CELL: The Unit of Life | PART 10 | NCERT Line by Line | NEET 2027 | Class 11 Biology | BY VIKAS SIR



🧬 Chapter 8 – Cell: The Unit of Life (NCERT Notes + Hinglish Tricks)

🌿 Introduction

  • Living vs Non-living → basic difference = cell.

  • Cell = fundamental structural & functional unit of life.

  • Cell discovered by Antonie von Leeuwenhoek (first live cell seen).

  • Robert Brown discovered nucleus.

  • Electron microscope → detailed cell structure.

👉 Trick:
 “L-B-M” = Leeuwenhoek (live cell), Brown (nucleus), Microscope (details).

8.1 What is a Cell? ⭐(PYQ)

  • Unicellular organisms → independent existence + all life functions.

  • Anything < complete cell = not living.

  • Cell = basic unit of structure & function.

👉 Trick:
 “Uni = All alone manage, Cell = basic manager.”

8.2 Cell Theory ⭐(High PYQ)

  • Matthias Schleiden (1838): all plants made of cells.

  • Theodor Schwann (1839): animals made of cells; plasma membrane; plant cell wall unique.

  • Together → Cell theory.

  • Limitation: didn’t explain new cell origin.

  • Rudolf Virchow (1855): Omnis cellula-e cellula = cells arise from pre-existing cells.

  • Final Cell Theory (modern):

    1. All living organisms are made of cells & their products.

    2. All cells arise from pre-existing cells.

👉 Trick:
 “SSV” = Schleiden (plants), Schwann (animals), Virchow (new cells).

8.3 Overview of Cell ⭐(PYQ: Prokaryote vs Eukaryote, examples)

  • Onion cell (plant): cell wall + cell membrane + nucleus.

  • Cheek cell (animal): cell membrane only.

  • Nucleus → chromosomes → DNA.

  • Eukaryotic = membrane-bound nucleus.

  • Prokaryotic = no membrane-bound nucleus.

  • Both have cytoplasm (main site of activities).

  • Eukaryotes → organelles (ER, Golgi, lysosome, mitochondria, plastids, vacuoles).

  • Ribosomes = non-membrane bound, present in all cells.

  • Animal cells → centrosome (cell division).

  • Size range:

    • Smallest: Mycoplasma = 0.3 µm.

    • Bacteria: 3–5 µm.

    • Largest single cell: Ostrich egg.

    • Human RBC: ~7 µm.

    • Longest: Nerve cell.

👉 Trick:
 “Ostrich = Biggest cell, Mycoplasma = Mini cell.”

8.4 Prokaryotic Cells ⭐(High PYQ)

  • Examples: Bacteria, Cyanobacteria (blue-green algae), Mycoplasma, PPLO.

  • Shape of bacteria: Coccus (spherical), Bacillus (rod), Vibrio (comma), Spirillum (spiral).

  • No true nucleus, only nucleoid (circular DNA).

  • Extra DNA = plasmid → antibiotic resistance, transformation.

  • Organelles absent except ribosomes (70S).

  • Mesosome: infoldings of plasma membrane; functions → cell wall formation, DNA replication, respiration, secretion.

  • Chromatophores in cyanobacteria → pigments.

8.4.1 Cell Envelope & Modifications

  • 3-layered envelope: Glycocalyx + Cell wall + Plasma membrane.

  • Bacteria classified:

    • Gram +ve (retain stain).

    • Gram -ve (do not retain).

  • Glycocalyx: slime layer (loose) / capsule (thick).

  • Cell wall: shape + support.

  • Plasma membrane: selectively permeable, like eukaryotes.

  • Flagella: filament + hook + basal body.

  • Pili & Fimbriae: attachment (not motility).

8.4.2 Ribosomes & Inclusions

  • Prokaryotic ribosome = 70S (50S + 30S).

  • Polyribosomes = ribosome chains on mRNA.

