A Venus flytrap closes due to a rapid cellular mechanism triggered by electrical signals generated when trigger hairs inside the trap are stimulated.
The Mechanism Behind Closure
The closure of a Venus flytrap is a fascinating process involving several key elements:
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Trigger Hairs: Inside each lobe of the trap are three to five sensitive trigger hairs (also called sensitive hairs). These hairs are critical for detecting potential prey.
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Electrical Signals: When a trigger hair is touched twice within a short time frame (about 20 seconds), or when one hair is touched, released, and touched again quickly, it generates an electrical signal, a form of action potential.
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Threshold and Accumulation: The Venus flytrap doesn't snap shut with just one touch. It has a "memory" that allows it to accumulate these electrical signals. This prevents the trap from closing on false alarms like raindrops or debris. When the accumulated signal reaches a threshold, the trap closes.
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Cellular Changes: The electrical signal triggers rapid changes in the turgor pressure (water pressure) of cells on the outer surface of the lobes. This causes them to expand rapidly, forcing the lobes to snap shut. This is a much faster process than previously thought involving cell growth.
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Acid Growth: While the initial rapid closure is due to turgor pressure changes, the tightening of the trap after capture involves "acid growth," a slower process where the cell walls are loosened by acid, allowing cells to expand and further enclose the prey.
Why Two Touches?
The requirement for two touches is an ingenious adaptation. It prevents the plant from wasting energy closing on non-nutritious items. Only live insects are likely to move enough to trigger the hairs twice in quick succession.
Speed of Closure
The closure is remarkably fast, typically occurring within a fraction of a second. The speed depends on factors like temperature, light intensity, and the size and health of the plant.
A Simplified Summary:
- Insect touches a trigger hair.
- An electrical signal is generated.
- A second touch within about 20 seconds causes the accumulated electrical signal to reach a threshold.
- Cells on the outer lobes rapidly change turgor pressure.
- The trap snaps shut.
