🆓 Free Preview
📖 Notes
LESSON 01 OF 16
Cell Theory — The Basis of Biology
Why Cells Matter
The cell is the fundamental unit of all life. Understanding cell biology is essential for MDCAT, A-Level Biology, and any medical career.
Cell Theory
Three Principles, 1839–1855
1839
Schleiden & Schwann propose that all organisms are composed of cells.
1855
Rudolf Virchow adds "omnis cellula e cellula" — all cells arise from pre-existing cells.
- All organisms are composed of cells
- The cell is the basic structural and functional unit of life
- All cells arise from pre-existing cells
Prokaryote vs Eukaryote
🦠
Prokaryote
No nucleus. Bacteria and archaea. Typically 1–10 µm in size.
🧬
Eukaryote
Has a nucleus. Animals, plants, fungi. Typically 10–100 µm in size.
Microscopy Resolution
0.2µm
Light microscope resolution
0.2nm
Electron microscope resolution — 1000x better
TEM
Reveals internal structure
SEM
Reveals surface structure
💡
Exam tip
MDCAT often tests which scientist contributed which principle — Virchow specifically gets credit for "all cells from pre-existing cells," a favourite recall question.