AP BIOLOGY

Detailed explanation-1: -Tropism is specific to the direction of the stimulus. Plants can either display a negative or positive movement in response to a stimulus. It is positive tropism when the movement is towards the direction of stimuli while it is negative tropism when the movement is away from the stimuli.

Detailed explanation-2: -A tropism is plant movement in response to an external stimulus in the environment. If a plant moves towards a stimulus, then it exhibits positive tropism; if a plant moves away from a stimulus, then it exhibits negative tropism.

Detailed explanation-3: -A positive tropism occurs when a plant (or a part of the plant) grows towards the stimulus, and a negative tropism is growth away from the stimulus. Phototropism is directional growth in response to light (Figure 14.1. 1).

Detailed explanation-4: -Plant Tropisms A tropism is a turning toward or away from a stimulus in the environment. Growing toward gravity is called geotropism. Plants also exhibit phototropism, or growing toward a light source. This response is controlled by a plant growth hormone called auxin.

Detailed explanation-5: -The movement of roots towards the pull of gravity is an example of positive geotropism, whereas the movement of plant stem in the direction opposite to the pull of gravity is an example of negative geotropism.