Hint: The plants show movement in response to stimuli. These movements help the plant to adapt with the environment and adverse conditions. This movement is called the tropic movement. These movements are important for growth and development of plants.
To answer this question, we must know about different types of tropic movement. The tropic movement is a response to sunlight, nutrients, water etc for facilitating proper growth and development.
a) According to the question given in fig. A- The root developed from the seeds is moving down towards the earth. This movement is referred to as Geotropism. Geotropism is the growth of the plant in response to the gravity. The growth of plant shoots against gravity is called negative geotropism.
In fig. B. the shoot moves towards the sunlight. This type of movement of shot towards the sunlight is called phototropism.
b) Mimosa is called touch me not plant. It shows seismonastic (thigmonastic) movement which is also called touch induced movement. This type of movement is not a growth movement unlike in fig. A and B. It is a rapid plant movement. The mimosa plant undergoes a change in the morphology of the leaves in response to touch.
Note: The other type of movement exhibited by plants is the tactic movement. It is a type of locomotion movement which is caused by unidirectional stimuli. This movement differs from nastic movement as the movement of plants is in the direction of the induced stimuli.