Plants do not have nervous system but still sense the things because of stimulus such as gravity light, chemicals(hormones), water, touch (touch -me -not plant).Hormones are responsible for the chemical coordination of plants by integrating their behaviour by affecting growth of a plant resulting in movement of that plant part in response to a stimulus. When sunlight falls on the side, the auxins hormone causes the shady side of the shoot to grow faster, making the towards sunlight