  • Inclusions = storage:

    • Phosphate granules.

    • Cyanophycean granules.

    • Glycogen granules.

    • Gas vacuoles (cyanobacteria).

👉 Trick:
 “PPLO = Smallest prokaryote; Shapes = CBVS (Coccus, Bacillus, Vibrio, Spirillum).”

8.5 Eukaryotic Cells ⭐(PYQ-heavy section)

  • Found in Protists, Plants, Animals, Fungi.

  • Key features: membrane-bound organelles, true nucleus, chromosomes.

  • Plant vs Animal differences:

    • Plant: cell wall, plastids, large vacuole.

    • Animal: centrioles, small vacuole, no cell wall.

8.5.1 Cell Membrane (Plasma Membrane) ⭐(PYQ)

  • Lipid + protein composition.

  • Fluid Mosaic Model (Singer & Nicolson, 1972):

    • Phospholipid bilayer (hydrophilic heads outside, hydrophobic tails inside).

    • Proteins: peripheral & integral.

    • Fluidity = lateral movement of lipids/proteins.

  • Functions: growth, junctions, secretion, endocytosis, division.

  • Transport:

    • Passive (diffusion, osmosis).

    • Facilitated (carrier proteins).

    • Active (ATP-dependent, e.g., Na⁺/K⁺ pump).

👉 Trick:
 “Singer Model sings ‘Fluid Mosaic’.”

8.5.2 Cell Wall

  • Non-living rigid outer covering (plants, fungi).

  • Function: shape, protection, interaction, barrier.

  • Composition:

    • Algae: cellulose, galactans, mannans, CaCO₃.

    • Higher plants: cellulose, hemicellulose, pectins, proteins.

  • Middle lamella: Ca-pectate, glues cells.

  • Plasmodesmata: cytoplasmic connections.

👉 Trick:
 “Cell wall = Cement + Channels (plasmodesmata).”

8.5.3 Endomembrane System

Includes: ER, Golgi, Lysosomes, Vacuoles.

  • ER:

    • Rough ER (RER): ribosomes; protein synthesis.

    • Smooth ER (SER): lipid + steroid synthesis.

  • Golgi:

    • Stacks of cisternae; cis face (receiving), trans face (maturing).

    • Functions: protein modification, packaging, glycoproteins/glycolipids.

  • Lysosomes:

    • Vesicles from Golgi.

    • Contain hydrolytic enzymes (lipase, protease, carbohydrase).

  • Vacuoles:

    • Tonoplast membrane.

    • Store sap, waste.

    • Contractile vacuole (Amoeba) = osmoregulation.

👉 Trick:
 “ER = Protein/Lipid factory, Golgi = Post office, Lysosome = Suicide bag, Vacuole = Storage bag.”

8.5.4 Mitochondria ⭐(PYQ)

  • Double-membrane.

  • Inner folds = Cristae (↑ surface area).

  • Inner fluid = Matrix.

  • Functions: aerobic respiration, ATP production → Powerhouse of cell.

  • Contains own DNA, RNA, 70S ribosomes.

  • Divide by fission.

👉 Trick:
 “Mito = Power + Semi-autonomous (DNA + 70S).”

8.5.5 Plastids ⭐(PYQ)

  • Only in plants + Euglenoids.

  • Types:

    • Chloroplasts: chlorophyll, carotenoids; photosynthesis.

    • Chromoplasts: carotenoids (yellow, orange, red).

    • Leucoplasts: colourless; storage.

      • Amyloplasts (starch), Elaioplasts (oil), Aleuroplasts (protein).

  • Chloroplast structure:

    • Double-membrane.

    • Stroma (fluid) + Thylakoids (flattened sacs).

    • Grana = stacks of thylakoids.

    • Stroma lamellae connect grana.

    • Thylakoid lumen inside.

    • Own DNA, RNA, 70S ribosomes.

