The Discovery of Cells and Microscopes: The History of Cell Research

Following the history of the discovery and study of cells shows that biology developed alongside advances in microscopy. This is also a frequent topic on the Common Test.

Basic Knowledge

History of cell research:
① 1665 Robert Hooke: Observed a piece of cork with a microscope he built himself and named the small room-like structures “cell.” This is the origin of the word “cell” (what he actually saw were the cell walls of dead cells).
② 1670s Leeuwenhoek: Observed pond water・blood・sperm・and microorganisms with a high-magnification simple microscope.
③ 1838 Schleiden: Proposed for plants that “all plants are made of cells.”
④ 1839 Schwann: Extended the idea to animals and established cell theory.
⑤ 1855 Virchow: Stated that “all cells arise from cells (Omnis cellula e cellula)” and completed cell theory.
Types of microscopes:
・Light microscope: Uses visible light. Maximum magnification of 1500×, resolution of about 0.2 μm. Living cells can also be observed.
・Electron microscope: Uses electron beams. Magnification of several hundred thousand times, resolution of about 0.2 nm (nanometers). Fine structures of organelles can be seen. There are transmission (TEM) and scanning (SEM) types.

In Depth

The resolution of a light microscope is limited to approximately half the wavelength of visible light (about 0.2 μm). This is a physical limit caused by the diffraction of light, so structures smaller than this cannot be seen with light. Because electrons have much shorter wavelengths than visible light (<0.005 nm), electron microscopes achieve much higher resolution. However, samples must be placed in a vacuum and prepared as thin sections, so living cells cannot be observed.
In recent years, fluorescence microscopes・confocal laser microscopes・and super-resolution microscopes (STED・PALM/STORM) have also developed and were recognized by the Nobel Prize in Chemistry (2014). In addition, cryo-electron microscopy (Nobel Prize in Chemistry 2017) can observe biomolecules in a frozen state and has revolutionized the analysis of protein three-dimensional structures. These advanced technologies are making textbook illustrations of cell structures increasingly precise.
As a standard topic on the Common Test, understand the approximate sizes of observation targets: human egg = 120 μm, human red blood cell = 8 μm, Escherichia coli = 2 μm, mitochondrion = 1〜2 μm, ribosome = 20 nm, influenza virus = 100 nm, diameter of the DNA double helix = 2 nm, atom = 0.1 nm. Light microscopes can show bacteria〜cells; smaller structures require an electron microscope.

Points to Note

① Do not confuse Hooke (England, 1665, named “cell”) with Leeuwenhoek (the Netherlands, discovered microorganisms). ② Resolution and magnification are different concepts. Increasing magnification does not make objects smaller than the resolution visible. ③ Living cells cannot be observed with an electron microscope (a vacuum and fixation are necessary). ④ Units of μm (micrometer) and nm (nanometer): 1 μm = 1000 nm = 10^-6 m. Understand the approximate sizes.

Practice

1. Which scientist first used the name “cell”?
2. Which scientist completed cell theory by stating, “All cells arise from cells”?
3. What is the approximate resolution of a light microscope in μm?