Question

Which plant movement is unidirectional
A) Phototaxis
B) Chemotaxis
C) Both A and B
D) Thigmotropism

Answer 1

Hint: Taxis means locomotion or movement in plants. Phototaxis and chemotaxis are unidirectional.

Complete answer
Phototaxis as the name suggests is related to the movement of an organism or plant towards or away from the stimulus of light. Phototrophic organisms are benefited with this mechanism in them as it allows them to be more efficient while receiving sunlight that facilitates photosynthesis. Like for example sunflowers.
Chemotaxis is the movement of an organism towards a chemical stimulus, in a direction corresponding to a gradient of increasing or decreasing concentration of a particular substance. The bacteria present in the plant body follows the gradient of chemicals it is directed towards and moves accordingly. Bacteria play a critical role in maintaining plant health.
Thigmotropism is the response of plants to touch stimulus. It is a directional movement of growth which occurs as a mechanosensory response to a touch stimulus. Thigmotropism is typically found in the tendrils of creepers and twining plants.
Like when Mimosa or Touch-me-not plants are touched, a stimulus runs through the plant body and the leaves close.
Phototaxis and chemotaxis are unidirectional since they are movements of plants towards the photon and the chemical gradient respectively. Thigmotropism can be bidirectional as well. It is directed from the point of touch to the rest of the plant body.

Hence the answer is (C.) Both A and B.

Note: Euglena and photosynthetic bacteria show phototaxism too. Flagellated microorganisms display chemotaxis. Thigmotropic responses are also seen in flowers and certain fungi.