Vardaan Learning Institute
Class 11 Biology | Chapter 8
CELL: THE UNIT OF LIFE
Chapter Overview
The cell is the fundamental structural and functional unit of all living organisms. This chapter covers Cell Theory, types of cells (Prokaryotic and Eukaryotic), and the detailed structure and function of every cell organelle. These concepts are foundational for understanding physiology, genetics, and all of biology at higher levels.
Reference: NCERT Class 11 Biology (kebo108.pdf) | B.R. Vashist — Cytology & Genetics | Alberts et al. — Molecular Biology of the Cell
1. Cell Theory
The Cell Theory was proposed by Matthias Schleiden (botanist, 1838) and Theodor Schwann (zoologist, 1839) and later modified by Rudolf Virchow (1855).
Cell Theory — Three Postulates
- All living organisms are composed of cells and products of cells. (Schleiden & Schwann)
- The cell is the basic structural and functional unit of life.
- All cells arise from pre-existing cells ("Omnis cellula e cellula" — Virchow, 1855).
Who coined the term "Cell"? Robert Hooke (1665) — observed dead cork cells under his compound microscope and named them "cells" because they resembled small rooms (Latin: cellula).
Who first observed living cells? Anton van Leeuwenhoek (1674) — observed bacteria and protists in pond water using his single-lens microscope.
📷 Fig. 8.1 (NCERT)
Robert Hooke's microscope and the cork cells he observed (first use of the word "cell")
NCERT Figure 8.1
"SS VR" — Schleiden, Schwann proposed; Virchow Revised
Schleiden → Plants | Schwann → Animals | Virchow → "Cells from cells" (Omnis cellula e cellula)
2. An Overview of the Cell
2.1 Cell Size and Shape
- Smallest cell: Mycoplasma (~0.3 μm) — also the smallest living organism
- Largest cell: Ostrich egg (Ovum of ostrich) — visible to naked eye (~170 mm diameter)
- Longest cell: Nerve cells (neurons) — up to 1 metre in length
- Smallest human cell: Red Blood Cells (~7 μm)
- Largest human cell: Ovum/Egg cell (~100 μm)
- Cell shape varies: spherical (RBC), elongated (muscle/nerve), cuboidal (kidney tubules), columnar (intestinal epithelium), irregular (WBC)
2.2 Prokaryotic vs Eukaryotic Cells
3. Prokaryotic Cell — Detailed Structure
📷 Fig. 8.2 (NCERT)
Prokaryotic cell — Structure of a bacterial cell showing cell wall, cell membrane, nucleoid, ribosomes, pili, flagella, plasmid
NCERT Figure showing bacterial cell structure
3.1 Cell Envelope
In most prokaryotes, the cell is surrounded by a cell envelope consisting of three layers:
Layers of Bacterial Cell Envelope
- Glycocalyx (outermost): May be a loose sheath called slime layer or a tough capsule. Composed of polysaccharides.
- Capsule — helps bacteria resist phagocytosis (makes them virulent/pathogenic)
- Slime layer — helps in attachment to surfaces (biofilm formation)
- Cell wall (middle): Made of peptidoglycan (murein) — a polymer of sugars (NAG & NAM) cross-linked by peptide chains.
- Gram-positive bacteria: Thick peptidoglycan layer → stains violet/purple
- Gram-negative bacteria: Thin peptidoglycan + outer membrane of lipopolysaccharide (LPS) → stains pink/red
- Plasma membrane (innermost): Similar structure to eukaryotic membrane — phospholipid bilayer with proteins
3.2 Prokaryotic Genetic Material
- Nucleoid: DNA is present in a poorly defined region called the nucleoid — no nuclear membrane
- DNA is circular, double-stranded, and naked (no histones; has basic proteins called HU proteins)
- Plasmids: Small, autonomously replicating circular DNA molecules; carry genes for antibiotic resistance, virulence factors
- Bacteria may also have mesosome (infolding of cell membrane) — aids in DNA replication, cell wall synthesis, and cellular respiration
3.3 Flagella, Pili & Fimbriae
- Flagella: Composed of protein flagellin; structure: filament + hook + basal body. Used for locomotion. Types: monotrichous (1), lophotrichous (cluster at one end), amphitrichous (both ends), peritrichous (all sides)
- Pili (Fimbriae): Short, hair-like projections. Functions:
- Conjugation — sex pili transfer DNA between bacteria
- Attachment to host cells (pathogenesis)
🎯 NEET PYQ Focus
NEET 2023
Which of the following has 70S ribosomes?
