What is the key distinction between the two types of movement in plants.

The key distinction between the two types of movement in plants lies in their response to external stimuli. Tropism is directional growth or movement in response to an external stimulus, such as light or gravity, where the plant moves towards or away from the stimulus. Nastic movements, on the other hand, are non-directional and reversible responses to stimuli, often independent of the direction of the stimulus. While tropisms involve growth and directional movement, nastic movements encompass non-directional, reversible responses like folding or opening of plant parts. Both mechanisms contribute to plant adaptation and survival in changing environments.