This blog provides commentary on interesting geological events occurring around the world in the context of my own work. This work is, broadly, geological fluid dynamics. The events that I highlight here are those that resonate with my professional life and ideas, and my goal is to interpret them in the context of ideas I've developed in my research. The blog does not represent any particular research agenda. It is written on a personal basis and does not seek to represent the University of Illinois, where I am a professor of geology and physics. Enjoy Geology in Motion! I would be glad to be alerted to geologic events of interest to post here! I hope that this blog can provide current event materials that will make geology come alive.

Banner image is by Ludie Cochrane..

Susan Kieffer can be contacted at s1kieffer at gmail.com

Wednesday, February 23, 2011

Fluid dynamics helps create the WORLD'S FASTEST PLANT!

On the left, a frontal view of the carnivour's trap, and
on the left two top views of the trap. The door faces
to the right.  (b) is before the trap fires and (c) is after.
Note the small hairs on the trap doors, on the right.
The scale bar is 500 microns.
This is Fig. 1 from the referenced article.

This may be biologic instead of geologic, but it's still cool!

In an article of the Proceedings of the Royal Society B, Olivier Vincent et al. investigated how aquatic carnivorous planets catch their prey. Here's a video of a bladderwort doing the catch!

Bladderworts have evolved in nutrient-poor habitats, and have become carnivorous as an adaptation.  The suction trap mechanism releases stored elastic energy to catch prey.  It is a two-phase mechanism. For about 1 hour, the bladderwort glands pump water out of the trap interior.  The internal hydrostatic pressure  body pressure is lowered, which results in the body storing elastic energy--imagine a fat rubberband that is stretched to become thin, storing elastic energy in the distorted shape.  The walls of the trap become concave in shape.  A flexible door keeps the entrance closed watertight.  There are protruding hairs on the door, which react when touched by the prey.  This begins the second phase in which the stored elastic energy is converted into kinetic energy.  The trap door opens, the trap wall relaxes and water (with the prey) is sucked in to the digestive chamber, where enzymes secreted by glands dissolve the prey and the nutrients are absorbed by the planet.  This release of the trap takes about a millisecond! Pretty speedy for a plant! If the trap is not used, it fires spontaneously after 5-20 hours to reset back to the "ready-to-catch" condition.

Vincent et al. then simulated the mechanisms by modeling the trap body and trapdoor as elastic shells with a given thickness, Young's modulus and Poisson ratio.  The potential energy is the sum of bending and stretching terms. Essentially, this is the mass-spring system of Physics 101. They then predicted the pressure for door buckling and the duration of the trap inflation. The Young's modulus is 5-20 MPa, comparable to "turgescent parenchymatous tissue." (What in the world is that? !!! Here's a link to a Wiki article on tissue if you feel like sorting that out.) The fast opening and closing of the door, with the dramatic changes in shape of the door, are attributed to an elastic buckling mechanism.

High speed cameras (15,000 frames per second) produced the videos that accompany the article.  The fluid speed was determined (by tracking small glass beads) to be 1.5 m/s, implying a Reynolds number of 900.  The acceleration is 600 g! (For comparison, astronauts experience a max of 4 g's.)

1 comment:

Earl said...

Here is another article on incredibly fast plant actions, although unlike the bladderwort these are one shot systems.
"Botanical ballistics"
Newscientist issue 2792 28 December 2010 Stephanie Pain