The Cell
What is a Cell?
A cell is the basic structural and functional unit of life.
All living organisms (plants, animals, microbes) are made of cells.
👉 First discovered by Robert Hooke in 1665.
Cell Theory
Proposed by Matthias Schleiden and Theodor Schwann, later expanded by Rudolf Virchow.
Main Points:
- All living organisms are made of cells
- Cell is the basic unit of life
- New cells arise from pre-existing cells
Types of Cells
1. Prokaryotic Cells
- No true nucleus
- DNA is free in cytoplasm
- No membrane-bound organelles
Example: Bacteria
2. Eukaryotic Cells
- True nucleus present
- Membrane-bound organelles present
Example: Plant cells, Animal cells
Plant Cell vs Animal Cell
| Feature | Plant Cell | Animal Cell |
|---|---|---|
| Cell wall | Present | Absent |
| Shape | Rectangular | Round/irregular |
| Vacuole | Large | Small |
| Chloroplast | Present | Absent |
Structure of a Cell
1. Cell Membrane (Plasma Membrane)
- Outer covering of cell
- Made of lipids & proteins
- Selectively permeable
Based on Fluid Mosaic Model
2. Cell Wall (Plant Only)
- Rigid outer layer
- Made of cellulose
- Provides protection & shape
3. Cytoplasm
- Jelly-like substance
- Contains organelles
4. Nucleus
- Control center of cell
- Contains DNA & chromosomes
Cell Organelles and Their Functions
Nucleus
- Controls activities
- Stores genetic material
Mitochondria
- “Powerhouse of the cell”
- Produces ATP (energy)
Endoplasmic Reticulum (ER)
- Rough ER → Protein synthesis
- Smooth ER → Lipid synthesis
Golgi Apparatus
- Packaging & transport of proteins
Lysosomes
- “Suicide bags”
- Digestion of waste
Chloroplast (Plants only)
- Contains chlorophyll
- Site of photosynthesis
Vacuole
- Storage of water, food, waste
- Large in plant cells
Ribosomes
- Protein synthesis
- Found on ER or free
Cell Functions
- Metabolism
- Growth
- Reproduction
- Response to stimuli
Cell Division
1. Mitosis
- Occurs in body cells
- Produces 2 identical cells
2. Meiosis
- Occurs in reproductive cells
- Produces 4 non-identical cells
Important Terms
- Osmosis → Movement of water across membrane
- Diffusion → Movement from high to low concentration
- Active Transport → Uses energy
Levels of Organization
Cell → Tissue → Organ → Organ System → Organism
Special Points (NEET Focus)
- Smallest cell → Mycoplasma
- Largest cell → Ostrich egg
- Longest cell → Nerve cell
- DNA present in nucleus & mitochondria
Summary
A cell is:
- The smallest living unit
- Capable of independent existence
- Performs all life processes
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