Tonicity is a comparative term that has no units. It is frequently used when describing what happens in the cell volume at equilibrium. Tonicity always compares a solution and a cell, and it is used to describe only a solution. Tonicity is related to its osmolarity. There are three terms, hypotonic, isotonic, and hypertonic that used to compare the extracellular fluid around.
A gene is (in informal use) a unit of heredity which is transferred from a parent to offspring and is held to determine some characteristic of the offspring.
