All living things respond to changes in their surroundings. These changes which they respond to, are called stimuli. The living things show response to stimuli such as heat, light, touch, sound, smell, taste, etc. The response of living things is usually in the form of some movement of their body part. Plants also perform movement, though at a slow rate. For example, chhui-mui, kachhan flowers of lotus and water lily show such type of activity. So all living things (animals and plants) respond to external stimuli.