Tropism

Tropism is a biological phenomenon, indicating growth or turning movement of a biological organism, usually a plant, in response to an environmental stimulus. In tropisms, the direction of movement is dependent on the direction of the stimulus.

Types of Tropism

There are several types of tropism, including phototropism, geotropism, chemotropism, hydrotropism, thigmotropism, and others. Each of these is a response to a different type of environmental stimulus.

Phototropism

Phototropism is the growth of an organism in response to a light stimulus. Phototropism is most often observed in plants, but can also occur in other organisms such as fungi. The cells on the plant that are farthest from the light have a chemical called auxin that reacts when phototropism occurs. This causes the plant to have elongated cells on the farthest side from the light.

Geotropism

Geotropism is a turning or growth movement by a plant or fungus in response to gravity. This type of tropism is also known as gravitropism. Roots show positive geotropism when they grow downwards, while shoots show negative geotropism when they grow upwards.

Chemotropism

Chemotropism is the growth of organisms navigated by chemical stimulus from the environment. A common example is the growth of a plant's roots towards a source of water.

Hydrotropism

Hydrotropism is a type of tropism where plant roots grow in the direction of water. It is a plant's natural instinct to grow towards water for survival.

Thigmotropism

Thigmotropism is a directional growth movement which occurs as a mechanosensory response to a touch stimulus. This type of tropism is generally found in twining plants and tendrils.

See also

• Auxin
• Plant physiology
• Heliotropism
• Nastic movements