Site Glossary

A preparation that stimulates the immune system to develop protection against a disease.

A fluid-filled structure; plant cells commonly have a large permanent central vacuole.

A region containing little or no matter.

An electron in the outermost shell of an atom that participates in chemical bonding.

The electrons in the outermost shell of an atom that are involved in chemical bonding.

A structure that prevents blood from flowing backward.

The gaseous form of a substance that is normally a liquid at room temperature.

The narrowing of blood vessels, reducing blood flow near the skin and decreasing heat loss.

The widening of blood vessels, increasing blood flow near the skin and increasing heat loss.

a mathematical entity that represents both magnitude and direction.

can be visualized as an arrow, where the length represents the magnitude and the direction indicates the orientation.