Chapter 3 — Chapter 3 — Cells and Subcellular Organelles

Magnification = image size / actual size; resolution = ability to distinguish two close points as separate. Light microscope: uses light and glass lenses; max magnification ~1500×, resolution ~200 nm; living cells can be seen. Electron microscope: electron beam and electromagnetic lenses; magnification up to ~500 000× or more, resolution ~0.1–1 nm; specimens dead, in vacuum; TEM shows internal structures, SEM surface 3-D. Cell theory (Schleiden, Schwann, Virchow): all organisms are made of cells; the cell is the basic structural and functional unit of life; all cells arise from pre-existing cells (omnis cellula e cellula). Validated by microscopy of all organisms and Pasteur's experiments disproving spontaneous generation. Exceptions: viruses (acellular), striated muscle fibres and fungal hyphae (multinucleate/syncytial — coenocytic), first cell origin, giant algae (Acetabularia), RBCs lacking nucleus.