Tag: movement and locomotion in living organisms

Phototropism in stem and root are due to differential phytohormonal effect. Stem grows positively phototropic. Roots grow negatively geotropic. Auxin is responsible for apical dominance and positive phototropism by stem.

Tropic movement is growth movement shown by plant in response to a unidirectional external stimulus. It is specific for direction and depends on the direction of stimulus. Movement towards the direction of stimuli is called as positive tropism while movement away from stimuli is called as negative tropism. It results in positioning of the plant part in the direction of the stimulus.

Turgor movement is a reversible change in position of a plant part due to a change in turgidity of cells. It is mostly caused by contact. In plants, turgor changes occur in thin walled cells of pulvinus present on lower side and pulvinnules present on upper side. Both side has different concentration of potassium and calcium ions. Upon touching, potassium ion concentration changes in the cells which results in turgor movement.

Thigmotropism is the directional response of a plant part to touch with a solid object. It is best seen in tendrils. Upon contact with the stimulus, it shows curving up towards the stimulus. Tendrils grow toward the touch stimulus, and wrap around the object.

The movement of parts of a plant in response to a touch stimulus is called as haptotropism. The movement of parts of a plant in response to external chemical stimulus is called as chemotropism. An example is growth of the pollen tube towards the ovules. The movement of parts of a plant in response to air current is called as anemotropism. The movement of parts of a plant in response to sunlight is called as heliotropism. 

Tropic movement is growth movement shown by plant in response to a unidirectional external stimulus. It is specific for direction and depends on the direction of stimulus. Movement towards the direction of stimuli is called as positive tropism while movement away from stimuli is called as negative tropism. Plant part shows tropic response in terms of cell elongation. For example, in phototropism, faster cell elongation is seen on the shaded side than on the illuminated side. 

Thigmotropism is a directional growth movement in response to a touch stimulus. It is found in twining plants and tendrils. Grape vine tendril entwines around a support due to thigmotropic movement. Nutation is the bending movement shown by plant during its development. Growth movement in response to gravity is called as gravitropism. Nastic movement in response to external stimulus is called as chemonasty. 

Auxin is a plant hormone that plays important role in phototropism, growth movement in response to light. It promotes cell elongation. It is unequally distributed in the plant cells. It is transported towards the shady side and thus present in higher concentration. However, less auxin is transported towards the side exposed to light. Due to this, the plant grows more on the shaded side and bend in the direction of the light source. It shows positive phototropism where faster cell elongation is seen on the shaded side and less on the illuminated side.