👉 Trick:
 “Chloro = Green energy, Chloro/Chromo/Leuco = 3 plastid types.”

8.5.6 Ribosomes ⭐(PYQ)

  • Non-membranous.

  • Discovered by George Palade (1953).

  • Types:

    • Prokaryotic = 70S (50S + 30S).

    • Eukaryotic = 80S (60S + 40S).

  • Function: protein synthesis.

👉 Trick:
 “Ribo = Protein factory, Palade = Discoverer.”

8.5.7 Cytoskeleton

  • Network of microtubules, microfilaments, intermediate filaments.

  • Function: shape, support, motility.

👉 Trick:
 “Cytoskeleton = Cell’s bone + muscle.”

8.5.8 Cilia & Flagella ⭐(PYQ)

  • Hair-like outgrowths.

  • Cilia: small, numerous, oar-like.

  • Flagella: longer, fewer, movement.

  • Axoneme structure = 9+2 microtubule arrangement.

👉 Trick:
 “9+2 = Magic formula of motility.”

8.5.9 Centrosome & Centrioles

  • Centrosome = 2 centrioles, perpendicular.

  • Centriole structure: 9 triplet tubulin fibrils.

  • Functions: basal body of cilia/flagella, spindle fibres in division.

👉 Trick:
 “Centrosome = Division manager.”

8.5.10 Nucleus ⭐(PYQ)

  • Discovered by Robert Brown (1831).

  • Chromatin → DNA + proteins.

  • Nuclear envelope = double, with pores.

  • Continuous with ER.

  • Nucleolus: rRNA synthesis, ribosome assembly.

  • Chromosomes:

    • Centromere + kinetochore.

    • Types (by centromere): Metacentric, Sub-metacentric, Acrocentric, Telocentric.

    • Secondary constriction → satellite.

👉 Trick:
 “Brown = Nucleus, Flemming = Chromatin, 4 types = M-S-A-T.”

8.5.11 Microbodies

  • Membrane-bound vesicles with enzymes.

  • Present in both plants & animals.

👉 Trick:
 “Microbodies = Small enzyme bags.”


VIDEO EXPLANATION


🧬 100 NEET MCQs – Chapter 8: Cell: The Unit of Life

Cell Discovery & Cell Theory (Q1–Q15)

  1. Who discovered the first living cell?
     A. Robert Hooke B. Leeuwenhoek C. Brown D. Virchow

  2. Nucleus was discovered by:
     A. Robert Brown B. Schleiden C. Schwann D. Virchow

  3. Cell theory was proposed by:
     A. Hooke B. Schleiden & Schwann C. Virchow D. Darwin

  4. “Omnis cellula e cellula” was stated by:
     A. Hooke B. Brown C. Virchow D. Schleiden

  5. Limitation of original cell theory was:
     A. Plants not included B. Animals not included C. Origin of new cell not explained D. Prokaryotes not considered

  6. Modern cell theory states:
     A. Only plants are made of cells B. Only animals are made of cells C. All living organisms are made of cells, new cells arise from pre-existing cells D. None

  7. Smallest cell is:
     A. Bacteria B. Mycoplasma C. Virus D. PPLO

  8. Largest cell is:
     A. Human ovum B. Ostrich egg C. Nerve cell D. RBC

  9. Longest cell in human body:
     A. RBC B. Muscle cell C. Nerve cell D. Sperms

  10. Average human RBC size:
     A. 3 µm B. 7 µm C. 10 µm D. 20 µm

  11. Prokaryotic DNA is:
     A. Linear, histone bound B. Circular, naked C. Linear, protein-bound D. Segmented

  12. Example of eukaryotic unicellular organism:
     A. Amoeba B. Bacteria C. Mycoplasma D. Cyanobacteria

  13. Example of prokaryote:
     A. Paramecium B. Bacteria C. Euglena D. Yeast

  14. All cells contain:
     A. Nucleus B. Ribosomes C. Plastids D. Centrosome

  15. Ribosomes were discovered by:
     A. Palade B. Brown C. Hooke D. Leeuwenhoek

Prokaryotic Cell (Q16–Q35)

