The main difference between tropic and nastic movements in plants is that tropic movements are directional responses where the plant grows toward or away from the stimulus, depending on its direction, while nastic movements are non-directional responses that occur irrespective of the stimulus direction.
Tropic Movements
- Directional growth responses toward or away from an external stimulus (e.g., phototropism, gravitropism).
- Dependent on the direction of the stimulus.
- Often involve growth (permanent changes).
- Controlled by hormones such as auxin.
- Examples: A shoot bending toward light (phototropism), roots growing downward due to gravity (geotropism).
Nastic Movements
- Non-directional responses; the movement direction does not depend on stimulus direction.
- Usually rapid and reversible movements often involving changes in turgor pressure in specialized motor cells.
- May or may not involve growth.
- Examples include the closing of Mimosa pudica leaves when touched (thigmonasty) and flowers opening and closing according to the day-night cycle (nyctinasty).
- Responses occur regardless of where the stimulus is applied.
In summary, tropic movements are growth-based, directional, and slower responses to stimuli, while nastic movements are typically fast, non- directional, and reversible movements often involving changes in cell turgor pressure rather than growth.
