The Cell — Basic Unit of Life
“All living organisms are composed of cells.” — Cell Theory
The cell is the structural and functional unit of all living organisms.
Types of Cells
Prokaryotic vs Eukaryotic
| Feature | Prokaryotic | Eukaryotic |
|---|---|---|
| Nucleus | Absent | Present |
| Size | 1–10 μm | 10–100 μm |
| Organelles | Few | Many |
| Example | Bacteria | Animal/Plant cells |
Cell Organelles
1. Nucleus
- Function: Controls cell activities, contains DNA
- Contains chromosomes made of DNA + Histone proteins
- Nuclear membrane has nuclear pores
2. Mitochondria
- Function: Cellular respiration (energy production)
- Known as the “Powerhouse of the Cell”
- Has its own DNA (maternal inheritance)
$$
C_6H_{12}O_6 + 6O_2 \rightarrow 6CO_2 + 6H_2O + \text{ATP}
$$
3. Endoplasmic Reticulum (ER)
- Rough ER: Has ribosomes → Protein synthesis
- Smooth ER: No ribosomes → Lipid synthesis
4. Chloroplast (Plant cells only)
- Function: Photosynthesis
- Contains chlorophyll (green pigment)
$$
6CO_2 + 6H_2O \xrightarrow{\text{sunlight}} C_6H_{12}O_6 + 6O_2
$$
5. Cell Membrane
- Phospholipid bilayer with embedded proteins
- Selectively permeable
- Controls entry and exit of substances
Plant Cell vs Animal Cell
| Feature | Plant Cell | Animal Cell |
|---|---|---|
| Cell Wall | Present | Absent |
| Chloroplast | Present | Absent |
| Vacuole | Large, central | Small, multiple |
| Shape | Fixed (rectangular) | Irregular |
| Centrioles | Absent | Present |
Key Terms to Remember
- Osmosis: Movement of water from low to high solute concentration
- Diffusion: Movement of molecules from high to low concentration
- Plasmolysis: Shrinking of cell membrane in hypertonic solution