The cell is the fundamental, structural, and functional unit of life. It was discovered by Robert Hooke (1665) in cork slices, while Anton van Leeuwenhoek was the first to observe living cells. Later, Schleiden and Schwann proposed the Cell Theory, stating that all living organisms are composed of cells, and Virchow later added that “all cells arise from pre-existing cells.”
Types of Cells
- Prokaryotic Cells
- Simple structure, lacking a well-defined nucleus.
- Genetic material lies in a region called nucleoid.
- Example: Bacteria, Cyanobacteria (Blue-green algae).
- Eukaryotic Cells
- Complex structure with a true nucleus bounded by a nuclear membrane.
- Have well-organized cell organelles.
- Example: Plant and Animal cells.
Cell Structure
1. Plasma Membrane
- Semi-permeable membrane made of lipid bilayer and proteins.
- Regulates entry and exit of materials.
2. Cell Wall (in plants)
- Rigid, non-living outer layer made of cellulose.
- Provides shape, protection, and support.
3. Cytoplasm
- Jelly-like fluid containing organelles.
- Site of many metabolic reactions.
4. Nucleus
- Control center of the cell.
- Contains DNA, organized into chromosomes.
- Surrounded by a double membrane (nuclear envelope) with pores.
Cell Organelles and Their Functions
- Mitochondria – Powerhouse of the cell; site of cellular respiration and ATP production.
- Endoplasmic Reticulum (ER)
- Rough ER: Has ribosomes; helps in protein synthesis.
- Smooth ER: Helps in lipid synthesis and detoxification.
- Ribosomes – Protein factories of the cell (non-membranous).
- Golgi Apparatus – Packaging and secretion of proteins and lipids.
- Lysosomes – Contain digestive enzymes; help in intracellular digestion (“suicidal bags”).
- Plastids (in plants)
- Chloroplasts: Contain chlorophyll; site of photosynthesis.
- Chromoplasts: Provide color.
- Leucoplasts: Store food (starch, protein, oil).
- Vacuoles – Storage sacs for water, food, and waste materials. Large in plant cells, small in animal cells.
- Cytoskeleton – Network of microtubules and microfilaments providing shape and movement.
Differences Between Plant and Animal Cells
| Feature | Plant Cell | Animal Cell |
|---|---|---|
| Cell wall | Present | Absent |
| Vacuole | Large central vacuole | Small or absent |
| Plastids | Present (chloroplasts, etc.) | Absent |
| Shape | Usually rigid and rectangular | Usually round or irregular |
Functions of Cell
- Provides structure and support.
- Carries out metabolic activities.
- Enables growth and reproduction.
- Facilitates communication and transport within the organism.
✅ Conclusion:
The cell is the building block of life, and understanding its structure and functions is essential to learning how organisms live, grow, and reproduce. It is the foundation of biology and a crucial part of Class 11 CBSE syllabus.
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