  1. Shape of Vibrio bacteria:
     A. Rod B. Comma-shaped C. Spiral D. Spherical

  2. Spirillum bacteria are:
     A. Rod B. Spiral C. Comma D. Oval

  3. Cocci are:
     A. Rods B. Spherical C. Spiral D. Comma

  4. Bacilli are:
     A. Rod-shaped B. Spherical C. Comma-shaped D. Spiral

  5. Plasmid DNA provides:
     A. Respiration B. Antibiotic resistance C. Photosynthesis D. Movement

  6. Infoldings of plasma membrane in bacteria are called:
     A. Chromatophore B. Mesosome C. Capsule D. Pili

  7. Function of mesosome:
     A. DNA replication B. Respiration C. Secretion D. All of these

  8. Chromatophores are found in:
     A. Mycoplasma B. Cyanobacteria C. Fungi D. Virus

  9. Gram +ve bacteria have:
     A. Thin wall B. Thick wall C. No wall D. Capsule only

  10. Gram –ve bacteria have:
     A. Thick wall B. Thin wall + lipopolysaccharide C. Capsule only D. None

  11. Prokaryotic ribosomes are:
     A. 80S B. 70S C. 50S D. 30S

  12. 70S ribosome subunits are:
     A. 50S + 30S B. 60S + 40S C. 70S + 10S D. 55S + 15S

  13. Storage granules in bacteria include:
     A. Glycogen B. Phosphate C. Cyanophycean D. All

  14. Gas vacuoles are found in:
     A. Fungi B. Cyanobacteria C. Animals D. Virus

  15. Pili help in:
     A. Motility B. Attachment & conjugation C. Respiration D. Photosynthesis

  16. Fimbriae differ from pili in:
     A. Structure only B. Short, numerous vs long, few C. Function only D. None

  17. Flagella in bacteria consist of:
     A. Basal body + Hook + Filament B. Cilia C. Microtubules 9+2 D. None

  18. Glycocalyx functions as:
     A. Protection B. Food production C. ATP production D. Ribosome synthesis

  19. Capsule form of glycocalyx is:
     A. Loose B. Thick & firm C. Absent D. Pigmented

  20. Slime layer form of glycocalyx is:
     A. Loose B. Firm C. Absent D. Pigmented

Eukaryotic Cell – Membrane & Wall (Q36–Q50)

  1. Fluid mosaic model was proposed by:
     A. Robertson B. Singer & Nicolson C. Palade D. Brown

  2. Plasma membrane is made of:
     A. Protein only B. Lipid only C. Lipid + Protein D. Lipid + Protein + Carbohydrate

  3. Hydrophilic part of phospholipid is:
     A. Fatty acid tail B. Phosphate head C. Sterol D. None

  4. Hydrophobic part of phospholipid is:
     A. Head B. Tail C. Both D. None

  5. Passive transport requires:
     A. Energy B. No energy C. Carrier proteins only D. Vesicles

  6. Active transport requires:
     A. Energy (ATP) B. No energy C. Diffusion only D. Osmosis only

  7. Facilitated transport uses:
     A. Lipids B. Channel/carrier proteins C. ATP only D. Vesicles

  8. Endocytosis includes:
     A. Phagocytosis B. Pinocytosis C. Both D. Exocytosis

  9. Cell wall of higher plants is made of:
     A. Cellulose + Hemicellulose + Pectin + Protein B. Chitin C. Lipids D. Starch

