Q&A

Focus-Science and Technology - - CONTENTS - TOBY GRA­HAM, LV

Your burn­ing sci­ence ques­tions an­swered.

The in­side sur­faces of the Venus fly­trap’s two ‘lobes’ have six sen­si­tive hairs – three on each one. The phys­i­cal move­ment of these ‘trig­ger hairs’ is what springs the trap – but two hairs have to be touched within 20 sec­onds of each other for this to hap­pen. This has evolved as a safety mea­sure to stop the trap from go­ing off when a rain­drop hits it.

The move­ment of the trig­ger hairs causes the re­lease of charged cal­cium par­ti­cles (ions) from the cells at the base of each hair. When the con­cen­tra­tion of cal­cium ions rises high enough, the trap closes in less than a sec­ond by snap­ping from a con­vex to a con­cave shape, like an in­verted con­tact lens pop­ping the right way around. Ini­tially, the trap closes quite loosely, with the long-fin­gered fringe at the edge of the lobes in­ter­lock­ing to form bars. This al­lows tiny in­sects that aren’t worth the trou­ble of di­gest­ing to es­cape. But any­thing large enough to touch the trig­ger hairs an­other five times will cause the trap to close all the way – even­tu­ally form­ing a wa­ter­tight seal so that en­zymes can be re­leased to digest the in­sect.

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