15.2.1—Venus fly trap rapid response

The Venus flytrap converts touch to a rapid electrical response that closes its leaf trap. Sensory hairs detect movement, and the resulting signal causes hinge cells to swell so the two leaf lobes fold together.

1. An insect touches the sensory hairs on the leaf.
2. Calcium ion channels open in hinge cells at the base of a sensory hair, so calcium ions enter and generate a receptor potential.
3. Repeated stimulation is required: two hairs stimulated together, or one hair stimulated twice within a short interval, can reach the condition for an action potential. The action potential is propagated across the trap cells; without the required repeat stimulation, the trap resets.
4. Water moves into the hinge cells, making them swell. This change in cell shape causes the two lobes to fold together and close the trap.

Continued movement by prey can maintain the closed state. Further stimulation can cause calcium ions to enter gland cells and stimulate release of digestive enzymes, but this is a downstream response after the electrical closure pathway.

This is plant electrical coordination, not an animal nervous pathway: the card does not require neurones, synapses, or neurotransmitters. The electrical signal is the trigger, while water-driven hinge-cell swelling provides the immediate mechanical change that closes the trap.