  10. Cell wall of fungi is made of:
     A. Cellulose B. Chitin C. Peptidoglycan D. Lipids

  11. Algal cell wall contains:
     A. Cellulose B. Galactans + Mannans + CaCO₃ C. Pectin D. Lignin

  12. Middle lamella is made of:
     A. Ca-pectate B. Chitin C. Lignin D. Suberin

  13. Plasmodesmata connect:
     A. Nuclei B. Cytoplasm of adjacent cells C. Vacuoles D. Lysosomes

  14. Cell wall is absent in:
     A. Plant cell B. Fungal cell C. Animal cell D. Algal cell

  15. Plasma membrane is:
     A. Selectively permeable B. Impermeable C. Permeable D. Non-living

Endomembrane System (Q51–Q65)

  1. RER is associated with:
     A. Protein synthesis B. Lipid synthesis C. Pigment synthesis D. None

  2. SER synthesises:
     A. Protein B. Lipid & steroid C. DNA D. RNA

  3. Cis face of Golgi apparatus is:
     A. Maturing face B. Receiving face C. Secretory face D. None

  4. Trans face of Golgi apparatus is:
     A. Receiving B. Maturing/Secretory C. Random D. None

  5. Functions of Golgi apparatus:
     A. Glycoprotein synthesis B. Glycolipid synthesis C. Packaging & transport D. All

  6. Lysosomes originate from:
     A. ER B. Golgi apparatus C. Ribosome D. Nucleolus

  7. Hydrolytic enzymes in lysosome include:
     A. Lipase B. Protease C. Carbohydrase D. All

  8. Vacuole membrane is called:
     A. Plasmalemma B. Tonoplast C. Peroxisome D. None

  9. Contractile vacuole in Amoeba is for:
     A. Digestion B. Osmoregulation C. Respiration D. Excretion

  10. Plant vacuole stores:
     A. Sap B. Protein C. DNA D. Lipid

  11. In animals, vacuoles are:
     A. Large B. Small C. Absent D. None

  12. Endoplasmic reticulum is continuous with:
     A. Nucleus B. Golgi C. Ribosomes D. Cell wall

  13. Proteins made on RER go to:
     A. Golgi B. Nucleus C. Ribosomes D. Lysosome

  14. Golgi apparatus is absent in:
     A. Animal cells B. Plant cells C. Bacteria D. Protozoa

  15. Lysosome is also called:
     A. Powerhouse B. Suicide bag C. Kitchen of cell D. Brain of cell

Mitochondria & Plastids (Q66–Q80)

  1. Mitochondria are called:
     A. Brain B. Kitchen C. Powerhouse of cell D. Storehouse

  2. Mitochondrial inner folds are called:
     A. Cisternae B. Cristae C. Thylakoids D. Lamellae

  3. Mitochondria matrix contains:
     A. DNA, RNA, 70S ribosome B. Only DNA C. Only RNA D. None

  4. Division of mitochondria:
     A. Amitosis B. Binary fission C. Mitosis D. None

  5. Plastids are present in:
     A. All eukaryotes B. Plants & Euglenoids C. Animals D. Fungi

  6. Chloroplast contains:
     A. Stroma + Thylakoids B. Matrix + Cisternae C. Cristae D. Lysosomes

  7. Grana are:
     A. Stacks of thylakoids B. Matrix folds C. Ribosomes D. None

  8. Stroma lamellae connect:
     A. Grana B. Cristae C. Cisternae D. None

  9. Plastid with carotenoids is:
     A. Chloroplast B. Chromoplast C. Leucoplast D. None

  10. Leucoplast types:
     A. Amyloplast (starch), Elaioplast (oil), Aleuroplast (protein) B. Chloroplast C. Chromoplast D. None

  11. DNA in plastids is:
     A. Absent B. Present (circular, naked) C. Only in chromoplasts D. None

  12. Ribosomes in plastids are:
     A. 70S B. 80S C. Both D. None

  13. Euglenoids contain:
     A. Chloroplasts with 3 membranes B. No plastids C. Chromoplasts only D. None

  14. Photosynthetic pigments are located in:
     A. Thylakoid membrane B. Stroma C. Matrix D. Cristae

  15. Energy currency of cell is:
     A. DNA B. ATP C. RNA D. Protein

Other Organelles & Nucleus (Q81–Q95)