Answer: Prokaryotes, Mitochondria, and Chloroplasts (all have 70S ribosomes)
NEET 2022
Peptidoglycan/Murein is the component of cell wall in:
Answer: Bacteria (Prokaryotes)
NEET 2020
Which structure helps bacteria in conjugation?
Answer: Sex pili (F-pili)
4. Eukaryotic Cell
📷 Fig. 8.3 a & b (NCERT)
Eukaryotic cells — (a) Animal cell (b) Plant cell — showing all organelles including nucleus, ER, Golgi, mitochondria, chloroplast (plant), centrioles (animal), vacuole
Combine both animal and plant cell diagrams from NCERT
4.1 Cell Membrane (Plasma Membrane)
Fluid Mosaic Model
The Fluid Mosaic Model was proposed by Singer and Nicolson (1972).
- Structure: A phospholipid bilayer with proteins embedded within it
- Phospholipids: Have hydrophilic (water-loving) head and hydrophobic (water-fearing) tail. In aqueous environment they form bilayer with tails facing inward
- Fluid: Phospholipids and proteins are not fixed — they can move laterally (fluid nature)
- Mosaic: Proteins are scattered throughout the lipid bilayer like tiles in a mosaic
- Peripheral (extrinsic) proteins: On the surface only
- Integral (intrinsic) proteins: Partially or fully embedded in the membrane; include channel proteins, carrier proteins, receptors
- Cholesterol: Present in animal cell membranes — maintains fluidity at low temperatures, stability at high temperatures
- Glycoproteins and Glycolipids: On outer surface — cell recognition, cell signalling
📷 Fig. 8.4 (NCERT)
Fluid Mosaic Model of the plasma membrane — showing phospholipid bilayer, integral proteins, peripheral proteins, cholesterol, glycoproteins
NCERT Figure — Fluid Mosaic Model
Functions of Plasma Membrane
- Semi-permeable (selectively permeable): Controls what enters and exits the cell
- Transport mechanisms:
- Passive transport: No energy required — Simple diffusion (small nonpolar molecules), Facilitated diffusion (channel/carrier proteins)
- Active transport: Energy (ATP) required — moves substances against concentration gradient (e.g., Na⁺/K⁺ ATPase pump)
- Osmosis: Movement of water molecules through selectively permeable membrane from hypotonic to hypertonic region
- Endocytosis: Taking material into cell — Phagocytosis (solid: "cell eating") and Pinocytosis (liquid: "cell drinking")
- Exocytosis: Releasing material from cell (secretion)
4.2 Cell Wall
Cell Wall Composition in Different Organisms
- Plants: Primary cell wall — Cellulose, Hemicellulose, Pectin; Secondary cell wall — Lignin (added in mature cells)
- Fungi: Chitin (polymer of N-acetylglucosamine)
- Bacteria: Peptidoglycan (Murein)
- Diatoms: Silica (SiO₂) — frustules
- Algae: Cellulose + other polysaccharides
Plasmodesmata: Fine cytoplasmic strands connecting adjacent plant cells through pores in the cell wall — allow communication and transport between cells
4.3 Endomembrane System
The endomembrane system consists of all membrane-bound organelles that work together as a coordinated unit: Endoplasmic Reticulum (ER), Golgi apparatus, Lysosomes, and Vacuoles. (Note: Mitochondria and Chloroplasts are NOT part of endomembrane system)
A. Endoplasmic Reticulum (ER)
Endoplasmic Reticulum
The ER is a network of tubules, vesicles, and sacs (cisternae) that extends from the nuclear envelope through the cytoplasm. First described by K.R. Porter (1945).
