacilli), spiral (spirilla). Helpful: Lactobacillus, Rhizobium. Harmful: Salmonella, Vibrio cholerae.

πŸ„

Fungi

Eukaryotic. No chlorophyll β€” cannot photosynthesise. Cell wall = chitin. Unicellular (yeast) or multicellular (mould, mushroom).

πŸ”΅

Protozoa

Eukaryotic, unicellular. Move using pseudopodia (Amoeba), cilia (Paramecium), flagella. Some cause diseases: Plasmodium β†’ malaria.

🌿

Algae

Eukaryotic. Have chlorophyll β€” can photosynthesise. Produce 50%+ of Earth's oxygen! Examples: Spirulina (superfood!), Chlorella, Diatoms.

⚠️

Viruses

Acellular β€” not cells at all! Only replicate inside a living host. Cause: COVID-19, flu, dengue, polio, rabies. Made of DNA/RNA + protein coat (capsid).

🎯 Virus Structure for NEET:
Viruses consist of: (1) Nucleic acid β€” either DNA OR RNA (never both). (2) Protein coat (Capsid) β€” made of capsomers; protects the genetic material. (3) Some have an envelope (lipid membrane stolen from host β€” e.g. HIV, Influenza, COVID-19). Envelope-less = naked viruses (Polio, Hepatitis A).

They have NO cell membrane, cytoplasm, ribosomes, or organelles. They are NOT cells β€” they hijack host cell machinery to replicate. This is why they are placed outside the five kingdoms by many scientists.

MicroorganismCell TypeUnicellular/MulticellularNucleus?Chlorophyll?
BacteriaProkaryoticUnicellularNo (nucleoid)No
ProtozoaEukaryoticUnicellularYesUsually No
AlgaeEukaryoticBothYesYes
FungiEukaryoticBoth (yeast=uni)YesNo
VirusAcellularβ€” (not a cell)NoNo
Five types of microorganisms illustration

Five Types of Microorganisms: Bacteria, fungi, protozoa, algae, and viruses with labelled structural features.

⚑ Quick Check β€” Section 5

1

What is the key difference between a bacterium and a protozoan?

Bacteria are prokaryotic β€” no true nucleus, no membrane-bound organelles. Protozoa are eukaryotic β€” have a true nucleus and organelles. Both are unicellular, but protozoa are more complex structurally.
2

Why are viruses called "acellular"? How are they different from all other microorganisms?

Viruses are not made of cells β€” no cell membrane, cytoplasm, nucleus, or organelles. They are just genetic material (DNA or RNA) in a protein coat. Unlike all other organisms, they can only replicate inside a living host cell β€” they cannot reproduce on their own.
3

🎯 NEET: Fungi cell walls are made of which substance? How does this differ from plant and bacterial cell walls?

NEETFungi = Chitin. Plant cells = Cellulose. Bacteria = Peptidoglycan. All three provide structural support, but their chemical composition is completely different β€” an important distinction for NEET.

🌿 Microbes & the Environment

Section 6 Β· Ecology Β· NCERT Chapter 2

Microorganisms are nature's recyclers β€” they break down complex organic matter back into simple substances that plants can use again. This process is called decomposition. Fungi and bacteria act on dead organic matter (leaves, dead animals, food waste) and break it down into nutrient-rich manure, which returns to the soil and improves fertility.

🌱 Rhizobium β€” The Nitrogen Fixer: Rhizobium bacteria live in nodules on the roots of legumes (beans, peas, lentils). They convert atmospheric Nβ‚‚ gas into ammonia/nitrates β€” forms plants can actually use. This is called nitrogen fixation. Farmers grow legumes in crop rotation to naturally add nitrogen to soil without chemical fertilisers!
πŸ’‘ Microalgae β€” Tiny Oxygen Factories: Microalgae produce more than 50% of Earth's oxygen through photosynthesis. Spirulina is called a "superfood" β€” over 60% protein, rich in Vitamin B₁₂. Chlorella, Diatoms, and others are used as health supplements and biofuel sources. Microalgae also help clean water (bioremediation).

πŸ§ͺ Activity 2.7 β€” Making Natural Manure (Composting)

  • Fill a container halfway with garden soil. Add fruit and vegetable peels. Cover with another soil layer.
  • Leave undisturbed for 2–3 weeks.
  • Result: peels turn into dark, nutrient-rich manure β€” caused by soil bacteria and fungi breaking down the organic waste (decomposition)!

