Reactivity – A description of how likely an element is to form bonds with other elements.
Recessive trait - A trait that only shows up if there is no dominant trait to mask it.
Relative Humidity - The ratio of the amount of water vapor present in the air to the maximum amount the air could hold at a given temperature, expressed as a percentage.
Renewable Resources - Energy sources that can be replenished quickly like solar energy and wind power.
Replication - The process by which DNA makes a copy of itself before cell division.
Revolution - The full movement of one object around another.
RNA - Ribonucleic Acid. This molecule helps build proteins for the cell with the help of the ribosomes. It is built inside the nucleus and moves out into the cytoplasm.
Rotation - The spinning of an object on its axis