The response of plants to environmental stimuli such as light and gravity are called

Tropism

It is a biological phenomenon, indicating growth or turning movement of a biological organism. This is usually a plant in response to the environmental stimulus. This response is dependent on the direction of the stimulus. The stimulus must be perceived first, followed by movement towards or away to the stimulus. There are various types of tropism which are chemotropism, exotropism, geotropism and electrotropism.