B. Golgi Apparatus (Golgi Body / Golgi Complex)
- Discovered by Camillo Golgi (1898) — stained with silver salt
- Structure: Stack of flat, membrane-bounded cisternae (4–8 per stack); each stack = dictyosome
- Cis face (forming face) — faces RER; receives transport vesicles from RER
- Trans face (maturing face) — faces plasma membrane; sends processed proteins to destination
- Functions:
- Processing, packaging, and sorting of proteins and lipids
- Glycosylation of proteins (addition of sugar groups) → glycoproteins
- Formation of lysosomes
- Cell plate formation during plant cell division
- Secretion (exocytosis of hormones, enzymes, mucus)
C. Lysosomes
Lysosomes — Suicide Bags
- Membrane-bound vesicles containing hydrolytic enzymes (acid hydrolases — active at pH ~5)
- Discovered by Christian de Duve (1955) — also discovered peroxisomes
- Called "Suicide bags" because they can digest the entire cell during autolysis
- Functions:
- Intracellular digestion: Digest bacteria/viruses brought in by phagocytosis
- Autophagy: Digest worn-out organelles and macromolecules
- Autolysis: Self-digestion of the cell (e.g., tadpole tail regression during metamorphosis)
- Extracellular digestion: Sperm releases lysosomal enzymes to penetrate egg
- Lysosomal enzymes synthesized by RER → processed by Golgi → packaged into lysosomes
D. Vacuoles
- Plant vacuoles: Large, central vacuole (tonoplast — surrounding membrane); may occupy 90% of cell volume; contain cell sap (water, sugars, organic acids, pigments like anthocyanins)
- Functions in plants: Maintains cell turgor; storage; colour of flowers/fruits; digestion (in some plants)
- Animal vacuoles: Small and temporary — food vacuoles (in Amoeba), contractile vacuoles (in Paramecium for osmoregulation)
- Contractile vacuole: Pumps excess water out of freshwater protists to prevent osmotic lysis
🎯 NEET PYQ Focus
NEET 2023
The Fluid Mosaic Model of plasma membrane was proposed by:
Answer: Singer and Nicolson (1972)
NEET 2022
Which organelle is called the "Suicide bag" of the cell?
Answer: Lysosome
NEET 2021
Which of the following is NOT a part of the endomembrane system?
Answer: Mitochondria (and Chloroplasts) — they have independent replication and semi-autonomous nature
NEET 2019
Lysosomes are formed from:
Answer: Golgi apparatus
5. Mitochondria
Mitochondria — Powerhouse of the Cell
- Discovered by Altmann (1890); named by Benda (1898)
- Called "Powerhouse of the cell" — site of cellular respiration and ATP production
- Shape: Sausage-shaped or oval; diameter 0.5–1.0 μm, length 1–10 μm
- Double membrane bound organelle:
- Outer membrane: Smooth, permeable (has porins/channel proteins)
- Inner membrane: Folded into cristae (finger-like projections) → increases surface area for ATP synthesis
- Intermembrane space: Space between outer and inner membrane
- Matrix: Interior fluid — contains enzymes for Krebs cycle, mitochondrial DNA (circular), 70S ribosomes, and tRNA
- Oxysomes (F₁ particles / Elementary particles): Stalked particles on inner surface of inner membrane (cristae) — site of ATP synthesis (ATP synthase / F₀F₁ ATPase)
- Semi-autonomous: Have their own DNA, RNA, and 70S ribosomes — can synthesize some of their own proteins
- Self-replicating: Arise only from pre-existing mitochondria by division
- Number varies: RBCs — none; Liver cells — ~1000–2000
📷 Fig. 8.5 (NCERT)
Structure of Mitochondria — showing outer membrane, inner membrane, cristae, matrix, intermembrane space, and oxysomes
NCERT Figure 8.5
"COPS" → Cristae, Oxysomes, Powerhouse, Self-replicating (Semi-autonomous)
70S ribosomes in Mitochondria & Chloroplasts → supports Endosymbiotic theory (Lynn Margulis, 1967) — these organelles were once free-living prokaryotes engulfed by ancestral eukaryotes
6. Plastids
Plastids are double membrane-bound organelles found only in plant cells and algae. They are of three types:
Sub-types of Leucoplasts:
- Amyloplast — stores starch (e.g., potato tubers)
- Elaioplast — stores oils/fats
- Aleuroplast — stores proteins
6.1 Structure of Chloroplast
Chloroplast Structure
- Double membrane: Outer membrane (smooth) + Inner membrane (less permeable)
- Stroma: Fluid-filled matrix inside inner membrane — contains enzymes for Calvin cycle (dark reactions), circular DNA, 70S ribosomes
- Thylakoids: Flattened membranous sacs within stroma — site of light reactions and chlorophyll molecules
- Granum (pl. Grana): Stack of thylakoids — connected to each other by stroma lamellae (intergranal lamellae)
- Quantasomes: Particles on thylakoid membrane — contain photosynthetic units (PSI and PSII)
- Number: 40–50 per mesophyll cell
- Interconversion: Chloroplasts ↔ Chromoplasts ↔ Leucoplasts (they are interconvertible)
📷 Fig. 8.6 (NCERT)
Structure of Chloroplast — showing outer membrane, inner membrane, stroma, grana (thylakoid stacks), stroma lamellae, and DNA
NCERT Figure 8.6
🎯 NEET PYQ Focus
NEET 2022
Stroma of chloroplast is the site of:
Answer: Dark reactions (Calvin cycle / Carbon fixation)
NEET 2021
Which plastid stores starch?
