Tropic movement is a directional growth response in plants where the plant turns or bends in response to an external stimulus. This movement can be either towards (positive tropism) or away from (negative tropism) the stimulus. A common example is phototropism, where the stem of a plant bends towards a light source, while the roots bend away from it.
Explanation:
Directional Response:
Unlike nastic movements, which are non-directional, tropic movements are always oriented towards or away from the stimulus.
Growth Based:
Tropic movements are not a quick twitch or shake, but rather a gradual change in the plant’s growth direction.
Stimulus-Dependent:
Different stimuli cause different tropic movements. Some examples include:
Phototropism: Response to light (stems grow towards light, roots grow away).
Geotropism: Response to gravity (roots grow down, stems grow up).
Hydrotropism: Response to water (roots grow towards water).
Chemotropism: Response to chemicals (pollen tube growth towards the ovule).
Thigmotropism: Response to touch or contact (tendrils coiling around objects).
Example:
A plant placed on its side will exhibit geotropism. Its roots will grow downwards, toward the earth’s gravity, and its stem will grow upwards, away from the earth’s gravity.