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Introduction to cells review

Key terms

CellThe smallest living unit of life
Cell theoryThe explanation of the relationship between cells and all living organisms
MicroscopeInstrument used to magnify objects too small to be seen with the naked eye
Simple light microscopeMicroscopy tool that uses visible light and one lens to magnify an object
Compound light microscopeMicroscopy tool that uses visible light and multiple lens to magnify an object
Electron microscopeMicroscopy tool that uses a beam of electrons to create a magnified image

Cell discovery and cell theory

Early 1600sRobert Hooke discovers dead cells using early microscope.
Late 1600sAnton von Leeuwenhoek develops a more powerful microscope that allows him to see living cells like bacteria.
Early 1800sMatthias Schleiden and Theodor Schwann conclude that all living organisms are made of cells, and that cells can be produced from other cells.
Mid 1800sRudolf Virchow confirms that all cells must come from pre-existing cells. (There is some evidence that this idea was stolen from Polish scientist Robert Remak.)
These events gave way to the modern cell theory, which states:
  1. All living things are composed of one or more cells.
  2. The cell is the basic unit of life.
  3. New cells arise from pre-existing cells.

Viewing cells

In order to view cells, scientists must use magnifying tools called microscopes.
Simple light microscopes, such as magnifying glasses, generally are not powerful enough to view cells. Therefore, scientists need to use compound light microscopes or electron microscopes to see detailed cell structures or very small objects, such as viruses.
Compound microscope
Compound microscope. Image from Public domain pictures, Public domain,

Comparing light microscopes and electron microscopes

Light microscopeElectron microscope
Uses visible lightUses beam of electrons
Lower resolution and magnificationHigher resolution and magnification
Cells can be alive or deadCells must be dead
Inexpensive, relatively smallExpensive, very large

Common mistakes and misconceptions

  • Not all cells are the same. Although cells are the basic units of life, there are many different kinds of cells that make up multicellular organisms. Some cells have specialized jobs that allow them to work with one another to perform an organism’s biological functions. Not all cells are the same shape or size either. For example, sperm cells are much smaller than, say, a muscle cell.
  • Cells are the smallest living thing, but they are not the smallest thing. Cells are small enough that we need microscopes to view them, but they are much larger than some other substances that we have learned about. In fact, cells are made out of many atoms, so they are larger than macromolecules and viruses!
  • Not all microscopes are just magnifying glasses! Magnifying glasses do qualify as simple microscopes since they have only one lens. However, there are also more complex microscopes. Microscopes with multiple lenses are known as compound microscopes, and they are able to bend light to produce a much more magnified image than a simple magnifying glass.

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