Units of Measure

The Metric System

The metric system is an internationally agreed upon measurement system based on decimals or powers of 10. Scientists use a refined version called the International System of Units (abbreviated SI). In biology, you will often find a need to describe measurements of length, volume, mass, time, temperature or amount of substance.

International System of Units

SI Units

Metric Units:

  • length: meter (m)
  • volume: liter (L)
  • mass: gram (g)
  • time: second (s)
  • temperature: Celsius (°C)
    • Kelvin (K) is a unit of thermodynamic temperature and is the SI unit. The Kelvin scale in the same as the Celsius or centigrade scale but offset by 273.16
    • Biology uses Celsius predominantly because of the range in which organisms live.
  • amount of substance: mole (mol)
    • A mole is a number representing 6.022×1023 of something
    • Just as a pair of shoes equals 2 shoes, a mole of shoes is 6.022×1023 shoes
    • Just as a dozen eggs equals 12 eggs, a mole of eggs is 6.022×1023 eggs
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