Final answer:
Living organisms respond to changes in their environment, such as light, touch, and chemicals. Plants can bend toward light and respond to touch, while bacteria can move toward or away from chemicals and light.
Step-by-step explanation:
Living organisms constantly respond to their environment, including changes in light, heat, sound, and chemical and mechanical contact. For example, plants can bend toward a source of light or respond to touch. Even tiny bacteria can move toward or away from chemicals or light. Movement toward a stimulus is considered a positive response, while movement away from a stimulus is considered a negative response.