Tropismer

Tropismer, also known as tropism, is a biological phenomenon observed in plants and other sessile organisms where directional growth occurs in response to an external stimulus. This response is not a movement of the entire organism, but rather a differential growth rate on different sides of the organ. The direction of growth is always towards or away from the stimulus.

There are several types of tropisms, categorized by the stimulus that elicits the response. Phototropism is growth in response to light. Plants typically exhibit positive phototropism, growing towards a light source, which is crucial for photosynthesis. Gravitropism, or geotropism, is growth in response to gravity. Shoots usually exhibit negative gravitropism, growing upwards against gravity, while roots show positive gravitropism, growing downwards. Thigmotropism is growth in response to touch, commonly seen in climbing plants like vines that coil around support structures. Hydrotropism is growth towards water, a vital response for root systems seeking moisture. Chemotropism is growth in response to chemical stimuli, which can influence root growth or the development of fungal hyphae.

The mechanisms underlying tropisms involve plant hormones, primarily auxins. These hormones accumulate on the side of the plant organ away from the stimulus (in the case of light or gravity), promoting cell elongation on that side. This differential growth causes the organ to bend towards or away from the stimulus. Tropisms are essential for the survival and successful adaptation of plants to their environment.