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Ready, set, slurp! Scientists discover the secret to chameleons' catapulting tongues.

DID YOU KNOW?

* Dutch biologists Jurrian H. de Groot and Johan L. van Leeuwen, of Wageningen University, calculated that the chameleon can shoot its tongue out of its mouth at a rate of 26 body lengths per second.

* "The largest chameleons can project their tongues close to 45.7 centimeters (18 inches)," says biologist Kiisa Nishikawa.

* At rest, the chameleon's tongue is folded like a fan and sits deep inside its mouth. After the reptile flicks its tongue to nab prey, it reels in the meal by scrunching the tongue back up.

CRITICAL THINKING:

* How are potential energy and kinetic energy used to perform different daily tasks?

CROSS-CURRICULAR CONNECTIONS:

GEOGRAPHY: The island of Madagascar is home to the largest and most diverse chameleon population in the world. Research to create a travel guide for this region. Be sure to include a section describing the island's chameleons.

RESOURCES

* "Power at the Tip of the Tongue," by Ulrike K. Muller and Sander Kranenbarg, Science, April 9, 2004. See: www.sciencemag.org/cgi/content/full/304/5668/217

* For a tutorial on potential and kinetic energy, visit: www.physicsclassroom.com/Class/energy/U5L1a.html

When a chameleon needs to grab a bite to eat, it discreetly aims its tongue at a passing insect. Then, wham! The tongue shoots out. Within a mere one-tenth of a second, the tongue extends as far as 1.5 body lengths to nab the unsuspecting prey. Scientists have long been puzzled by the chameleon's tongue-flicking trick. That's because the lizard's tongue muscles aren't strong enough to produce the power needed to fire the tongue so quickly and reach such a far target. Last year, two Dutch scientists from Leiden University uncovered what gives the reptile's tongue its superpower: The chameleon's tongue contains a launching mechanism that works like a slingshot.

FAR-FETCHED

Just as a slingshot has a Y-shape frame for sturdy support, the chameleon's tongue needs a solid structure to hold on to. A rodlike skeleton holds up the tongue tissue (see diagram, p. 17).

Hugging the skeleton is the tongue's innermost layer. This layer is a tubelike sheath made of elastic protein fibers, or collagen. "The fibers act like loads of little rubber bands," says Ulrike Muller, a biologist at Wageningen University in the Netherlands. And similar to a rubber band, the more the collagen fibers are stretched, the farther the tongue can reach.

But stretchiness only accounts for one part of the chameleon's long-distance lick. To flick the tongue at lightning speed, the collagen fibers need to build up potential energy. "Energy can be stored slowly and then used later at a much higher rate," says Muller.

POWER SHOT

That potential energy comes from an accelerator muscle, which surrounds the collagen sheath. This muscle works in a manner similar to your arm when you pull on the rubber band of a slingshot.

To build up energy, the accelerator muscle contracts, or squeezes tightly around the tongue bone. As it squeezes, the muscle becomes flatter and longer. Since the collagen sheath is attached to the muscle, it gets stretched too--like a rubber band. The muscle's build-up of energy gets transferred and stored in the collagen.

When the muscle and collagen sheath stretch far enough, they begin to slip off the tip of the tongue skeleton. This causes the stored energy in the collagen to release, converting into kinetic energy. Just like when your hand releases the slingshot's rubber band to send an object flying, the energy of motion launches the stretchy tongue at a dizzying speed.

If the chameleon didn't have such a fast and stretchy tongue, it might starve. "It would have to catch its prey by running it down," says Kiisa Nishikawa, a biologist at Northern Arizona University. The chameleon's feet, unlike its tongue, are far from swift.

RELATED ARTICLE: Nuts & bolts.

The chameleon's tongue works like a slingshot to nab prey.

A. READY: The tongue skeleton pokes out from beneath the accelerator muscle (pink) and the collagen sheath (blue).

B. SET: To gain potential energy, the accelerator muscle and the collagen sheath lengthen.

C. LAUNCH: When the accelerator muscle slips off the tongue skeleton's tip, the collagen sheath releases kinetic energy, launching the tongue.

CHECK FOR UNDERSTANDING

DIRECTIONS: Fill in the blanks to complete the following sentences.

1. Within a mere one-tenth of a second, the chameleon can flick its tongue as far as--body lengths to nab a--such as an insect.

2. The innermost layer of the chameleon's tongue is made of--, or elastic--fibers.

3.--energy can be stored and then used later. To build up this energy in the tongue, the chameleon--, or squeezes, its--muscle around the tongue bone.

4. Just like when your hand releases a slingshot's rubber band to send an object flying,--energy launches the chameleon's tongue forward at a dizzying speed.

ANSWERS

1. 1.5, prey 2. collagen, protein 3. Potential; contracts, accelerator 4. kinetic
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Title Annotation:Physical: energy
Author:Tucker, Libby
Publication:Science World
Date:Mar 28, 2005
Words:816
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