Behavior (Encyclopedia of Science)
Behavior is the way that all organisms or living things respond to stimuli in their environment. Stimuli include chemicals, heat, light, touch, and gravity. For example, plants respond with growth behavior when light strikes their leaves. Behavior can be categorized as either instinctive (present in a living thing from birth) or learned (resulting from experience). The distinction between the two is often unclear, however, since learned behavior often includes instinctive elements. Plants and animals that lack a well-developed nervous system rely on instinctive behavior. Higherdeveloped animals use both instinctive and learned behavior. Generally, behavior helps organisms survive.
The instinctive behavior of a plant depends mainly on growth or movement in a given direction due to changes in its environment. The growth or movement of a plant toward or away from an external stimulus is known as tropism. Positive tropism is growth toward a stimulus, while negative tropism is growth away from a stimulus. Tropisms are labeled according to the stimulus involved, such as phototropism (light) and gravitropism (gravity). Plants growing toward the direction of light exhibit positive phototropism. Since roots grow downward (with gravity),
(The entire section is 808 words.)
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