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Why does the following action take place in plants? Plant cells change shape by changing the amount of water in them, resulting in swelling or shrinking, and therefore in changing shape.
In immediate response to some stimulus
To maintain balance
To conserve energy
In fear
In immediate response to some stimulus
Plants exhibit nastic movements (like thigmonasty in Mimosa pudica) in response to external stimuli. These movements are achieved by rapid changes in the turgor pressure of specialized cells called pulvini, which cause the plant parts to droop or fold.
Plants exhibit nastic movements (like thigmonasty in Mimosa pudica) in response to external stimuli. These movements are achieved by rapid changes in the turgor pressure of specialized cells called pulvini, which cause the plant parts to droop or fold.
Think of it like a water balloon losing its shape and going limp the moment you let some water out of it; the plant cell's rigidity is maintained by the 'water pressure' (turgor) inside the cell wall.
T-O-P: Turgor Offers Plant-movement (Turgor pressure changes cause movement).
╬иwтАЛ=╬иsтАЛ+╬иpтАЛ тАФ where ╬иwтАЛ is water potential, ╬иsтАЛ is solute potential, and ╬иpтАЛ is pressure potential (turgor pressure).
The movement is triggered by a change in the water content of cells in the pulvinus. When the plant senses a stimulus, ion channels allow the movement of potassium (K+) ions out of the cell, leading to water loss via osmosis. This loss of turgor pressure causes the cells to shrink and lose their rigidity, resulting in the characteristic folding or drooping behavior.
Nastic movements are non-directional responses to stimuli.
Turgor pressure is the force exerted by the cell membrane against the cell wall.
The pulvinus is the swollen base of the petiole that acts as a hinge for leaf movement.
Protects the plant from herbivores (mechanical defense).
Reduces surface area exposed to environmental stress.
Closing of leaves in Mimosa pudica upon touch.
Solar tracking movements in certain flowers.
Nastic movements are distinct from tropisms because they are independent of the direction of the stimulus.
Options B, C, and D are incorrect because physiological responses like leaf folding are specifically triggered by external environmental stimuli, not by 'balance' or 'fear' or purely to 'conserve energy'.
A is correct тАФ Plant cells change shape and movement through rapid adjustments in turgor pressure as an immediate response to an external stimulus.
Always remember that plant movements like 'nyctinasty' (sleep movements) and 'thigmonasty' (touch responses) are always driven by turgor changes, not by muscular growth, which differentiates them from animal reflexes.
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