Answer: Amyloplast
NEET 2020
Light reactions of photosynthesis occur in:
Answer: Thylakoid membrane (Grana)
7. Ribosomes
Ribosomes — Protein Factory
- Discovered by George Palade (1955) — also called "Palade particles"
- Not membrane-bound — present in cytoplasm, on RER, and inside mitochondria & chloroplasts
- Composed of rRNA + Proteins
- Svedberg unit (S): Unit of sedimentation coefficient — measures rate of sedimentation in ultracentrifuge (NOT additive)
-
Two types:
- 70S: Found in prokaryotes, mitochondria, and chloroplasts → 50S + 30S subunits
- 80S: Found in eukaryotic cytoplasm → 60S + 40S subunits
- Polyribosomes (Polysomes): Multiple ribosomes attached to a single mRNA molecule — for simultaneous synthesis of many protein copies
- Function: Site of protein synthesis (translation) — mRNA is translated into polypeptide chain
"70 = 50 + 30" and "80 = 60 + 40"
Remember: S values are NOT additive! 50S + 30S ≠ 80S (they are measured differently based on shape/density, not just mass)
Antibiotics that target 70S ribosomes → kill bacteria but NOT eukaryotic host cells. Examples: Streptomycin (30S subunit), Erythromycin (50S subunit), Chloramphenicol (50S subunit)
8. Cytoskeleton, Cilia, Flagella & Centrosome
8.1 Cytoskeleton
- Network of protein filaments and tubules extending throughout the cytoplasm
- Three components:
- Microfilaments (Actin filaments): Thinnest (7 nm); solid; role in cell shape, movement, cytokinesis
- Intermediate filaments (8–10 nm): Mechanical strength; nuclear lamins; keratin in hair/skin
- Microtubules (25 nm): Hollow cylinders of tubulin protein; role in cell division (spindle fibres), intracellular transport, cilia/flagella structure
- Functions: Cell shape maintenance, intracellular transport, cell division, cell movement
8.2 Cilia and Flagella (Eukaryotic)
Structure — 9+2 Arrangement
- Both have identical internal structure — axoneme
- 9+2 arrangement: 9 peripheral doublets of microtubules + 1 central pair of microtubules
- Peripheral doublets connected by dynein arms (motor proteins that use ATP) → cause sliding of microtubules → bending movement
- Basal body anchors the axoneme — has 9+0 arrangement (9 triplets, no central pair)
- Cilia: Short, numerous; beat in coordinated waves (metachronal rhythm); e.g., respiratory tract epithelium, oviduct
- Flagella: Long, fewer in number; whip-like movement; e.g., sperm cells, Chlamydomonas
- Exception: Prokaryotic flagella — No 9+2; composed of flagellin protein (completely different structure)
8.3 Centrosome and Centrioles
- Centrosome: Found in animal cells (absent in higher plants); consists of two centrioles at right angles
- Centriole structure: 9+0 arrangement — 9 sets of triplet microtubules, no central pair; made of tubulin
- Functions:
- Organises spindle fibres during cell division (mitosis/meiosis)
- Forms basal bodies of cilia and flagella
- Centrosome = MTOC (Microtubule Organising Centre)
🎯 NEET PYQ Focus
NEET 2023
The internal structure of cilia and flagella shows:
Answer: 9+2 arrangement of microtubules (axoneme)
NEET 2022
Centrosome is absent in:
Answer: Higher plants (Angiosperms)
NEET 2020
Dynein is associated with:
Answer: Cilia and Flagella (axonemal microtubules)
9. Nucleus
The nucleus is the control centre of the cell, containing the genetic information (DNA). Discovered by Robert Brown (1831) in orchid root cells.