🎯 Nitrogen Cycle Introduction (NEET):
The atmosphere is 78% Nβ‚‚ but plants cannot use it directly. Steps:
(1) Nitrogen fixation: Rhizobium converts Nβ‚‚ β†’ NH₄⁺ (ammonium) in soil.
(2) Nitrification: Nitrosomonas + Nitrobacter convert NH₄⁺ β†’ nitrites β†’ nitrates (usable by plants).
(3) Plants absorb nitrates β†’ build proteins β†’ eaten by animals.
(4) Decomposition: bacteria + fungi break down dead organisms β†’ nitrogen returned to soil.
(5) Denitrification: some bacteria convert nitrates back to Nβ‚‚ gas β†’ cycle repeats.
This shows why microbes are absolutely essential for life on Earth!

πŸ‚Decomposers break dead matter into nutrients β†’ return to soil
🌱Rhizobium fixes Nβ‚‚ β†’ legumes grow without nitrogen fertilisers
🌊Microalgae produce 50%+ of Earth's oxygen via photosynthesis
β›½Bacteria produce biogas (methane + COβ‚‚) from organic waste

⚑ Quick Check β€” Section 6

1

What is decomposition and why is it important for the environment?

Decomposition is when microorganisms (bacteria and fungi) break down dead organic matter into simpler substances. It's important because: it returns nutrients to the soil; cleans up the environment; makes soil fertile for plant growth β€” it's nature's recycling system.
2

What is Rhizobium and why do farmers grow legumes in crop rotation?

Rhizobium is a bacterium in legume root nodules that fixes atmospheric nitrogen (Nβ‚‚) into usable forms for plants. Farmers grow legumes in rotation because Rhizobium naturally adds nitrogen to the soil β€” reducing the need for expensive chemical nitrogen fertilisers.
3

🎯 NEET: Name the two bacteria involved in nitrification and what they convert.

NEETNitrosomonas converts ammonia (NH₄⁺) β†’ nitrites (NO₂⁻). Nitrobacter converts nitrites (NO₂⁻) β†’ nitrates (NO₃⁻). Plants absorb nitrates through their roots.

🍞 Microbes & Food β€” Fermentation

Section 7 Β· Food Microbiology Β· NCERT Chapter 2

Many of our favourite foods are made WITH microorganisms through a process called fermentation β€” where microbes break down sugars and produce useful products like COβ‚‚, alcohol, or lactic acid. This process has been used by humans for thousands of years!

Yeast (a unicellular fungus) is key in bread and cake making. It breaks down sugar anaerobically (without oxygen), releasing COβ‚‚ gas. COβ‚‚ bubbles get trapped in dough, making it rise and become soft and fluffy. A small amount of alcohol is also produced (giving the characteristic smell).

🍞 Key Microorganisms in Indian Food:
πŸ«™ Lactobacillus β†’ curd (converts lactose β†’ lactic acid β†’ thickens and sours milk)
🧫 Yeast (Saccharomyces cerevisiae) β†’ bread, cake, bhatura (releases COβ‚‚)
🫢 Mixed bacteria β†’ idli/dosa batter (COβ‚‚ + lactic acid = soft texture + tangy flavour)
πŸ’Š Penicillium fungus β†’ source of Penicillin antibiotic!

πŸ§ͺ Activity 2.9 β€” Curd Formation (Warm vs Cold)

  • Bowl A: lukewarm milk + spoonful of curd β†’ keep in WARM place
  • Bowl B: cold milk + spoonful of curd β†’ keep in REFRIGERATOR
  • Result: Bowl A sets into curd; Bowl B does not.
  • Why? Lactobacillus grows best at ~37Β°C. Cold temperatures inhibit growth β†’ no fermentation β†’ no curd in Bowl B.

🎯 Fermentation Equations for NEET:

Alcoholic fermentation (Yeast β€” anaerobic):
Glucose β†’ 2 Ethanol + 2 COβ‚‚ + Energy (ATP)
Used in: bread, beer, wine, biofuel production.

Lactic acid fermentation (Lactobacillus):
Glucose β†’ Lactic acid + Energy
Used in: curd, yogurt, cheese, idli, dosa, sauerkraut.

Why don't pickles get infected? High salt/sugar concentration = hypertonic environment. Water moves OUT of microbial cells by osmosis β†’ cells undergo plasmolysis (shrink) and die. Salt and sugar are natural preservatives through this osmotic effect!

Food ItemMicroorganismProduct of FermentationFunction
Bread / CakesYeast (Saccharomyces)COβ‚‚ + ethanolMakes dough rise and fluffy
Curd (Dahi)LactobacillusLactic acidThickens milk; makes it sour
Idli / DosaMixed bacteria + yeastCOβ‚‚ + lactic acidSoft texture + tangy flavour
BhaturaLactobacillusCOβ‚‚Makes dough puffy

⚑ Quick Check β€” Section 7

1

What gas does yeast release during fermentation that makes bread dough rise?

