Cell Structure and Function - Complete NEET Biology Notes 2026
Master Cell Biology for NEET 2026 with comprehensive notes covering cell theory, prokaryotic vs eukaryotic cells, cell organelles, and their functions. NCERT-based content with previous year questions.
Key Takeaways
- 1Cell is the structural and functional unit of life - fundamental concept for NEET
- 2Prokaryotic cells lack membrane-bound organelles; Eukaryotic cells have them
- 3Nucleus contains genetic material and controls all cell activities
- 4Mitochondria (powerhouse) and Chloroplasts have their own DNA - endosymbiotic theory
- 5Cell membrane is selectively permeable with fluid mosaic model structure
Remember these points for your NEET preparation
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Cell Structure and Function - Complete NEET Biology Notes
Cell Biology contributes approximately 8-10 questions in NEET, making it one of the most important chapters from Class 11. This comprehensive guide covers everything you need to know for NEET 2026.
Introduction to Cells
The cell is the structural and functional unit of all living organisms. This concept was established through centuries of scientific discovery.
Discovery of Cell
| Scientist | Year | Contribution |
|---|---|---|
| Robert Hooke | 1665 | First observed cells in cork; coined term "cell" |
| Anton van Leeuwenhoek | 1674 | First to observe living cells (bacteria, protozoa) |
| Robert Brown | 1831 | Discovered nucleus |
| Schleiden | 1838 | All plants are made of cells |
| Schwann | 1839 | All animals are made of cells |
| Rudolf Virchow | 1855 | "Omnis cellula-e cellula" (all cells arise from pre-existing cells) |
Cell Theory
The Cell Theory states:
- All living organisms are composed of one or more cells
- Cell is the basic unit of life
- All cells arise from pre-existing cells
Exception to Cell Theory: Viruses are acellular (not made of cells) but show characteristics of life when inside a host.
Types of Cells
Prokaryotic vs Eukaryotic Cells
| Feature | Prokaryotic Cell | Eukaryotic Cell |
|---|---|---|
| Size | 1-10 μm | 10-100 μm |
| Nucleus | Nucleoid (no membrane) | True nucleus with membrane |
| Membrane-bound organelles | Absent | Present |
| DNA | Circular, naked | Linear, with histones |
| Ribosomes | 70S (50S + 30S) | 80S (60S + 40S) |
| Cell division | Binary fission | Mitosis/Meiosis |
| Examples | Bacteria, Cyanobacteria | Plants, Animals, Fungi |
NEET Tip: Remember that ribosomes in mitochondria and chloroplasts are 70S type, similar to prokaryotes - supporting endosymbiotic theory.
Cell Envelope and Its Components
Cell Wall
Plant Cell Wall Composition:
- Primary wall: Cellulose, hemicellulose, pectin
- Secondary wall: Lignin, suberin (in some cells)
- Middle lamella: Calcium pectate (holds cells together)
Bacterial Cell Wall:
- Gram-positive: Thick peptidoglycan layer
- Gram-negative: Thin peptidoglycan + outer membrane
Plasma Membrane
Fluid Mosaic Model (Singer and Nicolson, 1972):
- Phospholipid bilayer with embedded proteins
- Cholesterol provides stability (in animal cells)
- Glycocalyx present on outer surface
Components:
- Lipids: Phospholipids, cholesterol, glycolipids
- Proteins: Integral (transmembrane) and peripheral
- Carbohydrates: Glycoproteins, glycolipids
Membrane Transport:
| Type | Energy Required | Example |
|---|---|---|
| Passive (Diffusion) | No | O₂, CO₂ movement |
| Facilitated | No | Glucose via GLUT |
| Active Transport | Yes (ATP) | Na⁺/K⁺ pump |
| Osmosis | No | Water movement |
Cell Organelles
1. Nucleus - Control Center
Structure:
- Nuclear envelope: Double membrane with nuclear pores
- Nucleoplasm: Contains chromatin and nucleolus
- Chromatin: DNA + histone proteins
- Nucleolus: Site of rRNA synthesis and ribosome assembly
Functions:
- Stores genetic information
- Controls cell activities
- Site of DNA replication and transcription
2. Endoplasmic Reticulum (ER)
| Type | Structure | Function |
|---|---|---|
| Rough ER | Ribosomes attached | Protein synthesis and modification |
| Smooth ER | No ribosomes | Lipid synthesis, detoxification |
NCERT Point: SER is abundant in cells actively involved in lipid synthesis (adipocytes, cells secreting steroid hormones).
3. Golgi Apparatus (Golgi Complex)
Structure: Stack of flattened cisternae with cis (forming) and trans (maturing) faces.
Functions:
- Protein modification (glycosylation)
- Packaging and secretion
- Formation of lysosomes
- Cell plate formation in plants
4. Mitochondria - Powerhouse of the Cell
Structure:
- Double membrane (outer smooth, inner folded into cristae)
- Matrix contains 70S ribosomes, circular DNA
- Inter-membrane space
Functions:
- ATP production through oxidative phosphorylation
- Cellular respiration (Krebs cycle in matrix)
- Apoptosis regulation
NEET Important: Mitochondria and chloroplasts have their own DNA and ribosomes - evidence for Endosymbiotic Theory.
