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

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