Fundamental Principles of Cell Theory and Comparison of Prokaryotic and Eukaryotic Cells
Fundamental Principles of Cell Theory
Cell theory is a cornerstone of modern biology that explains the basic structure and function of all living organisms. It was developed in the 19th century by scientists like Matthias Schleiden, Theodor Schwann, and Rudolf Virchow. The main principles of cell theory are:
- All living organisms are made up of one or more cells.
Whether unicellular (like bacteria) or multicellular (like humans), every organism is composed of cells. - The cell is the basic structural and functional unit of life.
All physiological functions of organisms occur within cells or are mediated by cells. - All cells arise from pre-existing cells.
This idea, proposed by Rudolf Virchow, means new cells are produced by the division of existing ones, not from non-living material.
Modern additions to the theory include the concepts that:
- Cells contain hereditary information (DNA) that is passed on during cell division.
- All energy flow (metabolism and biochemistry) occurs within cells.
Comparison of Prokaryotic and Eukaryotic Cells
Cells are broadly categorized into two types: prokaryotic and eukaryotic. These differ significantly in structure and function.
| Feature | Prokaryotic Cells | Eukaryotic Cells |
|---|---|---|
| Size | Generally smaller (0.1 – 5 µm) | Larger (10 – 100 µm) |
| Nucleus | No true nucleus; DNA is in nucleoid region | Has a well-defined nucleus enclosed by a nuclear membrane |
| Membrane-bound Organelles | Absent | Present (e.g., mitochondria, ER, Golgi apparatus) |
| DNA | Single, circular DNA | Linear DNA within the nucleus, associated with histones |
| Cell Division | Binary fission | Mitosis and meiosis |
| Examples | Bacteria and Archaea | Plants, animals, fungi, protists |
| Ribosomes | Smaller (70S) | Larger (80S) |
| Cell Wall | Usually present (made of peptidoglycan in bacteria) | Present in plants (cellulose) and fungi (chitin), absent in animals |
Conclusion
Cell theory provides a universal explanation for the existence and functions of all living organisms. While prokaryotic and eukaryotic cells differ in complexity, both serve as the fundamental building blocks of life. Understanding their differences helps in studying cell biology, genetics, and the evolution of life forms.