Tropism is found virtually in all plants but nastic movements are mostly found in speacailaised organs and plants .

both tropic and nastic movement are influenced by environment.

in tropism there is directional movement of plant in response to the surrounding like gravity or light but the direction of nastic movement is independent .

in tropism stimulus controls the orientation of the growth , in nastic movements stimulus triggers response .

in tropism the effect is more or less permanent but in nastic movements the effect is temporary and reversible .

Tropic Movement:
Tropic movements in plants are directional responses to external stimuli, such as light, gravity, and touch. These movements occur due to the differential growth rates of plant cells on different sides of the organs involved. Tropic movements are generally slow and occur over a longer duration of time.

Nastic Movement:
Nastic movements, on the other hand, are non-directional responses to external stimuli. These movements occur due to changes in the turgor pressure of cells, rather than differential growth rates. Nastic movements are relatively faster and occur over a shorter duration of time compared to tropic movements.

Differences between Tropic and Nastic Movements:

1. Directionality:
Tropic movements are directional, meaning the plant responds by growing towards or away from the stimulus. In contrast, nastic movements are non-directional and the plant does not orient itself in a specific direction.

2. Stimulus:
Tropic movements are specifically triggered by external stimuli such as light (phototropism), gravity (gravitropism), and touch (thigmotropism). Nastic movements, on the other hand, can be triggered by various stimuli including light, temperature, humidity, touch, and chemicals.

3. Mechanism:
Tropic movements are primarily caused by differential growth rates in plant cells. The cells on one side of the organ elongate more than those on the other side, causing the organ to bend towards or away from the stimulus. In contrast, nastic movements are mainly due to changes in turgor pressure within cells, leading to the folding or unfolding of organs.

4. Speed:
Tropic movements are relatively slow, taking hours or even days to occur. Conversely, nastic movements are rapid, often happening within minutes or hours.

5. Duration:
Tropic movements can be sustained for a longer period, as they involve growth responses and changes in the direction of growth. Nastic movements, on the other hand, are transient and reversible, as they are mainly driven by changes in turgor pressure.

In summary, tropic movements are directional responses to external stimuli that involve differential growth rates, while nastic movements are non-directional responses that occur due to changes in turgor pressure. Tropic movements are slower, longer-lasting, and specific to certain stimuli, whereas nastic movements are faster, transient, and can be triggered by various stimuli.