Structure of the Nucleus
- Nuclear envelope: Double membrane (inner + outer) with nuclear pores — allow transport of RNA and proteins
- Outer nuclear membrane: Continuous with RER; has ribosomes on outer surface
- Nucleoplasm (Karyoplasm): Fluid inside nucleus containing nucleotides, enzymes, ions
- Nucleolus:
- Not membrane-bound; present inside nucleus
- Site of rRNA synthesis and ribosome assembly
- Disappears during cell division; reappears during interphase
- Number: 1 or more per nucleus; more active cells have larger nucleoli
- Chromatin: Complex of DNA + histone proteins (in eukaryotes). Two types:
- Euchromatin: Loosely packed, transcriptionally active (light-staining)
- Heterochromatin: Densely packed, transcriptionally inactive (dark-staining) — includes Barr body (inactive X chromosome in females)
- Chromosomes: Condensed chromatin during cell division — visible as distinct structures
📷 Fig. 8.7 (NCERT)
Structure of the Nucleus — showing nuclear envelope, nuclear pores, outer membrane (with ribosomes), nucleoplasm, nucleolus, chromatin fibres
NCERT Figure 8.7
9.1 Chromosomes
Chromosome Structure
- Each chromosome = one long DNA molecule + histone proteins packaged into nucleosomes
- Nucleosome: 146 bp of DNA wrapped around histone octamer (2 copies each of H2A, H2B, H3, H4) + linker histone H1
- Parts of chromosome:
- Centromere: Primary constriction — where spindle fibres attach (via kinetochore)
- Telomere: Repetitive DNA sequences (TTAGGG) at chromosome ends — protect chromosome from degradation; shorten with each cell division (cellular ageing)
- Secondary constriction: NOR (Nucleolar Organiser Region) — associated with nucleolus formation
- Satellite: Small chromosomal segment beyond secondary constriction
- Types based on centromere position:
- Metacentric: Centromere at centre → V-shaped; equal arms
- Submetacentric: Centromere off-centre → L-shaped; unequal arms
- Acrocentric: Centromere near end → J-shaped; very unequal arms
- Telocentric: Centromere at end → I-shaped; rod-shaped
AI IMAGE PROMPT
Types of Chromosomes based on centromere position. Pure white background (#ffffff). Draw 4 chromosome types side by side: (1) Metacentric — V-shape, centromere in middle; (2) Submetacentric — L-shape, centromere slightly off-centre; (3) Acrocentric — J-shape, centromere near one end; (4) Telocentric — rod/I-shape, centromere at tip. Label each type clearly. Mark centromere position with a dot/circle. Use blue for chromosome body. Clean educational biology diagram, black text labels, white background only.
🎯 NEET PYQ Focus
NEET 2023
Which is NOT associated with nucleus?
Answer: Mitochondrial DNA (it is in the matrix, not nucleus)
NEET 2022
Nucleolus is the site of:
Answer: rRNA synthesis and ribosome assembly
NEET 2021
Barr body is:
Answer: Inactivated X chromosome (heterochromatin) in somatic cells of females (Lyon's hypothesis)
NEET 2019
The histone octamer in nucleosome consists of:
Answer: 2 copies each of H2A, H2B, H3, H4 (total 8 histones)
10. Other Important Organelles
10.1 Peroxisomes
- Single membrane-bound vesicles containing oxidative enzymes (oxidases, catalase)
- Discovered by Christian de Duve (1965)
- Function: Oxidation of fatty acids, detoxification of H₂O₂ (hydrogen peroxide → H₂O + O₂ by catalase)
- Important in photorespiration in plants
10.2 Microbodies
- Include peroxisomes and glyoxysomes (plant cells — site of glyoxylate cycle, converting fatty acids to sugars)
10.3 Cell Inclusions
- Non-living deposits in the cytoplasm: starch grains, glycogen granules, oil droplets, crystals, pigment granules
11. Plant Cell vs Animal Cell — Complete Comparison
12. School Examination Practice Questions
Q1. Who proposed the Cell Theory? What is its modified form?
