Hint: Plants exhibit certain movements in response to a stimulus, popularly known as nastic movements. These types of movements are not dependent on direction.
Complete answer:
Touch-me-not plant is one of the members of the Mimosa family. They start folding up and dropping when we touch them. In response to touch, the leaves of this plant shift rapidly. This movement does not involve any type of growth. This type of movement is known as seismonastic movement.
Additional information:
In a very short span of time, some plant species undergo structural change; the so-called "quick plant motion". This occurs when a change or shift in the form of the plant stimulates receptors in the plant body. One of the few species which display this rapid movement is Mimosa pudica, better known as the 'touch-me-not plant' Though born in south and central America, the touch me notes of their impressive reaction to the human touch now find themselves all over the world.
Thigmonasty is defined as the movement of plants triggered by contact stimuli. Water in the cells and other cell contents apply some force against the cell walls of the plant in this mechanosensory response; this is called turgor pressure. The leaves of this plant are kept upright unless they are disturbed externally due to the turgor effect. The swollen base of the leaves, which includes some contractile proteins, is now activated when you strike or shake the leaves, known as seismonastic movements.
When externally disturbed, some parts of the plant release different chemicals, including potassium ions, into the plant's body. These chemical substances release water and electrolytes from the cell and cause cell pressure to decrease. The cell collapses and the leaves are shut down. In interaction with the stimulus, anything like this is often even transmitted to neighboring leaves.
Note:
Touch-me-not is a sensitive plant that exhibits leaves movement in response to touch. This plant takes a lot of energy to fold and recoil the leaves. In addition, photosynthesis is stated to be hindered by this response. It is not surprising therefore that botanists are puzzled that these plants have established this characteristic because it depletes and adversely impacts their energy depots. There is no definitive evidence why touch-me-plants have established this feature, but researchers suggest it may function as a kind of defensive mechanism for them.
