Biologists occasionally need to examine some microscopic animals or plants. Microscopes magnify the specimens 1000 times or more larger than normal. So, understanding about the measurements is a must. In biology, the units of length commonly employed include the micron (abbreviated by µ) and the Angstrom (abbreviated by Å). A micron is equivalent to 10 -3 millimeters (mm). An Angstrom is equivalent to 10-4 µ or 10 -7 mm.
Weights are expressed in milligrams (10-3 grams) micrograms (10-6 grams), and nanograms (10-9 grams).
The unit of molecular weight employed is the dalton. A dalton is defined as the weight of a hydrogen atom. For example, one molecule of water (H20) weighs about 18 daltons . One dalton weighs 1.674 x 10-24 grams.