Tag: movement and locomotion in living organisms

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 illuminated side. Auxin synthesis is inhibited on illuminated side. It moves from the illuminated side to shaded side. Due to this, the plant to grow more on the shaded side and bend in the direction of the light source. It shows phototropic response where faster cell elongation is seen on the shaded side than on the illuminated side. 

Auxin is a plant hormone that plays important role in the growth of stem and roots to gravity. Geotropism is the plant response to the gravity. Root shows positive geotropism and shoot shows negative geotropism. In stems, auxin accumulates towards the lower side. It results in increase in cell expansion and results in the shoot growing upright. In roots, auxin accumulates towards the lower side. However, it inhibits cell expansion and roots grow downwards.

Phototropism is the growth of plant in response to the light stimuli. Drooping of tamarind leaves after sunset is due to phototropism. Phototaxis is the movement shown by organism in the direction of the external light stimuli. Photonasty is the nastic movement shown by organism in response to the external light stimuli. Chemotaxis is the movement shown by organism in the direction of the external chemical stimuli. 

Geotropism is the response of plant parts to the gravity. Negative geotropism is growth of part of plant against the gravity. Positive geotropism is growth of part of plant in the direction of gravity. Downward growth of roots is example of positive geotropism. Primary stems grows against the gravity in upward direction and thus shows negative geotropism. 

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. 

The movement of plant part in response to contact with a solid touch is called as thigmotropism. The twining movements due to support seen in tendrils and twiners is an example of thigmotropism. Seismonasty is the nastic response of a plant to touch or vibration. Dropping of leaves of Mimosa pudica upon touching is due to seismonasty. Heliotropism is a growth movement or bending of stem in the direction of the light. It is also called as solar tracking. Diageotropism is plant part response to the gravity such that it grows horizontal to the gravity.

The movement or growth of any part of a plant in response to an external stimulus is called tropism or tropic movement because most of the time the root grows underground and stem grows up to the ground and bending of stem towards light are the good examples of negative and positive phototropism.

Chemotropism is the movement of plants in response to a chemical stimulus. A classic example of this type of movement is the growth of the pollen tube towards the ovule, during fertilization, in a flower.