Introduction
The cell is the basic structural and functional unit of life. All living organisms are composed of cells, and all vital activities occur within them.
The study of cells is called cytology.
Cell Theory
The cell theory was proposed by:
- Matthias Schleiden
- Theodor Schwann
Key Points of Cell Theory:
- All living organisms are made of cells
- The cell is the basic unit of life
- All cells arise from pre-existing cells (added by Rudolf Virchow)
Types of Cells
1. Prokaryotic Cells
- No true nucleus
- No membrane-bound organelles
- Example: Bacteria
2. Eukaryotic Cells
- True nucleus present
- Membrane-bound organelles present
- Example: Plant and animal cells
Differences Between Prokaryotic and Eukaryotic Cells
| Feature | Prokaryotic | Eukaryotic |
|---|---|---|
| Nucleus | Absent | Present |
| Organelles | Absent | Present |
| Size | Small | Larger |
Structure of a Cell
A typical cell consists of:
- Plasma membrane
- Cytoplasm
- Nucleus
Plasma Membrane
Structure
- Composed of lipids and proteins
- Fluid mosaic model proposed by Singer and Nicolson
Functions
- Selectively permeable
- Regulates entry and exit of substances
Transport Across Cell Membrane
1. Passive Transport
- No energy required
- Includes:
- Diffusion
- Facilitated diffusion
2. Active Transport
- Requires energy (ATP)
- Moves substances against gradient
3. Bulk Transport
- Endocytosis
- Exocytosis
Cell Wall (Plants Only)
- Present in plant cells
- Made of cellulose
- Provides rigidity and protection
Cytoplasm
- Semi-fluid matrix
- Contains organelles
- Site of metabolic activities
Cell Organelles
1. Endoplasmic Reticulum (ER)
Types:
- Rough ER: Ribosomes present, protein synthesis
- Smooth ER: Lipid synthesis
2. Golgi Apparatus
- Modifies, packages, and secretes proteins
- Known as the “post office” of the cell
3. Lysosomes
- Contain digestive enzymes
- Known as “suicide bags”
4. Mitochondria
- Powerhouse of the cell
- Site of ATP production
5. Ribosomes
- Site of protein synthesis
- Non-membranous
6. Plastids (Plant Cells)
Types:
- Chloroplast (photosynthesis)
- Chromoplast (color)
- Leucoplast (storage)
7. Vacuole
- Large central vacuole in plants
- Maintains turgor pressure
8. Centrosome (Animal Cells)
- Helps in cell division
- Contains centrioles
Nucleus
Structure
- Nuclear membrane
- Nucleoplasm
- Nucleolus
- Chromatin
Functions
- Controls cell activities
- Stores genetic material
Chromosomes
- Made of DNA and proteins
- Carry genes
Differences Between Plant and Animal Cells
| Feature | Plant Cell | Animal Cell |
|---|---|---|
| Cell wall | Present | Absent |
| Vacuole | Large | Small/absent |
| Plastids | Present | Absent |
Prokaryotic Cell Structure
- Nucleoid (no true nucleus)
- Ribosomes
- Cell membrane
- Cell wall
Important NEET & CBSE Points
- Cell is the basic unit of life
- Fluid mosaic model → Singer & Nicolson
- Mitochondria → ATP production
- Ribosome → protein synthesis
- Lysosome → intracellular digestion
Quick Revision Notes
- Prokaryote = simple
- Eukaryote = complex
- ER → synthesis
- Golgi → packaging
- Mitochondria → energy
Frequently Asked Questions (FAQs)
Q1. Who proposed cell theory?
Schleiden and Schwann.
Q2. What is the function of mitochondria?
ATP production.
Q3. What is the fluid mosaic model?
Structure of plasma membrane.
Q4. What are lysosomes?
Organelles containing digestive enzymes.
Conclusion
The cell is the foundation of life, and understanding its structure and functions is essential for mastering all biological concepts. This chapter is extremely important for CBSE exams and NEET preparation, especially for conceptual and diagram-based questions.