The movement of hairs in Drosera is referred to as thigmotropism. Thigmotropism is the directional growth or movement of an organism in response to touch or physical contact. In the case of Drosera, the hairs on its leaves are highly sensitive to touch. When an insect or small organism comes into contact with these hairs, they trigger a rapid movement response. The leaves of Drosera curl around the prey, trapping and securing it for digestion. This movement is a defensive mechanism and helps the plant in obtaining nutrients from the captured prey. Heliotropism, option 1, refers to the orientation of an organism towards the sun. Photonastic, option 3, refers to the movement of a plant in response to light stimulus. Seismonastic, option 4, refers to the movement of a plant in response to mechanical or physical stimuli other than touch.