5. Plastids (Plant Cells Only)
| Type | Pigment | Function |
|---|---|---|
| Chloroplast | Chlorophyll a, b, carotenoids | Photosynthesis |
| Chromoplast | Carotenoids, xanthophylls | Color in flowers, fruits |
| Leucoplast | None | Storage (starch, protein, oil) |
Chloroplast Structure:
- Double membrane
- Thylakoids (stacked as grana)
- Stroma (70S ribosomes, circular DNA)
6. Lysosomes - Suicidal Bags
Structure: Single membrane vesicles containing hydrolytic enzymes (active at acidic pH ~5).
Functions:
- Intracellular digestion
- Autophagy (self-eating)
- Autolysis (cell death)
Diseases Related: Tay-Sachs disease, Pompe disease (lysosomal storage disorders)
7. Ribosomes - Protein Factories
Structure:
- Made of rRNA + proteins
- No membrane
- 70S in prokaryotes; 80S in eukaryotes
Location:
- Free in cytoplasm (synthesize cytoplasmic proteins)
- Attached to RER (synthesize secretory proteins)
8. Cytoskeleton
Components:
| Element | Diameter | Protein | Function |
|---|---|---|---|
| Microtubules | 25 nm | Tubulin | Cell shape, cilia, flagella |
| Microfilaments | 7 nm | Actin | Cell movement, cytokinesis |
| Intermediate filaments | 10 nm | Various | Mechanical strength |
9. Centrioles and Centrosome
- Found in animal cells only
- Organize spindle fibers during cell division
- Form base of cilia and flagella (basal body)
10. Vacuoles
Plant Cell Vacuole:
- Large central vacuole
- Contains cell sap (water, sugars, ions, pigments)
- Maintains turgor pressure
Animal Cell Vacuoles:
- Small, numerous
- Contractile vacuole in protists (osmoregulation)
- Food vacuole for digestion
Important Diagrams for NEET
- Animal Cell - Label all organelles
- Plant Cell - Show cell wall, vacuole, plastids
- Mitochondria - Cristae, matrix, membranes
- Nucleus - Nuclear envelope, pores, nucleolus
Previous Year NEET Questions
Q1 (NEET 2023): Which of the following is not a function of the Golgi apparatus?
- (a) Formation of glycolipids
- (b) Protein sorting
- (c) ATP synthesis ✓
- (d) Lysosome formation
Q2 (NEET 2022): The 70S ribosomes are found in:
- (a) Cytoplasm of eukaryotes
- (b) Mitochondria and chloroplasts ✓
- (c) Endoplasmic reticulum
- (d) Golgi apparatus
Q3 (NEET 2021): Which organelle is called the "suicidal bag" of the cell?
- (a) Mitochondria
- (b) Golgi apparatus
- (c) Lysosome ✓
- (d) Ribosome
Q4 (NEET 2020): Middle lamella is made up of:
- (a) Calcium pectate ✓
- (b) Calcium carbonate
- (c) Magnesium pectate
- (d) Calcium phosphate
Quick Revision Points
- Cell Theory: Schleiden + Schwann + Virchow
- Largest organelle: Nucleus (or vacuole in plant cells)
- Smallest organelle: Ribosome
- Double membrane: Nucleus, mitochondria, chloroplast
- Single membrane: Lysosome, vacuole, ER, Golgi
- No membrane: Ribosome, centriole
- Own DNA: Mitochondria, chloroplast (semi-autonomous)
- Gram staining: Crystal violet → Iodine → Alcohol → Safranin
FAQs
Q: Why are mitochondria called the powerhouse of the cell? A: Mitochondria produce ATP (adenosine triphosphate) through oxidative phosphorylation, which is the energy currency of the cell. Most cellular ATP is generated in mitochondria.
Q: What is the difference between rough and smooth ER? A: Rough ER has ribosomes attached and is involved in protein synthesis. Smooth ER lacks ribosomes and is involved in lipid synthesis and detoxification.
Q: Why is lysosome called the suicidal bag? A: Lysosomes contain powerful hydrolytic enzymes. If their membrane ruptures, these enzymes can digest the entire cell (autolysis), hence called suicidal bags.
Q: What is the endosymbiotic theory? A: This theory suggests that mitochondria and chloroplasts were once free-living prokaryotes that were engulfed by ancestral eukaryotic cells, eventually becoming organelles. Evidence includes their own DNA, 70S ribosomes, and double membrane.
Q: Why do plant cells have cell walls but animal cells don't? A: Plant cells need rigid cell walls for structural support (since they don't have skeletons) and to maintain shape against turgor pressure. Animal cells have other support mechanisms (cytoskeleton, extracellular matrix).