  1. Ribosomes in eukaryotes are:
     A. 70S B. 80S C. 50S D. 60S

  2. Ribosomes in mitochondria:
     A. 80S B. 70S C. None D. 60S

  3. Ribosomes discovered by:
     A. Palade B. Brown C. Leeuwenhoek D. Schwann

  4. Cytoskeleton includes:
     A. Microtubules B. Microfilaments C. Intermediate filaments D. All

  5. Cilia & flagella arrangement:
     A. 9+0 B. 9+2 C. 9+1 D. 9+3

  6. Centrioles made of:
     A. 9 doublets B. 9 triplets C. 9+2 D. 13 protofilaments

  7. Centrosome present in:
     A. Plant B. Animal C. Fungi D. Algae

  8. Nucleus discovered by:
     A. Brown B. Palade C. Schwann D. Hooke

  9. Chromosomes with centromere in middle:
     A. Metacentric B. Submetacentric C. Acrocentric D. Telocentric

  10. Chromosomes with centromere near end:
     A. Metacentric B. Submetacentric C. Acrocentric D. Telocentric

  11. Telocentric chromosomes have:
     A. Centromere at end B. Middle C. Sub-median D. Secondary

  12. Secondary constriction in chromosomes forms:
     A. Nucleolus B. Satellite C. Centriole D. Centrosome

  13. Nuclear pores function:
     A. Transport RNA + protein B. Photosynthesis C. ATP synthesis D. None

  14. Nucleolus is site of:
     A. rRNA synthesis B. DNA replication C. ATP synthesis D. Lipid synthesis

  15. Microbodies are:
     A. Membrane bound B. Non-membranous C. Vacuoles D. None

Miscellaneous (Q96–Q100)

  1. Cell size is mostly determined by:
     A. Genome B. Surface area/volume ratio C. Nutrition D. Age

  2. Which is common to both prokaryotes and eukaryotes?
     A. Nucleus B. Ribosomes C. Mitochondria D. ER

  3. Which of these is double membraned?
     A. Mitochondria B. Plastids C. Nucleus D. All

  4. Which is not a prokaryote?
     A. Cyanobacteria B. Mycoplasma C. PPLO D. Yeast

  5. Semi-autonomous organelles include:
     A. Mitochondria + Plastids B. Ribosome C. Lysosome D. Golgi

✅ Answer Key

Q1–Q15: 1-B, 2-A, 3-B, 4-C, 5-C, 6-C, 7-B, 8-B, 9-C, 10-B, 11-B, 12-A, 13-B, 14-B, 15-A
 Q16–Q35: 16-B, 17-B, 18-B, 19-A, 20-B, 21-B, 22-D, 23-B, 24-B, 25-B, 26-B, 27-A, 28-D, 29-B, 30-B, 31-B, 32-A, 33-A, 34-B, 35-A
 Q36–Q50: 36-B, 37-D, 38-B, 39-B, 40-B, 41-A, 42-B, 43-C, 44-A, 45-B, 46-B, 47-A, 48-B, 49-C, 50-A
 Q51–Q65: 51-A, 52-B, 53-B, 54-B, 55-D, 56-B, 57-D, 58-B, 59-B, 60-A, 61-B, 62-A, 63-A, 64-C, 65-B
 Q66–Q80: 66-C, 67-B, 68-A, 69-B, 70-B, 71-A, 72-A, 73-A, 74-B, 75-A, 76-B, 77-A, 78-A, 79-A, 80-B
 Q81–Q95: 81-B, 82-B, 83-A, 84-D, 85-B, 86-B, 87-B, 88-A, 89-A, 90-C, 91-A, 92-B, 93-A, 94-A, 95-A
 Q96–Q100: 96-B, 97-B, 98-D, 99-D, 100-A



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