Carbon dioxide (COβ‚‚). Yeast ferments sugars anaerobically and releases COβ‚‚, which gets trapped as bubbles in the dough β€” making it rise and become light and fluffy when baked.
2

Why does curd form in warm milk (Bowl A) but not cold milk (Bowl B)?

Lactobacillus bacteria grow best at ~37Β°C (warm). In Bowl A, bacteria multiply rapidly, ferment lactose β†’ lactic acid β†’ milk proteins coagulate β†’ curd forms. In Bowl B, cold temperature inhibits bacterial growth β†’ no fermentation β†’ no curd.
3

🎯 NEET: Why don't microorganisms grow in pickles even though they contain food matter?

NEETHigh salt/sugar concentration creates a hypertonic environment. By osmosis, water moves OUT of microbial cells β†’ cells lose water β†’ undergo plasmolysis (shrinkage) and die. This is why salt and sugar are natural preservatives β€” they kill microbes by osmotic effect.

🎯 Why is Cell the Basic Unit of Life?

Section 8 Β· Cell Theory Β· NCERT + NEET Foundation

The cell is the basic unit of life because every living organism is made of at least one cell. A cell is the smallest structure that can carry out all fundamental life processes β€” nutrition, respiration, excretion, growth, and reproduction β€” independently. This is why viruses (which are smaller) are NOT considered fully "alive."

πŸ“œ Cell Theory (Schleiden, Schwann, and Virchow β€” 1838–1855):
1️⃣ All living organisms are made up of one or more cells.
2️⃣ The cell is the basic structural and functional unit of life.
3️⃣ All cells arise from pre-existing cells (Omnis cellula e cellula β€” Virchow, 1855).

🎯 Cell Size Facts for NEET:
β€’ Most cells: 1–100 micrometres (ΞΌm) in diameter.
β€’ Smallest cell: Mycoplasma (bacterium) β€” 0.1–0.5 ΞΌm. Also the only bacterium without a cell wall!
β€’ Largest cell: Ostrich egg yolk β€” single cell of 130–170 mm diameter!
β€’ Longest cell: Nerve cell (neuron) of a giraffe β€” can exceed 1 metre!
β€’ Human body: approximately 37 trillion (3.7 Γ— 10ΒΉΒ³) cells.
β€’ Bacterial cell wall = Peptidoglycan | Plant = Cellulose | Fungi = Chitin

FeatureProkaryote (Bacteria)Eukaryote (Plants/Animals)
NucleusAbsent (nucleoid)True nucleus + nuclear membrane
Membrane-bound organellesAbsentPresent (mitochondria, ER, Golgi)
Ribosomes70S (smaller)80S (larger) in cytoplasm
Cell wallPeptidoglycanCellulose (plants); absent (animals); chitin (fungi)
Size0.1–10 ΞΌm (smaller)10–100 ΞΌm (larger)
ExamplesBacteria, CyanobacteriaAmoeba, Yeast, plants, animals
⚠️ Remember: Yeast is Eukaryotic! Many students confuse yeast with bacteria because it is a microorganism. But yeast (Saccharomyces cerevisiae) is a eukaryotic fungus β€” it has a true nucleus and organelles. Only bacteria and archaea are prokaryotes. Everything else = eukaryote!

⚑ Quick Check β€” Section 8

1

State Cell Theory in three points.

(1) All living organisms are made of one or more cells. (2) The cell is the basic structural and functional unit of life. (3) All cells arise from pre-existing cells (not created from scratch).
2

Name the smallest known cell and the largest known cell.

Smallest: Mycoplasma β€” a bacterium (0.1–0.5 ΞΌm); also lacks a cell wall.
Largest: Ostrich egg yolk β€” a single cell (130–170 mm); visible to the naked eye.
3

🎯 NEET: Why can antibiotics kill bacteria without harming our own cells?

NEETBacteria have 70S ribosomes and peptidoglycan cell walls β€” both absent in human cells. Antibiotics like penicillin target peptidoglycan cell walls; streptomycin targets 70S ribosomes. Our cells have 80S ribosomes and no peptidoglycan β€” so antibiotics are selective and safe for us.

🧠 Multiple Choice Quiz

12 questions β€” NCERT + NEET Foundation. Purple-bordered = NEET level.

0 of 12 answered

✍️ Long Answer Questions

5 detailed questions β€” model answers and mark schemes included

⚑ One Word Quiz

20 quick-fire questions β€” NCERT + NEET Foundation