AP BIOLOGY

Detailed explanation-1: -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-2: -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-3: -The response of an organism, usually a plant, to an environmental stimulus is called a tropism. Some common plant stimuli include light, gravity, water, movement of the sun, and touch. The naming of the tropism is associated with the stimulus.

Detailed explanation-4: -Phototropism is a directional response that allows plants to grow towards, or in some cases away from, a source of light.

Detailed explanation-5: -Growth movement of plants towards the stimulus is known as positive tropism while movement of plant/plant parts away from the stimulus is known as negative tropism. A tropic movement is defined as either positive or negative tropism; not as downward and upward tropism.