Blood transfer is limited by the type and Rh factor of the blood. Someone who has Rh-factor negative blood cannot receive blood with a positive type but a person with Rh-factor positive type blood can receive Rh-negative blood. Type O negative blood is the universal donor because it can be given to a person with any blood type. Type AB positive is the universal recipient meaning someone with this blood type can receive any other type of blood.

The Earth is approximately 4.6 billion years old and its history is divided into time periods based on the events that took place and the forms of life that were dominant during those periods. The largest graduation of time is the eon and each eon is subdivided into eras, eras into periods, periods into epochs, and epochs into ages.

The rows of the Periodic Table are called periods and contain elements that have the same number of electron shells ordered from lower to higher atomic number.

A prefix is added to the base units of the metric system to indicate variations in size. Each prefix specifies a value relative to the base unit in a multiple of 10. Common prefixes are:

The small intestine is where most digestion takes place. As food travels along the small intestine it gets broken down completely by enzymes secreted from the walls. These enzymes are produced in the small intestine as well as in the pancreas and liver. After the enzymes break down the food, the resulting substances are then absorbed into the blood via capillaries in the small intestine walls.