Chemotaxis is the phenomenon in which somatic cells, bacteria, and other single-cell or multicellular organisms direct their movements according to certain chemicals in their environment.
In bacteria, chemotaxis is important for finding food by moving towards the highest concentration of food molecules, or to move away from dangers.
In multicellular organisms, chemotaxis is critical for development and function.
Positive chemotaxis occurs if the movement is toward a higher concentration of the chemical in question.
Negative chemotaxis occurs if the movement is in the opposite direction.