Answer: Originally proposed by Schleiden (1838) and Schwann (1839). Modified by Rudolf Virchow (1855) who added: "all cells arise from pre-existing cells" (Omnis cellula e cellula).
Q2. What is the Fluid Mosaic Model of the cell membrane? Who proposed it?
Proposed by Singer and Nicolson (1972). According to this model:
- The plasma membrane is a fluid phospholipid bilayer in which proteins float like tiles in a mosaic
- Fluid: Lipids and proteins can move laterally
- Mosaic: Proteins are embedded in varying patterns — some peripheral, some integral
Q3. Write the structural differences between RER and SER. Give one function of each.
Q4. Describe the structure of a mitochondrion with a labelled diagram. Why are mitochondria called semi-autonomous organelles?
Structure:
- Double membrane — outer (smooth, with porins) + inner (folded into cristae)
- Intermembrane space between two membranes
- Matrix — inner fluid; contains enzymes, circular DNA, 70S ribosomes
- Oxysomes (F₁ particles) on inner membrane — ATP synthesis
Semi-autonomous because:
- Have their own circular DNA (mitochondrial genome)
- Have 70S ribosomes → can synthesize some proteins independently
- Can self-replicate (arise from pre-existing mitochondria)
- BUT: most proteins are still encoded by nuclear DNA and imported — hence only partially autonomous
13. Quick Revision — One-Liners
⚡ Rapid Fire Revision
- First to see cells → Robert Hooke (1665) — dead cork cells
- First to see living cells → Anton van Leeuwenhoek (1674)
- Nucleus discovered → Robert Brown (1831)
- Ribosomes discovered → George Palade (1955)
- Lysosomes discovered → Christian de Duve (1955)
- Fluid Mosaic Model → Singer and Nicolson (1972)
- Golgi apparatus discovered → Camillo Golgi (1898)
- Endosymbiotic theory → Lynn Margulis (1967)
- Smallest cell → Mycoplasma (0.3 μm)
- Largest cell → Ostrich egg / Ovum
- Cell without nucleus → RBC (mature erythrocyte)
- Cell without mitochondria → RBC
- Cell with most mitochondria → Liver cells / Muscle cells
- Powerhouse of cell → Mitochondria
- Suicide bag → Lysosome
- Kitchen of cell → Chloroplast
- Protein factory → Ribosome
- Traffic police of cell → Golgi body
- 70S ribosomes found in → Prokaryotes, Mitochondria, Chloroplasts
- 80S ribosomes found in → Eukaryotic cytoplasm
- 9+2 arrangement → Cilia and Flagella (axoneme)
- 9+0 arrangement → Centriole and Basal body
- Centrosome absent in → Higher plants (angiosperms)
- Euchromatin → Active, loosely packed | Heterochromatin → Inactive, densely packed
- Barr body → Inactivated X chromosome in female somatic cells
- Histone octamer → 2 each of H2A, H2B, H3, H4 (8 molecules)
- Nucleolus function → rRNA synthesis + ribosome assembly
- Tonoplast → membrane of plant vacuole
- Plasmodesmata → cytoplasmic connections between plant cells
- Plasmids → extra-chromosomal circular DNA in bacteria
- Murein/Peptidoglycan → bacterial cell wall component
- Chitin → fungal cell wall; also exoskeleton of insects
🧠 Master Memory Tricks
Endomembrane system members: "ERG LV" — ER + Ribosomes (on RER) + Golgi + Lysosomes + Vacuoles
NOT in endomembrane: "MCP" — Mitochondria, Chloroplasts, Peroxisomes (all have own DNA!)
Histone proteins: "H1 is the Lone star; H2A, H2B, H3, H4 are the octamer team"
Prokaryote = 70S; Eukaryote = 80S: "PRO70 — EURO80"
Chromosome types: "My Sub Acro Telo" → Metacentric, Submetacentric, Acrocentric, Telocentric
🔑 Most Frequently Asked NEET Topics
Top 5 Topics from This Chapter in NEET
1. Fluid Mosaic Model — Singer & Nicolson 1972; peripheral vs integral proteins
2. Ribosome types — 70S vs 80S; location; S values not additive
3. Lysosome — suicide bag; discovery by de Duve; acid hydrolases
4. Endomembrane system — members and non-members
5. Mitochondria & Chloroplast — structure, 70S ribosomes, semi-autonomous nature
