Final answer:
Chemical stimulus causes chemotaxis, which is the directed movement of a cell or organism in response to a chemical attractant. It can be a positive movement towards the source of the chemical or a negative movement away from it.
Step-by-step explanation:
Chemical stimulus causes chemotaxis. Chemotaxis is the directed movement of a cell or organism in response to a chemical attractant. It can be a positive movement towards the chemical signal or a negative movement away from it. An example of positive chemotaxis is exhibited by the unicellular protozoan Tetrahymena thermophila, which moves directly towards the source of a chemical attractant by altering the frequency of its turning.